[Senate Hearing 108-359]
[From the U.S. Government Printing Office]
S. Hrg. 108-359
CLIMATE HISTORY AND THE SCIENCE UNDERLYING FATE, TRANSPORT, AND HEALTH
EFFECTS OF MERCURY EMISSIONS
ENVIRONMENT AND PUBLIC WORKS
UNITED STATES SENATE
ONE HUNDRED EIGHTH CONGRESS
JULY 29, 2003
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COMMITTEE ON ENVIRONMENT AND PUBLIC WORKS
one hundred eighth congress
JAMES M. INHOFE, Oklahoma, Chairman
JOHN W. WARNER, Virginia JAMES M. JEFFORDS, Vermont
CHRISTOPHER S. BOND, Missouri MAX BAUCUS, Montana
GEORGE V. VOINOVICH, Ohio HARRY REID, Nevada
MICHAEL D. CRAPO, Idaho BOB GRAHAM, Florida
LINCOLN CHAFEE, Rhode Island JOSEPH I. LIEBERMAN, Connecticut
JOHN CORNYN, Texas BARBARA BOXER, California
LISA MURKOWSKI, Alaska RON WYDEN, Oregon
CRAIG THOMAS, Wyoming THOMAS R. CARPER, Delaware
WAYNE ALLARD, Colorado HILLARY RODHAM CLINTON, New York
Andrew Wheeler, Majority Staff Director
Ken Connolly, Minority Staff Director
C O N T E N T S
JULY 29, 2003
Allard, Hon. Wayne, U.S. Senator from the State of Colorado,
prepared statement............................................. 11
Cornyn, Hon. Jon, U.S. Senator from the State of Texas, prepared
Inhofe, Hon. James M., U.S. Senator from the State of Oklahoma... 1
Jeffords, Hon. James M., U.S. Senator from the State of Vermont,
prepared statement............................................. 7
Voinovich, Hon. George V., U.S. Senator from the State of Ohio... 3
Legates, David R., director, Center for Climatic Research,
University of Delaware......................................... 12
Prepared statement........................................... 209
Levin, Leonard, program manager, Electric Power Research
Prepared statement........................................... 211
Mann, Michael E., assistant professor, University of Virginia,
Department of Environmental Sciences........................... 9
Prepared statement........................................... 173
Responses to additional questions from:
Senator Inhofe........................................... 178
Senator Jeffords......................................... 194
Myers, Gary, professor of Neurology and Pediatrics, Department of
Neurology, University of Rochester Medical Center.............. 44
Prepared statement........................................... 299
Rice, Deborah C., toxicologist, Bureau of Remediation and Waste
Management, Maine Department of Environmental Protection....... 42
Prepared statement........................................... 283
Responses to additional questions from Senator Jeffords...... 284
Soon, Willie, astrophysicist, Harvard-Smithsonian Center for
Prepared statement........................................... 58
Responses to additional questions from Senator Jeffords...... 155
Climate Research, Vol. 23:89-110, 2003, Proxy Climatic and
Environmental Changes of the Past 1000 years..............127-148
Energy & Environment Vol. 14, Nos. 2 and 3, 2003,
Reconstructing Climatic and Environmental Changes of the
Past 1000 Years: A Reappraisal.............................60-126
Geophysical Research Letters, Vol. 31, Estimation and
Representation of Long-term (>40 year) Trends of Northern-
Hemisphere-gridded Surface Temperature: A Note of Caution.149-154
Original Contributions, Effects of Prenatal and Postnatal
Methylmercury Exposure From Fish Consumption on
Personal Health, Tip the Scale in Favor of Fish: The
Healthful Benefits Await................................... 321
Risk Analysis, Vol. 23, No. 1, 2003, Methods and Rationale
for Derivation of a Reference Dose for Methylmercury by the
The Atlanta Journal-Constitution, June 6, 2003, Clear Skies
Mercury Curb Put in Doubt.................................. 317
The Lancet, Prenatal Methylmercury Exposure from Ocean Fish
Consumption in the Seychelles Child Development Study.....309-316
The New York Times, July 29, 2003, Does Mercury Matter?
Experts Debate the Big Fish Question....................... 319
The Philadelphia Inquirer, March 7, 2003, Mercury Rising..... 318
Chart, National Mean Mercury Concentration in Tissues of Selected
Fish Species (all sample types)................................ 289
Letter, to Senator Inhofe, from John Christy..................... 323
Report, EPRI, May 2003, A Framework for Assessing the Cost-
Effectiveness of Electric Power Sector Mercury Control Policie217-282
CLIMATE HISTORY AND THE SCIENCE UNDERLYING FATE, TRANSPORT, AND HEALTH
EFFECTS OF MERCURY EMISSIONS
TUESDAY, JULY 29, 2003
Committee on Environment and Public Works,
The committee met, pursuant to notice, at 9 o'clock a.m. in
room 406, Senate Dirksen Building, Hon. James M. Inhofe
(chairman of the committee) presiding.
Present: Senators Inhofe, Allard, Carper, Clinton, Cornyn,
Jeffords, Thomas and Voinovich.
OPENING STATEMENT OF HON. JAMES M. INHOFE, U.S. SENATOR FROM
THE STATE OF OKLAHOMA
Senator Inhofe. The meeting will come to order.
We have a policy that we announced when I became chairman
of the committee that we will start on time, whether anyone is
here or not here, members, witnesses or others. So I appreciate
all of you being punctual in spite of the fact that the
Senators are not.
One of my primary objectives as chairman of the committee
is to improve the way in which science is used. I think that
when I became chairman of this committee, I announced three
very outrageous things that we were going to do in this
committee that have not been done before. No. 1, we are going
to try to base our decisions, things that we do, on sound
science. No. 2, we are going to be looking at the costs of some
of these regulations, some of these policies that we have, and
determine what they are going to be. And No. 3, we are going to
try to reprogram the attitudes of the bureaucracy so that they
are here not to rule, but to serve.
Good public policy decisions depend on what is real or
probable, not simply on what serves our respective political
agendas. When science is debated openly and honestly, public
policy can be debated on firmer grounds. Scientific inquiry
cannot be censored. Scientific debate must be open. It must be
unbiased. It must stress facts rather than political agendas.
Before us today, we have two researchers who have published
what I consider to be a credible, well-documented, and
scientifically defensible study examining the history of
climate change. Furthermore, these are top fields of inquiry in
the Nation's energy environment debate and really the entire
world's energy environment debate. We can all agree that the
implications of this science are global, not only in terms of
the environmental impacts, but also energy impacts, global
trade impacts, and quite frankly, no less than global
We could also all agree that as a result of the import and
impact of these issues, it is absolutely crucial that we get
this science right. False or incomplete or misconstrued data
are simply not an acceptable basis for policymaking decisions
in which the Congress of the United States is involved. Such
data would violate the Data Quality Act, which we passed on a
bipartisan basis here in the Senate and which we have
bipartisanly embraced. If we need more data to satisfy our
standards, then so be it.
This Administration is prepared to do so in an aggressive
strategy that the climate change strategic plan outlines. The
1000-year climate study that the Harvard-Smithsonian Center for
Astrophysics has compiled is a powerful new work of science. It
has received much attention, and rightfully so. I would add at
this time, it did not receive much attention from some of the
liberal media who just did not want to believe that any of the
facts that were disclosed were accurate.
I think the same can be said in terms of work that has
recently received attention of the hockey stick study. In many
important ways, the Harvard-Smithsonian Center's work shifts
the paradigm away from the previous hockey stick study. The
powerful new findings of this most comprehensive study shiver
the timbers of the adrift Chicken Little crowd.
I look forward to determining whose data is most
comprehensive, uses the most proxies, maintains the regional
effects, avoids losing specificity through averaging
statistics, considers more studies, and most accurately
reflects the realities of the Little Ice Age, reflects the
realities of the Medieval Warming Period, and more.
Mercury presents a different set of issues. That would be
our second panel. It is well-established that high levels of
exposure to methyl-mercury before birth can lead to neuro-
development problems. But what about mercury consumed through
fish, the most common form of prenatal exposure? Mercury makes
its way into fish through various ways, but primarily though
deposition from air emissions, with 80 percent of emissions
deposited either regionally or globally, not locally. Global
mercury emissions are about 5,000 tons a year. About half of
those are man-made emissions.
In the United States, a little more than 100 tons are
emitted from non-power plant sources. Industry is making great
strides in reducing these emissions. I would like to submit for
the record this EPA document available on their Web site which
indicates that when rules now on the books are fully
implemented at non-power plant, nationwide emissions will be
cut by nearly 50 percent. Power plants emit about 50 tons of
mercury annually, about 1 percent of the worldwide emissions.
In setting policy, key questions need to be answered, such
as how would controls change this deposition; what portion of
mercury exposure can not be controlled; and what are the health
impacts of prenatal exposure. We will hear testimony today that
indicates any changes to mercury exposure in fish would be
minimal under even the most stringent proposal to regulate
mercury. Today, we will also hear testimony that the most
recent and comprehensive study to date found no evidence that
prenatal mercury exposure from ocean fish presents a
So we have diverse opinions that will be discussed today,
and that is the reason for this hearing, to wade through that
so that those on the panel that will be making policy decisions
will understand. I think it is no secret that we are not
scientists up here, so we look at things logically.
With that, I would recognize one of my colleagues here that
I have a great deal of respect for. Senator Voinovich and I
started out together as we were mayors of cities almost 25
years ago. I consider him to be one of the real experts in the
area of air. In fact, I can remember calling him in as an
expert when he was Governor of Ohio and we were holding these
hearings and I was chairman at that time of the Clean Air
Subcommittee. I would recognize Senator Voinovich for any
comments he would like to make or opening statements.
OPENING STATEMENT OF HON. GEORGE V. VOINOVICH, U.S. SENATOR
FROM THE STATE OF OHIO
Senator Voinovich. Thank you, Mr. Chairman.
I want to congratulate you for the very comprehensive floor
speech that you gave yesterday on the issue of climate change.
Senator Inhofe. I guess I should apologize. It was 12,000
words and I know you were anxious to get some floor time, so I
appreciate your patience.
Senator Voinovich. Your words were much more scientifically
based than mine.
Senator Voinovich. The two issues that we are going to
explore at the hearing today, the science of mercury and the
science of climate change, are both important and timely. I
commend you for holding this hearing.
I think I do not have to remind you that we have had
hearings on climate change now during the last 4 or 5 years. I
think I had a couple when I was chairman of even the
Transportation Infrastructure Committee. Senator Lieberman had
hearings over in Governmental Affairs when he was chairman of
the committee a year or so ago. So it is not a subject that is
brand new to this committee.
I have stated time and time again here in the committee and
on the floor that we must recognize that energy policy and
environmental policy are two sides of the same coin, and the
Senate has responsibility to harmonize these policies. We have
an obligation here in the committee to ensure that legislation
that we consider will protect our environment. We also have an
obligation to ensure that any legislation we consider takes
into account its potential impact on our economy and we have a
moral obligation to ensure that we consider a bill's particular
impact on the poor and the elderly who must survive on fixed
When the Senate takes up consideration of climate change
and multi-pollutant legislation, we must keep that moral
obligation in mind. We must ensure that we do not pass
legislation that will significantly drive up the cost of
electricity and home heating for those who can least afford
Several members of this committee have introduced pieces of
legislation this year to reduce power plant emissions,
including mercury, and address the issue of carbon emissions
and climate change by capping carbon. Examples include
Jeffords-Lieberman four-P bill, the Carper four-P bill, and the
McCain-Lieberman climate change bill, which I understand will
likely be offered as an amendment to the energy bill, just this
week we are going to be considering it.
These bills will establish a nationwide cap on carbon
emissions and their passage would force the utility sector,
that is now using coal to generate over half of our Nation's
electricity. To rely solely on natural gas for generation, we
will have fuel switching--capping carbon equals fuel switching
equals no-coal--to rely on natural gas regeneration despite the
fact we have over a 250-year supply of domestic coal and are
currently in the grips of a natural gas crisis in this country.
This crisis is a result of environmental policies that have
driven up the use of natural gas in electricity generation
significantly, while domestic supplies of natural gas have
fallen, partly because we cannot do the exploration that we
need to do for natural gas.
The result is predictable: tightening supplies of natural
gas, higher natural gas prices, and higher electricity prices.
Home heating prices are up dramatically, forcing folks on low
and fixed incomes to choose between heating their homes and
paying for other necessities such as food or medicine. The
language that has been offered by Senators Jeffords, McCain,
Lieberman and Carper if enacted will force our utilities to
fuel switch to natural gas; will significantly raise energy
prices; and will cause thousands of jobs to be lost,
particularly in manufacturing States like my State of Ohio,
which is already under duress in terms of manufacturing.
During the debate last year on the Jeffords-Lieberman four-
P bill, I put together a white paper that discussed the impact
that the bill would have if it were enacted. The numbers are
staggering: an overall reduction in GDP of $150 billion by
2020, the loss of over 900,000 jobs by 2020, and a decline in
national household earnings of $550 annually.
The cost of climate-change language such as the McCain-
Lieberman bill could come without any benefits to our air
quality or public health. Not even the most ardent supporter,
and I hope this comes up, of carbon regulation will claim that
there are demonstrable health benefits from carbon regulation.
Yet the Energy Information Administration estimates that the
passage of the McCain-Lieberman bill, if enacted, will raise
petroleum product prices by 31 percent, raise natural gas
prices by 79 percent, raise electricity prices by 46 percent,
and reduce GDP by up to $93 billion by 2025.
Carbon caps and unrealistic mercury caps means fuel
switching, again. The fuel switching means the end of
manufacturing in my State, enormous burdens on the least of our
brethren. It means moving jobs and production overseas, where
there are less stringent environmental programs. And will
actually, if you really think about it, increase global levels
The question we face in this committee is whether we should
do something reasonable to improve our understanding of the
issues surrounding carbon emissions and climate change, and
attempt to reduce atmospheric concentration of carbon and
mercury emissions without harming our economy, or rush into
short-sighted policy that will cap carbon and mercury at
unreasonable levels, shut down our economy, cut thousands of
jobs, and move manufacturing overseas.
In a recent column, former Secretary of Energy James
Schlesinger commented that:
``In climate change, we have only a limited grasp of the
overall forces at work. Uncertainties have continued to abound
and must be reduced. In any approach to policy formation, this
is very important, under conditions of such uncertainty should
be taken only on an exploratory or a sequential basis. A
premature commitment to a fixed policy could only proceed with
fear and trembling.''
I would like to have that column inserted in the record,
Senator Inhofe. Without objection, so ordered.
Senator Voinovich. As I mentioned previously once or twice,
I am working with Chairman Inhofe and the Administration on
moving Clear Skies forward, which I intend to mark up in my
subcommittee this fall. I am currently working with business
and environmental groups to find a bipartisan compromise on
dealing with carbon and global warming, with an emphasis on
sound science, carbon sequestration, development of clean coal
technologies, and a responsible approach that focuses more on
consensus rather than politics.
We need more Senators to focus on moving forward in a
responsible way and move away from harshly ideological
positions that advance nothing other than the agenda of some
environmental groups that have made carbon cap a political
I thank the chairman for holding this important hearing and
I look forward to hearing the testimony from our witnesses.
Senator Inhofe. That is an excellent opening statement,
Senator Voinovich. I go back to one of your first sentences
when you talked about the number of hearings we have had. We
have to keep in mind that each new hearing has new data. For
example, the 1,000-year Harvard-Smithsonian was not even out
until March of this year. So there are new things that are
coming along and I see a new trend-line which I discussed on
the House of the Senate yesterday. So this will be a very
Senator Cornyn, would you have any opening statement to
Senator Cornyn. I would like to reserve any statement until
later, Mr. Chairman.
Senator Inhofe. Yes, that is fine. First, I would like to
ask the first panel to come up. Dr. Legates, Dr. Willie Soon
and Dr. Mann, would you three come up? First of all, we are
honored to have who I consider three very excellent and
professional scientific witnesses here today. Normally, we
restrict the opening statements to 5 minutes, but it would be
fine if you want to go about 7 minutes because I know you have
come a long way and what we are dealing with here is probably
one of the most significant things facing America, facing our
economy, facing our environment today.
So I would introduce all three. Dr. David Legates is the
director of the Center for Climatic Research at the University
of Delaware. Dr. Willie Soon is the astrophysicist at Harvard-
Smithsonian Center for Astrophysics, and Dr. Michael Mann is
assistant professor at the University of Virginia Department of
Environmental Sciences. I will first ask Dr. Willie Soon to
give his opening statement.
STATEMENT OF WILLIE SOON, ASTROPHYSICIST, HARVARD-SMITHSONIAN
CENTER FOR ASTROPHYSICS
Dr. Soon. Mr. Chairman, distinguished Senators, my fellow
panelists, Dr. Mann and Dr. Legates, and members of the
audience, my name is Willie Soon. About a month or two ago, I
became a very proud and grateful U.S. citizen. I just cannot
believe where I am sitting today.
I am an astrophysicist with the Harvard-Smithsonian Center
for Astrophysics in Cambridge, Massachusetts. My training is in
atmospherics and space physics. My research interests for the
past 10 years include changes in the sun and their possible
impact on climate.
I am here today to testify that the climate of the 20th
century is neither unusual nor the most extreme. Around 1,000
years ago, the temperature over many parts of the world was
warm. A widespread cooling then set in for several centuries,
followed by a recovery to 20th century warming.
My colleague and I collected the information on climate by
proxy. We studied environmental indicators of local climate
change going back some 1,000 years from many locations around
the world. Based on work of approximately 1,000 researchers and
hundreds of peer-reviewed papers, we conclude the following
three points about climate history of the last 1,000 years.
On a location-by-location basis, point No. 1, there was
warming from 800 to 1300 A.D., all about 1,000 years ago, over
many parts of the world. This period is called the Medieval
Warm Period. Following the warming of 1,000 years ago was a
general cooling from about 1300 to 1900 A.D. This period is
called the Little Ice Age.
Point No. 2, there is no convincing evidence from local
proxy to suggest that the 20th century had higher temperatures
or more extreme climate than the warm period 1,000 years ago.
Point No. 3, local and regional, rather than global average
changes are the most relevant and practical measure of climate
changes and its impact. Much of the climate proxy results using
our work are new. Most papers were published in the scientific
literature in the recent 5 to 10 years. There are two points to
note about our methods. First, we keep the local or regional
information contained in each climate proxy. This is important
for studying geographical patterns of climate, which does not
change everywhere at the same time.
Second, climate is more than just temperature, so we keep
the climate information like rainfall, expansion or contraction
of forests, all advances or retreats of glaciers, et cetera.
Our approach makes use of the richness of information in
climate proxies, which map out local environmental and climate
properties, rather than just temperature alone.
The entirety of climate proxies over the last 1,000 years
shows that over many areas of the world, there has been and
continues to be large local climatic changes. Those changes
provide important changes for the computer simulations of
climate. The full models which explore the Earth region by
region can be tested against the natural patterns of change
over the last 1,000 years that are detailed by the climate
Having computer simulation, we produced past patterns of
climate which has been influenced predominantly by natural
factors and is key to making an accurate forecast that includes
all potential human-made warming and cooling effects.
In summary, based on expert conclusions from climate
proxies in several hundred peer-reviewed papers by over 1,000
researchers from around the world, we find the following. No.
1, from one location to another, large natural swings in
climate have occurred over the last 1,000 years. Those patterns
have not always been synchronous.
No. 2, there was widespread warmth about 1,000 years ago,
followed by widespread cooling ending by the beginning of the
No. 3, the local and regional climate proxies cannot
confirm that the 20th century is the warmest or most extreme
over much of the world, compared especially to the Medieval
Warm Period approximately 1,000 years ago.
This is all for my oral remarks and I thank you for the
opportunity to be here.
Senator Inhofe. Dr. Soon, we appreciate that excellent
opening statement. You did not even take all of your time. That
is very unusual.
At this time, Dr. Mann if you don't mind, I would like to
interrupt your testimony. We have been joined by the Ranking
Minority Member, Senator Jeffords. Senator Jeffords, do you
have an opening statement you would like to make at this time?
Senator Jeffords. I would ask unanimous consent that it be
made as part of the record and would prefer listening to the
[The prepared statement of Senator Jeffords follows:]
Statement of Hon. James Jeffords, U.S. Senator from the State of
We're here today to discuss two very important topics--climate
change and mercury pollution. As most of you know, I am the author of
ambitious legislation--the Clean Power Act of 2003--which addresses
these environmental problems, as well as ozone, acid rain, and human
health damage from fine particulate matter.
Unfortunately, we aren't here today to talk about moving forward to
find innovative solutions to these real world problems. Instead,
today's hearing will largely be a mirror or the reverse of the robust
and growing consensus in the mainstream scientific community on climate
and mercury pollution.
The disappointing result will be more delay. Delay on the part of
Congress, and even worse, the ongoing backsliding on the part of the
Administration, means that we fail to act responsibly as a society to
protect future generations. That means increasingly greater risks of
global warming and mercury poisoning.
There is no doubt that the scientific process must inform
policymakers as new information comes in. Unfortunately, there is no
new information to be found here today that would dissuade us from
acting quickly and responsibly to reduce greenhouse gas and mercury
emissions. In today's discussion of a literature survey of climate
research, the skeptics are trotting out an argument that is several
years old and already discarded by their peers.
It is abundantly clear that now is the time to act.
The National Academy of Sciences has said, ``Despite the
uncertainties, there is general agreement that the observed warming is
real and particularly strong within the past 20 years.''
NOAA currently says that,
``The climatic record over the last thousand years clearly
shows that global temperatures increased significantly in the
20th Century, and that this warming was likely to have been
unprecedented in the last 1200 years.''
EPA's website says that, ``There is new and stronger
evidence that most of the warming over the last 50 years is
attributable to human activities.''
One would have to be madder than a March hare to fail to see the
need to act. Yet, the Administration's new research plan falls squarely
into hare territory--denying the reality staring them in the face.
I want to show you the latest odds on warming. MIT says that there
is a one in five chance that the temperature of the earth will warm by
approximately 4 or 5 degrees over the course of this century, assuming
there is no action to reduce emissions.
As my dear departed friend, Senator John Chafee, said in 1989:
``It is clear that we are facing a serious threat. The
scientists are telling us that if we continue to stroll along
as if everything is fine, we will transform Earth into a planet
that will not be able to support life as we now know it.''
While mercury contamination does not have the same dramatic effect
on earth's systems, it is still a dangerous global and local pollutant
because it is bio-accumulative and toxic to human health.
Long ago, Congress decided that toxic air emissions should be
reduced and took very aggressive steps in 1990 to make that happen,
especially if they fall into the Great Lakes and other great waters
like Lake Champlain. Unfortunately, the Agency has fallen significantly
behind in complying with the Clean Air Act's schedule. A settlement
agreement mandates controlling toxic air pollutants from utilities by
In 1998, related to the controversy around EPA's late reports to
Congress on utility air toxics, Congress directed the National Academy
of Sciences (NAS) to recommend an appropriate reference dose for
mercury exposure. In 2000, the NAS reported that EPA's reference dose
was scientifically sound and adequate to protect most Americans. That
NAS review considered all health effects studies, including the
Seychelles study that we'll discuss today.
We know that mercury is a potent toxic. It affects the human brain,
spinal cord, kidneys, liver and the heart. It affects the ability to
feel, see, taste and move. We know that mercury can affect fetal
development, preventing the brain and nervous system from developing
normally. Long term exposure to mercury can result in stupor, coma and
``Mad as a Hatter'' is the phrase that was used in the 1800's to
describe the employees of the felt hat industry whose constant exposure
to mercury changed their behavior. Fortunately, Americans exposure from
commercial and recreational fish consumption is substantially less than
that, though dozens of health warnings are posted nationwide.
But, it's crazy for anyone to suggest that we should not reduce
mercury emissions significantly, since we know its health effects and
we have the technologies to control it.
We should have a hearing on how to export those control
technologies and Congress should urge the Administration to negotiate
binding global reductions in mercury, as the Senate did last year in
the Energy bill for greenhouse gas emissions.
At a minimum, we should pass four-pollutant legislation now that
gets reductions faster and deeper than required by the current Clean
Air Act. I'm sad to say that there have been no negotiations on that
front since I initiated some in early 2002. And the Administration has
done nothing to reduce these emissions with its abundant authority in
We can't afford to leave these problems to future generations to
solve. We can't let our children and grandchildren wake up to find that
our delays have cost them dearly in terms of health and the global and
local environment. It's time to act responsibly.
Finally, I ask that material from the journal EOS, the NOAA
website, the Atlanta Journal Constitution, the National Center for
Atmospheric Research, and the American Geophysical Union be included in
the hearing record.
Senator Jeffords. I might point out, we have got to do
something about this traffic out there.
Senator Inhofe. Well, the name of our subcommittee is
Transportation and Infrastructure, so maybe we can do something
about the traffic out there.
Senator Jeffords. I hope so.
Senator Inhofe. Dr. Mann, you are recognized.
STATEMENT OF MICHAEL E. MANN, ASSISTANT PROFESSOR, UNIVERSITY
OF VIRGINIA, DEPARTMENT OF ENVIRONMENTAL SCIENCES
Dr. Mann. Senators, my name is Michael Mann. I am a
professor in the Department of Environmental Sciences at the
University of Virginia. My research involves the study of
climate variability and its causes. I was a lead author of the
IPCC Third Scientific Assessment report. I am current
organizing committee chair for the National Academy of
Sciences' Frontiers of Science, and have served as a committee
member or adviser for other National Academy of Sciences'
I have served as editor for the Journal of Climate of the
American Meteorological Society for 3 years and I am a member
of the advisory panel for the NOAA Climate Change Data and
Detection Program. I am a member of numerous other
international and U.S. scientific working groups, panels and
steering committees. I have coauthored more than 60 peer-
reviewed publications on diverse topics within the fields of
climatology and paleoclimatology.
Honors I have received include selection in 2002 as one of
the 50 leading visionaries in science and technology by
Scientific American magazine, and the outstanding scientific
publication award of NOAA for 2000.
In my testimony here today, I will explain, No. 1, how
mainstream climate researchers have come to the conclusion that
late 20th century warmth is unprecedented in a very long-term
context and that this warmth is likely related to the activity
of human beings; and No. 2, why a pair of recent articles
challenging these conclusions by astronomer Willie Soon and his
coauthors are fundamentally unsound.
It is the consensus of the climate research community that
the anomalous warmth of the late 20th century cannot be
explained by natural factors, but instead indicates significant
anthropogenic, that is human influences. This conclusion is
embraced by the position statement on climate change and
greenhouse gases of the American Geophysical Union, by the 2001
report of the IPCC, the Intergovernmental Panel on Climate
Change, and by a National Academy of Sciences' report that was
solicited by the Bush Administration in 2001.
More than a dozen independent research groups have now
reconstructed the average temperature of the northern
hemisphere in past centuries, both by employing natural
archives of past climate information or proxy indicators such
as tree rings, corals, ice cores, lake sediments and historical
documents, and through the use of climate model simulations. If
I can have the first exhibit here, as shown in this exhibit,
the various proxy reconstructions agree with each other, as
well as with the model simulations, all of which are shown,
within the estimated uncertainties. That is the gray-shaded
The proxy reconstructions, taking into account these
uncertainties, indicate that the warming of the northern
hemisphere during the late 20th century, that is the northern
hemisphere, not the globe, as I have sometimes heard my study
incorrectly referred to, the northern hemisphere during the
late 20th century, that is the end of the red curve, is
unprecedented over at least the past millennium and it now
appears based on peer-reviewed research, probably the past two
The model simulations demonstrate that it is not possible
to explain the anomalous late-20th century warmth without the
contribution from anthropogenic influences. These are the
consensus conclusions of the legitimate community of climate
and paleoclimate researchers investigating such issues.
Astronomers Soon and Baliunas have attempted to challenge
the scientific consensus based on two recent papers, henceforth
collectively referred to as SB, that completely misrepresent
the past work of other legitimate climate researchers and are
deeply flawed for the following reasons. No. 1, SB make the
fundamental error of citing evidence of either wet or dry
conditions as being in support of an exceptional Medieval Warm
Period. Such an ill-defined criterion could be used to define
any period of climate as either warm or cold. It is pure
Experienced paleoclimate researchers know that they must
first establish the existence of a temperature signal in a
proxy record before using it to try to reconstruct past
temperature patterns. If I can have exhibit two, this exhibit
shows a map of the locations of a set of records over the globe
that have been rigorously analyzed by my colleagues and I for
their reliability as long-term temperature indicators. I will
refer back to that graphic shortly.
No. 2, it is essential to distinguish between regional
temperature changes and truly hemispheric or global changes.
Average global or hemispheric temperature variations tend to be
far smaller in their magnitude than those for particular
regions. This is due to a tendency for the cancellation of
simultaneous warm and cold conditions in different regions,
something that anybody who follows the weather is familiar
with, in fact.
As shown by exhibit three, if I can have that up here as
well now, thank you, this exhibit plots the estimated
temperature for various locations shown in the previously
displayed map. As you can see, the specific periods of relative
cold and warm, blue and red, differ greatly from region to
region. Climatologists, of course, know this. What makes the
late 20th century unique is the simultaneous warmth indicated
by nearly all the long-term records. It is this simultaneous
warmth that leads to the anomalous late-20th century warmth
evident for northern hemisphere average temperatures.
The approach taken by SB does not take into account whether
warming or cooling in different regions is actually coincident,
despite what they might try to tell you here today.
No. 3, as it is only the past few decades during which
northern hemisphere temperatures have exceeded the bounds of
natural variability, any analysis such as SB that compares past
temperatures only to early or mid-20th century conditions; you
repeatedly hear Dr. Soon refer to the 20th century;
climatologists do not consider that a meaningful baseline
because there has been a dramatic warming during the 20th
century and the early 20th century and the late 20th century
are almost as different as the late 20th century and any other
period during the past 1,000 years at least. So a study that
refers only to early or mid-20th century conditions or generic
20th century conditions and does not specifically address the
late 20th century, cannot address the issue of whether or not
late-20th century warmth is anomalous in a long-term context.
To summarize, late-20th century warming is unprecedented in
modern climate history at hemispheric scales. A flawed recent
claim to the contrary by scientists lacking expertise in
atology is not taken seriously by the scientific community.
The anomalous recent warmth is almost certainly associated
with human activity and this is the robust consensus view of
the legitimate climate research community.
Senator Inhofe. Thank you, Dr. Mann.
First, I would ask Senator Allard, did you want to make an
Senator Allard. Mr. Chairman, I do have an opening
statement and in deference to the panel and you I would just
like to have it put in the record. If you would do that, then I
would be happy.
Senator Inhofe. Without objection.
[The prepared statement of Senator Allard follows:]
Statement of Hon. Wayne Allard, U.S. Senator from the State of Colorado
Mr. Chairman, I want to thank you for holding this important
As a veterinarian, I have some scientific training in my
background. I strongly believe that we should use scientific principals
as a guidepost when formulating any regulation. This scientific
guidepost approach is particularly important when looking at
regulations with the implications and magnitude of regulations on
climate change and mercury control.
Climate change has been an ongoing discussion for many years.
However, during the 1970's the concerns were exactly opposite of what
they are now. Then we were told that there was a threat of massive
global cooling. Headlines screamed that we were in danger of entering
another ice age. Now we are told that massive warming trends are going
to cause overheating across the globe. We need answers, not rhetoric.
All of the witnesses here today have a great deal of experience.
All of the witnesses here have spent many years analyzing data related
to the areas of their expertise. But, I am concerned that, at times,
data may be reviewed selectively and in isolation. I am also concerned
that emphasis may fall on a limited number of studies. In science we
have all learned that the only way to solidly prove a theory is by
conducting tests, studies or experiments that repeatedly arrive at the
same result. We cannot simply ignore the studies that do not have the
outcome we are looking for. This applies whether we are looking at
climate change, mercury or any other issue.
I want to spend most of my time and attention today on potential
mercury regulations. While today's hearing is intended to focus on
science, I would also like to touch on the impact that potential
regulations will have on the economy of my state and the west. As many
of you know, western coal differs from other types of coal in several
ways. The higher chlorine content in western coal makes it more
difficult to remove mercury when burning it. And, while western coal
does contain mercury, when it is burned it gives off mercury in the
elemental form. It is my understanding that this is not the type of
mercury that deposits in the ecosystem to potentially be absorbed by
The economies of Colorado, and the entire west, will be impacted by
harsh regulations placed on their coal. Economies undoubtedly will be
damaged by the decrease in use of coal mined in the West. In addition,
while jobs are being lost due to the subsequent inability to fully
utilize western coal supplies, if power can no longer be generated by
using coal mined in the west, other less efficient coal types will have
to be transported across long distances. This additional expenditure
will add to the price of electricity generation, driving up electricity
costs and further damaging an economy that will already be struggling.
This is why it is so important to me that we be cautious when
dealing with situations such as these and why we should place strong
emphasis on the use of sound science. Our regulations must be
thoughtful reflections of what we know--they should not be reflexive or
reactive attempts to legislate a cure before we know what the disease
Again, Mr. Chairman, thank you for holding this hearing. I look
forward to hearing the witness testimony and discussions to come.
Senator Inhofe. That being the case, let's dispense with
any further opening statements.
Dr. Legates, thank you very much for being here. You are
STATEMENT OF DAVID R. LEGATES, DIRECTOR, CENTER FOR CLIMATIC
RESEARCH, UNIVERSITY OF DELAWARE
Dr. Legates. Thank you. Mr. Chairman, Distinguished
Senators, Doctors Mann and Soon, and members of the audience, I
would like to thank the committee for inviting my commentary on
this important topic of climate history and its implications.
My research interests have focused on hydroclimatology. That is
the study of water in the atmosphere and on the land, and as
well as on the application of statistical methodology in
I am familiar with the testimony presented here by Dr.
Soon. My contributions to Dr. Soon's research stem from my
grappling with the striking disagreement between the
longstanding historical record and the time series recently
presented by Dr. Mann and his colleagues. It also stems from my
own experiences in compiling and merging global estimates of
air temperature and precipitation from a variety of disparate
My Ph.D. dissertation resulted in the compilation of high-
resolution climatologies of global air temperature and
precipitation. From that experience, I have become acutely
aware of the issues associated with merging data from a variety
of sources and containing various biases and uncertainties. By
its very nature, climatological data exhibit a number of
spatial and temporal biases that must be taken into account.
Instrumental records exist only for the last century or so, and
thus proxy records can only be used to glean information about
the climate for earlier time periods. But it must be noted that
proxy records are not observations and strong caveats must be
considered when they are used. It, too, must be noted that
observational data are not without bias either.
Much research has described both the written and oral
histories of the climate, as well as the proxy climate records.
It is recognized that such records are not without their
biases. For example, trees respond not to just air temperature
fluctuations, but to the entire hydrologic cycle, including
water supply, precipitation, and demand, which is only in part
driven by air temperature.
Nevertheless, such accounts indicate that the climate of
the last millennium has been characterized by considerable
variability and that extended periods of cold and warmth
existed. It has been generally agreed that during the early
periods of the last millennium, air temperatures were warmer
and that temperatures became cooler toward the middle of the
millennium. This gave rise to the terms the Medieval Warm
Period and the Little Ice Age, respectively. However, as these
periods were not always consistently warm or cold, nor were the
extremes geographically commensurate in time, such terms must
be used with care.
In a change from its earlier reports, however, the Third
Assessment Report of the Intergovernmental Panel on Climate
Change, and now the U.S. National Assessment of Climate Change,
both indicate that hemispheric and global air temperatures
followed a curve developed by Dr. Mann and his colleagues in
1999. This curve exhibits two notable features, and I will
point back to Dr. Mann's exhibit one that he showed a moment
ago. First is a relatively flat and somewhat decreasing trend
in air temperature that extends from 1000 A.D. to about 1900
A.D. This feature is an outlier that is in contravention to
thousands of authors in the peer-reviewed literature.
This is followed by an abrupt rise in the air temperature
during the 1900's that culminates in 1998 with the highest
temperature on the graph. Virtually no uncertainty is assigned
to the instrumental record of the last century. This conclusion
reached by the IPCC and the National Assessment is that the
1990's was the warmest decade, with 1998 being the warmest year
of the last millennium.
Despite the large uncertainty, the surprising lack of
significant temperature variations in the record gives the
impression that climate remained relatively unchanged
throughout most of the last millennium, at least until human
influences began to cause an abrupt increase in temperatures
during the last century. Such characterization is a scientific
outlier. Interestingly, Mann et al replace the proxy data for
the 1900's by the instrumental record and present it with no
uncertainty characterization. This, too, yields the false
impression that the instrumental record is consistent with the
proxy data and that it is error-free. It is neither.
The instrumental record contains numerous uncertainties,
resulting from measurement errors, a lack of coverage over the
world's oceans, and underrepresentation of mountainous and
polar regions, as well as undeveloped nations and the presence
of urbanization effects resulting from the growth of cities. As
I stated before, the proxy records only in part reflect
temperature. Therefore, a simultaneous presentation of the
proxy and instrumental record is the scientific equivalent to
calling apples and oranges the same fruit.
Even if a modest uncertainty of plus or minus one-tenth of
a degree Celsius were imposed on the instrumental record, the
claim of the 1990's being the warmest decade would immediately
become questionable, as the uncertainty window would overlap
with the uncertainty associated with earlier time periods.
Note, too, that if the satellite temperature record, where
little warming has been observed over the last 20 years, had
been inserted instead of the instrumental record, it would be
impossible to argue that the 1990's was the warmest decade.
Such a cavalier treatment of scientific data can create
scientific outliers, such as the Mann et al curve.
So we are left to question why the Mann et all curve seems
to be at variance with the previous historical characterization
of climatic variability. Investigating more than several
hundred studies that have developed proxy records, we came to
the conclusion that nearly all of these records show
considerable fluctuations in air temperature over the last
millennium. Please note that we did not reanalyze the proxy
data. The original analysis from the various experts was left
intact, as it formed a voluminous refereed scientific
literature. Most records show the coldest period is
commensurate with at least a portion of what is termed the
Little Ice Age, and the warmest conditions at concomitant with
at least a portion of what is termed the Medieval Warm Period.
Our conclusion is entirely consistent with conclusions
reached by Drs. Bradley and Jones and not all locations on the
globe experience cold or warm conditions. Moreover, we chose
not to append the instrumental record, but to compare apples
with apples and determine if the proxy records themselves
indeed confirm the claim of the 1990's being the warmest decade
of the last millennium. That claim is not borne out by the
individual proxy records.
However, the IPCC report in the chapter with Dr. Mann as
the lead author and his colleagues as contributing authors,
also concludes that the research ``support the idea that the
15th to 19th centuries were the coldest of the millennium over
the northern hemisphere overall.'' Moreover, the IPCC report
also concludes that the Mann and Jones research shows
temperatures from the 11th to 14th centuries to be ``warmer
than those from the 15th to 19th centuries.'' This again is
entirely consistent with our findings and in contravention of
their own error assessment.
Where we differ with Dr. Mann and his colleagues is in the
construction of the hemisphere average time series and their
assertion that the 1990's was the warmest decade of the last
millennium. Reasons why the Mann et al curve fails to retain
the fidelity of the individual proxy records are detailed
statistical issues into which I will not delve. But a real
difference of opinion focuses solely on the Mann et al curve,
and how it is an outlier compared to the balance of evidence on
millennial climate change. In a very real sense, this is a
fundamental issue that scientists must address before the Mann
et al curve can be taken as fact.
In closing, let me state that climate is simply more than
annually averaged global air temperature. Too much focus, I
believe, has been placed on defining air temperature time
series and such emphasis obscures the true issue in
understanding climate change and variability. If we are truly
to understand climate and its impacts and driving forces, we
must push beyond the tendency to distill climate to a single
annual number. Proxy records which provide our only possible
link to the past are incomplete at best. But when these
voluminous records are carefully and individually examined, one
reaches the inescapable conclusion that climate variability has
been a natural occurrence and especially so over the last
Given the uncertainties and biases associated with the
proxy and instrumental records----
Senator Inhofe. Dr. Legates, we are going to have to cut it
off. You have exceeded your time and I am sure you will have an
opportunity to finish your thoughts during the question and
Dr. Legates. Thank you for the privilege.
Senator Inhofe. We are going to, if it is all right, use 5
minutes and maybe try to get a few rounds here. Is that
acceptable? These will be 5 minute rounds for questioning. I
First of all, Senator Thomas joined us. Thank you for
coming, Senator Thomas.
I will address my first question to Dr. Legates. In my
speech on the Senate floor yesterday, I noted your comments
regarding--can you find that chart of those comments?--the
comments regarding Dr. Mann's work as shown on the chart. I
have a small copy of this. No, that is not it. It is this chart
right here. OK.
First of all, this is a comparison. As I mentioned in my
opening statement, we sit up here as non-scientists so we try
to look at these things and see what is logical, how we should
weigh and compare diverse opinions. Now, the first thing I
noticed was that Dr. Mann, yours I believe was in the area of
the timeframe of 1999----
Dr. Mann. Excuse me. That is incorrect.
Senator Inhofe [continuing]. And Dr. Soon, you are 2003. So
I think that the timing would mean something because I know
that this is not a static target. This is a moving target.
May I first ask Dr. Legates, do you stand by the statements
that are made on this chart up here, on the contrasting methods
that were used?
Dr. Legates. I have not had a chance to actually look at
the chart before now.
Senator Inhofe. Is this the one that he had here? OK, let's
put that up. All right, then, this statement here,
``Although Mann's work is now widely used as proof of
anthropogenic global warming. We have become concerned that
such analysis is in direct contradiction to most of the
research and written histories available. My paper shows this
contradiction and argues that the results of Mann are out of
step with the preponderance of the evidence.''
I am not Tim Russert, but do you stand by these statements?
Dr. Legates. I do stand by them, sir.
Senator Inhofe. All right. I note that you are an expert in
statistical techniques. In my speech on the Senate floor
yesterday, I noted that even assuming all of the science used
by the political left, come the end of 50 years hence, the
Kyoto Protocol would have no measurable affect on temperature.
Do you agree with that?
Dr. Legates. Yes, generally.
Senator Inhofe. And if the Kyoto Protocol forces harsher
mandates, does it follow that the weaker legislative proposals
that are out there right now before us in the Senate would have
likewise no measurable effect?
Dr. Legates. That is likely true.
Senator Inhofe. All right. Let's see. Dr. Mann, since you
have characterized your colleagues there in several different
ways as nonsense, illegitimate, and inexperienced, let me ask
you if you would use the same characterization of another
person that I quoted on the floor yesterday. I would like to
call your attention to the recent op/ed in the Washington Post
by Dr. James Schlesinger, who was Energy Secretary under
President Carter. In it, he wrote, ``There is an idea among the
public that the science is settled. That remains far from the
truth.'' He has also acknowledged the Medieval Warming Period
and the Little Ice Age. Do you question the scientific
integrity of Dr. Schlesinger?
Dr. Mann. I do not think I have questioned scientific
integrity. I have questioned scientific expertise in the case
of Drs. Willie Soon and David Legates with regard to issues of
paleoclimate. As far as Schlesinger is concerned, I am not
familiar with any peer-reviewed work that he has submitted to
the scientific literature, so I would not be able to evaluate
his comments in a similar way. If I could clarify one----
Senator Inhofe. OK. Well, you can't because there isn't
time. I am going to stay within my timeframe and I want to get
to questions so others will have plenty of opportunity to
respond to questions I am sure.
Dr. Soon, how many studies did you examine in total and how
many were appropriate for the criteria you established?
Dr. Soon. Senator, the number is roughly in the order of,
if you speak in terms of the peer-reviewed literature, I would
say several hundred. And the number of people involved in these
paleoclimatic research would be at least 1,000. Of course, I
have to emphasize I am not a paleoclimate scientist, but all of
us are ruled by one simple goal, to understand the nature of
how climate works. The basis to get to the goal is to figure
out the exact expressions of the physical laws.
The short answer is there is a huge number of literature
that we consulted that feed the criteria. This is why we wrote
it as a scientific paper.
Senator Inhofe. I was trying to get to the 240 proxies that
were used and the number used.
Dr. Soon. Yes, we listed about 240 proxy studies in our
Senator Inhofe. Last, I would say, do you have more data in
your study than Dr. Mann did in his 1999 work? And is your data
Dr. Soon. Yes. I would emphasize that most of the proxy
records come from the most recent 5 years.
Senator Inhofe. Thank you, Dr. Soon.
Senator Jeffords. Dr. Mann, would you care to respond?
Dr. Mann. Yes, first of all I wanted to clarify a
misstatement earlier on the part of Senator Inhofe. The results
that I showed in my first graphic which demonstrate that it is
a clear consensus of the climate research community that a
number of different estimates, not just ours, but at least 12
different estimates of the history of the northern hemisphere
average temperature for the past 1,000 years give essentially
the same result, within the uncertainties. We published a paper
just a month ago demonstrating that that is a robust result of
a large number of mainstream researchers in the climate
Phil Jones and I also have a paper in press in the Journal
of Geophysical Research letters, which demonstrates those
results further. So in fact, the latest word and the word of
the mainstream climate research community is the one that I
have given you earlier.
Now, as far as the issue of data, how much data was used,
there are a number of misstatements that have been made about
our study. One of them is with regard to how much data we used.
We used literally hundreds of proxy records. We often
represented those proxy records, as statistical climatologists
often do, in what we call a state space. We represented them in
terms of a smaller number of variables to capture the leading
patterns of variability in the data. But we used hundreds of
proxy indicators, more in fact than Dr. Soon referred to. In
fact, we actually analyzed climate proxy records. Dr. Soon did
Senator Jeffords. Dr. Soon, in a 2001 article in Capitalism
magazine, you said that because of the pattern of frequent and
rapid changes in climate throughout the holocene period, we
should not view the warming of the last 100 years as a unique
event or as an indication of manmade emissions' effect on the
But according to NOAA's Web site ``upon close examination
of these warm periods,'' including all the ones that you cited
in your past and most recent article,
``It became apparent that these periods are not similar to
the 20th century warming for two specific reasons. One, the
periods of hypothesized past warming do not appear to be global
in extent or, two, the period of warmth can be explained by
known natural climate forcing conditions that are uniquely
different than those of the past 100 years.''
Why didn't either of your articles make an impact on the
state of the science or NOAA's position?
Dr. Soon. Thank you for your question, Senator. As you may
be aware, my paper just got published this year, January 2003
and April 2003, so it is all fairly recent. I have just written
up this paper very recently, so I do not know what impact it
will have on any general community, but I do know all my works
are done consulting works from all major paleoclimatologists in
the field, including Dr. Mann and his esteemed colleagues.
As to the comments about the Capitalism magazine, I am not
aware of that particular magazine. I do not know whether I
submitted anything to this journal or this magazine. I do stand
by the statement that it is important to look at the local and
regional change before one takes global averages because
climate tends to vary in very large swings in different parts
of the world. That really is the essence of climate change and
one ought to be really looking very carefully at the local and
regional change first, and also one should not look strictly at
only the temperature parameter, as Dr. Mann has claimed to have
done. That I think is very important to take into account.
Senator Jeffords. Dr. Mann, could you comment?
Dr. Mann. Yes. Both of those statements are completely
incorrect. If Dr. Soon had actually read any of the papers that
we have published over the past 5 years or so, he would be
aware of the fact that we use statistical techniques to
reconstruct global patterns of surface temperature. We average
those spatial patterns to estimate a northern hemisphere mean
temperature, just as scientists today seek to estimate the
northern hemisphere average temperature from a global network
of thermometer measurements. We use precisely the same approach
based on proxy reconstructions of spatial patterns of surface
So what Dr. Soon has said is completely inaccurate. The
first line on that contrasting methods table up there is also
In terms of variables other than temperature, my colleagues
and I have published several papers reconstructing continental
drought over North America and reconstructed sea-level pressure
patterns. We have looked at just about every variable that
climatologists are interested in from the point of view of
paleoclimate indicators. I think Dr. Soon needs to review my
work more carefully.
Senator Inhofe. Thank you, Senator Jeffords.
Senator Allard. Thank you, Mr. Chairman.
In my mind, I do not think there is any question that the
climate has shown a period of warming here. The question that I
bring up and where I see the debate is, what is causing it and
whether it is the changes that are happening and whether they
are significant or not.
I also wonder what your thinking this world might look like
1,000 years from now, looking at the data that we have now. I
wondered if maybe each one of you would just give me a brief
response as to what you think of what we are seeing today may
look like projected out over 1,000 years from now. I will start
with Dr. Soon.
Dr. Soon. The factors causing climate change are extremely
complicated. As I emphasized already, I am very much interested
to learn how the climate changes on a local or regional scale
first before I can speak in terms of global climate. After all,
local and regional climate are indeed the most relevant
climatic factors that human activities are being influenced by
or the reverse way.
As to the factors of climate change, I believe that it is
extremely difficult yet still to confirm the facts of being,
let's say, even the late 20th century has anything to do with
CO2. We do know that the CO2 is rising,
but at the same time we know that climate depends on many other
factors. It could be doing it internally all by itself because
of ocean current movements. It could be done, for example, by
variability imposed externally from the sun, variable outputs.
Our sun is a variable star. That is a very well known fact.
These are the kinds of factors one has to look very
comprehensively at. Additional important factors of human
activity would include land use changes. Those are very well
known factors that one has to keep a good record, or time
history, to really understand what are the causes of the
I don't think I should speculate anything about futures. It
is always very dangerous to talk about the future of any
Senator Allard. Dr. Mann.
Dr. Mann. Yes. Well, I certainly agree with your statement
that one of the key issues is what we call the detection or the
attribution of human influence on climate, not just how has
climate changed over the past 100 years or past 1,000 years,
but can we actually determine the causal agents of change.
There has been a solid decade of research into precisely
that question by, again, the mainstream climate research
community in addressing the issue of the relative role of
natural factors, as well as anthropogenic factors. That
includes the role of the sun, the role of human land use
changes, and the role of human greenhouse gas increases. The
model estimates are typically consistent with what we have seen
in the observations earlier.
As far as the next 1,000 years, that is not a particular
area of expertise of mine, but I am familiar with what the
mainstream climate research community has to say about that.
The latest model-based projections indicate a mean global
temperature increase of anywhere between .6 and 2.2 degrees
Centigrade. That is one degree to four degrees Fahrenheit
relative to 1990 levels by the mid-21st century under most
scenarios of future anthropogenic changes.
While these estimates are uncertain, even the lower value
would take us well beyond any previous levels of warmth seen
over at least the past couple of millennia. The magnitude of
warmth, but perhaps more importantly the unprecedented rate of
warming, is cause for concern.
Senator Allard. Dr. Legates.
Dr. Legates. Yes. I agree, too, that attribution is one of
our important concerns. As a climatologist, I am very much
interested in trying to figure out what drives climate. We know
that a variety of factors exist. These include solar forcing
functions; these include carbon dioxide in the atmosphere;
these include biases associated with observational methods;
these also include such things as land use changes. For
example, if we change the albedo or reflected amount solar
radiation, that too will change the surface temperature.
So it is really a difficult condition to try to balance all
of these possible combinations and to try to take a very short
instrumental record and discern to what extent that record is
being driven by a variety of different combinations.
My conclusion probably in this case to directly answer your
question is that the temperature likely would rise slightly,
again due to carbon dioxide, but it would be much more
responsive to solar output. If the sun should quiet down, for
example, I would expect we would go into a cooling period.
Senator Allard. I guess the question that I would have,
now, you know you have increased CO2. So how is the
environment in the Earth going to respond to increased
CO2? Have any of you talked to a botanist or
anything to give you some idea of what happens when
CO2 increases in the atmosphere? Plants utilize
CO2, extract oxygen. We inhale oxygen and extract
CO2. Will plants be more prosperous with more
CO2? How does that impact the plant life? Can that
then come back on the cycle and some century later mean more
O2 and less CO2?
So I am wondering if any of you have reviewed some of these
cycles with botanists and see if they have any scientific data
on how plants respond to CO2 when that is the sole
factor. I am not sure I have ever seen a study. There is
moisture and other things that affect plant growth, but just
CO2 by itself. Have any of you seen any scientific
studies in that regard?
Dr. Soon. I have seen that. In fact, I have written a small
paper that has a small section regarding that.
Senator Allard. And what was their conclusion?
Dr. Soon. The conclusion is that in general, of course,
under enrichment of the CO2 in the free air, that
yes, plant growth will be enhanced. For example, as indicated
by your chart, the crop yield can increase by 30 percent or
higher for a doubling of CO2, depending on the
actual constraints in the field, like types of crops, how wet
or how dry, etc. All of these examples are very well known and
well verified in the field of botany.
Senator Allard. My time has run out. Would the other two
agree with what he said?
Dr. Mann. Not quite.
Senator Allard. What is your modification?
Dr. Mann. In fact, a number of studies have been done, what
are called ``FACE'' experiments. They are open canopy
experiments in which CO2 is elevated in the forest
and scientists examine the changes in the behavior of that
forest. What scientists at Duke University are finding is that
while there is a tendency for an uptake of CO2 by
the plants in the near term, what happens is eventually those
plants will die. They will rot. When that happens, this happens
on generational time scales.
Senator Allard. Just CO2 being the variable and
not moisture and anything else?
Dr. Mann. Just CO2. The CO2 will go
back into the atmosphere because the plants that take it up----
Senator Allard. Do they have an explanation of why the rot
Dr. Mann. Well, just when things die, they will rot and
they will give up their CO2 back to the atmosphere
Senator Allard. Well, that really does not get to the point
I was trying to make.
Dr. Legates. To follow on that, enhanced CO2 and
dying plants would also provide the ability for more plants to
therefore grow in its place. In particular, one of the people
on our study, Dr. Sherwood Idso, has done a lot of this study
with carbon dioxide and enhanced where you can control the
amount of water and energy available to plants associated with
lowered CO2 and higher CO2.
Senator Allard. So your conclusion is that CO2
increases plant growth?
Dr. Legates. Yes.
Senator Allard. OK.
Thank you, Mr. Chairman.
Senator Inhofe. Thank you, Senator Allard.
Senator Carper, we were going to go by the early bird rule.
Is it all right if Senator Thomas goes ahead of you here?
Senator Carper. Sure.
Senator Inhofe. Senator Thomas.
Senator Thomas. Thank you. I am a little confused about
where we even ask the questions. Obviously, there is a
difference of view. We are expected to make some policy
decisions based on what we ought to be doing with regard to
these kinds of things, but yet there does not seem to be a
basis for that kind of a decision. Where would you suggest we
get the information that is the best information we could get
to make policy decisions for the future? Would each of you like
to comment shortly on that?
Dr. Mann. Sure. I guess I would reiterate the comments that
I made earlier, that in a National Academy of Sciences study
that was commissioned by the Bush Administration in 2001, the
National Academy of Sciences in essence stated their agreement
with the major scientific findings of the Intergovernmental
Panel on Climate Change, the IPCC, which is the United Nations
panel of scientists, thousands of scientists from around the
world who put together a report on the state of our knowledge
about all of these things--climate change scenarios, our
uncertainty about various attributes of the climate system. The
conclusions that I stated earlier are the consensus conclusions
of the IPCC.
Senator Thomas. That is where you would go.
Dr. Mann. That is where they have gone, yes.
Dr. Legates. I would generally argue the IPCC is a bit of a
political document to the extent to which it does present some
biased science. There is a lot of good science in there, but a
lot of the conclusions are sort of not borne out by the facts.
Having been president of the Climate Specialty Group of the
Association of American Geographers, which is probably the
largest group of climatologists available, I know from talking
to rank-and-file members that they generally--my impression is
that most climatologists agree it takes a rather strong
So I have real serious concerns that it really represents a
consensus, and in particular when, for example, in this
discussion when we change dramatically what a lot of people
have held true, that is the Little Ice Age, Medieval Warming
and so forth, and replace it with a flat curve very quickly, I
do not think we have given it enough time to really decide if
in fact that is an appropriate change in paradigm.
Dr. Soon. Although I am not able to comment on anything on
public policies, I am certainly able to testify that the
science is completely unsettled. There are just so many things
that we do not know about how the climate really works and what
are the factors that cause it to change, to really jump to the
conclusion that it will all be CO2.
Senator Thomas. Thank you. That helps a lot.
Senator Inhofe. You still have some time remaining. Did you
have an opportunity to see the chart up here that Dr. John
Reilly, MIT Joint Program on Science Policy and Global Change?
On the floor yesterday, I talked at some length on this. There
seems to be a lot of consensus that there are some very
Senator Thomas. It is really interesting, you know, in
Schlesinger's thing it indicates that the temperature after
1940 dropped until 1977. So that makes you wonder what we ought
to do. The rise in temperature during the 20th century occurred
between 1900 and 1940. So now we are faced with making policy
decisions where there is no real evidence that the things that
the greenhouse gases measurable by the U.N. is the basis for
doing these things.
I know in science everyone has little different ideas, but
I do think we are going to have to, Mr. Chairman, as you
pointed out yesterday, either take it a little more slowly in
terms of policy, or we are not going to have something more
basic to base it on than we have now in order to make
significant policy changes.
Senator Inhofe. Thank you, Senator Thomas.
Senator Carper. Thank you, Mr. Chairman. I want to welcome
our witnesses this morning. Dr. Legates, it is great to have a
fighting Blue Hen here from the University of Delaware. We are
delighted that you are here. Dr. Mann, thanks for coming up,
and Dr. Soon, welcome. We thank you for your time and your
interest and your expertise on these issues, and your
willingness to help us on some tough public policy issues that
Dr. Mann, I would start off if I could and direct a
question to you. I understand we have had thermometers for less
than 200 years, and yet we are trying to evaluate changes in
temperature today in this century and the last century with
those that occurred 500 or 1,000 or 2,000 years ago. I
understand that we use proxies for thermometers, if you will,
and for those kinds of changes in temperature.
I wonder if you could help me and maybe the committee
better understand how we compare today's temperature
measurements to the proxies of the past. Are there potential
risks with relying on some of those proxies?
Dr. Mann. Absolutely. We have to use them carefully when we
try to reconstruct the past temperature history. So when I say
we have to use them carefully, it means some of the things that
I discussed in my testimony earlier, that we need to actually
verify that if we are using a proxy record to reconstruct past
temperature patterns, that proxy record is indeed reflective of
temperature changes. That is something that typically
paleoclimate scientists first check to make sure that the data
they are using are appropriate for the task at hand. Of course,
we have done that in our work. I did not see evidence that Soon
and colleagues have done that.
First of all, we next have to synthesize the information.
There have been some misleading statements made here earlier on
the part of the other testifiers with regard to local versus
regional or global climate changes. Of course, we have to
assimilate the information from the local scale to the larger
scales, just as we do with any global estimate of quantity. So
we take the regional information; we piece together what the
regional patterns of change have been, which may amount to
warming in certain areas and cooling in other areas. Only when
we have reconstructed the true global or hemispheric regional
patterns of change can we actually estimate the northern
hemisphere average, for example.
A number of techniques have been developed in the climate
research community for performing this kind of estimate. My
colleagues and I have described various statistical approaches
in the detailed climate literature. Some of the estimates are
based on fairly sophisticated techniques. Some of them are
based on fairly elementary techniques. Yet all of the results
that have been published in the mainstream climate research
community using different techniques and different assortments
of proxy data have given, as I showed earlier in my graph, the
same basic result within the uncertainties. That has not
changed. An article that appeared last month in the American
Geophysical Union, which is actually the largest professional
association of climatologists, showed that indeed that is the
consensus viewpoint of the climate research community.
Senator Carper. Thank you.
Dr. Legates, if I could ask a question of you, please. Have
you or anyone of your colleagues, at the University of
Delaware, to your knowledge studied the historical climate and
temperature records in our part of the country, in Delaware,
the Delmarva Peninsula, or the mid-Atlantic region?
Dr. Legates. We do not have anybody on staff presently that
does paleoclimatology. One of the basic understandings that you
must come up with when you study climate is that you must
understand various things of hydroclimatology, physic
climatology, and that includes paleoclimate study. So you must
be at least versed in these things if you are not necessarily a
We do have Dr. Brian Hanson at the University of Delaware
who has looked at glacier movements over long time periods, as
well as Dr. Fritz Nelson who has looked at changes associated
with permafrost locations.
Senator Carper. If someone were to do a study for our part
of the country, what do you think they might find?
Dr. Legates. A study regarding?
Senator Carper. Historical climate and temperature changes.
Dr. Legates. Over the East Coast of the United States? Most
of the assessments indicated that generally the East Coast has
gone through a variety of changes over long time periods.
Historically, we have had a condition where in the 1960's, for
example, we had conditions where there was much more snowfall.
We have had a lot of variability associated with air
temperature rising and falling over the local conditions.
Variability is usually the characteristic of climate over the
near-term as well.
Senator Carper. OK. Dr. Soon, if I could ask you and maybe
Dr. Legates the same question, the following question. That
question is, do you believe that it is possible to emit
unlimited amounts of CO2 into our atmosphere without
having any impact on climate or temperature?
Dr. Soon. I do not know how to precisely answer the
question. If you fill up every single molecule of the air with
CO2, that would be poisonous, of course. I do not
know the answer to the question, but I do like to add about the
evidence available on climate change.
Senator Carper. Before you do that, let me direct, if I
could, the same question to Dr. Legates. I do appreciate your
candor. It is not everyday that we find that here in this hall.
Dr. Legates. Generally, what we have found is that as
carbon dioxide has increased, the temperature has followed,
where in some cases historically the temperature has gone up
and the carbon dioxide has fallen. So generally from a purely
physical point of view, if you do increase the carbon dioxide,
you should wind up with some trapping of gases, and hence wind
up with a slightly increased temperature.
The question is, there is a lot of additional feedbacks
associated with it. For example, warmer surface temperature
leads to more instability or rising air which leads to more
cloudiness. Clouds can warm at night, but also reflect energy
in the daylight. So you have these odd playbacks into the
climate system which make it very difficult to say that if I
hold everything else constant and change one variable, what
will happen. Well, in reality, it is impossible to hold
everything constant because it is a very intricate and
interwoven system that one change does have feedbacks across
the entire spectrum.
Senator Carper. Thanks. I think my time has expired, Mr.
Chairman. Is that correct?
Senator Inhofe. Yes. Thank you, Senator Carper.
Senator Carper. Thank you.
Senator Inhofe. We will have another round here. In fact, I
will start off with another round. Let's start with Dr.
Legates. Dr. Legates, was the temperature warmer 4,000 to 7,000
years ago than it is today?
Dr. Legates. My understand was during about 4,000 to 7,000
years ago, in a period referred to as the climatic optimum,
which sort of led to enhanced agriculture and led to
development of civilization, generally the idea is that warmer
temperatures lead to more enhanced human activity; colder
temperatures tend to inhibit. Again, as we get back 4,000 to
7,000 years ago, it becomes, the error bars are getting wide as
well. But the general consensus is that temperatures were a bit
warmer during that time period.
Senator Inhofe. OK. Senator Thomas had something about, he
had alluded to 1940. Yesterday when I was giving my talk and
doing the research for that, it was my understanding that the
amount of CO2 emitted since the 1940's increased by
about 80 percent. Yet that precipitated a period of time from
about 1940 to 1975 of a cooling-off period. Is that correct?
Dr. Legates. That is correct. It is sort of a perplexing
issue in the time series record that from 1940 to 1970
approximately, while carbon dioxide was in fact increasing,
global temperatures appear to be decreasing.
Senator Inhofe. Dr. Mann, you have I might say impugned the
integrity of your colleagues and a few other people during your
presentation today. The Wharton Econometric Forecasting
Associates did a study as to the effect of regulating
CO2 and what would happen. American consumers would
face higher food, medical and housing costs; for food, an
increase of 11 percent; medicine, an increase of 14 percent;
and housing, an increase of 7 percent. At the same time, the
average household of four would see its real income drop by
$2,700 in 2010.
Under Kyoto, the energy and electricity prices would nearly
double and gasoline prices would go up an additional 65 cents a
gallon. I guess I would ask at this point, what is your opinion
of the Wharton study?
Dr. Mann. OK. First, I would respectfully take issue with
your statement that I have impugned the integrity of the other
two testifiers here. I have questioned their, and I think
rightfully, their qualifications to state the conclusions that
they have stated. I provided some evidence of that.
Senator Inhofe. Well, ``illegitimate, inexperienced,
Dr. Mann. Those are words that I used. Correct.
Senator Inhofe [continuing]. That is a matter of
Dr. Mann. I would furthermore point out that the very
models that I have referred to track the actual instrumental
warming and the slight cooling in the northern hemisphere.
There was no cooling of the globe from 1940 to 1970, the
Senator Inhofe. OK. The question I am asking you is about
Dr. Mann. I am not a specialist in public policy and I do
not believe it would be useful for me to testify on that.
Senator Inhofe. Dr. Legates, have you looked at the report
that Wharton came out with concerning the possible effects,
economic results of this?
Dr. Legates. Again, I am not a public policy expert either,
and so the economic impacts are not something which I would be
qualified to testify on.
Senator Inhofe. OK, Dr. Legates, do you think you have more
data than Dr. Mann?
Dr. Legates. I think we have looked at a large variety of
time series. We have looked at essentially a large body of
literature that existed both prior to Dr. Mann's analysis and
since Dr. Mann's analysis, in attempting to figure out why his
curve does not reflect the individual observations. It is one
issue associated with when you put together data sets, to make
sure that the composite sort of resembles the individual
Senator Inhofe. OK. The timeline, Dr. Mann, is something I
have been concerned with, and those of us up here are listening
to you and listening to all three of you and trying to analyze
perhaps some of the data that you use and the conclusions you
came to, having been 4 or 5 years back, compared to a study
that was done referring to Smithsonian-Harvard, the 1,000-year
study that was just completed, or at least given to us in March
of this year. I would like to have each of you look at the
chart up here and just give us a response as to what you feel
in terms of the data that both sides are using today.
Dr. Mann. I guess you referred to me first?
Senator Inhofe. That is fine. Yes.
Dr. Mann. OK. Well, I think we have pretty much
demonstrated that just about everything there is incorrect. In
a peer-reviewed publication that was again published in the
Journal Eos of the American Geophysical Union about a month
ago, that article was cosigned by 12 of the leading United
States and British climatologists and paleoclimatologists. We
are already on record as pretty much pointing out that there is
very little that is valid in any of the statements in that
table. So I think I will just leave it at that.
Senator Inhofe. Do the other two of you agree with that?
Dr. Legates. If I may add, the Eos piece was actually not a
refereed article. It is an Eos Forum piece, which by definition
is an opinion piece by scientists for publication in Eos. That
is what is contained on the AGU Web site for Eos Forum.
Senator Inhofe. All right. Let me ask one last question
here. Dr. James Hansen of NASA, considered the father of global
warming theory, said that the Kyoto Protocol ``will have little
affect on global temperatures in the 21st century.'' In a
rather stunning followup, Hansen said it would take 30 Kyotos,
let me repeat that, 30 Kyotos to reduce warming to an
acceptable level. If one Kyoto devastates the American economy,
very much by the findings of Wharton, what would 30 Kyotos do?
Is Dr. Hansen one of the most respected scientists in your
field or is he way off base?
Dr. Mann. Dr. Hansen is certainly one of the most respected
scientists in my field and I personally have great scientific
respect for him. I think that his conclusions have been grossly
taken out of context. His point is simply that Kyoto would, and
this is his point, these are not my opinions, would do very
little to ameliorate the warming over the next century for two
No. 1, there is something that scientists call the
commitment to warming. Once we put CO2 into the
atmosphere, it takes many decades, on orders of decades to
maybe centuries for it fully to equilibrate with the ocean and
the atmosphere. So some of that CO2 is taken up by
the ocean. So the effect of it is delayed. So cutting back on
CO2 now may not affect global temperatures for 50
years, but 50 years later it is going to come back to roost.
Senator Inhofe. All right, that was a rather long answer,
so let me just, with the indulgence of my fellow Senators here,
I just want to ask one last question. I quoted Dr. Frederick
Seitz, the past president of the National Academy of Sciences
yesterday, and professor emeritus at Rockefeller University,
who compiled an Oregon petition which says there is no
convincing scientific evidence that human release of carbon
dioxide, methane and other greenhouse gases is causing, or will
in the foreseeable future cause catastrophic heating of the
Earth's atmosphere and disruption of the Earth's climate.
Moreover, there is substantial scientific evidence that
increases in atmospheric carbon dioxide produce many beneficial
effects upon the natural plant and animal environments of the
Earth. Do each of the three of you agree or disagree with his
Dr. Soon. I agree.
Dr. Mann. I find little in there to agree with.
Dr. Legates. I would tend to agree.
Senator Inhofe. All right.
Senator Jeffords. As you may know, this is to all of you,
the editor-in-chief of the magazine Climate Research resigned
the position yesterday over problems with Dr. Soon's paper. In
an e-mail sent to my staff, he said,
``My view, which is shared by many, but not all editors and
review editors of Climate Research, is that the review of the
Soon et al paper failed to detect significant methodological
flaws in the paper. The critique published in the Eos journal
by Mann et al is valid. The paper should not have been
published in this forum, not because of the eventual
conclusion, but because of the insufficient evidence to draw
What methodological flaws does he mean?
Dr. Mann. Well, I have tried to outline the most severe of
those methodological flaws. I believe it is the mainstream view
of just about every scientist in my field that I have talked to
that there is little that is valid in that paper. They got just
about everything wrong. They did not select the proxies
properly. They did not actually analyze any data. They did not
produce a reconstruction. They did not produce uncertainties in
a reconstruction. They did not compare to the proper baseline
of the late-20th century in trying to make conclusions about
So I think it is the collective view of our entire research
community that that is one of the most flawed papers that has
appeared in the putative peer-reviewed research in recent
Senator Jeffords. Dr. Soon, do any scientists besides your
coauthors support using wetness or dryness as indicators of
past temperatures, instead of actual temperatures or proxy data
that reflects temperatures?
Dr. Soon. As we explain clearly in our paper, and as it has
been highly mischaracterized by my fellow colleague here, Dr.
Mann, we certainly agree when we speak in term of the Medieval
Warm Period, temperature is one of the important parameters. As
we emphasize and specify in our papers that climate is not
temperature alone. One has to look in terms of the water cycle,
in terms of even the air cycles, in terms of the vegetation
changes. These are the kind of details that we did not make any
presumptions, but simply want to look at the patterns of change
geographically all over the world, and see how complete the
datas are, and then begin to start to see how do we assemble
all such information.
Senator Jeffords. This is for the whole panel. I would like
to know whether the unusual melting of Greenland ice sheets
shown in this picture over the years 2001, 2002 and 2003, has
been matched in the long-term climate history any other time?
And according to NASA, by the end of the year 2002 season, the
total area of surface melt in the Greenland ice sheet had
broken all known records. By the end of that summer ``Sea ice
levels in the Arctic were the lowest in decades and possibly
the lowest in several centuries.''
NASA says this warming is happening faster and earlier than
in previous periods. What is happening now and what is going to
happen if this continues?
Dr. Mann. Well, this is, of course, one particular region,
one potentially isolated region, Greenland, in which there is
evidence of mass oblation of ice. But if we look at what is
going on the world over, mountain glaciers in the tropics
throughout the world, glaciers in both the northern hemisphere
and the southern hemisphere, what is seen is that glacial
retreat during the late 20th century is unprecedented on
similar time scales to the time scales I have spoken of before,
the past 1,000 to 2,000 years.
I believe Professor Lonnie Thompson of Ohio State
University has testified in this Senate before with regard to
the dramatic evidence of worldwide glacier retreat. So that is
a cause for concern. It is a harbinger of the warming because
in fact the warming that is shown in those glacier retreats is
actually warming that we are already committed to for decades
Dr. Legates. Historically, it has been demonstrated in the
refereed literature that much of this glacial retreat actually
began in the late 1800's, before much of the carbon dioxide
came into the atmosphere. This is very much consistent with the
demise of the Little Ice Age and longer time-scale variations.
Therefore, it is very difficult to say that these kind of
events are directly attributable to human impacts on the
climate, when they in fact pre-date human impacts on the
Senator Jeffords. Dr. Soon.
Dr. Soon. My only comment regarding that kind of chart or
the claim that it has never happened before is that to think
about the available, detailed observation that we have. We do
not really have any satellite record longer than 20 to 30
years, so the statement that it has never happened before I
think is dangerously inaccurate.
Senator Jeffords. Dr. Mann.
Dr. Mann. Yes. It is unfortunate to hear comments about the
supposed inconsistencies of the satellite record voiced here,
years after that has pretty much been debunked in the peer-
reviewed literature, in Nature and Science. Both journals have
in recent years published several rigorously peer-reviewed
articles indicating that in fact the original statement that
the satellite record showed cooling was flawed because the
original author, John Christy, did not take into account a
drift in the orbit of that satellite, which actually leads to a
bias in the temperatures from the satellite.
Christy and colleagues have claimed to have gone back and
fixed that problem, but just about every scientist who has
looked at it says that their fix is not correct. If you fix it
correctly, then the satellite record actually agrees with the
surface record, indicating fairly dramatic rates of warming in
the past two decades.
Senator Jeffords. I have one last question, Dr. Mann. What
are the implications of your peer-reviewed work for future
Dr. Mann. As I said before, there have been a number of
modeling simulations that have shown a fairly good match to our
reconstruction and that of several independent research groups
who have also produced these reconstructions of northern
hemisphere temperature. So to the extent that the models match
that record of the past 1,000 years when they are forced with
various estimates of natural changes in the system, it gives us
reason to trust what the models say about the future. As I
testified before, the models tell us that we are likely to see
a one degree to four degree Fahrenheit warming by the mid-20th
century, given most predicted scenarios of continued
anthropogenic influence on the climate.
Dr. Legates. If I may add something, one of the things I
have heard is that science has been debunked and, for example,
we pointed to Dr. Christy's curve up here and said that because
one paper has been written, that curve is now called into
question. We have talked about--you mentioned von Storch's
resignation from Climate Research because apparently he has
admitted that this paper never should have been published.
I want to point out that science debate goes on and on. In
particular, Dr. Christy has had some very important
contributions to indicate that his curve is not incorrect. That
is part of scientific debate. Furthermore, I will say with
respect to Climate Research, Otto Kinne, who is director of
Inter-Research, the parent organization of Climate Research,
asked Chris de Freitas who was the editor who served on the
Soon and Baliunus papers, and I can relay this because I am a
review editor of Climate Research so I am familiar with what
has been taking place.
There were several people complaining that Chris de Freitas
should be removed simply because he published the Soon and
Baliunus paper. That question was brought to Otto Kinne. He
asked for Chris de Freitas to provide him with the reviews, the
changed manuscripts and so forth. He provided a letter in late
June to all of us in which he said,
``I have reviewed the evidence and I have indicated that the
reviews, four for each manuscript, in fact there was a second
or an earlier Soon and Baliunus article on another topic that
was also called into question by these people leveling
Essentially what he concluded was that the reviewers
provided good and appropriate comments; that Doctors Soon and
Baliunus provided an appropriate dressing or incorporation of
these concerns; and that Chris de Freitas had in fact provided
Toward that end, Dr. von Storch was approached. Climate
Research was putting in an editorial stating essentially this
article should never have been published. Otto Kinne was
informed and he has asked him not to submit that because it is
not founded, and as a result Dr. von Storch, I now understand,
has said he would resign.
Senator Jeffords. Dr. Mann.
Dr. Mann. Yes, just a very short comment. It is
unprecedented in my career as a scientist to hear of a
publisher of a journal going in and telling the editor-in-chief
that he cannot publish an editorial. I find that shocking and a
bit distressing. I do not know what the circumstances are
behind it, but it is disturbing.
Dr. Legates. It is also unprecedented to find an editor
being attacked, and this has also happened with the editorial
staff of Energy and Environment, which is the other paper, to
find an editor attacked for simply publishing an article that
has been peer-reviewed and approved by reviewers.
Senator Inhofe. All right. The time has expired. We are 4
Senator Jeffords. I think that my witness should have the
last word on my question, if I could. Dr. Mann, do you have any
response to that?
Dr. Mann. Actually, my understanding is that Chris de
Freitas, the individual in question, frequently publishes op/ed
pieces in newspapers in New Zealand attacking IPCC and
attacking Kyoto and attacking the work of mainstream
climatologists in this area. So this is a fairly unusual editor
that we are talking about.
Senator Inhofe. All right, thank you.
Senator Clinton has joined us. Senator Clinton would you
like to have your round now?
Senator Clinton. Thank you very much, Mr. Chairman. I thank
you for this hearing. I understand that the questioning and the
testimony has been somewhat lively, if not controversial and
contested. The bottom line for me is whether we are doing what
we need to do to ensure the best possible climatology outcome
for future generations. I would stipulate that the Earth's
climate has changed through the millennia. There is no doubt
about that. I have read enough to know that we have had ice
ages and we have had floods and we have had volcanoes. We have
had lots of naturally occurring events which have affected our
climate. We have El Nino and his spouse, El Nina. We have all
of that. That is not debatable.
The issue is whether the introduction and acceleration of
anthropogenic activity primarily related to the burning of
fossil fuels is putting into place conditions that will make it
difficult, if not impossible for the Earth to regain its
balance, that will support the conditions of life that we have
inherited and are blessed with.
I know these debates have political implications because
heaven forbid that we would tell somebody in the private sector
not to do something, or that we might have to make sacrifices
in the quality of our life for future generations. I think that
it is not useful to carry out this kind of argumentation when
it is clear that by the very nature of human development and
industrialization, we have changed what is in the atmosphere,
what is in the earth, what is in the waters.
That does not mean there was no change before we came
along, and certainly in the last century that change has
accelerated because the quality of life has improved, we have
created chemicals that were never known in nature before. We
have done a lot of things.
But I think that our goal should be to try to figure out
how to do no harm or do the least amount of harm, and to ask
ourselves, what are we willing to perhaps sacrifice to make
sure that we are not contributing to irreversible changes. I
know that academia is probably the most political environment
in America. I was once on a staff of a law school. It was more
difficult than any politics I had ever been involved in
beforehand. I know that people have very strong opinions and
hold on to them.
From my perspective, I just want to believe that I am
making a contribution to ensuring that the quality of life for
future generations is not demonstrably diminished. I would feel
terrible if I participated, either as a willing actor or a
bystander, in this potential undermining of our Earth's
So Dr. Mann let me ask you, what was the Earth's climate
like the last time that there was atmospheric concentration of
carbon dioxide at today's levels of 370 parts per million?
Dr. Mann. Thank you, Senator, that is an excellent
question. We have to go back fairly far into the past to find
CO2 levels approaching the CO2 levels
today. Ice core studies that have been done over the past
decade or so have told us that today's CO2 level is
unprecedented now in at least four glacial or inter-glacial
cycles. That is more than 400,000 years.
In fact, now as we look back from other evidence that is a
bit more tentative, it appears that modern CO2
levels probably have not been observed in 10 million to 20
million years. So we have to go back to the time of the
dinosaurs, probably, to find CO2 levels that we know
were significantly higher than CO2 levels today.
Some people will say, ``Well look that was a great time.''
The dinosaurs were roaming near the poles. It was warm near the
north pole. There were palm trees in the poles. Isn't that what
we want? Well, that was a change that occurred on time-scales
of tens of millions of years. What we are observing right now
is a similar change that is occurring on time-scales of
Senator Clinton. Thank you. Thank you, Dr. Mann.
Senator Inhofe. Senator Clinton, if you would like to have
some more time, since we are on the second round now, feel free
to take another couple of minutes.
Senator Clinton. Thank you very much, Mr. Chairman.
I guess that is, for me, the dilemma, because I certainly
understand the testimony of the other two witnesses, and I read
with great interest former Secretary Schlesinger's op/ed. I
know that there are those, who are in a minority, let's at
least admit that, who are in a minority, but who certainly have
a very strongly held set of beliefs, and I respect that.
But I do believe that the compression of time in which
these changes are occurring is extraordinarily significant. We
can go back and look at the Earth's natural 125,000-year cycle,
but I do not think we want to risk the enormous changes that
could occur. I do not think we have a million or 10 million
years or even 100,000 to experiment.
I think that the challenge confronting us is not to put our
heads in the sand and let the academic argument take place, but
figure out how in a sensible, prudent manner we could
ameliorate these changes significantly enough so that if Dr.
Soon and Dr. Legates are right, no harm done. If Dr. Mann is
right, we will have saved ourselves a lot of potential damage
So I hope that we could put our heads together. I commend
my two colleagues, both Senator Jeffords and Senator Carper,
who have very sensible legislative answers to trying to get a
handle on this. As I have said in this committee before, I
stand ready to figure out ways to hold harmless our industrial
base and others. I think it is a significant enough political,
economic and moral challenge that if there are ways to make it
financially possible for companies to do what needs to be done
with respect to carbon dioxide and other atmospheric pollutants
that have accelerated their presence in our atmosphere so
dramatically in the last 100 years, I think we should do that.
This is not just a private sector problem. We all have
benefited from the increasing use of fossil fuels, for example.
Our standard of living is dramatically better. One of our
problems is what is going to happen if China and India get a
standard of living anywhere comparable to ours, and then begin
to really--and I see Dr. Soon nodding--I mean really dump into
the atmosphere untold amounts of new pollutants of whatever
kind, leading certainly with carbon dioxide.
So this is a problem we need to get ahead of, and it is not
a problem that the United States alone should be responsible
for. It is not a problem that the private sector alone should
be responsible for. But I believe, just as a prior generation
of decisionmakers really put a lot of work into the law of the
oceans and trying to figure out how we could protect our
oceans, we need to do the same on the atmospheric level. There
has got to be a way that we can come together on this big
So Mr. Chairman, I appreciate your continuing attention to
this. I, for one, stand ready to work with you and our other
colleagues because I just think this is too risky a proposition
not to act on, given the weight of opinion, even with the
dissenters, who I think do rightly point out the incredible
natural cycle, but we are now so influencing that natural
cycle, I do not know if we have the time to contemplate the
balance once again regaining itself in our wonderfully
Senator Inhofe. Thank you, Senator Clinton.
Senator Carper. Thanks, Mr. Chairman. I just want to
followup. Senator Clinton was kind in her comments on the
legislation, the one that Senator Jeffords has introduced and
second on legislation I have introduced along with Senators
Judd Gregg, Lincoln Chafee and Lamar Alexander.
Are any of you familiar with that legislation? Would you
like to become familiar over the next 5 minutes?
Dr. Soon. No, we will stick to science. Politics is too
Senator Carper. All right. That may be the best approach.
We are trying to figure out if there is a reasonable middle
ground on this issue. I am part of a group that Buddy MacKay, a
former colleague of mine from Florida, calls the flaming
moderates or flaming centrists. We can spend a whole lot of
time discussing the impact of Kyoto caps, or we can focus on
what steps we actually need to take.
The approach that Senators Gregg and Chafee and Alexander
and myself have taken, at least with respect to four
pollutants, we say unlike the President's proposal where he
only addresses sulfur dioxide and nitrogen oxide and mercury,
and does not address CO2, as you know, because he
thinks we need to study it a bit more. Our approach says that
there ought to be caps on CO2; that they should be
phased in; that we should use a cap and trade system; we should
give utilities the opportunity to buy credit for levels of
CO2 emissions that they maintain at high levels; and
they should be able to contract with, among others, farmers and
those who would be forced out of lands to change their planning
patterns or change their animal feedlot operations in order to
be able to sequester some of the CO2 that occurs in
We have something called new source review. The President
would eliminate it entirely. I think in Senator Jeffords'
approach, it is pretty much left alone. There is a good
argument that says that utilities under current law, if they
make some kind of minor adjustment and minor investment in
their plant, that they have to make a huge investment with
respect to the environmental controls. As a result, it keeps
them from making even common sense kinds of investments in
their plants--sort of the laws of unintended consequences. That
is sort of the approach that we have taken.
Now that you know all about it, if you were in our shoes,
what kind of an approach would you take? Let me just start with
our University of Delaware colleague here, Dr. Legates.
Dr. Legates. Generally, I favor no regrets policies, where
they have other applications as well. But again, getting into
the politics and the non-science aspects of what to do is out
of my area of expertise. I may have my own beliefs, but they
are no more important or less important than the average
person. I would rather not testify to those here.
Senator Carper. If you were convinced, and some of my
colleagues have heard me talk about Dr. Thompson before, I
don't know that they testified before this committee, but
Doctors Knoll and Thompson spend their lives going around the
world and they chart the disappearance of snow caps in some of
the tallest mountains. I first met them here in Delaware about
5 or 6 years ago to receive an award for their research.
But they tell us that the snow caps around some of the
tallest mountains in the world, the Himalayas and others, are
not just disappearing, they will be gone, and they will be gone
in our lifetime. When I heard them speak and talk about their
work and what they were charting and finding, it got my
attention. When you hear that, Dr. Legates and Dr. Soon, how
does it affect you?
Dr. Soon. As a scientist, I am still questioning the actual
evidence. The fact is that meltings may be recorded for certain
glaciers. But among the things that we know is that there are
about 160,000 glaciers around the Earth, but only 40 to 50
glaciers have been measured for 10 years or longer to tell us
how much the ice has accumulated or has ablated.
Some of the specific melting examples, like Kilimanjaro,
that Dr. Lonnie Thompson has looked at, or some places in Peru
may be true. But the quality of the data records is really
telling us that we do not have enough strong evidence to
suggest that all the ice will disappear quickly and completely,
or that all of it is unprecedented. Climate change is part of
nature. As I tried to emphasize in my research by looking
carefully into all the climate proxies, there are large local
swings in the climatic changes.
Senator Carper. Dr. Soon, what would it take to convince
you that this is a problem we need to deal with?
Dr. Soon. As to some of the glaciers disappearing now in
some parts of the mountains, I do not consider that to be
either a problem or strong evidence----
Senator Carper. No, no, the big issue. What would it take
with respect to the concerns about global warming fed by
CO2 accumulation, what would it take to convince you
that this is a problem we need to do something about?
Dr. Soon. OK. Scientifically, I would go by this very
simple test. The simple test should be that the warming should
be occurring first at the troposphere, the layer of air about
four kilometers above us. That is a key part of the atmosphere
that one should expect the CO2 greenhouse effect to
work its way downward toward the surface. I would urge, of
course, very seriously that we do not lose sight in all these
debates about science, we must sustain a certain kind of level
of observational effort to keep track of data so that while we
are arguing around what to do, that one has some records about
any level of change that may occur.
So what it would take is that the CO2 warming
should happen at the layer of air four kilometers first. I
would require it be strongly sustained for maybe 20 years or
so. Then I would really believe that we have clear
CO2 fingerprints somewhere.
Senator Carper. Mr. Chairman, I know my time has expired.
Could I just ask that same question of Dr. Legates? What would
it take to convince you?
Dr. Legates. Proof. Generally the problem we have seen in
the record is that there is an awful lot of variability and
there are things where changes occur, for example, between 1940
and 1970 where the temperature decreased, even though carbon
dioxide was increasing. That sort of indicates to me that
carbon dioxide may not be the biggest player in the game. Solar
variability is likely to be the bigger player, changes in solar
output. After all, if the sun goes out, our temperature drops
considerably. We know historically that as the sun fluctuates
in terms of its output, the climate does respond.
So there are a lot of other factors involved and I am not
entirely convinced, based upon the proof, that carbon dioxide
is a driving force. It is a contributory force in a small case,
but not driving enough, because we wind up making policies
potentially that can lead us to try to keep back the ocean, if
you will. You cannot stop the waves from coming in.
Senator Carper. Dr. Mann.
Dr. Mann. Two quick points. First of all, it grates on me
to hear this argument about cooling from 1940 to 1970
continually cited here as evidence against anthropogenic
climate change. That cooling was almost certainly anthropogenic
and there has been a decade of research demonstrating that,
anthropogenic sulphate aerosols, which have a cooling effect on
the climate. What is happening now is that the much greater
effect of increasing greenhouse gas concentrations is
overtaking that small cooling effect of sulphate aerosols, also
an anthropogenic influence, but not the one that is going to
take us to doubled levels of CO2 in the next
One quick other comment, if I could. Lonnie Thompson's
work, which is some of the best work in our field, it is not
like he has been looking for ice cores that are melting. He is
actually looking for ice cores that are not melting because he
wants to get long records. So if there is any belief that there
might be some bias in the glaciers that he has gone to, if
anything it is the opposite. He is looking for long records, so
that makes it that much more impressive that they are all
Senator Carper. Thank you.
Senator Inhofe. Senator Allard.
Senator Allard. Thank you, Mr. Chairman.
What agency do you think we probably have the most
expertise in as far as climatology change and what is happening
with global climate? Would that be the agency on the National
Oceanographic and Atmospheric Science, would that probably be
where we would have most of our experts? If not, which agency
do you think we would have most of our experts as far as the
government is concerned? To any member of the panel, I would
like to know whether any of you concur or not.
Dr. Mann. Well, I think that the different agencies
specialize in different areas of the climate change research
question, if you will. NOAA's specialty is in looking at
climate variability, particularly with regard to oceanic
variability. So they emphasize that area of the research. A lot
of the peer-reviewed research, for example Lonnie Thompson's
work that we just spoke of, is funded by the National Science
Foundation in large part. There are other organizations.
Senator Allard. The Foundation, is that an agency of the
Dr. Mann. Well, not directly.
Senator Allard. The question is, what is an agency of the
Federal Government? The only one that I could think of was
NOAA, but are there other agencies?
Dr. Legates. NASA does a lot of research, satellite-related
efforts trying to estimate climate trends, incorporating
satellite measurements as well.
Dr. Mann. As well as the Department of Energy and EPA.
Senator Allard. Yes, the Department of Energy.
Dr. Legates. The Department of Interior as well.
Senator Allard. OK. But we do not have any, say, each
agency would have their own area of interest, but it seems to
me that we need to look at global warming from a total
perspective and I am trying to figure out if there is an agency
that does that. I have talked to people within NOAA. There are
arguments going on within that agency on the very topic that we
are talking about here. There is absolutely no consensus within
the agency, and I am trying to figure out if there is an agency
out here that is taking on an overall view. I guess really
there is not. We are just going to have to rely on the science
community somehow or the other pulling all these views out from
these various agencies. They look at the atmosphere, like you
say, NASA looks at the stratosphere and higher up where your
Dr. Legates. On the surface, too.
Senator Allard. We need somebody that looks at the effect
on plant life, animal life, the total cycle; oxygen,
CO2 and all that before you reach conclusions. I am
just wondering who pulls all this together so that we can come
up with a total picture of what is happening as far as changes
to this Earth is concerned, because it is more than just one
Dr. Mann. There is a program, the U.S. Global Change
Research Program, which seeks to coordinate the various
agencies on issues of fundamental importance in the research of
climate variability and climate change. So I think that is
Senator Allard. OK. I want to get back a little bit to the
absorption of sunlight, for example, on the Earth's surface. It
seems to me, and I don't know how accurate this is. I want to
check this out because it has been suggested to me by a number
of people, that our absorptive surface on the Earth has
increased. We still have the same amount of surface, but for
example you have pavement in urban areas. We know that pavement
is absorptive. Has that had an impact on global warming?
Dr. Mann. Most definitely.
Senator Allard. In your view?
Dr. Mann. Yes, your statement is correct. The main increase
in the absorption by the Earth's surface is due to the melting
of snow and ice. That has certainly had a very large influence
on the warming, but it is part of the warming.
Senator Allard. So you do not think the construction of--we
have more pavement than we did two centuries ago or a century
Dr. Mann. Most models suggest that that is a cooling.
Senator Allard. Is there enough of that that we have more
fields probably because of agriculture throughout the world,
just not the United States. This is all over the world.
Dr. Mann. Yes. Most estimates suggest that there is a small
cooling of the Earth's surface due to those changes.
Senator Allard. Would you all agree to that?
Dr. Legates. The pavements are associated with the
urbanization effect, which is part of the problem associated
with where we have observational measurements. Generally where
you have a decrease in the light and heat exchange that is
evaporation of water taking place because we have removed
trees; the fact that you have darker surfaces; you have canyon-
like effects. All of these lead to warmer temperatures in the
city. The urban heat ion effect is well-documented and that is
where virtually all of our observations are located.
But there are also changes in land surface effects by the
fact that we are removing vegetation and replacing it with
grasslands, for example, deforestation, de-vegetation. A lot of
these are on very large-scales too, and they do change the
color and character of the Earth's surface and hence the
A lot of the cryosphere, a lot of the ice and snow is
temporally variable. We have a growing area and decreasing
area, so that does integrate itself out over time to some
Senator Allard. Does the absorptive surface of the Earth's
surface have an impact on whether we have a warmer temperature
or not today?
Dr. Legates. Yes, absolutely.
Dr. Soon. Oh certainly, yes.
Senator Allard. I am a little bit confused of what the
final view is. Do we increase temperature or do we cool the
Dr. Mann. Can I comment?
Senator Allard. Yes. You said that it cooled.
Dr. Mann. Yes, the effects that----
Senator Allard. OK, now, I would like to hear from----
Dr. Mann [continuing]. That is not the whole story. What he
said is correct, but the effect that is dominant in models in
about three or four different studies published in the past 2
years on precisely this question is actually the change in
absorption by the land surface due to deforestation and other
agricultural changes. That leads to an overall cooling of the
globe, even in the face of other possible effects of warming.
Senator Allard. Would you agree with that?
Dr. Legates. Not necessarily. In particular, you are
changing a characteristic, but you are also changing the other
interactions. You are changing the vegetation and you are
changing the evaporative characteristics.
Senator Allard. But your bottom line is that you think
that, with increased absorptive rate on the Earth's surface, it
has a cooling or a warming effect?
Dr. Legates. If you increase the absorption rate on the
Earth's surface, you will have to have a net warming effect.
Dr. Soon. You have to have a warming.
Senator Allard. You have a warming.
I mean, to me this is a fairly fundamental concept, and
here we are, we have disagreement at this table about that.
Dr. Soon. I don't think Dr. Mann is listening to your
Senator Allard. To me, from my practical experience, it
seems to me that there is a warming effect. When I walk out on
a pavement with my bare feet, they get burnt. If I walk on
grass, my feet feel a lot cooler. I just look at it from a
practical aspect. So Dr. Mann, would you explain to me why
there is a difference in what you say and what I am feeling
physically when I walk on the surface of the Earth?
Dr. Mann. Sure. When you are walking, you are only covering
a pretty small fraction of the surface area of the Earth. The
effect that you are talking about, for example, the urban heat
island effect of blacktop and its tendency to absorb heat, that
is overwhelmed by larger-scale changes that we do not
necessarily see because they are not where we are walking
around. Large areas of the surface area of the Earth are being
changed in terms of their vegetation characteristics. That has
a net cooling. The answer on that is clear in the peer-reviewed
Senator Allard. The reason I bring this up is that in the
State of Colorado we have a lot of variation. We go from 3,000
to over 14,000 feet and we have a lot of different ecological
systems in Colorado, depending on altitude and moisture and
We have a weather reporting station in a rural area, in the
plains of Colorado, and the data that I am getting from them,
there is no indication of change as far as temperature is
concerned. Yet as we move into the more urban areas, then we
get weather stations that are indicating a higher temperature.
So I am wondering worldwide, with the urbanization of the
world, is there a possibility that we could be dealing with
some temperature changes that are a result of the absorptive
surface on the Earth like urbanization, you mentioned
urbanization, we have a lot more than we used to have. Doesn't
this have an impact on temperature?
Dr. Legates. Yes, definitely. Essentially, I do not think
Dr. Mann answered the question appropriately in that your basic
question was, if we absorb more radiation at the surface, will
the temperature not go up? That is correct. The temperature
will go up. In a sense, that is physics.
Senator Allard. Would you agree with that, Dr. Mann?
Dr. Mann. No. He has gotten about three different things
Senator Allard. No, listen.
Dr. Mann. His first statement is wrong.
Senator Allard. I understand your statement. You are taking
a broader atmospheric picture. You are taking a total picture.
But the statement he made at this point, would you agree with
Dr. Mann. No. It is not correct.
Senator Allard. You would not agree?
Dr. Mann. The statement that he made was that there is an
urban heat bias in the estimate of the surface temperature
changes of the Earth.
Senator Allard. I did not hear him say that.
Dr. Mann. He said that earlier when he talked about urban
Senator Allard. I am talking about the comment that he just
made. Would you repeat the comment, Dr. Legates?
Dr. Legates. I essentially said the basic physics is that
if you make the Earth's surface darker, you will absorb more
energy, you will reflect less energy, as a result the surface
temperature should increase.
Senator Allard. Would you agree with that scientific fact?
Dr. Mann. That statement would be in the first chapter of
most textbooks. Yes.
Senator Allard. Dr. Soon, I did not mean to ignore you. You
wanted to say something?
Dr. Soon. I tried to just emphasize that that is all you
Senator Allard. Yes.
Dr. Soon. If you increase absorptivity of the surfaces by
changing it through any means, then more heat will be retained.
Senator Allard. I think part of the problem that we are
running into here on the testimony is that we are not talking
on the same terms. I think that we have to be very careful when
we review the record and when we are listening to the witnesses
here, Mr. Chairman, that we understand that we are all talking
on the same terms in making the same point. I think the
committee gets confused when we start talking from different
terms and different perspectives.
I am just trying to simplify this argument down. I guess
what I am coming to is that, as I have stated earlier, it is
easy for me to believe that there is a trend in warming. The
bottom line is what is causing it and what is going to be the
long-term effects with this.
To me, the science is not entirely clear on that, and I do
not see that that is being entirely clear on this panel because
when I asked that question earlier, nobody gave me a specific
on what they saw the effects were going to be. Maybe Dr. Mann
did, and said that there was going to be warming. But most
scientists when I talk to them just won't give me what they
think the Earth is going to look like 1,000 years from now, or
they will not necessarily step right out and say what are the
causes of it because there are an awful lot of variables. I am
not sure that scientists understand all those variables.
Dr. Legates. I think that is the issue. It is so uncertain
and there are so many things that go into the mix, that to say
fairly definitively it will be such in the future is very
difficult to say.
Dr. Soon. We have to keep emphasizing that CO2
is not the only player, the only factor. It is just highly
short-sighted to just look at CO2 as just one sole
cause of change for every other change that we see or any
variations that we manage to record.
Senator Allard. Yes. And when we talk about greenhouse
gases, I think there is a tendency for us to think just in
terms of CO2.
Dr. Soon. Right.
Senator Allard. But isn't water vapor? Water vapor is a big
part of greenhouse gases.
Dr. Soon. That would be the area of expertise by Professor
David Legates. He studied that for almost 20 years.
Senator Allard. I do not know as we understand all of the
aspects of each one of those fractionated, if we were to pull
out each CO2 or put out water vapor. What other
gases do we have out there? Those are the main ones.
Dr. Mann. The other two have commented. May I comment as
Senator Allard. Let me finish my point. What are the
greenhouse gases that we have?
Dr. Mann. I will speak to that.
Dr. Soon. Methane.
Senator Allard. Oh, methane. OK. We have methane. But the
main ones are water vapor and CO2. Water vapor being
the largest, right?
Dr. Soon. Yes.
Dr. Mann. Can I comment on that?
Senator Allard. Dr. Mann.
Dr. Mann. Yes. There are trace gases like methane, carbon
dioxide, chlorofluorocarbons, which we can actually control.
Senator Allard. Well, carbon dioxide is a very small part
of greenhouse gases? Is that what you are saying?
Dr. Mann. No. There are several different greenhouse gases
that we have to keep in mind, and it would be short-sighted to
only talk about carbon dioxide. That is absolutely true.
Senator Allard. Right.
Dr. Mann. It is extremely misleading, however, when
scientists cite the role of water vapor as a greenhouse gas.
The concentration of water vapor in the atmosphere cannot be
controlled by us directly, unlike the other trace gases. It is
fixed by the surface temperature of the Earth itself. This is
actually another chapter one textbook-type of result that we
know to be true in the scientific community.
So we cannot change that freely. We can only change the
other trace gases. When we do change those, we warm the Earth.
We evaporate more water vapor and that gives us what we call a
positive feedback that actually exaggerates the problem. But
the water vapor itself cannot be the source of the problem.
Dr. Soon. It is really also scientifically inaccurate to
say that we can really control CO2. The global
carbon cycle--we do not understand it well enough to really
match or account for the CO2 that we emitted. How
much of it is really going into the ocean? How much of it has
really gone into the forest? We do not have actually a full
control of those parameters, as Dr. Mann would like to state on
Senator Allard. Dr. Legates, do you have any comment?
Dr. Legates. Generally, the idea is that water vapor is the
most important greenhouse gas. Period. That is Chapter One of
any introductory text. The issue is, then, if we are
associating with the effects of carbon dioxide and methane,
which by the way has actually started to decrease over time,
what we have found out is that in particular we are dealing
with with small matters where the bigger issues are not
Again, the sun is the biggest game in town and it is not
controllable. At least I do not know that we can turn off the
sun or control its output.
Senator Allard. OK. Senator Carper I think has a few
Senator Inhofe. We have a serious problem here now, I am
sorry to say, and that is that we are 30 minutes past our first
panel and we are going to have to cut it off right now.
Senator Allard. OK, Mr. Chairman.
Senator Inhofe. I am very, very sorry. Thank you very much.
I appreciate the fact that you are here.
We would call our next panel up. I apologize to the next
panel because of the length of the first panel, we will have to
cut this one short.
Dr. Leonard Levin is the program manager, Electric Power
Research Institute; Dr. Gary Myers, professor of neurology and
pediatrics, University of Rochester Medical Center; and Dr.
Deborah Rice, the toxicologist, Maine Department of
Environmental Protection, Bureau of Remediation and Waste
I would like to ask each of you to confine your opening
comments to 5 minutes, if you would. Your entire statement will
be made a part of the record. We would start, Dr. Levin, with
STATEMENT OF LEONARD LEVIN, PROGRAM MANAGER, ELECTRIC POWER
Dr. Levin. Thank you, Mr. Chairman, members of the
I am Dr. Leonard Levin. I have come to discuss recent
findings on mercury in the human environment. I serve as
technical leader at EPRI, which is a nonprofit collaborative
research organization. My remarks today represent my synthesis
of research findings and are not an official statement of EPRI
It is a privilege to provide the committee this testimony
on the science of mercury. I would like to address three key
questions: sources of mercury; its deposition from the
atmosphere to the Earth's surface; its potential accumulation
Where does mercury in the U.S. environment originate?
Mercury is clearly a global issue. Recent estimates are that
2,340 tons of industry-related mercury are emitted globally.
Over half of these originated from Asian sources. Of the global
total, the United States is estimated to emit roughly 166 tons
in total; U.S. utilities about 46 tons. In addition, it is
estimated that another 1,300 tons of mercury emanates from
land-based natural sources around the globe, and another 1,100
or so tons comes from the world's oceans.
Recent findings from the joint United States and Canadian
METAALICUS field experiment show that a fairly small amount of
deposited mercury, no more than 20 percent or so, re-admits to
the atmosphere, even over a 2-year period. The implications are
that mercury may be less mobile in the environment than we
Studies by EPRI have shown that much of the mercury
depositing in the United States may originate on other
continents. Model results show that for three-quarters of the
continental U.S. land area, more than 60 percent of the mercury
received comes from outside the country. Only 8 percent of U.S.
territory receives two-thirds or more of its mercury from U.S.
To check this with data, aircraft measurements were carried
out by EPRI and the National Center for Atmospheric Research in
Boulder, Colorado. Mercury and winds from the Shanghai, China
region were tracked over the Pacific for 400 miles toward the
United States. A second set of flights from Monterey, CA found
that same plume from China crossing the California coast and
entering U.S. territory. One implication is that there may be a
management floor for U.S. mercury, a level below which the
amount of mercury depositing to the surface cannot be reduced
by domestic action alone.
Second, what are the primary sources of mercury in fish in
the environment? Global mercury emissions appear to have peaked
in the 1980's and declined or held steady since then. Professor
Francois Morel of Princeton University, and colleagues,
recently analyzed specific tuna for mercury, comparing recent
catches with those from the 1970's. Despite changes in mercury
emissions over those 30 years, mercury levels in tuna did not
change between the samples. One conclusion they reached is that
the mercury in such marine fish is not coming from emission
sources on land, but from natural submarine sources of mercury.
Again, this implies there may be a management floor for mercury
in marine fish, which make up most of the U.S. fish diet.
Third, how can potential mercury reductions change mercury
deposition? EPRI recently completed work to assess what might
ensue in the atmosphere and in U.S. fish if further mercury
emission reductions are carried out in the United States. The
approach linked models of atmospheric mercury chemistry and
physics with Federal data on mercury in fish in the U.S. diet,
along with a model of costs that would be needed to attain a
given reduction level. There are currently about 179 tons of
mercury depositing each year in the United States from all
sources, global and domestic. Current U.S. utility emissions of
mercury are about 46 tons per year.
EPRI examined one proposed management scenario that cut
these utility emissions from 46 tons to 25 tons per year. The
analysis showed that this emissions cut of 47 percent resulted
in an average 3 percent decline in mercury deposition in the
United States. Some isolated locations making up less than one
one-hundredth of the U.S. land area experienced drops of up to
30 percent. The economic model showed that costs to attain
these lower levels would be between $2 billion and $5 billion
per year for 12 years. This demonstrated U.S. mercury patterns
may be relatively insensitive to the effects of this single
category of sources.
In addition, most of the fish consumed in the United States
are ocean fish which would be only slightly impacted by a
reduction of 24 tons of mercury per year solely in the United
States, out of 2,300 tons globally. Wild freshwater fish within
the United States might show a greater reduction in mercury
content, but they make up a very small part of the U.S. diet,
compared to ocean or farm-raised fish.
These deposition changes were translated into how much less
mercury might enter the U.S. diet via these three categories of
fish. We found that less than one-tenth of 1 percent fewer
children would be born at-risk due to their mother's taking in
mercury at lower levels from fish consumed in the diet.
So to summarize, a drop of nearly half in utility mercury
emissions resulted in an average drop of 3 percent in mercury
depositing to the ground, and a drop of less than one-tenth of
a percent in the number of children at risk. These recent
findings are a small part of the massive international research
effort to understand mercury and its impacts. EPRI and others,
including U.S. EPA and the Department of Energy, are jointly
racing to clarify the complex interactions of mercury with
natural systems, an important part of its cycling, and its
impacts on human health. With improved understanding, informed
decisions can be made on the best ways to manage mercury.
Thank you for this opportunity to deliver these comments to
Senator Inhofe. Thank you, Dr. Levin.
STATEMENT OF DEBORAH C. RICE, TOXICOLOGIST, BUREAU OF
REMEDIATION AND WASTE MANAGEMENT, MAINE DEPARTMENT OF
Dr. Rice. I would like to thank the committee for this
opportunity to present information on the adverse health
consequences of exposure to methyl-mercury in the United
I am a neurotoxicologist who has worked on the
neurotoxicity of methyl-mercury for over two decades and have
published over 100 papers on the neurotoxicity of environmental
chemicals. Until 3 months ago, I was a senior toxicologist at
the Environmental Protection Agency. I am a coauthor of the
document that reviewed the scientific evidence on the health
effects of methyl-mercury for EPA. This document included the
derivation of the acceptable daily intake level for methyl-
I would like to focus on four points. No. 1, there is
unequivocal evidence that methyl-mercury harms the developing
human brain. No. 2, EPA used analyses of three large studies in
its derivation of an acceptable daily intake, including the
studies in the Seychelles Islands which found no adverse
effects. No. 3, 8 percent of women of childbearing age have
levels of methyl-mercury in their bodies above this acceptable
level, and studies have documented cardiovascular disease in
men at low levels of methyl-mercury, suggesting that an
additional potentially large segment of the population is at
Studies performed around the world have documented harmful
effects of environmental methyl-mercury exposure on children's
mental development. Three major studies were analyzed by the
National Research Council panel in their expert review: In the
Faroe Islands in the North Atlantic, and the Seychelles Islands
in the Indian Ocean, and in New Zealand. Two of these major
studies, as well as six smaller studies, identified impairment
associated with methyl-mercury exposure. The Seychelles Island
study is anomalous in finding no effects. Adverse effects
include decreased IQ and deficits in memory, language
processing, attention and fine motor coordination.
The NRC modeled the relationship between the amount of
methyl-mercury in the mother's body and the performance of the
child, and calculated the level associated with the doubling of
the number of children that would perform in the abnormally low
range. The NRC panel did this for each study separately and for
all of the three studies combined, including the negative
EPA used the NRC analyses in deriving its acceptable daily
intake level of methyl-mercury. EPA performed the relevant
calculations based on each of the two positive studies, as well
as the integrative analysis of all three studies. The
acceptable level is the same whether it is based on the
integrative analysis of all three studies, or on the Faroe
Islands study alone.
The acceptable level would be lower if only the New Zealand
study were considered. Only if the negative Seychelles study
alone were used, while ignoring the values calculated for the
Faroe Islands and New Zealand studies, would the acceptable
intake level be higher than the current value. EPA believed
that to do so would be scientifically unsound and would provide
insufficient protection to Americans.
Data from a survey representing the U.S. population
collected over the last 2 years revealed that about 8 percent
of women of childbearing age had blood concentration of methyl-
mercury above the level that EPA believes is safe. This
translates into over 300,000 newborns at risk for adverse
effects on intelligence and memory, ability to pay attention,
language skills and other abilities that are required to be
successful in our highly technological society.
There is an additional concern regarding the potential for
harm as a result of environmental methyl-mercury exposure.
Three studies found a relationship between increased methyl-
mercury levels and atherosclerosis, heart attacks and death,
and it is unknown whether there is a level of mercury that will
not produce harm. It is important to understand that the
cardiovascular effects associated with methyl-mercury may put
an additional very large portion of the population at risk.
In summary, there are four points that I would like the
committee to keep in mind. First, at least eight studies based
on populations around the globe found an association between
methyl-mercury levels and impaired neuropsychological function
in children. The Seychelles Islands study is anomalous in
finding no effects. Second, both the NRC and the EPA included
the Seychelles Islands study in their analysis. The only way
that the acceptable intake of methyl-mercury could be higher
would be to ignore the two major positive studies, as well as
six smaller studies and rely solely on the one study that
showed no effects.
Third, there is a substantial percentage of women of
reproductive age in the United States with levels of methyl-
mercury in their bodies above what EPA considers safe. As a
result, over 300,000 newborns each year are exposed to
potentially harmful levels of methyl-mercury. Fourth, increased
exposure to methyl-mercury may result in cardiovascular disease
and even death in men from heart attack, suggesting an
additional large segment of the population is at risk.
Additional information has been provided to the committee.
Thank you for your time and attention.
Senator Inhofe. Thank you, Dr. Rice.
STATEMENT OF GARY MYERS, PROFESSOR OF NEUROLOGY AND PEDIATRICS,
DEPARTMENT OF NEUROLOGY, UNIVERSITY OF ROCHESTER MEDICAL CENTER
Dr. Myers. Thank you for the opportunity to present the
views of our research group on the health effects of methyl-
mercury exposure. My name is Gary Myers. I am a pediatric
neurologist and a professor at the University of Rochester in
New York, and just one member of a large international team
that has been studying the human health effects of methyl-
mercury for nearly 30 years. For 20 of those years, our group
has specifically studied the effects of prenatal methyl-mercury
In 1971 and 1972, there was an epidemic of methyl-mercury
poisoning in Iraq. The source of exposure, unlike in Japan, was
maternal consumption of sea grain coated with a methyl-mercury
fungicide. We looked at a number of children in that study and
measured the exposure of the fetus using the maternal hair as
the biomarker. It is the only biomarker that has been
correlated with brain levels. We concluded that there was a
possibility that exposure as low as 10 parts per million in
maternal hair might be associated with adverse effects on the
fetus. This value is over 10 times the average in the United
States and five times the average in Japan, but individuals
consuming large quantities of fish can easily achieve this
The hypothesis of our study in the Seychelles was that
methyl-mercury from fish consumption might affect child
development. In fact, we all thought it would. Since millions
of people around the world consume fish as their primary source
of protein, we thought it was only reasonable to investigate
the question directly. We selected the Seychelles because of
two reasons. First, they eat large amounts of fish. The average
mother eats 10 times as much as women here in the United
Second, the fish in Seychelles has an average mercury
content of about 0.3 parts per million, which is approximately
the same as commercial fish here in the United States. The
Seychelles study is a collaborative study which was begun under
the auspices of the WHO and has been carried out by a U.S.-led
team of international researchers from the University of
Rochester, Cornell University and the Ministries of Health and
Education in Seychelles. The funding has come from the National
Institutes of Environmental Health Sciences, with some minor
funding from the Food and Drug Administration and the
governments of Seychelles and Sweden.
The Seychelles was chosen for a number of reasons,
primarily because there was no overt mercury pollution and many
of the factors that complicate epidemiological studies of low-
level exposures were simply not present. There was universal
free and readily available health care in Seychelles. Prenatal
care is nearly 100 percent. The birthrate is high and the
general health of the mothers and children is very good. In
addition, education is free, universal, and it starts at age
Before starting the study, we carefully controlled for a
number of things. To minimize the possibility of bias, a number
of decisions were made. First, no one in Seychelles, including
any of the researchers who visit the island, would know the
level of exposure of any child or mother unless our results
indicated that children were indeed at risk. Second, because of
the known problems with developmental delay in certain
disorders, those children would be excluded from the study.
Third, the tests administered would include all of the tests
that have been used in other studies, plus other things that we
thought might detect subtle changes.
Fourth, we would do this testing at specific age windows.
Fifth, we would adjust for multiple confounding factors, things
that are actually known to affect child development such as
socioeconomic status, the mother's intelligence, and birth
weight. And sixth, we established a data analysis plan before
the data were collected to minimize the possibility that the
data would just be repeatedly analyzed until the anticipated
effect was in fact determined.
We have now carried out five evaluations of the children
over 9 years. The study has focused on prenatal exposure. The
exposure of both mothers and children has been in the range of
concern, from 1 to 27 parts per million. We have done extensive
testing with over 57 primary endpoints determined so far. The
study has found three statistical associations with prenatal
methyl-mercury exposure. One was adverse; one was beneficial;
and one was indeterminate. These results might be expected to
occur by chance and do not support the hypothesis that adverse
developmental effects result from prenatal methyl-mercury
exposure in the range commonly achieved by consuming large
amounts of fish.
The findings from our research have been published in the
world's leading medical journals, including the Journal of the
American Medical Association, the Lancet, and a soon-to-be-
published review in the New England Journal of Medicine. We do
not believe that there is presently good scientific evidence
that moderate fish consumption is harmful to the fetus. In the
words of Dr. Lyketsos, a distinguished researcher from Johns
Hopkins, who wrote the editorial with our Lancet articles:
``On balance, the evidence suggests that methyl-mercury
exposure from fish consumption during pregnancy of the levels
seen in most parts of the world does not have measurable
cognitive or behavioral effects in later childhood. However,
fish is an important source of protein in many countries and
large numbers of mothers around the world rely on fish for
proper nutrition. Good maternal nutrition is essential to the
Senator Inhofe. Thank you, Dr. Myers.
We are going to try to adhere to a 5-minute round of
questioning. Let me just share with you, which I think you
already know, you folks are looking at the medical effects of
mercury. We also up here have to consider the economic
effects--the problems that are out there. Right now on the
Senate floor, they are debating the energy bill. We have an
energy crisis in this country, and if cofire should go out, and
that could happen from either CO2 or mercury, it
would be a very serious crisis. I think anticipating that this
will happen, several people have moved off-shore, moved to
other places. So that is something that is really, I guess you
would say our major, at least one of my major concerns.
Now, just for all of the witnesses, you stated that the
U.S. utility mercury emissions are 46 tons a year. Tell us what
happens to this mercury. Help us visualize where does it come
from; where does it go; how much is deposited in the United
States; how does this compare with the amount that is deposited
in the United States from global sources.
Would you like to start, Dr. Rice?
Dr. Rice. That is really not my area of expertise, so I
cannot speak to it.
Senator Inhofe. All right.
Dr. Myers. It is not my area of expertise.
Senator Inhofe. Come on, Dr. Levin.
Dr. Levin. All right.
Dr. Levin. Utility mercury of the various sources of
mercury is probably the best-studied category, partially
because there are more individual sources than there are of
many of the other categories. We believe that roughly half on
average coming out from utilities is made up of the divalent
form of mercury, which is about a million times or so more
soluble in water than the elemental form, which is the silvery
liquid that you probably remember from high school chemistry.
So of this mercury emitting from all utilities in the United
States, roughly half of it is more highly water soluble and the
other half will tend to go into regional and global
We calculate that about 70 percent or so of the mercury
emitted from utilities leaves the United States, and the other
30 percent or so deposits within the United States across the
country. These are somewhat similar to the numbers that EPA is
deriving as well. Some of this mercury that deposits to the
surface will wind up in receiving waters, and a very small
fraction of it, probably less than 1 percent, will eventually
be turned into the organic form by bacterial action. It is that
organic form that has the potential to reach humans through
accumulation in some fish.
Again this does not happen in all waterways and with all
fish species. It tends to happen in waterways that have full
food webs that go to high-level fish that grow quite large, and
it is larger, older fish that tend to accumulate more mercury.
Of the exposure in the community in the United States,
almost all of it is through intake from fish and the mercury in
those fish, although the levels taken in can vary from very
little or almost none, to amounts of concern. There is almost
no exposure by inhalation. That is a very small part of the
So our concern is to follow this mercury from its sources
through to where it winds up in fish and eventually may be
consumed by humans. That is the trick, scientifically.
Senator Inhofe. Thank you, Dr. Levin.
Dr. Rice, the American Heart Association and the World
Health Organization recommend that fish should be a part of
everyone's diet, concluding that the benefits of eating fish
outweigh the risks of adverse effects, which as you state in
your testimony are potential risks. Since eating fish offers
substantial health benefits, shouldn't the EPA's referenced
dose be revised to take this into account, or does it?
Dr. Rice. Well, I agree totally, and I have to say that I
am no longer with EPA so I am not speaking as a representative
of the agency. I need to make that clear. So some of these
opinions will be those of the agency when I left, and some will
But the scientific community at large and the EPA and me
personally recognize that fish is a good source of protein. It
also confers cardio-protective effects. There are also omega-
three fatty acids in fish that are essential when the fetus is
building its brain. There is new evidence that eating fish also
may be beneficial to the mental development or the mental
function of the elderly. I suspect that it is probably
important for all of us.
So the dichotomy is not eat fish/don't eat fish. The
important thing to be able to do is to come out with some
recommendations to the community that allow people to eat fish,
but not to eat fish that has increased levels of methyl-
mercury. So EPA thinks that, I was part of that EPA panel, so
when I was part of that EPA panel we firmly believe that the
RFD should not be any higher, and in the light of some evidence
that we were not able to analyze at the time, might even should
be lower than it is presently.
So it is not a question of increasing the reference dose.
It is a question of making sure that the American public can
eat fish that does not have undue levels of methyl-mercury in
Senator Inhofe. Thank you very much.
Dr. Myers, in selecting the Seychelles as a location for
your research, what other locations did you consider other than
the Seychelles Islands?
Dr. Myers. We started studies on the coast of South America
and looked also at the Maldive Islands as another possibility.
Senator Inhofe. Yes. I kind of wanted to get to the Faroe
Islands. Did you consider them for your research?
Dr. Myers. We did not consider the Faroes in our research.
Senator Inhofe. It is my understanding that, and for those
of us who are not scientists here, that some of the problems,
let's take the Faroe Islands and see if I have this right, that
there is an inordinate amount of whale meat that is consumed
there and there are PCBs in there. I do not know whether you
can distinguish between the harm of one or the other, but is
this a factor that should be considered?
It is my understanding, and I won't say this right, but
there are different levels of mercury that are found. One is
from the primary fish, and the other is from whales that eat
other fish, so it has a multiplying effect. Is this taken into
Dr. Rice. The Faroe Islands study and the Seychelles
Islands together have been reviewed by at least two very
distinguished peer-review panels. That issue, the issue of the
pattern of intake of methyl-mercury and potential co-exposure
for PCBs has been discussed extensively by the scientific
The Faroe Islands' population does eat whale meat. They may
eat a large whale dinner occasionally. They also tend to dry
the whale meat, and so they snack on it in addition to eating a
so-called bolus dose, what we call a bolus dose. So they have a
low level of methyl-mercury intake which may be occasionally
punctuated with a higher intake level. The source of methyl-
mercury does not matter, whether it is through fish or through
whale. So the fact that it is whale meat per se is not really
None of the panels, including the National Research Council
panel, could come to any kind of conclusion about the
importance of the pattern of intake, because the data just are
not available. There just are not scientific data that speak
directly to that. But what the Faroe Islands investigators have
done because this was raised as a concern and because they have
hair, and they had hair from their population that was stored,
they were able to go back and do segmental analysis, so that
you cut the hair up into tiny little pieces and look at mercury
levels across the length of the hair.
What they did was they eliminated the mothers that had the
most variable hair levels that might suggest that there was
this bolus exposure of these particular women and these
particular fetuses. What they found was that the effect was
actually stronger when they eliminated these women, which makes
a certain amount of sense because you are decreasing
variability when you do that.
Senator Inhofe. Thank you, Dr. Rice.
Senator Jeffords. Thank you all for your testimony on this
very important and timely topic.
Some of you have seen this morning's New York Times full-
page article on mercury and its health effects. This helps to
set a context for our discussion.
Dr. Rice, what exactly is a reference dose level and what
does it mean in terms of the so-called safe levels of fish
consumption? Does EPA reference dose level include a built-in
tenfold safety threshold?
Dr. Rice. The reference dose is designed to be a daily
intake level that a person could consume over the course of
their lifetime without deleterious effects. So it is designed
to be the amount of mercury you could eat every day in your
life and not harm yourself.
Now, when EPA did its calculation, it is important to
understand that when the National Academy of Sciences modeled a
number of endpoints for each of the studies, and those were the
Faroe Islands study, the New Zealand Study, both of which found
effects, as well as the Seychelles study which did not, they
identified not a no-effect level. They identified a very
specific effect level. That effect level is associated with a
doubling of the number of children that would perform in the
abnormal range, in other words, the lowest 5 percent of the
population. So this is in no way a no-effect level.
To that, the EPA applied a tenfold so-called uncertainty
factor. The point of that was to take into account things that
we did not know, data that we did not have, as well as the
pharmacodynamic and the pharmacokinetic variability. Now, there
were actually data that was again modeled by the NAS and
reviewed by the NAS, that says that the pharmacokinetic
variability, in other words the woman's ability to get rid of
methyl-mercury from her body, differs by a factor of three. So
that already takes up half of the uncertainty factor.
But in addition to that, it is important to understand that
when the Faroe Islands folks analyzed their data, they
eliminated mothers with mercury levels above 10 ppm in their
hair, which was really right about at the effect level that the
NAS identified. The effects were just about as strong even
below 10 ppms. So again, that is very strong evidence that
there is not a factor of 10 safety.
In addition to that, when the NAS modeled their data, it
turned out that both of the New Zealand study and the Faroe
Islands study not only was there no evidence that there was a
threshold, in other words a level below which there were no
effects, but in fact the curve was actually steeper at the
lower levels. The NAS used a straight line when they modeled
the data because they were uncomfortable about using curves
that were steeper at the lower end than they were at the higher
end, but subsequent to that there have been studies come out
with regard to lead exposure, for example. There are now
several studies where that has also been found for lead
So this may in fact be a very real effect. So not only is
there not a safety factor of 10. There might be virtually no
safety factor at all.
In addition to that, something that EPA recognized at the
time, but we were not able to quantitate because we did not
have the data, but it has now been quantitated, we assumed that
the relationship between the mother's blood level of methyl-
mercury and the fetus' blood level of methyl-mercury were the
same, because of course we have the body burden; we have cord
blood in the fetus, we have to get back to intake by the
mother. We know now that in fact the ratio is more like 1.7,
and for some mothers it is as much as over 3.
So if we were to recalculate the reference dose just based
on this new information, it would decrease from 0.1 to 0.06.
Senator Jeffords. Dr. Rice and Dr. Myers, would you
recommend that Members of Congress and regulatory agencies base
their decisions on whether and how much to reduce human-made
mercury emissions on the findings from any one study?
Dr. Myers. Our group has been involved in the science of
studying whether you could find effects at low levels, and we
have not been involved in policy. There is a general scientific
principle, I think it is important to look at multiple
different studies. However, these studies are complicated and
one has to look at what kind of studies you are dealing with.
Some are simply descriptive. They take a group of people and
describe something. It is a basic epidemiological principle
that you cannot assign causation from a descriptive study.
So one has to look at the studies that are larger and
follow children over time, and control for a lot of confounding
factors which complicate these type of studies very much
actually. The Seychelles study in fact is not a negative study,
as has been stated. We did, in fact, find associations with
things that are known to affect child development, such as
socioeconomic status, maternal intelligence, the home
environment and other things. What we did not find was an
adverse association with prenatal methyl-mercury exposure in
Senator Jeffords. Dr. Rice.
Dr. Rice. I agree with Dr. Myers. These studies are very
complex. I think that that is even more reason not to rely on
one study while eliminating other studies for consideration.
Again, these studies have been peer-reviewed numerous
times. The Seychelles Islands study and the Faroe Islands study
have been reviewed now by several panels. They are both thought
to be very high quality, very well-designed and well-executed
The NAS, as well as the previous panel, talked at great
length about what might account for the differences between
these studies. We really do not know what accounts for the
differences between these studies. The NAS modeled three
studies. The New Zealand study was also a positive study.
The National Academy of Sciences and the EPA agreed with
them that it was not scientifically justifiable for protection
of the health of the American public to rely on the negative
study and exclude the two positive studies. I said at least a
couple of times in my testimony that what the NAS did to try to
address that was to do an integrative analysis that included
all three studies, including the Seychelles Islands study, and
modeled it statistically.
When EPA then took those analyses and derived, what we did
was we derived a series of reference doses, kind of sample
reference doses, that were based on a number of endpoints from
both the New Zealand study and the Faroe study, as well as the
integrative analysis of all three studies. The integrative
analysis of all three studies also yields a reference dose of
0.1. So that made me personally very comfortable that we were
doing the right thing scientifically in our derivation of the
Senator Inhofe. These are supposed to be 5-minute rounds
and it has been 8 minutes, so we will recognize Senator Allard.
Senator Allard. Dr. Rice and Dr. Myers, you have in your
comments talked about methyl-mercury as being the toxic
compound as far as human health is concerned. Are there other
mercurial compounds that are toxic to humans?
Dr. Rice. Yes. All forms of mercury are toxic to humans.
Senator Allard. Including the elemental form?
Dr. Rice. Yes.
Senator Allard. OK.
Dr. Rice. But in terms of environmental exposure, it is
really the methyl-mercury form that we are worried about
because that is the form that gets into the food chain and is
concentrated and accumulated up the food chain. That is what
people actually end up being exposed to.
Senator Allard. OK. Thanks for clarifying that. I
appreciate that. So this gets into the environment and
consequently in the fish or food chain or whatever. Is the
starting point always bacteria operating on the elemental form
of mercury? Or is it these various compounds that bacteria
operate on and then end up being assimilated into the food
chain? How does that happen?
Dr. Rice. In most circumstances, it is the inorganic form,
not the elemental mercury, but the inorganic form that is
available to be taken up by various microorganisms.
Senator Allard. How do we get to that organic form, the
methyl-mercury? How do we get there?
Dr. Rice. The microorganisms actually put a methyl group on
as part of their metabolic processes.
Senator Allard. Do they get that from elementary mercury?
Is that the origin, or is it various compounds of mercury?
Dr. Rice. Yes, it is just straight mercury. Now, in the
Japanese outbreak, it was actually methyl-mercury that was put
into the water, but that is a relatively unusual situation.
Senator Allard. I see. OK, so my understanding, Dr. Levin,
is that a lot of the mercury that is introduced into the
environment of this country does not originate within the
borders of this country. Is that correct? The suggestion is
that a lot of the sources of mercury that come across that we
may pick up in the soil is actually carried over by wind and
what not from the Asian countries. Is that correct?
Dr. Levin. That is correct, Senator, as far as the modeling
shows, and that is consistent with work that EPRI has done, EPA
and others have also done in the modeling.
Senator Allard. Is this the elemental mercury that is being
Dr. Levin. It is elemental, or the elemental form. It is
also the inorganic form or the form that can be combined into
Senator Allard. Now, the inorganic form is not processed
into the food chain? Did I understand that correctly?
Dr. Levin. It is the inorganic form that is processed into
the food chain.
Senator Allard. Yes, it is the organic form.
Dr. Levin. The two forms that are emitted from combustion
sources are the elemental form, the chemicals found on the
Senator Allard. Right.
Dr. Levin. And the inorganic form, which combines with, for
example, chlorine, to form the pure chloride, or is the form
also found in minerals. Those two forms that wind up in the
proper aquatic environments, it is the inorganic form that may
be methylated and turned into the organic form.
Senator Allard. Right.
Dr. Levin. But it has to go from elemental to inorganic
before the methylation can occur.
Senator Allard. But my question is, is that the type of
mercury that is being brought in from Asia, what form of
mercury is that?
Dr. Levin. Because of its long-range transport, it is
primarily the elemental form, but the atmospheric chemistry of
mercury changes that progressively into the inorganic form,
which is the form that readily deploys.
Senator Allard. Now, can the inorganic form be transferred
Dr. Levin. Yes, sir. That is the form.
Senator Allard. So all those type of compounds get acted on
by bacteria and then that is how that gets into the food chain.
Dr. Rice. The elemental form and the inorganic form are
converted back and forth.
Senator Allard. I see.
Dr. Rice. So it does not make any difference whether it
reaches the North American shores as elemental mercury or
inorganic mercury. Once it is deposited into the soil or the
river, it is going to become inorganic mercury that then
becomes available to be able to be turned into methyl-mercury.
Senator Allard. OK, thank you.
Now, here is the question, and I would like to have all of
you respond to this. In your opinion, would a decrease in U.S.
anthropogenic mercury emissions have an effect on global
mercury levels? And part of the rest of the question is,
apparently there is a high percentage of mercury present in the
United States from outside our borders, so what effects can we
expect from a decrease in our emissions? We have a couple of
questions there and I would like to have all of you respond to
those if you would.
Dr. Rice. There is no question that there is a global
cycling of mercury. A lot of the mercury in the United States
comes in from someplace else, comes in from the West, but some
of it may have in fact originated in the United States
originally. This stuff really does circle the globe. So just
because it is coming in from the West does not mean it wasn't
ours to start with.
Senator Allard. We do not know how much starts here.
Dr. Rice. No, we do not, and I am not a modeler so I really
cannot speak to that. But what I do know is that there is local
deposition. In other words, the mercury that is released from
power plants in the Midwest ends up downwind. I just moved to
Maine, and Maine is the so-called tailpipe for that local
deposition, for that local emission. There is a percentage of
it, and Dr. Levin can tell you what the percentage is better
than I can, that is locally deposited. I think it is something
like 30 percent.
Getting rid of those local sources would certainly at least
help the Northeastern United States. Originally, the modeling,
it was thought that this would take a long, long time. There
are newer data now where small studies have actually been done
that suggest that it might not be as grim as we originally
thought; that these local changes can take place in a
relatively shorter time, over the course of several years,
rather than decades and decades as we originally may have
Senator Allard. Dr. Myers, do you have a comment on that?
Dr. Myers. It is outside of my area of expertise.
Senator Allard. Dr. Levin.
Dr. Levin. Dr. Rice is primarily correct on that. The
deposition within the United States makes up about 30 percent
of U.S. emissions. The rest of the emission go globally. Our
modeling considered the fate of U.S. emissions and accounted
for the amount that basically circles the globe and comes down
after one trip around the world.
It is also correct that there is local deposition that in
some cases may be significant near particular groupings of
sources. I indicated that in my testimony, that although the
average change in deposition for the scenario was 3 percent,
there were some small areas where it was as much as 10 times
that on a percentage basis.
So it calls for more detailed studies and particularly more
looking at the science of tracking mercury found in fish back
to its sources scientifically, that is, figuring out where it
Senator Allard. Thank you, Mr. Chairman. I believe my time
Senator Inhofe. Yes, thank you.
Senator Carper. Thank you, Mr. Chairman.
To our witnesses, again thank you for joining us. Thank you
for your patience in bearing with us.
Dr. Rice, did I understand you to say you have concluded
two decades of work at EPA?
Dr. Rice. Well actually most of it was not at EPA. I was at
Health Canada for 22 years. I am American, but I graduated from
the University of Rochester, got my Ph.D. from the University
of Rochester so I have known Dr. Myers for many years. Then I
went up there to work at Health Canada.
Senator Carper. I see. Thank you for your service at EPA,
and thank you all for real interesting testimony today.
Sometimes these are fairly technical issues. What is
helpful for me as I listen to the comments of each of your
testimonies and your responses to our questions is to look for
threads of consensus; not to focus so much on where you
disagree, but to find some areas where you agree. I would just
ask each of you to take a minute or two and just to talk about
some of the areas where you think you agree, and which might be
helpful to us as we wrestle with whether to craft legislation,
enact legislation along the lines that Senator Jeffords has
introduced, I have introduced, or the President has proposed.
Can you help me with that? Dr. Levin, why don't you go
Dr. Levin. Thank you, Senator. We agree that mercury is a
highly toxic compound. Its presence in the U.S. diet may in
some instances cause concerns for development of children
neurologically. We agree that there may be other effects that
have to be looked for in terms of the health effects.
We also agree that the science of mercury is still
emerging; that the linkage between health effects in particular
areas, or for that matter in entire regions of the United
States, and the sources of mercury is a critical question that
would shape a wise course toward management decisionmaking. The
work that I have been describing today is a step in doing that.
The work that has been described by the other two witnesses
today on health effects is a critical part of that linkage.
Bringing this source-receptor issue together with the
health effects on a specific geographic basis and among
specific populations within the United States is a key part in
answering the management questions.
Senator Carper. Thank you.
Dr. Myers, would you take a shot at my question please?
Dr. Myers. I think we all agree that mercury is poisonous,
every form. In high enough amounts, it is not only damaging to
human health, but fatal generally. We all agree that it is
worthwhile cleaning up the environment, I think. The question
resolves at what level and at what cost. I think we all agree
that these studies are extremely difficult to carry out and
they are equally difficult to interpret because there are so
many details to them. So it is so easy to end up with a bias
either knowingly or unknowingly, generally I think unknowingly,
that the interpretation of the details becomes incredibly
important in these studies.
Senator Carper. Thank you.
Dr. Rice. I agree that we all know that methyl-mercury is
toxic at high levels. There is absolutely no question about
that. I agree with Dr. Myers that it is incredibly difficult to
interpret these studies very often. They are very complex
studies. There are a lot of variables, many of which we do not
know. Epidemiology is an extremely blunt instrument. So that is
why I think that it is important to look at the weight of
evidence. There are a number of studies in humans that have
documented effects of methyl-mercury at relatively low body
burdens. In addition to that, there is a huge animal literature
documenting effects and looking at the mechanisms of effects.
We do not know why one study may be positive, whereas
another may be negative. So we really have to go with the
evidence as a whole.
Senator Carper. And maybe cite your most serious area of
disagreement among you as panelists.
Dr. Levin. I would say disagreement probably rests in the
question of the direction of research overall on the mercury
issue, and how far that should continue.
Senator Carper. Dr. Myers.
Dr. Myers. I think the most serious area of disagreement is
in the interpretation of the studies. We think that the Faroe
Islands research is outstanding research. They have done a
wonderful job. They have a great design. We are just not sure
that they have been able to tease out from the mixture of
chemicals present in whales a methyl-mercury component to it.
That requires a lot of faith in their statistics and the
details of the studies.
In the case of the New Zealand study, most people
discounted the New Zealand study for many years. It was only
when it was reanalyzed in the late 1990's that people began to
start thinking of it in other terms. So I think our biggest
disagreement is in the interpretation of it.
In addition, I think the weight of hundreds of small poorly
done studies in difficult places such as the Amazon would never
outweigh a really good study done looking at fish consumption.
Senator Carper. Dr. Rice.
Dr. Rice. I guess everything that Gary Myers just said is
my biggest point of disagreement. All of the smaller studies
are not poorly done. Some of them are well done. The Faroe
Islands study and the Seychelles study have been extensively
reviewed. They are both considered to be very, very good
The National Academy of Sciences looked at the issue of PCB
co-exposure very, very carefully and asked the investigators to
go back and do a number of additional analyses. Their
conclusion was that the effects seem to be independent of each
other. These are both neurotoxicants. Although they both had
effects in the study, the NAS conclusion was that they were
Again, I think that we have go with a preponderance of
evidence and not on just one study, no matter how well it has
Senator Carper. Mr. Chairman, I think this panel has been
especially helpful to me. We thank you very, very much for your
contributions today. Thank you.
Senator Inhofe. Thank you, Senator Carper.
Senator Clinton. Thank you, Mr. Chairman. I, too, want to
thank the panel and welcome Dr. Myers from the University of
Rochester, and Dr. Rice, your connection with Rochester, we
will claim that as well.
I want to pick up where Dr. Rice just concluded. We have
set up a system of evidence in our legal system that looks at
the preponderance of evidence; that looks at a reasonable
person standard. I share Dr. Rice's concern that we are not
adequately responding to the evidence we already have, which I
think the preponderance of it, certainly based on the review by
the National Academy of Sciences, suggests that we have a
problem with the transmission mostly in utero by mother to
child that leads to neurological problems that in turn lead to
poor school performance.
The 2000 report of the National Academy of Sciences found,
I believe, that about 60,000 children might be born in the
United States each year with this level of exposure that could
affect school performance, but in your testimony you claim that
more recent results from the CDC's National Health and
Nutrition Examination Survey translate into over 300,000
newborns per year. Is that correct?
Dr. Rice. Yes. When the NAS did their analysis, the NHANES
data was not available. The NHANES just started taking mercury
blood and hair levels a couple of years ago, so those data have
really become available since the NAS. They state that their
60,000 children was an estimate. It is actually about 320,000
children. Based on actual data that is representative of the
U.S. population, it is above the EPA's reference dose.
Senator Clinton. To me, this is truly alarming, that we
have actual blood, hair sample, other kinds of physical
examination which demonstrates that hundreds of thousands of
our children are born each year potentially at risk for adverse
affects on intelligence, memory, ability to pay attention,
ability to use language and other skills.
Mr. Chairman, we are facing an increasing number of
children in our school systems with learning disabilities.
There are not any easy answers as to why the numbers of
children with such learning disabilities has increased. Senator
Jeffords has been a champion of making sure that all children
are given an adequate education. In New York alone, we have
260,000 learning-disabled children. That is 50 percent of our
special ed population. We spend $43 billion each year--$43
billion--on special ed programs for individuals with
developmental disabilities between three and twenty-one.
Of course, not all special ed needs are the direct result
of methyl-mercury exposure, but if it is demonstrably shown as
we now have with evidence from the CDC's annual survey that we
have levels of methyl-mercury in our children's bodies that is
above what the EPA has determined to be healthy, and in fact
some of us think the EPA standard is too low, but nevertheless
if it meets that standard, then I would argue we have got to
figure out how to address this environmental health challenge
in a very short order.
I have been working with a number of colleagues to try to
address the better data collection and environmental health
tracking that they need in the Individuals With Disabilities
Act, and I think similarly on the scientific side with respect
to better research and better analysis. But it is troubling to
me that we are looking at a problem where the preponderance of
the evidence I think is clear, where we know that there is a
transmission, whether it is 60,000, 150,000, 300,000-plus
children, and it needs some more effective response.
I wanted to ask you, Dr. Rice, now that you are in Maine,
from the State perspective, how closely do you work with the
State health department on environmental health issues? Do you
exchange information with the State health department and even
with the State education department about some of the work that
you are doing?
Dr. Rice. I actually knew the State toxicologist for Maine
quite well before I went up there, so I do interact with the
health department. The methyl-mercury issue is very important
to Maine. Maine has a very good program for trying to get rid
of methyl-mercury from dental amalgams, from thermometers, from
the kinds of things that can be controlled; to not put mercury
in landfills because Maine understands that we are at the end
of the pipeline for methyl-mercury deposition. Maine has a
terrible problem with fish advisories. There are a lot of
places where fish cannot be eaten in Maine because of the
deposition of methyl-mercury.
So I do work closely with the folks over there, and in fact
my way here was paid by the air office, the Maine air office
because the State of Maine is so very concerned about this
issue. Maine is rural and it is poor, and it cannot really
absorb the consequences of these kinds of additional exposures
on the health of the people of Maine.
Senator Clinton. Similarly, new science is demonstrating
that we need lower standards for lead, based on what we are now
determining. A lot of that groundbreaking work was done at the
University of Rochester about lead exposures and the impacts of
lead exposure. We can take each of these chemicals or compounds
piece by piece, but I think that certainly when it comes to
mercury and lead and their impacts on children's development,
it is not something I feel comfortable studying and waiting too
much longer on, particularly because there are so many indirect
costs. I know that Dr. Levin's work looked at some of the risks
and cost-benefits, but people do not seem to factor in this
special education population that has been growing.
Dr. Rice. If I may make a comment, I think your analogy is
an apt one, and I think it is a very informative one. In 1985,
there was a report to Congress on the cost-benefits of lead, of
keeping lead out of gasoline, in fact. The benefits based on
not only special education and things like lower birth weight
with respect to lead, but also just the economic consequences
of lowering the IQ of workers amounted to billions and billions
of dollars a year in 1985 dollars or 1994 dollars. So as this
effort goes forward in terms of figuring out how much it is
going to cost to reduce mercury emissions, this other side of
the equation, how much it is going to cost not to, needs to be
kept very, very well in mind.
Senator Clinton. Thank you, Dr. Rice.
Senator Inhofe. Thank you, Senator Clinton.
I thank the panel very much for their testimony.
Senator Jeffords. I had a couple more questions.
Senator Inhofe. Well, all right. It has to end at 12
o'clock. Go ahead.
Senator Jeffords. Dr. Levin, before setting a mercury max
standard, would you agree that it makes sense for EPA to
conduct a full modeling analysis of all available technology
options and their emissions reduction potential, including the
most stringent options?
Dr. Levin. Yes, Senator. I think it is important for EPA to
carry out a parallel study as EPRI has done, and to make that
study public, as we have as well. I am not aware yet that they
have actually done any modeling of a max standard since there
has been no official proposal of one yet.
Senator Jeffords. Dr. Myers, I believe your testimony is
that the fish consumed with an average mercury content of 0.3
parts per million has about the same mercury concentration as
commercial fish in the United States. What are the
concentration in non-commercial fish?
Dr. Myers. Are you talking about the United States or the
Senator Jeffords. In the United States.
Dr. Myers. Well, all fish has some mercury in it. Most of
the commercial fish in the United States, I understand, has
less than \1/2\ part per million, but some of the fish, I am
not sure what the non-commercial ones are, but it can go up to
over two or three parts per million in some freshwater fish.
Senator Jeffords. Dr. Rice and Dr. Myers, can you
characterize the body burden of the pollutants like mercury in
American children compared to the levels found in the
Dr. Myers. The average hair level in the mothers in
Seychelles is 6.9 in the group we were studying. The average in
the United States is less than one part per million. The
average in Japan is somewhere around two parts per million.
Senator Jeffords. Dr. Rice, any comment?
Dr. Rice. No. That is correct, but I think it is important
to understand that the NHANES data did identify some women, a
very small percentage of women with higher hair mercury levels.
I think it is important also to understand that the NHANES data
are designed to be representative of the U.S. population as a
whole, so that women who may eat more fish and may be at more
risk for increased body burdens of methyl-mercury, such as
immigrant populations or populations of people who are
subsistence anglers and who eat inland fish. This is not
captured. These populations are not captured by the NHANES data
and I think that this needs to be kept in mind.
Senator Jeffords. I have some further questions I would
like to submit.
Senator Inhofe. That would be perfectly appropriate. I
appreciate it very much, and I appreciate the panel coming and
also your patience from the long first session.
We are now adjourned.
[Whereupon, at 12 o'clock p.m. the committee was adjourned,
to reconvene at the call of the chair.]
[Additional statements submitted for the record follow:]
Statement of Hon. Jon Cornyn, U.S. Senator from the State of Texas
Mr. Chairman, I commend you for holding this important hearing
examining what is known about the science of climate change, mercury
and the potential health effects of mercury emissions from power
Given the timing of the energy debate on the Floor and this
Committee's ongoing consideration of the Clear Skies Act, this is a
very timely and important topic and I commend the Chairman for setting
time aside to focus on the issue. I realize our focus today in regards
to climate change is on the science, principally on temperature change.
Two very different trains of thought are about to be presented to us
today and I think this is positive and encourages a good, healthy
debate. The question that this panel has to wrestle with is moving
ahead with a greenhouse gas policy that may or may not be based on
sound science. I am concerned about the costs in moving forward when
there is a large body of science out there that says there isn't a
To shift our focus just a bit, an issue of particular concern to me
is the available technology to control greenhouse gas emissions,
specifically CO2. I am fairly certain that some of my
colleagues agree with the line of thought about to be outlined by Dr.
Mann, and this could very well lead this committee to a debate imposing
mandatory controls on CO2. If this turns out to be the case
it is imperative that this Committee determine whether or not the
technology is currently available to accomplish CO2
reductions that are effective enough to solve the ``problems'' thought
to be faced. I realize this is a topic for another hearing, but one
that causes me concern.
In regards to mercury, in the 1990 amendments to the Clean Air Act,
Congress specifically requested that EPA conduct an analysis of the
health effects of mercury emissions from power plants and report back.
EPA did conduct that study in 1997 and concluded that there was a
``plausible link'' between mercury emission and potential health
effects, but was unable to quantify the link.
Six years have passed since EPA's 1997 study. Unfortunately, we
still have not received any clarification from the EPA as to the
magnitude of the health risks posed by power plant emissions, even
though we are currently on the verge of spending billions of dollars to
reduce those emissions.
I suspect that one of the reasons for this lack of information is
that we are dealing with a global problem. Many people today may find
it surprising to learn that most of the mercury that is deposited in
the United States originates from outside our borders. In fact, for
most of the country, over 60-80 percent of the mercury deposited in the
United States comes from emission sources located in another country.
Additionally, natural sources of mercury, such as forest fires and
vegetation burning, account for over half of the world's mercury
What this means is that we have control over only a very small
portion of total mercury emissions. Of the 5500 tons of mercury emitted
globally, the U.S. accounts for only about 155 tons, or 3 percent of
global emissions. U.S. power plant emissions which are estimated to be
48 tons per year, represent less than 1 percent of total global
emissions. Given how small this fraction is, it is both reasonable and
prudent to ask what impact controls on power plants will have on actual
While EPA has unfortunately not provided us with any data on that
question as of yet, Leonard Levin from the Electric Power Industry has.
According to his very detailed analysis, control programs to reduce
mercury emissions from power plants are likely to have less than a 1-
percent impact on public exposure in this country. In fact, he
estimates an impact of less than 0.3 percent. I do not know if this
number is correct, but I think his very detailed analysis deserves
comment from EPA, especially given that this was exactly the kind of
information Congress sought in 1990 when it amended the Act.
I look forward to hearing Dr. Levin's testimony, as well as Dr.
Rice's and Dr. Myers'. Your collective input is critical to this
committee as we continue to debate the Clear Skies initiative.
I yield back the balance of my time.
Statement of Dr. Willie Soon, Harvard-Smithsonian Center
Distinguished Senators, panelists, and audience: My name is Willie
Soon. I am an astrophysicist with the Harvard-Smithsonian Center for
Astrophysics in Cambridge, Massachusetts. My training is in atmospheric
and space physics and my sustained research interests for the past 10
years include changes in the Sun and their possible impact on climate.
This very rich area of scientific research, though still far from
having definitive answers, has seen exciting and important progress
from our increasing technical ability to measure, quantify, and
interpret the changes in the Sun which could be linked to changes of
the Earth's climate.
Today I focus on my latest research conclusions regarding climate
change over roughly the last 1000 years, especially the geographical
pattern of those changes. My scientific study is only possible because
of the careful research produced by nearly one thousand scientists
around the world. Their expertise covers a very wide range, including
physical, chemical, biological, and geological sciences.
Together with several colleagues whose names are listed in the two
scientific papers that I am submitting today for the record of this
testimony, we have synthesized the results from several hundred studies
of proxy records of climate, including much new work that has appeared
in the scientific literature in the last 5 to 10 years.
Climate proxies are indirect climate sensors based on information
from tree rings, ice and seafloor sediment cores, corals, glaciers and
other natural evidence. They also include important cultural and
It is important to recognize that these climate proxies are not
temperature readings, but some proxies may be calibrated to give
temperature changes. One example is the measurement of the flow of heat
in boreholes drilled through rocks or ice, yielding century-scale
temperature changes over several millennia. On the other hand, some
proxies are sensitive to local rainfall as well as temperature, as in
the case of annual tree growth in the southwest United States. Any
given proxy may respond to temperature differently from other proxies,
depending on, for instance, the type of proxy, location, or season.
For all those reasons, it remains a big challenge to produce an
accurate global temperature record over the past 1000 years from the
diverse set of climate proxies.
But within the limits and lessons learned from our research papers,
we can offer three conclusions:
First, local and regional, rather than ``global'', changes are the
most relevant and practical measure of climate change and impact. This
is because truly global averages rarely are available from the distant
past, before modern satellite measurements, and because such averages
can hide the significant changes that can occur over large parts of the
Second, on a location by location basis, there was a widespread
Medieval Warm Period between approximately 800 and 1300 A.D. This
Medieval Warm Period was followed by a widespread colder period, called
the Little Ice Age, that lasted from approximately 1300 to 1900 A.D.
Third, there is no convincing evidence from each of the individual
climate proxies to suggest that higher temperatures occurred in the
20th century than in the Medieval Warm Period. Nor is there any
convincing evidence to suggest that either the rate of increase or the
duration of warming during the 20th century were greater than in the
Medieval Warm Period.
The fact that local and regional climate has been varying with
significant swings in amplitude over many locations provides important
challenges for computer simulation of climate. The full models that
explore the Earth region by region can test for the natural patterns of
change over the last 1,000 years through the use of the climate proxies
we just discussed. In that way, the effects of human-caused climate
change can be weighed against observed natural variability in the
climate system. Having computer simulations reproduce past climate,
which has been influenced predominantly by natural factors, is key to
making an accurate forecast that includes all potential human-made
warming and cooling effects.
Further research could yield a deeper, quantitative improvement to
our knowledge of local and regional climate variability during the past
1000 years. As we could be inspired by Mr. Thomas Jefferson who
``It is a common opinion that the climates of the several
states of our union have undergone a sensible change since the
dates of their first settlements; that the degrees of both cold
& heat are moderated. The same opinion prevails as to Europe;
if facts gleaned from history give reasons to believe that,
since the times of Augustus Caesar, the climate of Italy, for
example, has changed regularly at the rate of 1 [degree] of
Fahrenheit's thermometer for every century. May we not hope
that the methods invented in latter times for measuring with
accuracy the degrees of heat and cold, and the observations
which have been & will be made and preserved, will at length
ascertain this curious fact in physical history?''--Marginal
notes from Thomas Jefferson's Monticello Weather Diary (January
1, 1810 to December 31, 1816).
I strongly believe that the time for research in paleoclimatology
to fulfill this important role is now.
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Response by Dr. Willie Soon to Additional Questions from Senator
Question 1. In testimony, you said that you did not know whether
you submitted something for publication to Capitalism magazine. Here is
the title and web address: ``Global Warming Speculation vs. Science:
Just Ask the Experts'' by Sallie Baliunas & Willie Soon (Capitalism
Magazine--August 22, 2002) http://capmag.com/article.asp?ID=1816. Did
you submit or approve submission of this article for publication?
Response. With the benefit of your reminder, I hereby confirm that
the above mentioned article in Capitalism Magazine was taken from the
original article ``Just Ask the Experts'' by Baliunas and Soon
originally published by the TechCentralStation.com at the link: http://
www.techcentralstation.com/072302B.html. I did not submit the article
to Capitalism Magazine.
Question 2. In your testimony you indicated that your training is
in ``atmospherics.'' Could you please explain this term more fully, and
indicate your formal training in paleoclimatic studies and analysis?
Response. My PhD thesis\1\ was on collisional-radiative properties
of high-temperature, partially ionized nitrogen, oxygen, helium and
hydrogen plasmas at conditions relevant to the Earth's atmosphere. This
is why I mentioned that I had formal training in ``atmospheric and
space physics'' in my oral remarks. If necessary, please consult my
thesis advisor, Professor Joseph Kunc at firstname.lastname@example.org for further
details about my educational background.
\1\ Which was awarded the 1989 nation-wide IEEE Nuclear and Plasma
Sciences Society Graduate Scholastic Award and the 1991's Rockwell
Dennis Hunt Scholastic Award for ``the most representative PhD thesis
work'' at the University of Southern California.
I would add that the quality of knowledge about climate science or
any other subject of interest must be judged on its own merits, and
does not and must not be determined by invoking the amount of formal
schooling or consensus viewpoints adopted by particular interest
My research interests and learning about paleoclimatology has been
obtained mainly through the following individuals and sources:
(1) Professor Eric Posmentier (Eric.S.Posmentier@Dartmouth.EDU),
who is also my colleague.
(2) Professor David Legates (legates@UDel.Edu), who is also my
(3) Participation, both as a student and as lecturer, in numerous
national and international workshops, conferences and summer schools
including (a) the 1993's NATO Advanced Research workshop on ``Solar
engine and its influence on terrestrial atmosphere and climate'', (b)
the 1994's NASA-NOAA Summer School on Processes of Global Change, (c)
the 1996's (French) CNRS ``Chaos et Fractales dans l'activite
Solaire'', (d) the 2000's ``1st Solar and Space Weather Euroconference:
The Solar Cycle and Terrestrial Climate,'' and other specialized
(4) Many other scientists also have been helpful in my eager
learning of the subject: the late Professor Jean Grove (Girton College,
Cambridge University), Professor Jim Kennett (University of California
Santa Barbara), Professor David J. A. Evans (University of Glasgow),
Professor Lowell Stott (University of Southern California), Professor
Hong-Chun Li (University of Southern California), Professor Reid Bryson
(University of Wisconsin), Professor Henri Grissino-Mayer (University
of Kentucky), Professor Emi Ito (University of Minnesota), Dr. ShaoPeng
Huang (University of Michigan), Dr. Zhonghui Liu (Brown University),
Dr. Ming Tang (Institute of Geology and Geophysics, Chinese Academy of
Sciences), Dr. Yang Bao (Cold and Arid Regions Environmental and
Engineering Research Institute, Chinese Academy of Sciences), and
Professor Bin Wang (University of Hawaii).
Question 3. Do you maintain that the proxy-based temperature
reconstructions of the Mann and colleagues do not extend into the
latter half of the 20th century?
Response. The proxy-based temperature reconstructions for the
Northern Hemisphere by Mann et al. (1998, Nature, vol. 392, 779-782)
and Mann et al. (1999, Geophysical Research Letters, vol. 26, 759-762)
extend from 1400-1980 and 1000-1980, respectively. So it is true that
those proxy-based temperature series did not cover the 1981-2000
interval of the late 20th century.
Here is what close colleagues and co-authors (Bradley and Hughes)
of Professor Mann admitted in their independent (i.e., without Prof.
Mann as co-author) and updated publication, ``A caveat to [our]
conclusion [about northern hemisphere temperature change over the last
1000 years] is that the current proxy-based reconstructions do not
extend to the end of the 20th century, but are patched on to the
instrumental record of the last 2-3 decades [emphasis added]. This is
necessary because many paleo data sets were collected in the 1960's and
1970's, and have not been up-dated [NOTE: this statement by Bradley et
al. (2003) referred primarily to the tree-ring data base from the
International Tree-Ring Data base.], so a direct proxy-based comparison
of the 1990's with earlier periods is not yet possible.'' [p. 116 of
Bradley et al., 2003, In: Alverson, K., R.S. Bradley and T.F. Pedersen
(eds.) Paleoclimate, Global Change and the Future. Springer Verlag,
Agreeing with discussion on p. 260-261 of Soon et al. (2003),
Bradley et al. (2003) cautioned that ``in the case of tree rings from
some areas in high latitudes, the decadal time-scale climatic
relationships prevalent for most of this century appear to have changed
in recent decades, possibly because increasing aridity &/or snowcover
changes at high latitudes may have already transferred the ecological
responses of trees to climate (cf. Jacoby and D'Arrigo 1995; Briffa et
al. 1998). For example, near the northern tree limit in Siberia, this
changing relationship can be accounted for by a century-long trend to
greater winter snowfall. This has led to delayed snowmelt and thawing
of the active layer in this region of extensive permafrost, resulting
in later onset of the growing season (Vaganov et al. 1999). It is not
yet known how widely this explanation might apply to the other regions
where partial decoupling has been observed, but regardless of the
cause, it raises the question as to whether there might have been
periods in the past when the tree ring-climate response changes, and
what impact such changes might have on paleotemperature reconstructions
based largely on tree ring data.'' (p. 116-117).
Bradley et al. (2003) also worried that ``Paleoclimate research has
had a strong northern hemisphere, extra-tropical focus (but even there
the record is poorly known in many areas before the 17th century).
There are very few high resolution paleoclimatic records from the
tropics, or from the extra-tropical southern hemisphere, which leaves
many questions (such as the nature of climate in Medieval times)
unanswered.'' (p. 141). Bradley et al. continued ``All large-scale
erature reconstructions suffer from a lack of data at low latitudes. In
fact, most ``northern hemisphere'' reconstructions do not include data
from the southern half of the region (i.e. [missing comma] areas south
of 30N). Furthermore, there are so few data sets from southern
hemisphere that it is not yet possible to reconstruct a meaningful
``global'' record of temperature variability beyond the period of
instrumental records. For the northern hemisphere records, it must be
recognized that the errors estimated for the reconstructions of Mann et
al. (1999) and Briffa et al. (2001) are minimum estimates, based on the
statistical uncertainties inherent in the methods used. These can be
reduced by the use of additional data (with better spatial
representation) that incorporate stronger temperature signals. However,
there will always be additional uncertainties that relate to issues
such as the constancy of the proxy-climate function over time, and the
extent to which modern climate modes (i.e., those that occurred during
the calibration interval) represent the full range of climate
variability in the past [i.e., similar unresolved research questions
had been raised in p. 239-242 and p. 258-264 of Soon et al. 2003].
There is evidence that in recent decades some high latitude trees no
longer capture low frequency variability as well as in earlier decades
of the 20th century (as discussed below in Section 6.8) which leads to
concerns over the extent to which this may have also been true in the
more distant past. If this was a problem (and currently we are not
certain of that) it could result in an inaccurate representation of low
frequency temperature changes in the past. Similarly, if former
climates were characterized by modes of variability not seen in the
calibration period, it is unlikely that the methods now in use would
reconstruct those intervals accurately. It may be possible to constrain
these uncertainties through a range of regional studies (for example,
to examine modes of past variability) and by calibration over different
time intervals, but not all uncertainty can be eliminated and so
current margins of error must be considered as minimum estimates
[meaning the actual range of error is larger than shown in Mann et al.
1999 or the IPCC TAR's charts].'' (p. 114-115).
It is also very important to heed warnings and cautions from other
serious researchers about not over stating the true confidence of a
reconstructed climatic result based on indirect proxies. Esper et al.
(2003, Climate Dynamics, vol. 21, 699-706) modestly apprised of the
current situation in reconstructing long-term climatic information from
tree rings: ``Although these long-term trends agree well with ECS
[i.e., Esper, Cook, Schweingruber in 2002, Science, vol. 295, 2250-
2253], the amplitude of the multi-centennial scale variations is,
however, not understood. This is because (1) no single multi-centennial
scale chronology could be built that is not systematically biased in
the low frequency domain, and (2) no evidence exists that would support
an estimation of the biases either in the LTM [Long-term mean
standardization] nor in the RCS [Regional curve standardization] multi-
centennial chronologies. Consequently, we also avoided providing formal
climate calibration and verification statistics of the chronologies.
Note also that the climate signal of the chronologies' low frequency
component could not be statistically verified anyway. This is because
the high autocorrelations, when comparing lower frequency trends,
significantly reduce the degrees of freedom valid for correlation
analyses. We believe that a formal calibration/verification/transfer
function approach would leave the impression that the long-term climate
history for the Tien Shan [i.e., the location of Esper and five
colleagues' study] is entirely understood, which is not the case.
Further research is needed to estimate the amplitude of temperature
variation in the Alai Range [south of Kirghizia] over the last
millennium.'' (p. 705)
Question 4. Do you claim that the Mann study does not reconstruct
regional patterns of temperature change in past centuries?
Response. In Soon et al. (2003, Energy & Environment, vol. 14, 233-
296), I and my colleagues cautioned that the regional temperature
patterns resulted from Mann and colleagues' methodology are too
severely restricted by the calibration particular, we are concerned
that the regional (and hence larger spatial-scale averages) variability
of temperature on multidecadal and centennial time scales deduced from
such a method will be underestimated.
Recently, the methodology of Mann et al. (1998) has been seriously
challenged by McIntyre and McKitrick (2003, Energy & Environment, vol.
14, 751-771) in that ``poor data handling, obsolete data and incorrect
calculation of principal components'' were shown as the errors and
defects of Mann et al's. paper. The exchange between Mann and
colleagues and McIntyre and McKitrick is ongoing, but the use of
obsolete data is a clear case of misrepresentation of regional basis of
change in Mann et al's work. Further problems in Mann et al. (1998) are
outlined under Question No. 13 below. Additional documentation
(including responses by Prof. Mann and his colleagues) and updates can
be found in http://www.uoguelph.ca/rmckitri/research/trc.html.
Question 5. Do you maintain that the Mann study extrapolated global
temperature estimates from the northern hemisphere?
Response. I have not seen any global temperature curves presented
in the two earlier studies by Mann et al. (1998 and 1999). But please
consider the deep concerns about the lack of proxy data especially over
the tropics (30N to 30S) and the southern hemisphere raised by Soon et
al. (2003) and even in the independent paper by Professor Mann's close
colleagues and co-authors (Bradley and Hughes), i.e., in Bradley et al.
(2003), discussed under Question No. 3 above.
``Global'' temperature estimates, based on indirect climate
proxies, from 200-1980 were shown in Mann and Jones (2003, Geophysical
Research Letters, vol. 30 (15), 1820) as Figure 2c. But I am unsure if
the temperature series presented by Mann and Jones (2003) could
adequately represents the variability over the whole globe since it was
openly admitted that the proxies used covered only 8 ``distinct
regions'' in the Northern Hemisphere and 5 for the Southern Hemisphere
(see the coverage of proxies shown in Figure 1 of Mann and Jones,
More importantly, Soon et al. (2004, Geophysical Research Letters,
vol. 31, L03209) showed that the 40-year smoothed instrumental
temperature trend for the Northern Hemisphere shown as Figure 2a of
Mann and Jones (2003) has a physically implausible high value at year
2000 (see more discussion in Question No. 6 below). We caution that the
extremely rapid rate of warming trend of 1 to 2.5+ C per decade implied
by the published results by Mann and his colleagues over the last one
to 2 years [comparing Mann and Jones (2003) with both Mann (2002,
Science, vol. 297, 1481-1482) and Mann et al. (2003, Eos, 84(27), 256-
257)], is most likely due to the artifacts of methodology and their
procedure of trend smoothing. I am submitting the pdf file (SLB-GRL04-
NHtempTrend.pdf) of Soon et al. (2004) for the record of the committee.
Question 6. Do you maintain that historical and instrumental
temperature records that are available indicate colder northern
hemisphere temperature conditions than the Mann et al northern
hemisphere temperature reconstruction in the past centuries?
Response. I am not sure about the meaning of this question. But
when contrasted with borehole-based reconstruction, the Northern
Hemisphere terrestrial temperatures produced by Mann et al. (1998,
1999) over the last 500 years may have been too warm by about 0.4:+ C
during the 17th-18th century (see Huang et al. 2000, Nature, vol. 403,
756-758). Recent attempts by Mann et al. (2003, Journal of Geophysical
Research, vol. 108. (D7), 4203) and Mann and Schmidt (2003, Geophysical
Research Letters, vol. 30 (12), 1607) to rejustify and defend the Mann
et al. (1998, 1999) results have been shown to be either flawed or
invalid by Chapman et al. (2004, Geophysical Research Letters, vol. 31,
L07205) and by Pollack and Smerdon (2003, Geophysical Research Abstract
of EGS, vol. 6, 06345). The eventual fact will no doubt emerge with
increased understanding, but Chapman et al. (2004) warned that ``A
second misleading analysis made by Mann and Schmidt  concerns use
of end-points in reaching a numerical conclusion. . . . It is based on
using end points in computing changes in an oscillating time series,
and is just bad science.''
With regard to instrumental thermometer data of the past 100-150
years, it is important to note that Soon et al. (2004) has recently
shown that the 40-year smoothed Northern Hemisphere temperature trend
shown in Mann and Jones (2003) has a physically implausible high value
at the year 2000 endpoint especially when studied in context with
previous published results by Mann et al. (2003, Eos, vol. 84 (27),
256-257) and Mann (2002, Science, vol. 297, 1481-1482). This important
updated information, admittedly with the benefit of hindsight, together
with the works by Chapman et al. (2004) and McIntyre and McKitrick
(2003), showed clearly that the Northern Hemisphere temperature trends,
either proxy-based or instrumental, derived by Mann et al. (1998, 1999)
and Mann and Jones (2003) are not reliable.
Question 7. Is it your understanding that during the mid-Holocene
optimum period (the period from 4000-7000 B.C.) that annual mean global
temperatures were more than a degree C warmer than the present day?
Response. Again, I am not sure if there are sufficient proxy data
that would allow a meaningful quantitative estimate of annual mean
global temperatures back six to nine thousand years. But in a new paper
for the Quaternary Science Reviews, Darrell Kaufman and 29 co-authors
(2004, Quaternary Science Reviews, vol. 23, 529-560) found that indeed
there are clear evidence for warmer than present conditions during the
Holocene at 120 out of 140 sites they compiled across the Western
Hemisphere of the Arctic. Kaufman et al. (2004) estimated that, at the
16 terrestrial sites where quantitative data are available, the local
Holocene Thermal Maximum summer temperatures were about
1.60.8+ C higher than the average of the 20th century. The
coarse temperature map sketched on the NOAA's Paleoclimatology web
suggests that the summer temperatures 6000 years ago may have been 2 to
4+ C warmer than present in the other sector (Eastern Hemisphere) of
Question 8. As a climatologist, can you explain what kind of
quantitative analysis it takes to determine whether or not the last 50
years has been unusually warm compared to the last 1000 years?
Response. The theoretical requirement is fairly simple: (a) find
local and regional proxies that are sensitive to variations of
temperature on timescales of decade, several decades and century; (b)
have sufficient spatial coverage of these local and regional proxies.
Then one would be able to compare the last 50 years of the 1000-year
record with the previous 950 years.
Soon et al. (2003) had indeed initiated an independent effort in
this direction and concluded that a truly global or hemispheric
averaged temperature record for the past 1000 years is not yet
forthcoming because of the large and disparate range of the indirect
local and regional proxies to temperature such that a robust ability of
different proxies in capturing all the necessary scales of variability
cannot yet be confirmed. The main problem I foresee in having any
definitive answers for now is related to the fact that the statistical
association of each proxy to climatic variables like temperature can
itself be variable and changing depending on the location and time
interval. But I am not sure if the sole focus on temperature as the
measure of ``climate'' is sensible if not unnecessarily narrow.
In Soon et al. (2003), we consider climate to be more than just
temperature so we did not narrowly restrict ourselves to only
temperature-sensitive proxies. For example, in addition to temperature,
we are equally concerned about expansion and reduction of forested and
desert-prone areas, tree-line growth limit, sea ice changes, balances
of ice accumulation and ablation in mountain glaciers and so on. When
studying the ice balance for a glacier, it is important to insist that
although glaciers are very important indicators of climate change over
a rather long time-scale, they are not simply thermometers as often
confused by heated discussion pointing to evidence for global warming
by carbon dioxide (see additional discussion on factors, especially
atmospheric carbon dioxide, in determining Earth's climate and its
change under Questions No. 19, 20, 25, 30 and 35 below). Examples
include statements by Will Stefen, director of the International
Geosphere-Biosphere Program, ``Tropical glaciers are a bellweather of
human influence on the Earth system'' (quoted in the article ``The
melting snows of Kilimanjaro'' by Irion, 2001, Science, vol. 291, 1690-
1691) or by Professor Lonnie Thompson, Ohio State University,
``We have long predicted that the first signs of changes
caused by global warming would appear at the few fragile, high-
altitude ice caps and glaciers within the tropics . . . [t]hese
findings confirm those predictions. We need to take the first
steps to reduce carbon dioxide emissions. We are currently
doing nothing. In fact, as a result of energy crisis in
California--and probably in the rest of the country by this
summer--we will be investing even more in fuel-burning power
plants. That will put more power in the grid but, at the same
times it will add carbon dioxide to the atmosphere, amplifying
the problem'' (quoted in Ohio State University's press release,
A clarification about the physical understanding of modern glacier
retreats and climate change, especially those on Kilimanjaro, is
necessary and has been forthcoming with important research progress.
First, Molg et al. (2003, Journal of Geophysical Research, vol. 108
(D23), 4731) recently concluded that their study:
``highlights that modern glacier retreat on Kilimanjaro is much
more complex than simply attributable to `global warming only',
a finding that conforms with the general character of glacier
retreat in the global tropic [Kaser, 1999]: a process driven by
a complex combination of changes in several different climatic
parameters . . . with humidity-related variables dominating
In another new paper for the International Journal of Climatology,
Kaser et al. (2004, International Journal of Climatology, ``Modern
glacier retreat on Kilimanjaro as evidence of climate change:
Observations and facts'', vol. 24, 329-339; available from http://
geowww.uibk.ac.at/glacio/LITERATUR/index.html) provided clear answers
that neither added longwave radiation from a direct addition of
atmospheric CO2 nor atmospheric temperature were the key
variables for the observed changes, as revealed in this long but highly
``Since the scientific exploration of Kilimanjaro began in
1887, when Hans Meyer first ascended the mountain (not to the
top at this time, but to the crater rim), a central theme of
published research has been the drastic recession of
Kilimanjaro's glaciers (e.g., Meyer, 1891, 1900; Klute, 1920;
Gilman, 1923; Jager, 1931; Geilinger, 1936; Hunt, 1947; Spink,
1949; Humphries, 1959; Downie and Wilkinson, 1972; Hastenrath,
1984; Osmastion, 1989; Hastenrath and Greischar, 1997). Early
reports describe the formation of notches, splitting up and
disconnection of ice bodies, and measurements of glacier snout
retreat on single glaciers, while later books and papers
advance to reconstructing glacier surface areas. . . . Today,
as in the past, Kilimanjaro's glaciers are markedly
characterized by features such as penitentes, cliffs (Figure
3a/b) [not reproduced here], and sharp edges, all resulting
from strong differential ablation. These features illustrate
the absolute predominance [emphasis added] of incoming
shortwave radiation and latent heat flux in providing the
energy for ablation (Kraus, 1972). A positive heat flux from
either longwave radiation or sensible heat flux, if available,
would round-off and destroy the observed features within a very
short time ranging from hours to days. On the other hand, if
destroyed, the features could only be sculptured again under
very particular circumstances and over a long time. Thus, the
existence of these features indicates that the present summit
glaciers are not experiencing ablation due to sensible heat
(i.e., from positive air temperature). Additional support for
this is provided by the Northern Icefield air temperature
recorded from February 2000 to July 2002, which never exceeded
-1.6+ C, and by the presence of permafrost at 4,700 m below
Arrow Glacier on the western slope . . .''
Kaser et al. (2004) continue with this ``synopsis of interpretations
``A synopsis of (i) proxy data indicating changes in East
African climate since ca. 1850, (ii) 20th century instrumental
data (temperature and precipitation), and (iii) the
observations and interpretations made during two periods of
fieldwork (June 2001 and July 2002) strongly support the
following scenario. Retreat from a maximum extent of
Kilimanjaro's glaciers started shortly before Hans Meyer and
Ludwig Purtscheller visited the summit for the first time in
1889, caused by an abrupt climate change to markedly drier
conditions around 1880. Intensified dry seasons accelerated
ablation on the respectively illuminated vertical walls left in
the hole on top by Reusch Crater as a result of volcanic
activity [emphasis added]. The development of vertical features
may also have started on the outer margins of the plateau
glaciers before 1900, primarily as the formation of notches, as
explicitly reported following field research in 1898 and 1912
(Meyer, 1900; Klute, 1920). A current example of such a notch
development is the hole in the Northern Icefield (see Figure
2). Once started, the lateral retreat was unstoppable,
maintained by solar radiation despite less negative mass
balance conditions on horizontal glacier surfaces, and will
come to an end only when the glaciers on the summit plateau
have disappeared. This is most probable within next decades, if
the trend revealed in Figure 1 continues. Positive air
temperatures have not contributed to the recession process on
the summit so far. The rather independent slope glaciers have
retreated far above the elevation of their thermal readiness,
responding to dry conditions. If present precipitation regime
persists, these glaciers will most probably survive in
positions and extents not much different from today. This is
supported by the area determinations in Thompson's et al.
(2002) map, which indicate that slope glaciers retreated more
from 1912 to 1952 than since then. From a hydrological point of
view, melt water from Kibo's glaciers has been of little
importance to the lowland in modern times. Most glacier
ablation is due to sublimation, and where ice does melt it
immediately evaporates into the atmosphere. Absolutely no signs
of runoff can be found on the summit plateau, and only very
small rivers discharge from the slope glaciers. Rainfall
reaches a maximum amount at about 2,500 m a.s.l. [above sea
level] (Coutts, 1969), which primarily feeds the springs at low
elevation on the mountain; one estimate attributes 95 percent
of such water to a forest origin (Lambrechts et al., 2002). The
scenario presented offers a concept that implies climatological
processes other than increased air temperature [emphasis added]
govern glacier retreat on Kilimanjaro in a direct manner.
However, it does not rule out that these processes may be
linked to temperature variations in other tropical regions,
e.g., in the Indian Ocean (Latif et al., 1999; Black et al.,
Lindzen (2002, Geophysical Research Letter, vol. 29, paper
2001GL014360) further added that ``Recent papers show that deep ocean
temperatures have increased somewhat since 1950, and that the increase
is compatible with predictions from coupled GCMs [General Circulation
Models]. The inference presented is that this degree of compatibility
constitutes a significant test of the models. . . . [But] it would
appear from the present simple model (which is similar to what the IPCC
uses to evaluate scenarios) that the ocean temperature change largely
reflects only the fact that surface temperature change is made to
correspond to observations, and says almost nothing about model climate
sensitivity. . . . It must be added that we are dealing with observed
surface warming that has been going on for over a century. The oceanic
temperature change [at depth of 475 m or so] over the period reflects
earlier temperature change at the surface. How early depends on the
rate at which surface signals penetrate the ocean.'' In other words,
the recently noted warming of the deeper ocean is not a proof of global
surface and atmospheric warming by increasing CO2 in the air
because the parameters of climate sensitivity and rate of ocean heat
uptake are not sufficiently well quantified. In addition, if the
earlier oceanic surface temperature warming mentioned by Lindzen were
indeed initiated and occurred substantially long ago, then there would
be no association of that change to man-made CO2 forcing.
Question 9. The IPCC has found that the late 20th century is the
warmest period in the last 1000 years, for average temperature in the
northern hemisphere. Does your paper provide a quantitative analysis of
average temperatures for the northern hemisphere for this specific time
period--that is, for the later half of the 20th century?
Response. It should be understood that (1) the conclusion of the
IPCC Working Group I's Third Assessment Report (2001; TAR), (2) the
evidence shown in Figure 1b of the Summary for Policymaker, (3) Figure
5 of the Technical Summary, and (4) Figure 2.20 in Chapter 2 of TAR
were all derived directly from the conclusion in Mann et al. (1999) and
Figure 3a of Mann et al. (1999). Therefore all comments and criticisms
presented in this Q&A about Mann et al. (1999) apply to the IPCC TAR's
conclusion. In addition, Soon et al. (2004) recently cautioned that the
40-year smoothed northern hemisphere temperature trend shown in Figure
2.21 of TAR (2001) cannot be replicated according to the methodology
described in the caption of Figure 2.21. The failure in replication
introduces a significant worry about the actual quality of scientific
efforts behind the production of Figure 2.21 in TAR (2001).
The answer to the second part of your direct question is no. Here
are the related reasons why a confident estimate of the averaged
northern hemisphere temperature for the full 1000 years (including the
full 20th century) is not yet possible, despite what had been claimed
by Mann et al. (1999). First, several authors, including those detailed
in section 5.1 of Soon et al. (2003) and those pointed out in Question
No. 6, had shown that the 1000-year series of mathematical temperature
derived by Mann et al. (1999) has significantly underestimated the
multidecadal and centennial scale changes. Second, the focus of Soon et
al. (2003) is to derive understanding of climatic change on local and
regional spatial scales, instead of over the whole northern hemisphere
per se, because those are the most relevant measures, in practical
sense, of change. In addition, we provided the first-order attempt to
collect all available climate proxies relevant for local and regional
climatic changes, but not restricted to temperature alone. But more
pertinent to your question is the fact discussed in Soon et al. (2003)
that different proxies respond with differing sensitivities to
different climatic variables, seasons, plus spatial and temporal
scales, so that a convenient derivation of a self-consistent northern
hemisphere averaged annual mean temperature for the full 1000 years,
desirable as the result may be, is not yet possible.
Question 10. Does your paper provide any quantitative analysis of
temperature records specifically for the last 50 years of the 20th
Response. Soon et al. (2003) considered all available proxy records
with no particular prejudice. If the individual proxy record covers up
to the last 50 years of the 20th century, then quantitative comparisons
are performed, mostly according to the statements from the original
authors. Please consider some of the detailed quantitative discussion
in section 4 of Soon et al. (2003) and the qualitative results compiled
in Table 1 of that paper.
Question 11. In an article in the Atlanta Journal Constitution
(June 1, 2003), you were quoted as acknowledging during a question
period at a previous Senate luncheon that your research does not
provide a comprehensive picture of the Earth's temperature record and
that you questioned whether that is even possible, and that you did
not, ``. . . see how Mann and the others could `calibrate' the various
proxy records for comparison.'' How then does your analysis provide a
comprehensive picture of Earth's temperature record or have any bearing
on the finding by the IPCC, that the late 20th century is the warmest
in the last 1000 years?
Response. Thank you for referencing the article. I must first state
on the record that contrary to the claim in this Atlanta Journal
Constitution (June 1, 2003) article http://www.ajc.com/business/
content/business/0603/01warming.html, the writer, never, as claimed,
conducted a telephone interview with me. No such conversation took
place and I am rather shocked by this false claim. This fact has gone
uncorrected until now.
The strengths and weaknesses of my research works are fully
discussed in Soon et al. (2003). The paper documented detailed local
and regional changes in several climatic variables to try to obtain a
broader understanding of climate variability. We concluded that:
``Because the nature of the various proxy climate indicators
are so different, the results cannot be combined into a simple
hemispheric or global quantitative composite. However,
considered as an ensemble of individual observations, an
assemblage of the local representations of climate establishes
the reality of both the Little Ice Age and the Medieval Warm
Period as climatic anomalies with worldwide imprints, extending
earlier results by Bryson et al. (1963), Lamb (1965), and
numerous other research efforts. Furthermore, these individual
proxies are used to determine whether the 20th century is the
warmest century of the 2nd Millennium at a variety of globally
dispersed locations. Many records reveal that the 20th century
is likely not the warmest nor a uniquely extreme climatic
period of the last millennium, although it is clear that human
activity has significantly impacted some local environments.''
The question on the difficult problem of calibrating proxies of
differing types and sensitivities to climatic variables is discussed in
Soon et al. (2003) and some criticisms on the weaknesses of the
reconstruction by Mann et al. (1999) or the related IPCC TAR's
conclusion are listed especially under Questions No. 6 and 9.
Question 12. Do you believe that appropriate statistical methods do
not exist for calibrating statistical predictors, including climate
proxy records, against a target variable, such as the modern
instrumental temperature record?
Response. True progress in the field of paleoclimatology will
certainly involve a better and more robust means of interpreting and
quantifying the variations and changes seen in each high-resolution
proxy record. The issue is not merely a problem awaiting solution
through appropriate statistical methods like the EOF methodology
adopted by Mann et al. (1998, 1999). On pp. 241-242 of Soon et al.
(2003), we briefly outlined our straight-forward approach and
contrasted it to the one used by Mann and colleagues that does not
necessarily lead to results with physical meaning and reality.
Question 13. In determining whether the temperature of the
``Medieval Warm Period'' was warmer than the 20th century, does your
study analyze whether a 50-year period is either warmer or wetter or
drier than the 20th century? If so, why is it appropriate to use
indicators of drought and precipitation directly to draw inferences of
past temperatures? Please list peer-reviewed works that specifically
support the use of these indicators for inferring past temperature.
Response. The detailed discussion behind our usage of the term
``Medieval Warm Period'' or ``Little Ice Age'' was described in Soon et
al. (2003). We are mindful that the two terms should definitely include
physical criteria and evidence from the thermal field. But we emphasize
that great bias would result if those thermal anomalies were
dissociated from hydrological, cryospheric, chemical, and biological
factors of change. So indeed our description of a Medieval Climatic
Anomaly (see a similar sentiment later reported by Bradley et al. 2003,
Science, vol. 302, 404-405) in Soon et al. (2003) includes a warmer
time that contains both drought or flooding conditions depending on the
With regard to the last part of your question, I would answer by
detailing only one example--Mann et al (1998). This influential study
used both direct precipitation measurements and precipitation proxies
as temperature indicators. This study was indeed applied by the IPCC
TAR (2001). These include historical precipitation measurements in 11
grid cells, two coral proxies (reported in Mann et al.  as
precipitation proxies; see http://www.ngdc.noaa.gov/paleo/ei/data--
supp.html for this and following references), two ice core proxies, 3
reconstructions of spring precipitation in southeast United States by
Stahle and Cleaveland from tree ring data, 12 principal component
series for tree rings in southwestern United States and Mexico reported
as precipitation proxies by Stahle and Cleaveland (and Mann et al.
1998) and one tree ring series in Java--making a total of 31
precipitation series used as proxies in temperature reconstruction by
Mann et al. (1998). In this peer-reviewed article, for the
precipitation data in a grid cell in New England, the researchers
apparently used historical data from Paris, France (please see Figure 2
of McIntyre and McKitrick, 2003 and their discussion on pp. 758-759).
For a grid cell near Washington DC, the researchers used historical
data from Toulouse, France. For a grid cell in Spain, the researchers
used precipitation data from Marseilles, France. Of the 11
precipitation series used in Mann et al. (1998), only one series
(Madras, India) is correctly located. The precipitation data used by
these authors cannot be identified in the source cited in paper Mann et
al. (1998). While precipitation data and precipitation-related proxies
can be instructive in providing information on past distribution of
moisture and circulation patterns (and thus temperature), it is
important to correctly identify the series used and important not to
use data from the wrong continent for historical reconstructions.
Question 14. Do you maintain that any two 50-year periods that
occur within a multi-century interval can be considered 'coincident'
from a climatic point of view?
Response. The question raised here about the connection of any two
50-year periods in any two regions to be related from climatic point of
view is both important and interesting. But the answer will be strongly
dependent on the nature of forcings and feedbacks involved. If longer-
term cryospheric or oceanic processes are involved then the answer
would be yes.
Question 15. Do your two recent studies employ an analysis (that
is, a statistical or analytical operation performed upon numerical
data) of a single proxy climate record?
Response. The meaning of this question is not entirely clear to me.
But I would say yes under the context of what is being said.
Question 16. Has your study produced a quantitative reconstruction
of past temperature patterns? Do you have a measure of uncertainty or
verification in your description of past temperatures?
Response. The results and conclusion of Soon et al. (2003) are best
judged by the paper itself. Quantitative assessments of local and
regional changes through the climatic proxies are discussed in section
4 of that paper as well as some qualitative picture described in
Figures 1, 2 and 3 of that paper. Again, Soon et al. (2003) did not
tried to distill all the collected proxies down to produce a strict
temperature-only result since we are interested in a broader
understanding of climate variability. Part of the answers given under
Questions No. 9 and 11 can help elaborate what was done by Soon et al.
(2003). I would also like to direct your attention to the two warnings
listed under Question No. 3 by Bradley et al. (2003) and Esper et al.
(2003) concerning any undue, over confidence in promoting quantitative
certainties in the reconstruction of past temperatures through highly
imprecise black boxes of indirect proxies.
Question 17. Your study indicates that you have compiled the
results of hundreds of previous paleo-climate studies. Have you
verified your interpretation of the hundreds of studies with any of the
authors/scientists involved in those studies? If so, how many?
Response. Specific authors and scientists that provided help in our
work were listed in the acknowledgement section (p. 272) of Soon et al.
(2003). We have also received generous help and comments from several
scientists who are certainly highly qualified in terms of paleoclimatic
studies. But the ultimate quality and soundness of our research shall
always be our own responsibility.
In the September 5, 2003 Chronicle for Higher Education article (by
Richard Monastersky), there were indeed two very serious accusations
that suggested that Soon et al. (2003) had misrepresented or abused the
conclusions by two original authors whose work we had cited. Our
corrections and explanations to these unfortunately false claims can be
studied from the documentation listed in the URL http://cfa-
www.harvard.edu/wsoon/ChronicleHigherEducation03-d (read especially
Sep12-lettoCHE3.doc and Sep12-lettoCHE4.doc).
Question 18. What was earth's climate like the last time that
atmospheric concentrations of carbon dioxide were at today's levels or
about 370 parts per million (ppm) and what were conditions like when
concentration were at 500 ppm, which will occur around 2060 or so?
Response. Co-answer to this question is listed under Question No.
Question 19. Please describe any known geologic precedent for large
increases of atmospheric CO2 without simultaneous changes in
other components of the carbon cycle and the climate system.
Response. My July 29, 2003 testimony was about the climate history
of the past 1000 years detailed in Soon et al. (2003) rather than any
potential (causal or otherwise) relationship between atmospheric carbon
dioxide and climate. The fact remains that the inner working of the
global carbon cycle and the course of future energy use are not
sufficiently understood or known to warrant any confident prediction of
atmospheric CO2 concentration at year 2060. Please consider
co-answer to this question under Question No. 25 below.
However, it is abundantly obvious that atmospheric CO2
is not necessarily an important driver of climate change. It is indeed
a puzzle that despite the relative low level of atmospheric CO2
of no more than 300 ppm in the past 320-420 thousand years (Kawamura et
al., 2003, Tellus, vol. 55B, 126-137) compared to the high levels of
330-370 ppm since the 1960's there is the clear suggestion of
significantly warmer temperatures at both Vostok and Dome Fuji, East
Antarctica, during the interglacials at stage 9.3 (about 330 thousand
years before present; warmer by about 6+ C) and stage 5.5 (about 135
thousand years before present; warmer by about 4.5+ C) than the most
recent 1000 years (see Watanabe et al., 2003, Nature, vol. 422, 509-
512; further detailed discussion on environmental changes in Antartica
over the past 1000 years or so, including the most recent 50 years can
be found in section 4.3.4 or pp. 256-257 of Soon et al. 2003).
But there are important concerns about the retrieval of information
on atmospheric CO2 levels from ice cores. Jaworowski and
colleagues (1992, The Science of the Total Environment, vol. 114, 227-
284) explained that:
``Ice is not a rigid material suitable for preserving the
original chemical and isotopic composition of atmospheric gas
inclusion. Carbon dioxide in ice is trapped mechanically and by
dissolution in liquid water. A host of physico-chemical
processes redistribute CO2 and other air gases
between gaseous, liquid and solid phases, in the ice sheets in
situ, and during drilling, transport and storage of the ice
cores. This leads to changes in the isotopic and molecular
composition of trapped air. The presence of liquid water in ice
at low temperatures [`even below--70+ C'] is probably the most
important factor in the physico-chemical changes. The permeable
ice sheet with its capillary liquid network acts as a giant
sieve which redistributes elements, isotopes and micro-
particles. Carbon dioxide in glaciers is contained: (1) in
interstitial air in firn; (2) in air bubbles in ice; (3) in
clathrates; (4) as a solid solution in ice crystals; (5)
dissolved in intercrystalline veins and films of liquid brine;
and (6) in dissolved and particulate carbonates. Most of the
CO2 is contained in ice crystals and liquids, and
less in air bubbles. In the ice cores it is also present in the
secondary gas cavities, cracks, and in the traces of drilling
The concentration of CO2 in air recovered from the
whole ice is usually much higher than that in atmospheric air.
This is due to the higher solubility of this gas in cold water,
which is 73.5- and 35-times higher than that of nitrogen and
oxygen, respectively. The composition of other atmospheric
gases (N2, O2, Ar) is also different in
ice and in air inclusions than in the atmosphere. Argon-39 and
85Kr data indicate that 36-100 percent of air recovered from
deep Antarctic ice cores is contaminated by recent atmospheric
air during field and laboratory processing. Until about 1985,
CO2 concentrations in gas recovered from primary air
bubbles and from secondary gas cavities in pre-industrial and
ancient ice were often reported to be much higher than in the
present atmosphere. After 1985, only concentrations below the
current atmospheric level were published. Our conclusion is
that both these high and low CO2 values do not
represent real atmospheric content of CO2.
Recently reported concentrations of CO2 in primary
and secondary gas inclusions from deep cores, covering about
the last 160,000 years, are much below the current atmospheric
level, although several times during this period the surface
temperature was 2-4.5+ C higher than now. If these low
concentrations of CO2 represented real atmospheric
levels, this would mean (1) that CO2 had not
influenced past climatic changes, and (2) that climatic changes
did not influence atmospheric CO2 levels.'' (p. 272-
Additional historical evidence reveals natural occurrences of
large, abrupt climatic changes that are not uncommon and they occurred
without any known causal ties to large radiative forcing change. Phase
differences between atmospheric CO2 and proxy temperature in
historical records are often not fully resolved; but atmospheric
CO2 has shown the tendency to follow rather than lead
temperature and biosphere changes (see e.g., Dettinger and Ghil, 1998,
Tellus, vol. 50B, 1-24; Fischer et al., 1999, Science, vol. 283, 1712-
1714; Indermuhle et al., 1999, Nature, vol. 398, 121-126).
In addition, there have been geological times of global cooling
with rising CO2 (during the middle Miocene about 12.5-14
million years before present [Myr BP], for example, with a rapid
expansion of the East Antarctic Ice Sheet and with a reduction in
chemical weathering rates), while there have been times of global
warming with low levels of atmospheric CO2 (such as during
the Miocene Climate Optimum about 14.5-17 Myr BP as noted by Panagi et
al., 1999, Paleocenoragphy, vol. 14, 273-292). A new study of
atmospheric carbon dioxide over the last 500 million years (Rothman,
2002, Proceedings of the (US) National Academy of Sciences, vol. 99,
4167-4171) concluded that, ``CO2 levels have mostly
decreased for the last 175 Myr. Prior to that point [CO2
levels] appear to have fluctuated from about two to four times modern
levels with a dominant period of about 100 Myr. . . . The resulting
signal exhibits no systematic correspondence with geologic record of
climatic variations at tectonic time scales.''
Question 20. According to a study published in Science magazine,
[B. D. Santer, M. F. Wehner, T. M. L. Wigley, R. Sausen, G. A. Meehl,
K. E. Taylor, C. Amman, W. M. Washington, J. S. Boyle, and W.
Bruggemann Science 2003 July 25; 301: 479-483], manmade emissions are
partly to blame for pushing outward the boundary between the lower
atmosphere and the upper atmosphere. How does that fit with the long-
term climate history and what are the implications?
Response. It should first be noted that Pielke and Chase (2004,
Science, vol. 303, 1771b; and see p. 1771c by Santer et al. and
additional counter-reply by Pielke and Chase, with input from John
Christy and Anthony Reale, available as paper 278b at http://
criticized and challenged Santer et al.'s claim and conclusion that,
``[o]ur results are relevant to the issue of whether the `real-
world' troposphere has warmed during the satellite era. . . .
The direct evidence is that in the ALL experiment [i.e.,
climate model results that included changes in well-mixed
greenhouse gases, direct scattering effects of sulfate
aerosols, tropospheric and stratospheric ozone, solar total
irradiance and volcanic aerosols; see more discussion below],
the troposphere warms by 0.07+ C/decade over 1979-1999. This
warming is predominantly due to increases in well-mixed
greenhouse gases. . . . Over 1979-1999, roughly 30 percent of
the increase in tropopause height in ALL is explained by
greenhouse gas-induced warming of the troposphere.
Anthropogenically driven tropospheric warming is therefore an
important factor in explaining modeled changes in tropopause
In contrast, Pielke and Chase (2004) offered the observed evidence
and concluded that
``[g]lobally averaged tropospheric temperature trends are
statistically indistinguishable from zero. Thus, the elevation
of the globally averaged tropopause report in [Santer et al.,
2003] cannot be attributed to any detectable tropospheric
warming over this period.'' In addition, ``the climate system
is much more complex than defined by tropospheric temperature
and tropopause changes. Linear trend analysis [in Santer et
al., 2003] is of limited significance. Changes in global heat
storage provide a more appropriate metric to monitor global
warming than temperature alone.''
Soon and Baliunas (2003, Progress in Physical Geography, vol. 27,
448-455) had also previously outlined the incorrect fingerprint of
CO2 forcing observed in even the best and sophisticated
version of climate models thus far. A more general and comprehensive
discussion about the fundamental difficulties on modeling the effects
of carbon dioxide using current generation of climate models is given
in Soon et al. (2001, Climate Research, vol. 18, 259-271). Thus, the
new paper by Santer et al. (2003) does not supercede or overcome the
difficulties with respect to General Circulation Climate Models raised
in Soon and Baliunas (2003).
Both the meaning and strength of the model-dependent results shown
in Santer et al. (2003) remain doubtful and weak for several additional
First, Figure 2 of Santer et al. (2003) itself confirmed that the
modeled changes in tropopause height are caused mainly by large
stratospheric cooling related to changes in stratospheric ozone (they
admitted so even though their note No. 35 indicates that their
numerical experiments did not separate tropospheric and stratospheric
ozone changes) rather than by the well-mixed greenhouse gases that are
supposed to be the subject of concern. Second, the model experiments of
Santer et al. (2003) did not include changes in stratospheric water
vapor which is known to be a significant factor for the observed
stratospheric cooling (see e.g., Forster and Shine, 1999, Geophysical
Research Letters, vol. 26, 3309-3312). Third, the failure to account
for stratospheric water vapor contradicted the documented significant
increases of stratospheric water vapor in the past half-century from a
variety of instrumentations (e.g., Smith et al, 2000, Geophysical
Research Letters, vol. 27, 1687-1690; Rosenlof et al., 2001,
Geophysical Research Letters, vol. 28, 1195-1198; though Randel et al.
[2004, Journal of the Atmospheric Sciences, submitted] recently noted
that unusually low water vapor has been observed in the lower
stratosphere for 2001-2003). Fourth, the model experiments by Santer et
al. (2003) had clearly neglected (see note No. 18 of that paper) the
role of the Sun's ultraviolet radiation that is not only known to be
variable (e.g., Fontenla et al. 1999, The Astrophysical Journal, vol.
518, 480-499; White et al., 2000, Space Science Reviews, vol. 94, 67-
74) but also known to exert important influence on both the chemistry
and thermal properties in the stratosphere and troposphere (e.g.,
Larkin et al., 2000, Space Science Reviews, vol. 94, 199-214).
Finally, the physical representation of aerosol forcing (which
should not be restricted to sulfate alone) in Santer et al. (2003) is
clearly not comprehensive and at best highly selective. Early on,
Russell et al. (2000, Journal of Geophysical Research, vol. 105, 14891-
14898) cautioned that
``[o]ne danger of adding aerosols of unknown strength and
location is that they can be tuned to give more accurate
comparisons with current observations but cover up model
Anderson et al. (2003, Science, vol. 300, 1103-1104 and see also
exchanges in Crutzen et al., 2003, vol. 303, 1679-1681) recently
``we argue that the magnitude and uncertainty of aerosol
forcing may affect the magnitude and uncertainty of total
forcing [i.e., `the global mean sum of all industrial-era
forcings'] to a degree that has not been adequately considered
in climate studies to date. Inferences about the causes of
surface warming over the industrial period and about climate
sensitivity may therefore be in error. . . . Unfortunately,
virtually all climate model studies that have included
anthropogenic aerosol forcing as a driver of climate change
(diagnosis, attribution, and projection studies; denoted
`applications' in the figure) have used only aerosol forcing
values that are consistent with the inverse approach. If such
studies were conducted with the larger range of aerosol
forcings determined from the forward calculations, the results
would differ greatly. The forward calculations raise the
possibility that total forcing from preindustrial times to the
present . . . has been small or even negative. If this is
correct, it would imply that climate sensitivity and/or natural
variability (that is, variability not forced by anthropogenic
emissions) is much larger than climate models currently
indicate. . . . In addressing the critical question of how the
climate system will respond to this [anthropogenic greenhouse
gases'] positive forcing, researchers must seek to resolve the
present disparity between forward and inverse calculations.
Until this is achieved, the possibility that most of the
warming to date is due to natural variability, as well as the
possibility of high climate sensitivity, must be kept open.
To further understand the complexity of calculating aerosol
forcing, Jacobson (2001, Journal of Geophysical Research, vol. 106,
1551-1568) has to account for a total of 47 species ``containing
natural and/or anthropogenic sulfate, nitrate, chloride, carbonate,
ammonium, sodium, calcium, magnesium, potassium, black carbon, organic
matter, silica, ferrous oxide, and aluminium oxide'' in his recent
estimate of only the global direct radiative forcing by aerosols.
(Jacobson  found that the global direct radiative forcing by
anthropogenic aerosols is only -0.12 W/m\2\ while the forcing by
combined natural and anthropogenic sources is -1.4 W/m\2\.) There are
also the indirect aerosol effects. Temperature or temperature change is
clearly not the only practical measure of effects by aerosols. Haywood
and Boucher (2000, Reviews of Geophysics, vol. 38, 513-543) stressed
the fact that the indirect radiative forcing effect of the modification
of cloud albedo by aerosols could range from -0.3 to -1.8 W/m\2\, while
the additional aerosol influences on cloud liquid water content (hence,
precipitation efficiency), cloud thickness and cloud lifetime are still
highly uncertain and difficult to quantify (see e.g., Rotstayn and Liu,
2003, Journal of Climate, vol. 16, 3476-3481). This is why one can
easily appreciate the difficulties faced by Santer et al. (2003)
because climate forcing by aerosols is not only known within a wide
range of uncertainties but also to a large degree of unknown.
Therefore, I conclude that in addition to the fundamental issues
related to climate model representation of physical processes, papers
like Santer et al. (2003) have also failed the basic requirement for
internal consistencies in the accounting for potentially relevant
climatic forcing factors and feedbacks. This is why I cannot comment on
the implication of this particular study and the meaning of the study
for long-term climate history.
Question 21. In your testimony, you discussed there being
``warming'' and ``cooling'' for different periods. If you did not
construct an integral across the hemisphere or a real timeline, don't
your findings really just say there were some warm periods and cool
periods, and therefore cannot speak to the issue of the rate of warming
Response. I am not sure about the meaning of this question and the
quotes. My oral remark was merely referring to ``making an accurate
forecast that includes all potential human-made warming and cooling
effects.'' The detailed discussion about the climatic and environmental
changes for the past 1000 years as deduced from the collection of
proxies I had studied was given in Soon et al. (2003). I can certainly
speak to the rate of warming or cooling at any given location or region
when the available proxy, with sufficient temporal resolution, is known
or proven to be temperature sensitive.
Question 22. Is there any indication that regional climate
variations are any larger or smaller at present than over the last 1000
years (with 2003, for example, perhaps being a case with large regional
variations from the normal)?
Response. I would not recommend considering the pattern of change
from a single year, i.e., 2003, and called it a climate change. But the
fact is that in Soon et al. (2003) we had carefully studied individual
proxy records from various locations and regions. As an example, the
2000-year bottom-sediment record from Moon Lake, North Dakota, shows
there is perhaps a distinct shift in the mode of hydrologic variability
in the Northern Great Plain region starting around 1200 AD with the
more recent period being more variable from the past. But, as indicated
in the chart below, the author of this paper also noted that the severe
droughts of the 1890's and 1930's around this area are ``eclipsed by
more extensive droughts before the beginning of the instrumental
[GRAPHIC] [TIFF OMITTED] T2381.096
Question 23. In your oral presentation, you talked about ``[h]aving
computer simulation.'' Could you please explain what you [as in your
original] computer simulation or modeling to which you are referring,
and, (a) Has this model gone through the appropriate set of model
intercomparison studies like the various othe global models? (b) What
forcings have been used to drive it? (c) How does it develop regional
climate variations, and are these comparable to observations? and, (d)
How does it perform over the 20th century, for example?
Response. I apologize for any potential confusions.
In my oral remark, I said,
``The entirety of climate proxies over the last 1,000 years
shows that over many areas of the world there has been, and
continues to be, large climate changes. Those changes provide
challenges for the computer simulations of climate. The full
models, which explore the Earth region by region, can be tested
against the natural patterns of change over the last 1,000
years that are detailed by the climate proxies. Having computer
simulations reproduce past patterns of climate, which has been
influenced predominantly by natural factors, is key to making
an accurate forecast that includes all potential human-made
warming and cooling factors.''
So in the context of what I said, this question is clearly
misdirected by someone who did not understand my remark. I was speaking
on the potential application of works like Soon et al. (2003) for
improving our ability to calculate with confidence the potential
effects from man-made factors by first and foremost having a climate
model that can at least reproduce some of the observed local and
regional changes of the past.
Personally, I am also conducting my research through the help of
several climate models (both simple and complex types) appropriate for
my interests and I would certainly apply what I found in Soon et al.
(2003) to my own future studies using climate models. Any additional
comments will be beyond the simple context of my oral testimony. But,
it may be useful to take note of the comments by Green (2002, Weather,
vol. 57, 431-439):
``It has always worried me that simple models of climate do
not seem to work very well. Experts on numerical models say
that this is because the atmosphere is very complicated, and
that large numerical models and computers are needed to
understand it. I worry because I do not know what they have
hidden in those models and the programs they use. I wonder what
I can compare their models with. Not with each other because
they belong to a sort of club, where to have a model that
disagrees with everyone else's puts you outside. That is not a
bad system, unless of course they are all wrong. Another
curiosity of complicated models is that their findings are
rarely used to improve the model that preceded them. I would
have expected that the more complex model would show where the
simpler one had got it wrong, and allow it to be corrected for
Question 24. Based on the various comments of your scientific
colleagues regarding your paper, including the methodological flaws
pointed out in that paper by the former editor-in-chief of Climate
Research, are you planning any reworking of your study or any further
studies in the paleoclimatic area?
Response. The use of a phrase like ``methodological flaws'' is a
very convenient attempt to dismiss the weight of scientific evidence
presented in Soon et al. (2003) but unfortunately without any clear nor
confirmable basis. Thus far, the only formal criticism of Soon et al.
(2003) was by Mann et al. (2003, Eos, vol. 84(27), 256-257) and we had
provided our response to that criticism in Soon et al. (2003b, Eos,
vol. 84(44), 473-476). My research interest and work to fully discern
and quantitatively describe the local and regional patterns of climate
variability over the past 1000 years or so will certainly continue
despite this mis-characterization.
It should however not be left unnoticed that several very serious
problems in Mann et al. (1998, 1999), Mann and Schmidt (2003) and Mann
and Jones (2003) had been found recently. Those unresolved anomalies
are outlined in my answers to your Questions No. 3, 4, 5, 6, 9 and 13.
A careful reworking with a fully open access to all data as well as a
fully disclosed transparency of the actual methodologies and detailed
applications will be the next important step for paleoclimate
Question 25. You indicated that there would likely be relatively
small climatic response to even substantial increases in the CO2
concentration. Do you disagree with the radiation calculations that
have been done and the trapped energy that they calculate, as per the
peer-reviewed literature? If so, please explain.
Response. First, please consider the above discussion on climate
forcing factors and climate response sensitivities under Question No.
20 as part of the answers to this question.
Second, I do not believe that I had made any strong claim, one way
or another, about the CO2 forcing and potential response in
any specific quantitative term during my testimony (since factually no
one can). I do want to comment, as in my response under Question No.
19, that CO2, as a minor greenhouse gas, is not a
determinant of Earth's climate and therefore not entirely obvious a
driver of its change. Most calculations in peer-reviewed literature (or
not) that focus on the CO2 factor indeed would only like us
to believe that CO2, especially under the realm of radiative
forcing, is the predominant factor for driving anomalous climate
responses, while the unavoidable and very difficult core subject about
the actual dynamical state of Earth's ``mean'' climate is ignored.
Third, some 10 years ago, Lindzen (1994, Annual Review in Fluid
Mechanics, vol. 26, 353-378) pointed out a rather serious internal
inconsistency regarding the role of water vapor and clouds when the
physics of greenhouse effect is normally evaluated even among expert
scientists or expert sources of information. (See e.g., the comment
``without [the greenhouse effect], the planet would be 65 degrees
colder'' by Jerry Mahlman in the February 2004 issue of Crisis
Magazine, http://www.crisismagazine.com/february2004/feature1.htm) and
the description of Greenhouse Effect in the EPA's ``global warming for
kids'' webpage: http://www.epa.gov/globalwarming/kids/greenhouse.html.)
Lindzen notes the ``artificial inevitability'' for the predominance of
CO2 radiative forcing as a climatic factor in the following
``In most popular depictions of the greenhouse effect, it is
noted that in the absence of greenhouse gases, the Earth's mean
temperature would be 255 K [about 0+ F], and that the presence
of infrared absorbing gases elevates this to 288 K [59+ F]. In
order to illustrate this, only radiative heat transfer is
included in the schematic illustrations of the effect (Houghton
et al. 1990, 1992) [IPCC reports]; this lends an artificial
inevitability to the picture. Several points should be made
concerning this picture: 1. The most important greenhouse gas
is water vapor, and the next most important greenhouse
substance consists in clouds; CO2 is a distant third
(Goody & Yung 1989). 2. In considering an atmosphere without
greenhouse substances (in order to get 255 K), clouds are
retained for their visible reflectivity while ignored for their
infrared properties. More logically, one might assume that the
elimination of water would also lead to the absence of clouds,
leading to a temperature of about 274 K [or 278 K depending on
what value of the solar irradiation factor is used] rather than
255 K. 3. Pure radiative heat transfer leads to a surface
temperature of about 350 K rather than 288 K. The latter
temperature is only achieved by including a convective
adjustment that consists simply in adjusting vertical
temperature gradient so as to avoid convective instability
while maintaining a consistent radiative heat flux. . . . ``
\2\ A more pedagogical discussion of the greenhouse effect is given
by Lindzen and Emanuel (2002) in Encyclopedia of Global Change,
Environmental Change and Human Society, Volume 1, Andrew S. Goudie,
editor in chief, p. 562-566, Oxford University Press, New York, 710 pp.
Hu et al. (2000, Geophysical Research Letters, vol. 27, 3513-3516)
added that as the sophistication of parameterization of atmospheric
convection increases, there is a tendency for climate model sensitivity
to variation in atmospheric CO2 concentration to decrease
considerably. In Hu et al. (2000)'s study, the change is from a
decrease in the averaged tropical warming of 3.3 to 1.6+ C for a
doubling of CO2 that is primarily associated the
corresponding decrease in the calculated total atmospheric column
increase in water vapor from 29 percent to 14 percent.
Question 26. If you accept those radiation calculations as valid,
please explain why you seem to believe that the energy trapped by the
greenhouse gases will have a small effect whereas you seem to believe
that small changes in solar energy will have very large climatic
Response. In addition to my answers under Questions No. 19, 20 and
25 above, I would like to point out that the Sun's radiation is not
only variable but it varies in the ultraviolet part of the
electromagnetic spectrum often by factors of 10 or more. The question
about the relative effects of anthropogenic greenhouse gases and the
Sun's radiation in terms of radiative forcing is certainly of interest
but it does not add much to my current research quest to understand the
Earth's mean climatic state and its nonlinear manifestations.
Question 27. Please explain why you think the physically based
climate models seem to quite satisfactorily represent the seasonal
cycles of the climate at various latitudes based on the varying
distributions of solar and infrared energy, but then would be so far
off in calculating the climatic response for much smaller perturbations
to solar radiation and greenhouse gases?
Response. As indicated below, the first part of this sentence about
a satisfactory representation of seasonal cycles of climate by computer
climate models is not any assured statement of fact. This is why the
followup question cannot be logically answered.
For example, E. K. Schneider (2002, Journal of Climate, vol. 15,
449-469) noted that:
``[a]t this writing, physically consistent and even flux-
corrected coupled atmosphere-ocean general circulation models
(CGCMs) have difficulty in producing a realistic simulation of
the equatorial Pacific SST [sea surface temperature], including
annual mean, annual cycle, and interannual variability. Not
only do the CGCM simulations have significant errors, but also
there is little agreement among models.''
In a systematic comparison of the performance of 23 dynamical ocean-
atmosphere models, Davey et al. (2002, Climate Dynamics, vol. 18, 403-
420) found that ``no single model is consistent with the observed
behavior in the tropical ocean regions . . . as the model biases are
large and gross errors are readily apparent.'' Without flux adjustment,
most models produced annual mean equatorial sea surface temperature in
the central Pacific that are too cold by 2-3+ C. All GCMs except one
simulated the wrong sign of the east-west SST gradient in the
equatorial Atlantic. The GCMs also incorrectly simulated the seasonal
climatology in all ocean sections and its interannual variability in
the Pacific ocean.
Question 28. In regard to your answers to the previous questions,
to what extent is your indication of a larger climate sensitivity for
solar than greenhouse gases due to quantitative analysis of the physics
and to what extent due to your analysis of statistical correlations? Is
this greater responsiveness for solar evident in the baseline climate
system, or just for perturbations, and could you please explain?
Response. Please see my answers to Questions No. 26 above and 30
Question 29. Please explain why you seem to accept that solar
variations, volcanic eruptions, land cover change, and perhaps other
forcings can have a significant climatic influence, but changes in
CO2 do not or cannot have a comparable influence?
Response. Please see my answers to Question No. 30.
Question 30. Could you please clarify why it is that you think the
best way to get an indication of how much the climate will change due
to global-scale changes in greenhouse gases or in solar radiation is to
look at the regional level rather than the global scale? How would you
propose to distinguish a natural variation from a climate change at the
local to regional level?
Response. Questions No. 28, 29 and 30 seem to be based on the
unreasonable presumptions that some special insights about the effects
of solar irradiation or land cover changes or even volcanic eruptions
must be invoked or answered in order to challenge the role of carbon
dioxide forcing in the climate system. That presumption is illogical.
My basic view and research interest about carbon dioxide and the
ongoing search for the right tool for modeling aspects of the Earth's
climate system can be briefly summarized by my answers to Questions No.
19, 25, 26, 27 and perhaps 20.
As to your specific question on distinguishing a natural variation
(either internally generated or externally introduced by solar
variation or volcanic eruption) from a climate change by anthropogenic
factors like land cover changes or carbon dioxide at the local to
regional level, there is possibly a somewhat surprising answer. If one
wish to single out the potential effects of man-made carbon dioxide
against other natural and anthropogenic factors as hinted by your
question, then the answer is clear--the CO2 effect is
expected to be small in the sense that its potential signals will be
likely be overwhelmed when compared with expected effects by other
factors. It is a scientific fact that the signal of CO2 on
the climate may be expected only over a very long time baseline and
over a rather large areal extent. For example, Zhao and Dirmeyer (2003,
COLA Technical Report No. 150; available at http://grads.iges.org/pubs/
tech.html), in their modeling experiments that attempt to account for
the realistic effects of land cover changes, sea surface temperature
changes and for the role of added atmospheric CO2, found
``[w]hen observed CO2 concentrations are specified
in the model across the 18-year period, . . . we do not find a
substantially larger warming trend than in CTL [with no change
in CO2 concentration], although some small increase
is found. The weak impact of atmospheric CO2 changes
may be due to the small changes in specified CO2
during the model simulation compared to the doubling CO2
simulation, or the short length of the integrations. It is
clear that the relatively strong SST [sea surface temperature]
influence in this climate model is the driver of the [observed]
Please also consider the point made by Lindzen (2002) under Question
No. 8 above concerning the difficulties in linking the observed warming
trend of the deep ocean (without challenging the quality and error of
those deep ocean temperature data) to anthropogenic CO2
forcing. Finally, I wish to note that Mickley et al. (2004, Journal of
Geophysical Research, vol. 109, D05106) managed to use climate model
simulations results to demonstrate ``the limitations in the use of
radiative forcing as a measure of relative importance of greenhouse
gases to climate change. . . . While on a global scale CO2
appears to be a more effective `global warmer' than tropospheric ozone
per unit forcing, regional sensitivities to increase ozone may lead to
strong climate responses on a regional scale.''
Question 31. How does your recent article relate to your
assignments at the Harvard Smithsonian Observatory? Is paleoclimate
part of the task of this observatory?
Response. The publications of Soon et al. (2003) or Soon et al.
(2004) are possible because of research grants that I and my
collaborators obtained through competitive proposals to several
research funding sources. I am a trust-fund employee at the Harvard-
Smithsonian Center for Astrophysics and the support of my position and
research work here is mainly through my own research initiative and
proposal application. The scientific learning about paleoclimatic
reconstruction presented in Soon et al. (2003) is related to my
research interest in the mechanisms of sun-climate relation, especially
for relevant physical pathways and processes on multidecadal and
centennial time scales. Additional fruit of my independent research and
labor in the area of sun-climate physics, funded or unfunded, is
exemplified by the March 2004 book ``The Maunder Minimum and The
Variable Sun-Earth Connection'' (see http://www.wspc.com/books/physics/
5199.html) by W. Soon and S. Yaskell (published by World Scientific
Publishing Company). It might also be instructive to note that
paleoclimate researchers have been speculating about long-term
variability of the sun as the cause of centennial- to millennial-scale
variability seen in their proxy records.
Question 32. In your testimony, you said that ``climate change is
part of nature.'' Please describe what you meant, since obviously,
climate change have occurred due, in part, to changes in various
forcings, such as solar, continental drift, atmospheric composition,
asteroid impacts, etc. rather than being just completely random events.
Could you provide estimates of how large you consider future forcings
might be and how big the climate change they might cause could be?
Response. In this occasion, I am referring to the fact that any
change or variability in climate is most likely a rule, rather than the
exception, of the climate system. But I was not speaking about or
trying to imply the factors of change, either naturally produced or
man-made. I apologize for any potential confusion. It is certainly
reasonable to suggest that those climatic changes may arise from
``forcings'' but it would be unwise to rule out internally generated
manifestations of climatic variables that could be purely stochastic in
origin. I would strongly recommend the pedagogical discussion by
Professor Carl Wunsch of MIT in Wunsch (1992, Oceanography, vol. 5, 99-
106) and Wunsch (2004, ``Quantitative estimate of the Milankovitch-
forced contribution to observed Quaternary climate change'', working
manuscript downloadable from http://puddle.mit.edu/cwunsch/).
I cannot speculate on future climate forcings and resultant
climatic changes because I found no basis for doing so.
Question 33. Please provide a comparable estimate, with some
supporting examples from the past, of how big you think the decadal (or
50-year if you prefer) change in the hemispheric/global climate could
be due to natural variability? If you prefer to focus on the regional
scale change, could you provide an indication of any expected change in
the degree of regional variability about the hemispheric and global
values, and what the mechanism for this might be?
Response. This question seems a related question trying to get at a
quantitative comparison of how large natural climate variability on
regional or hemispheric scale can be under the shadow of expected
future changes. Again, with no intention to devalue this interesting
question, I do not have sufficient knowledge nor ability to venture
such an estimate. In fact, I would go so far to say that if the
estimates of variability for both the past and future are known within
a reasonable range of uncertainties, then the actual scientific
research program to address questions about the role of added carbon
dioxide no longer require further funding or execution since we have
obtained all the relevant answers. But you may have judged from my
answers given throughout this Q&A that much remains to be quantified
and understood and the hard scientific research must continue.
Question 34. Please explain the scientific basis for your testimony
that ``one should expect the CO2 greenhouse effect to work
its way downward toward the surface.''
Response. Co-answer to this question is given under Question No.
Question 35. Do you believe that there is greater greenhouse
trapping of energy in the troposphere than at the surface and that the
atmosphere has a low heat capacity? If so, how big is this temperature
Response. It is broadly agreed and assumed that carbon dioxide,
when released into the air, has a tendency to get mixed up quickly and
so is distributed widely through out the whole column of the
atmosphere. The air near the surface is already dense and moist, so
addition of more carbon dioxide will introduce very little imbalance of
radiation energy budget there. In contrast adding more carbon dioxide
to the thinner and drier air of the troposphere will cause a chain of
noticeable effects. First, the presence of more carbon dioxide in the
uppermost part of the atmosphere will cause more infrared radiation to
escape into space because there are more carbon dioxide molecules to
channel this infrared radiation upward and outward unhindered. Part of
that infrared radiation is also being emitted downward to the lower
parts of the atmosphere and the surface where it is reabsorbed by
carbon dioxide and the thicker air there. The layer of air at the lower
and middle troposphere, being more in direct contact with this down-
welling radiation, is expected to heat more than air near the surface.
Thus, adding more carbon dioxide to the atmosphere should cause more
warming of the air around the height of two to seven kilometers.
(Please consider for example the discussion by Kaser et al. (2004)
under Question No. 8 about the ineffectiveness of an added longwave
radiation from a direct addition of atmospheric CO2 or
atmospheric temperature change in explaining the modern retreat of
glaciers at Kilimanjaro.) In other words, the clearest impact of the
carbon dioxide greenhouse effect should manifest itself in the lower-
and mid-troposphere rather than near the earth's surface. Here, I am
mostly speaking on the basis of expectation from pure radiative forcing
Such a qualitative description is not complete, even though that is
roughly what was modeled in the most sophisticated general circulation
models (see e.g., Chase et al., 2004, Climate Research, vol. 25, 185-
190), because it misses the key roles of atmospheric convection and
waves as well as all the important hydrologic processes (please see
e.g., Neelin et al., 2003, Geophysical Research Letters, vol. 30 (no.
24), 2275 and consider additional remarks about water vapor and
atmospheric convection under Question No. 25 as well as discussion on
climate forcing factors and climate response sensitivities under
Question No. 20). Some theoretical proposals expect a warming of the
surface relative to the low- and mid-troposphere because of nonlinear
climate dynamics (Corti et al., 1999, Nature, 398, 799-802). That
expectation is because of the differential surface response with the
pattern of Cold Ocean and Warm Land (COWL) that becomes increasingly
unimportant with distance away from the surface (rather than just the
difference in heat capacity mentioned in your question) [see Soon et
al., 2001 for additional discussion]. Nevertheless, no GCM has yet
incorporated such an idea into an operationally robust simulation of
the climate system response to greenhouse effects from added
CO2. In the latest ``global warming'' work, Neelin et al.
(2003), for example, still distinctly differentiate between mechanisms
for tropical precipitation that are initiated through CO2
warming of the troposphere and through El Nino warming rooted in
oceanic surface temperature and subsurface thermocline dynamics.
(Further note that their model experiments [see Figure 2b+2c and
10b+10c of Chou and Neelin, 2004, ``Mechanisms of global warming
impacts on regional tropical precipitation'' in preparation for Journal
of Climate; available at http://www.atmos.ucla.edu/?csi/REF/] also
clearly shown that the troposphere warmed significantly more than
surface with the doubling of atmospheric CO2 as discussed by
Chase et al. 2004 below.)
But it is worth noticing that the current global observation shows
that, at least over the 1979-2003 interval, the lower tropospheric
temperatures are not warming as fast as the surface temperatures (see
Christy et al. 2003, Journal of Atmospheric and Oceanic Technology,
vol. 20, 613-629; for additional confidence on the results derived by
the University of Alabama-Huntsville group, please see Christy and
Norris, 2004, Geophysical Research Letters, vol. 31, L06211). This
observed fact is in contradiction to the accelerated warming of the mid
and upper troposphere relative to surface simulated in current models
(Chase et al. 2004). Chase et al. (2004) arrives at the following
conclusions, upon examining results from 4 climate models in both
unforced scenarios and scenarios forced with increased atmospheric
greenhouse gases and the direct aerosol effect\3\:
\3\ Such a study should also be consistently challenged by the
discussion under question No. 20 about the adequacy of studying
responses from a combination of incomp;ete forcings--through my primary
purpose here is to illustrate the theoretical expectation of CO2
forcing deriving from state-of-the-art climate models.
``Model simulations of the period representative of
the greenhouse-gas and aerosol forcing for 1979-2000 generally
show a greatly accelerated and detectable warming at 500 mb
relative to the surface (a 0.06+ C
Considering all possible simulated 22 yr trends
under anthropogenic forcing, a strong surface warming was
highly likely to be accompanied by accelerated warming at 500
mb [i.e., 987 out of 1018 periods or 97 percent of the cases
had a larger warming at 500 mb than at the surface] with no
change in likelihood as forcings increased over time.
In simulated periods where the surface warmed more
quickly than 500 mb, there was never a case [emphasis added] in
which the 500 mb temperature did not also warm at a large
fraction of the surface warming. A 30 percent acceleration at
the surface was the maximum simulated as compared with an
observed acceleration factor of at least 400 percent the mid-
In cases where there was a strong surface warming
and the surface warmed more quickly than at 500 mb in the
forced experiments, there was never a case in which the 500 mb-
level temperatures did not register a statistically significant
(p< 0.1) trend (i.e., a trend detectable with a simple linear
regression model). The minimum p value of approximately 0.08
occurred in the single case in which the significance was not
greater than 99 percent.
It was more likely that surface warmed relative to
the mid-troposphere under control simulations than under forced
At no time, in any model realization, forced or
unforced, did any model simulate the presently observed
situation of a large and highly significant surface warming
accompanied with no warming whatsoever aloft.'' (p. 189)
Question 36. The grants that are described as supporting your
analysis seem to have much more to do with the sun or unrelated pattern
recognition that with climate history (Air Force Office of Scientific
Research-Grant AF49620-02-1-0194; American Petroleum Institute-Grants
01-0000-4579 and 2002-100413; NASA-Grant NAG-7635; and NOAA-Grant
NA96GP0448). Could you please describe how much funding you received
and used in support of this study, all of the sources and the duration
of that funding, and the relevance of those grant topics to the
Response. All sources of funding for my and my colleagues' research
efforts that resulted in the publication of Soon and Baliunas (2003)
and Soon et al. (2003) were openly acknowledged. In other words, all
sources of funding were disclosed in the manuscripts when they were
submitted for publication; all sources of funding were also disclosed
to readers in the printed journal articles. I am not the principal
investigator for some of the grants we received (e.g., the NOAA grant
was awarded to Professor David Legates), so I am not in the privilege
position to provide exact quantitative numbers. But throughout the
2001-2003 research interval in which our work was carried out, the
funding we received from the American Petroleum Institute was a small
fraction of the funding we received from governmental research grants.
The primary theme of my research interest is on physical mechanisms
of the sun-climate relationship. This is why researching into the
detailed patterns of local and regional climate variability as
published in Soon et al. (2003) is directly relevant to that goal.
Please also consider my research position listed under Question No. 31
Question 37. Have you been hired by or employed by or received
grants from organizations that have taken advocacy positions with
respect to the Kyoto Protocol, the U.N. Framework Convention on Climate
Change, or legislation before the U.S. Congress that would affect
greenhouse gas emissions? If so, please identify those organizations.
Response. I have not knowingly been hired by, nor employed by, nor
received grants from any such organizations described in this question.
Question 38. Please describe the peer review process that took
place with respect to your nearly identical articles published both in
Climate Research and in Energy and Environment, including the number of
reviewers and the general content of the reviewers' suggested edits,
criticisms or improvements.
Response. The Climate Research paper (Soon and Baliunas, 2003,
Climate Research, vol. 23, 89-110) was submitted for publication and
went through a routine peer-review process and was eventually approved
for publication. The main content of the review was to propose: (a)
reorganizing of materials including elimination of discussions on ENSO
and GCMs; (b) removing ``tone'' problems by eliminating criticisms of
previous EOF and superposition analyses; (c) reducing quotes especially
those by Hubert Horace Lamb to improve readability; and (d) reviewing
changes in each region with same thoroughness. The July 3, 2003's email
(as Attachment I below) from the director of Inter-Research, Otto
Kinne, who publishes Climate Research is enclosed below to confirm that
the review process was fairly rigorous and all parties involved had
carried out their roles and duties in this time-honored system
The extended and more complete paper by Soon et al. (2003, Energy &
Environment, vol. 14, 233-296) was submitted to Energy & Environment
for consideration together with the accepted Climate Research
manuscript. Energy & Environment's editorial decision was to send our
manuscript for review, and after acceptance, include in its editorial
in Energy & Environment, volume 14, issues 2&3, a footnote referring to
the Climate Research paper.
Finally, we wish to correct that the false impression introduced by
Professor Mann both during the testimony and in public media that his
attack on the papers by Soon and Baliunas (2003) and Soon et al.
(2003), in a FORUM article in the American Geophysical Union Eos
newspaper (Mann et al., 2003, Eos, vol. 84, 256-258), were either
rigorously peer-reviewed or represented widespread view of the
community. Contrary to Professor Mann's public statements, a FORUM
article in Eos is said to be only stating ``a personal point of view''
(http://www.agu.org/pubs/eos--guidelines.html#authors). Whatever peer-
reviewing that was done did not include soliciting comments from the
authors of the papers being criticized. We first learned of this FORUM
article from the AGU's press release No. 03-19 ``Leading Climate
Scientists Reaffirm View that Late 20th Century Warming Was Unusual and
Resulted From Human Activity'' (http://www.agu.org/sci--soc/prrl/
prrl0319.html). See Soon et al. (2003b, Eos, vol. 84 (44), 473-476) for
our own response to the Mann et al. FORUM article.
Statement of Professor Michael E. Mann, Department of Environmental
Services, University of Virginia
My name is Michael Mann. I am a professor in the Department of
Environmental Sciences at the University of Virginia. My research
involves the use of climate models, the analysis of empirical climate
data, and statistical methods for comparing observations and model
predictions. One area of active current research of mine involves the
analysis of climate ``proxy'' records (that is, natural archives of
information which record past climate conditions by their biological,
physical, or chemical nature). These data are used to reconstruct
patterns of climate variability prior to the period of the past century
or so during which widespread instrumental climate records are
available. A primary focus of this research is deducing the long-term
behavior of the climate system and the roles of various potential
agents of climate change, both natural and human.
I was a Lead Author of the ``Observed Climate Variability and
Change'' chapter of the Intergovernmental Panel on Climate Change
(IPCC) Third Scientific Assessment Report and a scientific contributor
for several other chapters of the report. I am the current organizing
committee chair for the National Academy of Sciences `Frontiers of
Science' and have served as a committee member or advisor for other
National Academy of Sciences panels related to climate change. I have
served as editor for the `Journal of Climate' of the American
Meteorological Society. I'm a member of the advisory panel for the
National Oceanographic and Atmospheric Administrations' Climate Change
Data and Detection Program, and a member of numerous other
international and U.S. scientific working groups, panels and steering
committees. I have co-authored more than 60 peer-reviewed articles and
book chapters on diverse topics within the fields of climatology and
paleoclimatology. Honors I have received include selection in 2002 as
one of the 50 leading visionaries in Science and Technology by
Scientific American magazine, the outstanding scientific publication
award for 2000 from the National Oceanographic and Atmospheric
Administration, and citation by the Institute for Scientific
Information (ISI) for notable recognition of my peer-reviewed research
by fellow scientists.
In my testimony here today, I will explain: (1) How mainstream
climate researchers have come to the conclusion that late-20th century
warmth is unprecedented in a very long-term context, and that this
warmth is likely related to the activity of human beings. (2) Why a
pair of recent articles challenging these conclusions by astronomer
Willie Soon and his co-authors are fundamentally unsound.
CLIMATE HISTORY AND ITS IMPLICATIONS
Evidence from paleoclimatic sources overwhelmingly supports the
conclusion that late-20th century hemispheric-scale warmth was
unprecedented over at least the past millennium and probably the past
two millennia or longer.
Modeling and statistical studies indicate that such anomalous
warmth cannot be explained by natural factors but, instead, requires
significant anthropogenic (that is, `human') influences during the 20th
century. Such a conclusion is the indisputable consensus of the
community of scientists actively involved in the research of climate
variability and its causes. This conclusion is embraced by the position
statement on ``Climate Change and Greenhouse Gases'' of the American
Geophysical Union (AGU) which states that there is a compelling basis
for concern over future climate changes, including increases in global-
mean surface temperatures, due to increased concentrations of
greenhouse gases, primarily from fossil-fuel burning. This is also the
conclusions of the 2001 report of the Intergovernmental Panel on
Climate Change (IPCC), affirmed by a National Academy of Sciences
report solicited by the Bush administration in 2001 which stated, ``The
IPCC's conclusion that most of the observed warming of the last 50
years is likely to have been due to the increase in greenhouse gas
concentrations accurately reflects the current thinking of the
scientific community on this issue.''
THE MAINSTREAM SCIENTIFIC VIEWPOINT
Human beings have influenced modern climate through changes in
greenhouse gas concentrations, the production of industrial aerosols,
and altered patterns of land-use. By studying both the record of
ancient climate variability and the factors that may have influenced
it, we can establish how and why the climate system varied naturally,
prior to any large-scale anthropogenic impacts. Large changes in
climate certainly occurred in the distant past. If we look 60 million
years back in time, Dinosaurs were roaming the polar regions of the
earth, and the globe was almost certainly warmer than today. Carbon
dioxide levels were probably about double their current level, and had
slowly attained such high levels due to changes in the arrangements of
the continents (`plate tectonics') which influence the outgassing of
carbon dioxide from the solid earth and thus, atmospheric greenhouse
gas concentrations. These changes occur on timescales of tens of
millions of years. 10,000 years ago, large ice sheets existed over
North America due to natural changes that occur in the earth's orbit on
timescales of tens of thousands of years. Trying to study distant past
climates for insights into modern natural climate variability is
hampered by the fact that the basic external constraints on the system
(the continental arrangement, the geometry of the earth's astronomical
orbit, the presence of continental ice sheets--what we call the
`boundary conditions') were significantly different from today.
Focusing on the evolution of climate in the centuries leading up to the
20th century provides a perspective on the natural variability of the
climate prior to the period during which large-scale human influence is
likely to have occurred, yet modern enough that the basic boundary
conditions on the climate system were otherwise the same. This provides
us, in essence, a `control' for diagnosing whether or not recent
climate changes are indeed unusual.
Instrumental data for use in computing global mean surface
temperatures are only available for about the past 150 years. Estimates
of surface temperature changes prior to the 20th century must make use
of historical documents and natural archives or ``proxy'' indicators,
such as tree rings, corals, ice cores and lake sediments, to
reconstruct the patterns of past climate change. Due to the paucity of
data in the Southern Hemisphere, recent studies have emphasized the
reconstruction of Northern Hemisphere rather than global mean
temperatures. A number of independent reconstructions of the average
temperature of the Northern Hemisphere support the conclusion that the
hemispheric warmth of the late 20th century (i.e., the past few
decades) is likely unprecedented over at least the past millennium.
Preliminary evidence suggests that such a conclusion may well hold for
at least the past two millennia, though more work, requiring the
development of a more complete set of reliable proxy records spanning
the past few millennia, are necessary to further decrease the
uncertainties. Climate model simulations employing estimates of natural
and anthropogenic radiative forcing changes agree well with the proxy-
based reconstructions (Figure 1). The simulations, moreover, show that
it is not possible to explain the anomalous late 20th century warmth
without the contribution from anthropogenic influences. Such consensus
findings are expressed in the recently published article co-authored by
myself and 12 other leading climate scientists from the United States
and Britain that appeared recently in the journal `Eos', the official
transactions of the American Geophysical Union, the largest
professional society in the field.
FLAWS IN A RECENT STUDY DISPUTING THE SCIENTIFIC CONCENSUS
Two deeply flawed (and nearly identical) recent papers by
astronomers Soon and Baliunas (one of them with some additional co-
authors--both henceforth referred to as `SB') have been used to
challenge the scientific consensus. I outline the 3 most basic problems
with their papers here:
[GRAPHIC] [TIFF OMITTED] T2381.097
(1) In drawing conclusions regarding past regional temperature
changes from proxy records, it is essential to assess to make sure that
the proxy data are indicators of temperature and not precipitation or
drought. SB make this fundamental error when they cite evidence of
either `warm', `wet', or `dry' regional conditions as being in support
of an exceptional `Medieval Warm Period' or `MWP'. Their criterion, ad
absurdum, could be used to define any period of climate as `warm' or
`cold'. Experienced paleoclimate researchers know that they must first
establish the existence of a temperature signal in a proxy record
before using it to evaluate past temperature changes (Figure A1).
(2) It is essential to distinguish between regional temperature
changes and truly hemispheric or global changes. SB do not make this
essential distinction. The wavelike character of weather (i.e., the
day-to-day wiggles of the Jet Stream) ensures that certain regions tend
to warm when other regions cool. This past winter is a case in point.
January was about 2+ C below normal on the east coast of the U.S., but
about 4+ C above normal over much of the west. Utah, Nevada and parts
of California and Alaska had the warmest January on record (the change
in location of the Iditarod dog sled race was a casualty of the Alaskan
winter warmth!). The average temperature over the entire U.S. was about
1+ C above normal, much less warm than for the western U.S., and of the
opposite sign of the eastern U.S.
In a similar manner, average global or hemispheric temperature
variations on longer timescales tend to be much smaller in magnitude
than those for particular regions, due to the tendency for a
cancellation of warm and cold conditions in different regions. While
relative warmth during the 10th-12th centuries, and cool conditions
during the 15th-early 20th centuries are evident from reconstructions
and model simulations of the average temperature of the Northern
Hemisphere (Figure 1), the specific periods of cold and warmth
naturally differ from region to region (Figure A2). The notion of an
unusually cold 17th century `Little Ice Age', for example, arose in a
European historical context. What makes the late 20th century unique is
the simultaneous warmth indicated by nearly all long-term records
(Figure A2), leading to the anomalous warmth evident during this period
in Northern Hemisphere average temperatures (Figure 1).
(3) It is essential, in forming a climate reconstruction, to
carefully define a base period for modern conditions against which past
conditions may be quantitatively compared. The concensus conclusion
that late-20th century mean warmth likely exceeds that of any time
during the past millennium for the Northern Hemisphere, is based on a
careful comparison of temperatures during the most recent decades with
reconstructions of past temperatures, taking into account the
uncertainties in those reconstructions. As it is only the past few
decades during which Northern Hemisphere temperatures have exceeded the
bounds of natural variability, any analysis such as SB that compares
past temperatures only to early or mid-20th century conditions, or
interprets past temperatures using proxy information not capable of
resolving decadal trends cannot address the issue of whether or not
late-20th century warmth is anomalous in a long-term context.
The concentration of greenhouse gases in the atmosphere is higher
than at any time in at least the last 400,000 years, and, it
increasingly now appears, probably many millions of years. This
increase is undeniably due to the activity of human beings through
fossil fuel burning. Late 20th century warming is unprecedented in
modern climate history at hemispheric scales. This is almost certainly
a result of the dramatic increase in greenhouse gas concentrations due
human activity. The latest model-based projections indicate a global
mean temperature increase of 0.6 to 2.2+ C (1+ C to 4+ F) relative to
1990 levels by the mid-20th century. While these estimates are
uncertain, even the lower value would take us well beyond any previous
levels of warmth seen over at least the past couple millennia. The
magnitude of warmth, but perhaps more importantly, the unprecedented
rate of this warming, is cause for concern.
[GRAPHIC] [TIFF OMITTED] T2381.098
Response by Michael Mann to Additional Questions by Senator Inhofe
Question 1. You have used the term ``climate scientist'' to
distinguish certain individuals. What, in your view, does it take for
one to earn the title ``climate scientist''? What specific credentials,
or the lack thereof, would lead you to refuse to recognize someone as a
Response. The term ``climate scientist'' is used, in my experience,
to describe an individual with specific training in oceanographic,
atmospheric, and coupled ocean-atmosphere processes relevant to
understanding climate variability and the behavior of the climate
system. An individual might obtain this training through either an
advanced degree in those areas of study, or through years of research
in those areas associated with numerous publications in the peer-
reviewed climate literature such as ``Journal of Geophysical Research--
Atmospheres'', ``Journal of Geophysical Research-Oceans'', ``Climate
Dynamics'', ``The Holocene'', ``Geophysical Research Letters'',
``Paleoceanography'' (or publication of climate papers in leading
international science journals such as ``Nature'' and ``Science''). I
would not, for example, consider scientists with advanced degrees in
Astronomy, Astrophysics, or Physics who have published primarily in
those areas, as ``climate scientists''--nor do I believe would most of
my colleagues in the climate research community. In addition to
training and publishing in a field, leading scientists would normally
be expected to be actively interacting and collaborating in studies
with colleagues and ensuring their understanding of cutting edge
science through attendance and active participation in meetings
convened by the leading professional societies and organizations.
Question 2. Your work and testimony contends that the Little Ice
Age was not global, but restricted to only portions of Europe. A
forthcoming article by Shindell et al. (Shindell, D.T. et al., 2003:
Volcanic and solar forcing of climate change during the pre-industrial
era. Journal of Climate, in press), however, indicates the Little Ice
Age could have resulted from a combination of solar and volcanic
forcing. Do you agree with these conclusions from Shindell et al.? If
so, how can solar and volcanic forcings generate climatic effects that
are not observed across the entire hemisphere?
Response. The statement is incorrect. I never testified that the
``Little Ice Age was . . . restricted to only portions of Europe''.
It should first be noted that many paleoclimatologists have
questioned the utility of terms such as ``Little Ice Age'' and
``Medieval Warm Period'' which provide misleading descriptions of past
climate changes in many regions. There is a complex pattern of climate
variability in past centuries, and the lack of evidence for synchronous
temperature variations worldwide in past centuries [e.g. Bradley, R.S.,
and P.D. Jones, ``Little Ice Age'' summer temperature variations: their
nature and relevance to recent global warming trends, The Holocene, 3,
367-376, 1993; Hughes, M.K., and H.F. Diaz, Was there a `medieval warm
period', and if so, where and when, Climatic Change, 26, 109-142,
1994]. The cited paper by Shindell et al (2003), of which I am a co-
author, is fully consistent with such findings. The paper, rather than
demonstrating globally uniform patterns of warming or cooling in past
centuries, shows that surface temperature changes were dominated by
regional overprints associated with the response of the ``North
Atlantic Oscillation'' atmospheric circulation pattern to radiative
forcing. This response leads to a pattern of cooling during the 17th/
18th centuries in certain regions (not just Europe, but many regions
throughout the Northern Hemisphere extratropics) and warming in other
regions. The paper shows that this pattern of warming and cooling
closely resembles the pattern of surface temperature change during that
interval reconstructed by Mann and colleagues (MBH98). It is worth
noting, moreover, that the tropical Pacific seems to have been in a
warmer, rather than a ``colder'' state, during the conventionally
defined ``Little Ice Age'' [Cobb, K.M., Charles, C.D., Edwards, R.L.,
Cheng, H., & Kastner, M. El Nino-Southern Oscillation and tropical
Pacific climate during the last millennium, Nature 424, 271-276 (2003).
Climate dynamists understand the importance of such phenomena in
understanding the highly variable pattern of surface temperature
changes in past centuries, and rarely, if ever, argue for the existence
of globally uniform or synchronous temperature change in past
centuries. The response of the climate to solar and volcanic radiative
forcing is known to involves dynamical responses associated with
regionally differentiated temperature trends that overprint far smaller
global mean responses. This contrasts strongly with the response of the
climate to anthropogenic climate forcing, for which the integrated
global mean radiative forcing is considerably greater, and the
associated large-scale warming typically rises above the regional
Question 3. That same paper finds ``long-term regional response to
solar forcing [that] greatly exceeds unforced variability . . . and
produces climateanomalies similar to those seen during the Little Ice
Age. Thus, longterm regional changes during the pre-industrial [era]
appear to havebeen dominated by solar forcing.'' You further state that
``For the few centuries prior to the industrial era, however,
externally driven climate change is thought to have been forced
primarily by only two factors: variation in solar output and volcanic
eruptions . . . These forcings likely played a large role in the so-
called Medieval Warm Period (MWP) and Little Ice Age (LIA) epochs of
the last millennium, which saw significant climate changes on at least
regional scales . . .'' You then define ``regional'' ``to mean
continental in scale . . .'' Do you claim that total solar irradiance
change is the only solar forcing mechanism that has any significant
climate effect? List your formal training in, plus courses you have
taught, in solar physics. Do you agree with the paper's claim that the
MWP and LIA exist on regional scales, in accordance with climate
experts like R. Bryson and H.H. Lamb, starting with their work in the
1960's, and recently updated in summary in Soon et al. (2003)?
Response. Expertise in ``solar physics'' is not the expertise
required to evaluate what is happening to the Earth's climate--what
matters are the changes in solar radiation at the top of the atmosphere
and then down through it. As is made clear in our paper, we are
considering not only ``total solar irradiance'' but also its spectral
distribution. Indeed, because much of the change in solar radiation
occurs in UV wavelengths, induced changes in stratospheric ozone can be
lead to significant changes in atmospheric circulation in the
troposphere. The model simulations indicate that such atmospheric
circulation changes can, acting with other factors, lead to regional
variations in the climate such as were observed over the last
millennium. As a co-author of this paper, I of course, agree with its
findings. However, the inference that this paper confirms the work of
Soon et al. (2003) is very mistaken.
With respect to my training, teaching, I would encourage that my
Curriculum Vitae, which I have provided separately, be included in the
record to be compared to those of the other witnesses with respect to
relevant expertise and standing in the climate research community.
Question 4. In your testimony, you stated that you hold the
``mainstream'' view with respect to climate theory of air temperature
trends over the past two millennia. Provide supporting citations in the
refereed scientific literature that are not authored or co-authored by
you or your colleagues, collaborators, students or former students, or
associates (i.e., Phil Jones, Ray Bradley, Malcolm Hughes), where
others hold this Emainstream\1\ view.
Response. The statement once again mischaracterizes my comments. As
there is only one reconstruction of Northern Hemisphere annual mean
temperature over the past two millennia, published only recently by
Phil Jones and myself, it is hardly meaningful to discuss whether
``other studies'' support this finding. The peer-review and publication
process typically unfolds on timescales of a year or longer, not
months. Any careful reading of my comments would reveal that I was not
referring to this one specific reconstruction in the comments I made
characterizing what I believe to be the mainstream viewpoint of the
climate research community. This review, as discussed in my testimony,
refers rather to the widespread evidence that late 20th century warmth
is unprecedented in a long-term context, anywhere from the past several
centuries to nearly the past two millennia, depending on the timeframe
of the particular study.
Second, the description of ``collaborators, associates, former
students'', depending on how interpreted, is so broad a category as to
include just about every leading scientist in the field. The following
publications all come to the same conclusion that late 20th century
Northern Hemisphere warmth is anomalous in a long-term context:
Bauer, E., Claussen, M., Brovkin, V., Assessing climate
forcings of the earth system for the past millennium, Geophys. Res.
Lett., 30 (6), 1276, doi: 10.1029/2002GL016639, 2003.
Bertrand C., Loutre M.F., Crucifix M., Berger A., Climate
of the Last millennium: a sensitivity study. Tellus, 54(A), 221-244,
Bradley, R.S., and P.D. Jones, ``Little Ice Age'' summer
temperature variations: their nature and relevance to recent global
warming trends, The Holocene, 3 (4), 367-376, 1993.
Bradley, R.S., Briffa, K.R., Crowley, T.J., Hughes, M.K.,
Jones, P.D, Mann, M.E., Scope of Medieval Warming, Science, 292, 2011-
Bradley, R.S., M.K.Hughes and H.F. Diaz., Climate in
Medieval Time. Science, 302, 404-405, 2003.
Pollack, H.N., S. Huang, and P.-Y. Shen, Climate Change
Record in Subsurface Temperatures: A Global Perspective, Science, 282,
Briffa, K.R., T.J. Osborn, F.H. Schweingruber, I.C.
Harris, P.D. Jones, S.G. Shiyatov, S.G. and E.A. Vaganov, Low-frequency
temperature variations from a northern tree-ring density network. J.
Geophys. Res., 106, 2929-2941, 2001.
Crowley, T.J., Causes of Climate Change Over the Past 1000
Years, Science, 289, 270-277, 2000.
Crowley, T.J., and T. Lowery, How Warm Was the Medieval
Warm Period, Ambio, 29, 51-54, 2000.
Gerber, S., F. Joos, P. Brugger, T. F. Stocker, M. E.
Mann, S. Sitch, and M. Scholze, Constraining temperature variations
over the last millennium by comparing simulated and observed
atmospheric CO2, Climate Dynamics, 20, 281-299, 2003.
Hegerl, G.C., T.J. Crowley, S.K. Baum, K-Y. Kim, and W. T.
Hyde, Detection of volcanic, solar and greenhouse gas signals in paleo-
reconstructions of Northern Hemispheric temperature. Geophys. Res.
Lett., 30 (5), doi: 10.1029/2002GL016635, 2003.
Huang, S., H. N.Pollack and P.-Y. Shen, Temperature Trends
Over the Past Five Centuries Reconstructed from Borehole Temperature,
Nature 403, 756-758, 2000.
Jones, P.D., M. New, D.E. Parker, S. Martin, and I.G.
Rigor, 1999: Surface air temperature and its changes over the past 150
years. Reviews of Geophysics 37, 173-199.
Jones, P.D., T.J. Osborn, and K.B. Briffa, The Evolution
of Climate Over the Last Millennium, Science, 292, 662-667, 2001.
Overpeck, J., K. Hughen, D. Hardy, R. Bradley, R. Case, M.
Douglas, B. Finney, K. Gajewski, G. Jacoby, A. Jennings, S. Lamoureux,
A. Lasca, G.M.J. Moore, M. Retelle, S. Smith, A. Wolfe, and G.
Zielinski, Arctic Environmental Change of the Last Four Centuries,
Science, 278, 1251-1256, 1997.
Pollack, H.N., S. Huang, and P.-Y. Shen, Climate Change
Record in Subsurface Temperatures: A Global Perspective, Science, 282,
Question 5. Your work has been characterized as ``global'' in
several venues, including the National Assessment. Is that a fair
characterization, or are those sources confused by your use of Northern
and Southern Hemisphere proxies in your Northern Hemisphere
reconstruction? Can you explain why the National Assessment did not
include error bars on your temperature reconstruction?
Response. The proxy records on which our work is based represent
conditions over much of the Northern Hemisphere and a small fraction of
the Southern Hemisphere. While in any given year there can be some
difference in the anomalies in the two hemispheres, the instrumental
record indicates that over periods of a few decades or more, the
anomalies in the two hemispheres are quite similar because of the
thermodynamic and dynamic coupling between them. Thus, the major
features of the temperature record, and in particular the unusual 20th
century warming, are similar in the two hemispheres and thus global
features. It was this aspect of the record to which the text of the
National Assessment report refers in presenting the overall
significance of our study, and the report is correct in suggesting that
the 20th century warming is global in nature. The caption for Figure 2
of Chapter 1 in the Foundation report (page 22 and page 544) states
that ``Although this record comes mostly from the Northern Hemisphere,
it is likely to be a good approximation to the global anomaly based on
comparisons of recent patterns of temperature fluctuations.'' This
accurately reflects the situation. In the Overview report (page 13),
although the figure title says ``Global CO2 and Temperature
Change,'' the caption next to the figure says ``Records of Northern
Hemisphere surface temperatures, CO2 concentrations, and
carbon emissions show a close correlation. Temperature change:
reconstruction of annual-average Northern Hemisphere surface air
temperatures derived from historical records, tree rings, and corals
(blue), and air temperatures directly measured (purple).'' This quite
clearly makes the point this is mainly a Northern Hemisphere
With respect to the question about the presentation of the figure,
it is misleading to imply that the term ``error bars'' indicates that
the central line is off by this amount--rather the limits mean that
there is only 1 chance in 20 that the actual value is outside this
range. That is, what we are showing is the likely range within which
the anomaly lies, with there being a 95 percent chance the value is
within this range. The line that we present in many of our figures, and
that was presented in the National Assessment report, is the most
likely value within this range (rather a natural choice to display in
explaining a complex issue to the public). In looking at the National
Assessment report, the caption for Figure 2 of Chapter 1 in the
Foundation report (page 22 and page 544) states that ``The error bars
for the estimate of the annual-average anomaly increase somewhat going
back in time, with one standard deviation being about 0.25+ F (0.15+
C).'' Quite clearly, the reader interested in investigating the
accuracy of the records would followup by reading the original
reference, which is cited in the text.
In that I was not involved in the National Assessment report, the
questioner should consult the authors of that report for any further
information or questions.
Question 6. You testified that the late 20th century warming is
likely caused byman-made CO2 forcing on climate; what is
your scientific proof for thatclaim Please detail how you removed the
potential effects from other factors including those of sulfate
aerosols, tropospheric and stratospheric ozone, volcanic dust veiling,
black soot, solar particleand wave length-dependent variability, sea
ice, land use, vegetation andother greenhouse gases?
Response. The question inconsistently equates my statement of a
``likely'' causal relationship with the standard of ``scientific
proof''. Scientists do not speak in terms of ``proof''. We speak in
terms of likelihoods and the strength of evidence in support of a
A large number of peer-reviewed scientific studies have been
published in the leading scientific journals such as Nature and Science
in the past two decades elucidating the role of natural and
anthropogenic factors in observed climate changes. Physically based
models have been developed and validated against observations, and
these models reproduce complex climate phenomena such as El Nino. These
same models have been driven with the primary ``external'' factors that
are believed to govern climate variations on timescales of decades and
centuries. These external factors include natural factors, such as the
modest estimated variations in radiative output of the Sun, which
varies by a fraction of a percent over time, variations in the
frequency and intensity of explosive volcanic eruptions, which have a
several-year cooling effect on the climate through the injection of
reflective volcanic aerosols into the stratosphere, and very small
changes in the Earth's orbit relative to the Sun that occur on multi-
century timescales. These external factors also include the
``anthropogenic'' influences of increased greenhouse gas concentrations
due to fossil fuel burning, changes in the reflective properties of the
land surface due to human land use alterations, and the regional
cooling effect of anthropogenic sulphate aerosols in certain industrial
regions. When driven with these factors, these climate models have
demonstrated a striking ability to reproduce observed global and
hemispheric temperature trends during the 20th century, as well as
longer-term trends in past centuries as reconstructed from proxy data.
Such results have been demonstrated in the following peer-reviewed
Wigley, T.M.L., R.L. Smith, and B.D. Santer, Anthropogenic
Influence on the Autocorrelation Structure of Hemisoheric-Mean
Temperatures, Science, 282, 1676-1680, 1998.
Tett, S.F.B., P.A. Scott, M.R. Allen, W.J. Ingram, and
J.F.B. Mitchell, Causes of Twentieth-Century Temperature Change Near
the Earth's Surface, Nature, 399, 569-572, 1999.
Hegerl, G.C., P.A. Scott, M.R. Allen, J.F.B. Mitchell,
S.F.B. Tett, and U. Cubasch, Optimal detection and aftribution of
climate change: sensitivity of results to climate model differences,
Climate Dynamics, 16, 737-754, 2000.
Crowley, T.J., Causes of Climate Change Over the Past 1000
Years, Science, 289, 270-277, 2000.
Stott, P.A., S.F.B. Tett, G.S. Jones, M.R. Allen, J.F.B.
Mitchell, and G.J. Jenkins, External Control of 20th Century
Temperature by Natural and Anthropogenic Forcings, Science, 290, 2133-
Stott, P.A., S.F.B. Tett, G.S. Jones, M.R. Allen, W.J.
Ingram, and J.F.B. Mitchell, Attribution of twentieth century
temperature change to natural and anthropogenic causes, Climate
Dynamics, 17, 11-21, 2001.
These conclusions, furthermore, were endorsed by the 2001 IPCC
scientific working group report (Chapter 12), and the followup National
Academy of Sciences report that endorsed most of the key IPCC
Question 7. A number of expert studies have produced individual
proxy records that show the existence of a local Medieval Warm Period
or Little Ice Age. Such studies cover a large portion of the globe. How
do you reconcile your hemispheric reconstruction with these individual
Response. It is unclear to me what precisely the questioner means
by ``a number of expert studies'' or how he defines the ``existence''
of a ``Medieval Warm Period'' or ``Little Ice Age''. As discussed in my
response to question 2, the regionally and temporally variable nature
of climate changes in past centuries makes such descriptors of past
climate change naive and often useless as a characterization of past
changes. A sampling of some of the longest, high-quality best term
proxy temperature estimates over the globe was provided in Figure 2 of
the article: Mann, M.E., Ammann, C.M., Bradley, R.S., Briffa, K.R.,
Crowley, T.J., Hughes, M.K., Jones, P.D., Oppenheimer, M., Osborn,
T.J., Overpeck, J. T., Rutherford, S., Trenberth, K.E., Wigley, T.M.L.,
On Past Temperatures and Anomalous Late 20th Century Warmth, Eos, 84,
256-258, 2003. This figure demonstrates the lack of evidence for any
periods in earlier centuries that are comparable in terms of evidence
for sychronous warmth to the late 20th century. This same conclusion
was also demonstrated by the recent article in Science: Bradley, R.S.,
M.K. Hughes and H.F. Diaz., Climate in Medieval Time. Science, 302,
Question 8. Do you claim 22 proxies to be a sufficient sample of
observations for reconstructing a Northern Hemisphere temperature? If
not, why did you consider it sufficient for the 1400-1450 interval in
your 1998 Nature paper? If you do, there are 29 proxies that continue
to 1984 in the data base you used for your 1998 paper. Why then did you
terminate your temperature reconstruction at 1980? What efforts have
you made to extend the proxy re-constructions up to the present?
Response. The question is wrongly premised. The Mann et al (1998)
study made use of almost 100 proxy series over the interval AD 1400-
1450. The question appears to confuse the number of proxy series that
was used, with the number of statistical indicators that were used to
represent these proxy data. For example, the 70 series that make up the
North American International Tree Ring Data Base date back to 1400,
were represented in terms of their leading patterns of variance through
a procedure known as ``Principal Component Analysis''. These patterns
represented, however, a much larger number of underlying data. Most of
the proxy records used in that analysis ended by 1980, limiting the
useful upper limit to the calibration period used. A more recent paper
(in press) extends proxy-based hemispheric temperature reconstructions
through the mid-1990's, demonstrating the ability of the reconstruction
to capture the accelerated warming evident in the instrumental record
Question 9. What are the patterns of temperature change in all
proxies after 1980?
Response. It is unclear what is meant by the question. Every proxy
series which extends past 1980 exhibits its own particular pattern. A
recent paper (in press), as referred to in Question No. 8, demonstrates
that a composite of proxy temperature indicators with reliable low-
frequency variability that are available through the mid-1990's capture
the accelerated warming after 1980.
All of the data used in our study have been available since July
2002 on the public ftp site: ftp://holocene.evsc.virginia.edu/pub/
Question 10. Do you have any external (not derived by you) method
or data to provide verification of your temperature reconstruction
Response. We used the method of cross-validation to independently
demonstrate the statistical reliability of our reconstructions. This is
detailed in MBH98 and MBH99. We did not derive the method of cross-
validation--it is a well established statistical procedure, detailed in
many introductory level statistics textbooks.
Question 11. Are you aware of any errors in your data compilation
for MBH98 or MBH99? If so, what are they?
Response. We are not aware of any errors. We are, however, aware of
recent spurious claims of such errors by the authors of an article
published in the social science journal ``Energy and Environment''.
These claims have already been widely discredited by a cursory analysis
of the paper, and a manuscript detailing the numerous fundamental
errors made in the Energy and Environment paper has been submitted to
the peer-reviewed literature. We would be happy to provide a copy of
the paper to be made part of the official Senate record once it is
Question 12. Are you aware of any errors in any calculations that
you made in MBH98 or MBH99? If so, what are the errors?
Response. See response to question 11.
Question 13. Vegetation grows as a result of a number of factors,
including energy input, moisture supply, fire frequencies, and species
competition. Do you claim it is possible to accurately remove the
effects of these factors from your tree ring proxy datasets to produce
a resulting time-series represents fluctuations in only air
temperature? What is the magnitude of the error introduced in
developing a procedure to remove these other effects? Please detail the
analyses and list peer-reviewed works that specifically outline
techniques to remove the effect of these other indicators for inferring
Response. One of the co-authors of MBH98 (Malcolm Hughes) is among
the world's foremost experts in dendroclimatology, so the team of MBH98
hardly needs to be informed of the processes that influence tree
growth. The method of MBH98 does not ``remove'' various factors from
tree ring proxy information (which would be a most unwise approach!)
but, rather, uses multivariate statistical methods similar to those
commonly used in climate and paleoclimate field reconstruction [see
e.g. Cook, E.R., K.R. Briffa, and P.D. Jones, Spatial Regression
Methods in Dendroclimatology: A Review and Comparison of Two
Techniques, International Journal of Climatology, 14, 379-402, 1994;
Smith, T.M., R.W. Reynolds, R.E. Livezey, and D.C. Stokes,
Reconstruction of Historical Sea Surface Temperatures Using Empirical
Orthogonal Functions, Journal of Climate, 9, 1403-1420, 1996; Kaplan,
A., Y. Kushnir, M.A. Cane, and M.B. Blumenthal, Reduced space optimal
analysis for historical data sets: 136 years of Atlantic sea surface
temperatures, Journal of Geophysical Research, 102, 27835-27860, 1997]
to separate the information in the data that can meaningfully be
related to surface temperature variations from that related to other
Question 14. Define the difference between variability and error in
a statistical analysis. In EOF analyses, is the variation of the first
principal component indicative of the uncertainty associated with the
data? Why or why not?
Response. Variability in an estimated quantity can be thought of as
representing both `signal' (the physical quantity one is interested in
and `noise' (everything else). The definition of noise and signal
depends on a number of assumptions regarding the nature of the process
that generated the times series of interest and the specification of
the statistical model for the data in question. Uncertainty, which is
associated with the partitioning of data variance into ``noise and
signal'', as defined above, depends on such detailed considerations.
There are no general statistical principles that I am familiar with
that relate uncertainty, thusly defined, to the first, or any other,
principal component of a dataset containing both signal and noise
contributions. Uncertainty is typically diagnosed by the analysis of
residual variance from a statistical model based on a combined
calibration/cross-validation procedure. Introductory text books such as
``Statistical Methods in the Atmospheric Sciences'' (D. Wilks, Academic
Press) deal with this topic in detail.
Question 15. Specifically, how do you construct regional patterns
of temperature changes in past centuries when data are limited, either
spatially, temporally, or both?
Response. Our methods are described in detail in the following
peer-reviewed scientific publications, which I would like to have made
part of the official Senate record:
Mann, M.E., Jones, P.D., Global Surface Temperatures over
the Past two Millennia, Geophysical Research Letters, 30 (15), 1820,
D'Arrigo, R.D., Cook, E.R., Mann, M.E., Jacoby, G.C.,
Tree-ring reconstructions of temperature and sea level pressure
variability associated with the warm-season Arctic Oscillation since AD
1650, Geophysical Research Letters, 30 (11), 1549, doi: 10.1029/
Mann, M.E., Rutherford, S., Bradley, R.S., Hughes, M.K.,
Keimig, F.T., Optimal Surface Temperature Reconstructions Using
Terrestrial Borehole Data, Journal of Geophysical Research, 108 (D7),
4203, doi: 10.1029/2002JD002532, 2003.
Rutherford, S., Mann, M.E., Delworth, T.L., Stouffer, R.,
Climate Field Reconstruction Under Stationary and Nonstationary
Forcing, Journal of Climate, 16, 462-479, 2003.
Mann, M.E., Large-scale climate variability and
connections with the Middle East in past centuries, Climatic Change,
55, 287-314, 2002.
Cook, E.R., D'Arrigo, R.D., Mann, M.E., A Well-Verified,
Multi-Proxy Reconstruction of the Winter North Atlantic Oscillation
Since AD 1400, Journal of Climate, 15, 1754-1764, 2002.
Mann, M.E., Rutherford, S., Climate Reconstruction Using
`Pseudoproxies', Geophysical Research Letters, 29 (10), 1501, doi:
Mann, M.E., Large-scale Temperature Patterns in Past
Centuries: Implications for North American Climate Change, Human and
Ecological Risk Assessment, 7 1247-1254, 2001.
Mann, M.E., Climate During the Past Millennium, Weather
(invited contribution), 56, 91-101, 2001.
Cullen, H., D'Arrigo, R., Cook, E., Mann, M.E.,
Multiproxy-based reconstructions of the North Atlantic Oscillation over
the past three centuries, Paleocean-
ography, 15, 27-39, 2001.
Mann, M.E., Gille, E., Bradley, R.S., Hughes, M.K.,
Overpeck, J.T., Keimig, F.T., Gross, W., Global Temperature Patterns in
Past Centuries: An interactive presentation, Earth Interactions, 4-4,
Delworth, T.L., Mann, M.E., Observed and Simulated
Multidecadal Variability in the Northern Hemisphere, Climate Dynamics
16, 661-676, 2000.
Mann, M.E., Bradley, R.S. and Hughes, M.K., Northern
Hemisphere Temperatures During the Past Millennium: Inferences,
Uncertainties, and Limitations, Geophysical Research Letters, 26, 759-
Mann, M.E., Bradley, R.S., and Hughes, M.K., Global-Scale
Temperature Patterns and Climate Forcing Over the Past Six Centuries,
Nature, 392, 779-787, 1998.
Question 16. Do you claim that the instrumental temperature record
is known without error? If not, what error and uncertainty would you
associate with the annual Northern Hemisphere averaged air temperature
for 1900? For 1950? For 2000? How were these estimates incorporated
into your analysis?
Response. The claim made by Dr. Legates in his testimony that we
present the instrumental record without uncertainty is incorrect. If
Legates, for example, were familiar with studies of the instrumental
surface temperature record, he would understand that the uncertainties
in this record during the 20th century are small compared to the
uncertainties shown for our reconstruction [see e.g. Figure 2.1b in
Folland, C.K., Karl, T.R., Christy, J.R., Clarke, R. A., Gruza, G.V.,
Jouzel, J., Mann, M.E., Oerlemans, J., Salinger, M.J., Wang, S.-W.,
Observed Climate Variability and Change, in Climate Change 2001: The
Scientific Basis, Houghton, J.T., et al. (eds.), Cambridge Univ. Press,
Cambridge, 99-181, 2001.]. Furthermore, all scientists with a proper
training in statistics know that uncertainties add ``in quadrature''.
In other words, you have to square them before adding them. This means
that the relatively small uncertainty in the instrumental record makes
a relatively small contribution to the total uncertainty. Legates
claimed in his testimony that including the uncertainty in the
instrumental record, which he estimates as 0.1oC would change the
conclusions expressed by us and other mainstream climate scientists
that the 1990's are the warmest decade in at least the past 1000 years
within estimated uncertainties. This claim is very misleading for
several reasons, First, the standard error in Northern Hemisphere mean
annual temperatures during the 1990's is far smaller than the amount
cited by Legates [see again Folland et al, 2001 cited above]. Even more
problematic, however, Legates claim indicates a fundamental
misunderstanding of the statistical concepts of standard error and
uncertainty. The shaded region shown along with the Mann et al
reconstruction (and other similar plots shown in recent articles such
as the aforementioned ``Eos'' article, and the IPCC report) indicates
two standard error intervals. The decade of the 1990's is roughly two
standard errors warmer (i.e., about 0.4oC)] than any decade prior to
the 20th century in the reconstruction. Based on a one-sided test for
anomalous warmth, this translates to a roughly 97.5 percent level of
significance. Modifying the uncertainties to include the small
additional contribution due to uncertainties in the instrumental record
itself would modify this only slightly, and would not lower the
significance level below the 95 percent level. Though there is no such
thing as an absolute estimate of uncertainty, despite Legate's
implications to the contrary, a 95 percent confidence is often adopted
as an appropriate criterion for significance. Legates' statement that
including instrumental contributions to the uncertainty would change
the conclusions is thus clearly false.
Question 17. Assuming a proxy record extended back to 1000 A.D.,
what specifically would be required to disqualify this proxy record
from your analyses? Provide supporting evidence where others have
disqualified such records from temperature analyses on these criteria.
Response. It is unclear what type of ``analyses'' are being
referred to here. I have used a variety of different statistical
methods and data in various published studies describing paleoclimate
reconstruction, so the question as worded is implicitly vague. In any
case, our approaches do not ``disqualify'' proxy data. They use
objective statistical criteria to evaluate the strength of the signal
available for reconstruction of the particular climate field or index
(be it related to surface temperature, atmospheric circulation,
drought, or other variables) to be reconstructed. Such statistical
approaches, and the related approaches used by other climate
researchers, are described in the various publications listed above in
the response to Questions No. 13 and 15.
Question 18. Have you made available via FTP the coefficients
developed to relate proxies to principal components? If not, would you
make those coefficients available at NGDC/paleo?
Response. The question is based on two false premises. The first
involves a naive view of what is required and expected of scientific
researchers. It is unprecedented in my experience for any scientist to
post in the public domain every single computational aspect of a
complicated analysis. The methods of our study were adequately
described in our paper and supplementary information, and the data used
were made available in the public domain. Indeed, we made far more of
our results, data, and methodological details available in the public
domain than is provided in most similar scientific studies. The
scientific funding agencies (DOE, NSF, and NOAA) would have informed us
if we had not followed the appropriate protocols in the provision of
data and results.
The second false premise is a technical one. A proper understanding
of the methodology employed by MBH98 would reveal that there is no one
fixed set of ``coefficients'' that relate a particular proxy record to
a particular principal components. The relationship is determined based
on time-dependent inverse problem for which the weights on different
records are not fixed over time, as described in our published
Question 19. Have you made available via FTP any specialized
computer studies, such as Matlab scripts, in connection with your
temperature reconstruction? If not, would you make any such scripts
used in developing the temperature reconstructions in MBH98 and MBH99
available through NGDC/paleo?
Response. The methodologies have been described, and other climate
researchers have independently, successfully implemented the
methodology, e.g.: Zorita, E., F. Gonzalez-Rouco, and S. Legutke,
Testing the Mann et al. (1998) Approach to Paleoclimate Reconstructions
in the Context in a 1000-Yr Control Simulation with the ECHO-G Coupled
Climate Model, Journal of Climate, 16, 1378-1390, 2003.
Question 20. Do you claim your method of reconstructing past
temperature from proxies is the only correct one? If not, please submit
some published papers that use methods you consider to be correct as
well. If you do consider yours the only correct method, can you provide
a list of names of scientists whom you have contacted to tell them they
are using the wrong methods in their work?
Response. The question is based on the false premise that my
colleagues and I use any one particular ``method'' of reconstructing
past temperatures from proxy data. In fact, I have published on the
application of at least five fundamentally independent methods for
using proxy data to reconstruct past climate patterns in the peer-
reviewed literature. Examples of the applications of different methods
can be found in the following peer-reviewed scientific publications:
Zhang, Z., Mann, M.E., Cook, E.R., Alternative Methods of
Proxy-Based Climate Field Reconstruction: Application to the
Reconstruction of Summer Drought Over the Conterminous United States
back to 1700 From Drought-Sensitive Tree Ring Data, Holocene, in press,
Mann, M.E., Jones, P.D., Global Surface Temperatures over
the Past two Millennia, Geophysical Research Letters, 30 (15), 1820,
Mann, M.E., Rutherford, S., Bradley, R.S., Hughes, M.K.,
Keimig, F.T., Optimal Surface Temperature Reconstructions Using
Terrestrial Borehole Data, Journal of Geophysical Research, 108 (D7),
4203, doi: 10.1029/2002JD002532, 2003.
D'Arrigo, R.D., Cook, E.R., Mann, M.E., Jacoby, G.C.,
Tree-ring reconstructions of temperature and sea level pressure
variability associated with the warm-season Arctic Oscillation since AD
1650, Geophysical Research Letters, 30 (11), 1549, doi: 10.1029/
Mann, M.E., Bradley, R.S., and Hughes, M.K., Global-Scale
Temperature Patterns and Climate Forcing Over the Past Six Centuries,
Nature, 392, 779-787, 1998
On occasion, there are approaches used that are not adequate. For
example, the approach of simply counting papers and not properly
defining what constitutes an anomaly, as was the case for the paper by
Soon et al. (2003), is most decidedly not adequate. Also, the analysis
approach used by McIntyre and McItrick (2003) in which the authors
attempted to reproduce the results of the previous study of MBH98 based
on an analysis which used neither the same data (the authors eliminated
the majority of data used by MBH98 for the first two centuries of the
reconstruction) , or method as the original authors, was woefully
inadequate. In fact, this latter study was described as ``seriously
flawed'' and ``silly'' in a recent article in USA Today (``Global
Warming Debate Heats Up Capitol Hill'', 11/19/03). When deeply flawed
studies such as this are published, I am interested in determining what
errors have been made and, if necessary as in this latter case,
promptly submitting a rebuttal to the peer-reviewed scientific
literature to ensure that the scientific community is not misled by the
use of inadequate approaches. To my knowledge, I am not considered to
be shy in offering criticism where criticism is due.
Question 21. If there are other acceptable methods, did you try any
of them on your data set prior to its publication to see what the
results would be? If so would you please submit the results. If not,
have you done so since? Why do you claim your multi-proxy results
represent a ``robust consensus,'' as you said in your Eos publication,
if you have not verified that its results would also be obtained using
other acceptable methods?
Response. As demonstrated both in the Eos article, and the various
references provided in my response to Question 4, about a dozen
different recent estimates based on a variety of data and approaches,
published by different groups, yield statistically indistinguishable
histories of Northern Hemisphere mean temperature changes in past
centuries. I define such a result as characterizing a ``consensus''.
Question 22. Did you at any time prior to publication compute the
analysis up to 1984 or later? What were the results? If you did not,
even though you had sufficient data, why not? If you did but you did
not use those results, explain why. If the results were different,
where did you publish a discussion of those differences? If they were
the same, why did you delete them? Why, in other words, did you throw
out data for the period of maximum interest?
Response. Most of the proxy records used in MBH98 and MBH99 ended
by 1980, limiting the useful upper limit to the calibration period
used. A more recent paper (in press) extends proxy-based hemispheric
temperature reconstructions through the mid-1990's, demonstrating the
ability of the reconstruction to capture the accelerated warming
evident in the instrumental record since 1980. We would be happy to
provide a copy of this paper to be made part of the official Senate
record when it is formally published.
Question 23. On your web site http://www.ngdc.noaa.gov/paleo/ei/
data--supp.html where you explain the assembling of the data base for
your 1980 paper you say: ``Small gaps have been interpolated. If
records terminates lightly before the end of the 1902-1980 training
interval, they are extended by persistence to 1980.'' Does this mean
you made up some observations to fill in blank spots in the data
records? Have you ever provided a complete public listing of all the
data you made up? Please provide such a listing now. Of the 112
proxies, in how many of them did you fill gaps? Why in some of them but
not others? What is the longest interval of time over which you filled
in missing observations?
Response. Extension of missing values by `persistence' of the final
available value is a typical statistical approach to estimating small
amounts of unavailable data at the end of a time series (see e.g. the
textbook by Wilks, referred to in the response to Question No. 14). The
fact that this approach was used to infill a modest number of missing
observations between 1972 and 1980 was described in the Nature
supplementary information. All of the data used in our study have been
available since July 2002 on the public ftp site: ftp://
Question 24. What was the effect on your results of filling in the
missing data? Did you run your analysis without it? Please submit the
results when the filled-in data are dropped from the analysis. If it
changes your results, where is that discussed If it makes no
difference, why did you do it?
Response. The use of infilled data has essentially no effect on the
reconstruction, as demonstrated by the fact that the same result is
achieved if a 1902-1971 calibration period (which predates the use of
any infilled proxy data) is used instead of a 1902-1980 calibration
period. It is advisable to use the full 1902-1980 calibration interval,
however, because the increased statistical constraint provided by the
lengthening of the calibration period more than offsets the impact of
the use of a modest amount of in-filled data in a small number of
Question 25. Do you agree that statistical methods based on linear
extrapolation from data representing the far extreme of the line are
associated with an added error/uncertainty? If so, how was this
incorporated into the assessment of the error/uncertainty in your
temperature reconstructions? Please provide citations from your
publications. If not, please explain why the uncertainty envelope of a
linear regression grows larger as a function of the distance from the
mean of the data used to fit the parameters and why this was not
included in your research.
Response. The so-called ``leverage effect'' which the question
appears to refer to, is taken into account through consideration of the
spectrum of the calibration residuals, allowing for resolution of any
enhancement of uncertainty as a function of frequency (see MBH99).
Alternatively, the uncertainties can be evaluated from an independent
sample (i.e., cross-validation, rather than calibration, residuals)
that eliminates any influence of calibration period leverage in the
estimation of uncertainties. Both approaches give similar results [e.g.
Rutherford, S., Mann, M.E., Osborn, T.J., Bradley, R.S., Briffa, K.R.,
Hughes, M.K., Jones, P.D., Proxy-based Northern Hemisphere Surface
Temperature Reconstructions: Sensitivity to Methodology, Predictor
Network, Target Season and Target Domain, Journal of Climate,
Question 26. Please describe the peer review process that took
place with respect to your Forum article that appeared in EOS on July
8, 2003. If, according to the AGU, the EOS Forum contains articles
stating a personal point of view on a topic related to geophysical
research or the relationship of the geophysical sciences to society,
how can you claim that your article is peer reviewed?
Response. The article was independently reviewed and evaluated for
suitability for publication by an editor who has expertise in the
particular subject area. The associated process is correctly described
as ``peer review''. Appropriate to the relatively short and non-
technical nature of Eos ``Forum'' pieces, the associated peer review
process is not as extensive as that employed for articles in the more
technical literature such as Geophysical Research Letters, or Journal
of Geophysical Research. I would suggest that the questioner contact
representatives at AGU for more details on the peer-review process
employed for their different journals and paper categories.
Question 27. Do you claim that producing estimates of past climate
states is an exact science If so, explain why different authors can get
such significantly different results when investigating and
reconstructing past temperature, and detail the errors that other
authors must have made. If not, explain how there can be, as you put it
in your EOS article, a ``robust consensus'' regarding the correct
estimate of the climate state of the past millennium.
Response. The term ``exact science'' is generally not used, or
considered meaningful or appropriate by scientists, as science almost
always involves the testing of hypotheses based on the use of
intrinsically uncertain data or observations. Consistent with this
fundamental aspect of nearly all scientific endeavors, my colleagues
and I, and other researchers in the paleoclimate community, typically
interpret the results of paleoclimate reconstructions within the
context of sometimes substantial associated uncertainties. When a large
number of estimates agree with each other within estimated
uncertainties, and those uncertainties are modest enough to still allow
for non-trivial conclusions (for example, that late 20th century warmth
is anomalous in a long-term context), those conclusions can be
considered as both ``robust'' and a ``consensus''.
Question 28. Please describe the peer review process that took
place with respect to your 1999 Geophysical Research Letters paper.
What were the criticisms or improvements suggested by the referees? Why
was no reference made to the anomalous global warming caused by the
very strong El Nino event of 1997-98 in your paper? Is this 1999 paper
continuation of your 1998 paper in Nature where you stopped your
reconstruction at AD 1400?
Response. The comments of reviewers on a manuscript are considered
a confidential matter, involving the editor, reviewers, and authors.
Providing these comments for public record would be ethically
questionable, and probably violates the confidentiality policies of the
associated journals. Minor suggestions were made by the reviewers and
editor, and addressed to their satisfaction prior to the acceptance and
publication of the paper.
Question 29. In Mann and Jones 2003 Geophysical Research Letters,
did you change your methodology in the reconstruction of the
hemispheric or global scale temperature from your prior publications?
If so, why did you, and what is the rationale for the change of
Response. The question is wrongly premised, as it presumes, through
the use of the language ``change your methodology'' that scientists
only have one particular methodological approach that can be applied to
a problem at hand. As discussed in my answer to question 20, my
research has involved the use of a variety of different methods for
reconstructing past climate patterns from proxy data. The paper by Mann
and Jones (2003), for example, uses a coarser resolution proxy dataset
than MBH98/MBH99 and a compositing methodology that allows for the
reconstruction of decadal, but not annual, changes, and the
reconstruction of hemispheric mean, but not spatially resolved,
patterns of temperature in past centuries. In doing so, the study was
able to make use of a more restricted set of temperature records
available over a longer timeframe than those used in previous high-
resolution proxy reconstructions of hemispheric temperature change.
Question 30. Did IPCC carry out any independent programs to verify
the calculations that you made in MBH98 or MBH99? If so, please provide
copies of the reports resulting from such studies.
Response. It is distinctly against the mission of the IPCC to
``carry out independent programs'', so the premise of the question is
false. However, the IPCC's author team did engage in a lively
interchanges about the quality and overall consistency of all of the
papers as the chapter was drafted and revised in the course of review.
Question 31. Did IPCC carry out any independent quality control on
the data that you used in MBH98 and MBH99? If so, please provide copies
of the reports resulting from such studies.
Response. The IPCC doesn't ``carry out studies'', so the premise of
the question is false. The IPCC instead depends that the normal
scientific peer-review process, especially when done in a leading
journal, has ensured an acceptable level of quality. In addition, the
IPCC does check to see if any criticisms have been raised postreview in
comments and response to the journal articles.
Question 32. Did IPCC carry out any studies to validate the
statistical procedures and methodologies used in MBH98 and MBH99? If
so, please provide copies of the reports resulting from such studies.
Response. The IPCC doesn't ``carry out studies'', so the premise of
the question is false. Instead, as indicated above, the IPCC relies on
earlier stages of review to cover such matters.
Question 33. Has any organization other than IPCC or your
associates carried out any independent programs to verify the
calculations that you made in MBH98 or MBH99? If so, please provide
copies of the reports resulting from such studies.
Response. I know of no ``organizations'' that carry out
``independent programs'' to verify calculations of individual co-
authors. If the question is, have other scientists reproduced the basic
results of MBH98 and MBH99, the answer is yes. Numerous other groups
(see the dozen or so independent estimates of various groups shown in
Figure 1 of: Mann, M.E., Ammann, C.M., Bradley, R.S., Briffa, K.R.,
Crowley, T.J., Hughes, M.K., Jones, P.D., Oppenheimer, M., Osborn,
T.J., Overpeck, J.T., Rutherford, S., Trenberth, K.E., Wigley, T.M.L.,
On Past Temperatures and Anomalous Late 20th Century Warmth, Eos, 84,
256-258, 2003) have produced reconstructions that are remarkably
similar to those of MBH98 based on a variety of data and methods. Refer
back to my answer to question 4 for further details. I would like to
see each of these papers made an official part of the Senate record.
Question 34. Has any organization other than IPCC conducted
independent quality control on the data that you used in MBH98 and
MBH99? If so, please provide copies of the reports resulting from such
Response. The IPCC doesn't ``carry out studies'', so the premise of
the question is false. The data used by MBH98 (and MBH99) were produced
by other researchers, not Mann and colleagues. It is thus not clear
what kind of ``independent quality control'' is being referred to here.
However, it is fair to say that each of these papers has been subject
to rigorous peer review in a leading scientific journal, which is
considered by scientists to be an independent quality control process.
We are aware of no criticisms of the datasets in the peer-reviewed
Question 35. Has any organization other than IPCC carried out any
studies to validate the statistical procedures and methodologies used
in MBH98 and MBH99? If so, please provide copies of the reports
resulting from such studies.
Response. The IPCC doesn't ``carry out studies'', so the premise of
the question is false. If the question were asked: Have other
independent groups tested the methodology of Mann et al (1998) in a
publication in the peer-reviewed climate literature, the answer would
be ``yes''. I would refer the questioner to the following paper:
Zorita, E., F. Gonzalez-Rouco, and S. Legutke, Testing the Mann et al.
(1998) Approach to Paleoclimate Reconstructions in the Context in a
1000-Yr Control Simulation with the ECHO-G Coupled Climate Model,
Journal of Climate, 16, 1378-1390, 2003.
The paper arrives at the conclusion that the methodology of MBH98
performs well with networks of data comparable to those used by MBH98.
Question 36. Have you ever received any communications that
suggested that there might be computational errors in MBH98 or MBH99?
Please provide such communications together with any responses.
Response. I receive many emails, often from list-serves of self-
professed ``climate skeptics'' making numerous spurious claims against
my work and that of many of my colleagues. I have received no
correspondence providing credible evidence of any errors in our work.
Nor has any such credible evidence been published in the peer-reviewed
Question 37. Did the peer reviewers for Nature in MBH98 carry out
any independent quality control or validation studies? If so, please
provide copies of such reports.
Response. Neither I, nor authors of peer-reviewed journal articles
in general, are made privy to the detailed analyses that peer reviewers
may or may not have performed in the process of reviewing a manuscript.
Authors only receive the comments that were selected to be made
available to them by the reviewer and editor. This question is thus
impossible to answer. Numerous other groups (see the dozen or so
independent estimates of various groups shown in Figure 1 of: Mann,
M.E., Ammann, C.M., Bradley, R.S., Briffa, K.R., Crowley, T.J., Hughes,
M.K., Jones, P.D., Oppenheimer, M., Osborn, T.J., Overpeck, J.T.,
Rutherford, S., Trenberth, K.E., Wigley, T.M.L., On Past Temperatures
and Anomalous Late 20th Century Warmth, Eos, 84, 256-258, 2003) have
produced reconstructions that are remarkably similar to those of MBH98
based on a variety of data and methods. See my answer to Question No.
Question 38. 38. Did the peer reviewers for Geophysical Research
Letters in MBH99 carry out any independent quality control or
validation studies? If so, please provide copies of such reports.
Response. See response to Question No. 37.
Question 39. How many people have requested the underlying digital
information in MBH98? Please provide dates of such requests and dates
of your reply.
Response. My collaborators and I have not kept a specific record.
The data has been provided to any scientific groups that have requested
it, and has been made available on an open access basis through a
public ftp site: ftp://holocene.evsc.virginia.edu/pub/MBH98/, since
Question 40. Were you one of the primary or lead authors of IPCC/
TAR chapter 2?
Response. The convening lead authors of chapter 2 of the IPCC TAR
were Dr. Chris Folland and Thomas Karl. I was one of eight additional
co-authors contributing to chapter 2.
Question 41. In your capacity as IPCC/TAR author, did you prepare
any drafts that referred to your own papers? Please provide all drafts
that you prepared for IPCC.
Response. I contributed to numerous sections of the chapter and
provided contributions that referenced the work of the leading
paleoclimatologists, which includes me and many of my colleagues. Those
interested in drafts of IPCC chapters should inquire of the appropriate
IPCC working group. I am not in possession of such drafts, and even if
I were, I would not be at liberty to distribute the various drafts of
the chapters of the report.
Question 42. Was any language from your drafts referring to your
own reports ultimately used by IPCC/TAR? Please provide highlighted
versions from IPCC.
Response. The wording of the question is unclear. If the question
is, did I, in my contributions to the chapter, provide summaries that
included references to my own work as well as that of other scientists,
the answer is of course yes. Since each of the authors was asked to
contribute sections related to their particular areas of expertise, and
since the IPCC authors were chosen from among the leading scientists in
the world, it would be distinctly odd if it were not the case that most
authors referred to their work, as well as that of others, in their
Question 43. Did IPCC/TAR have any policies governing how lead
authors used their own work? Did IPCC/TAR have any quality control
procedures in the event that a lead author used his own work? Please
provide a short summary of your understanding of such procedures.
Response. I am not a spokesperson for the IPCC. However, it is my
understanding that the IPCC carries out a process for developing its
summarization of the understanding of science that leads to one of the
most rigorously peer-reviewed scientific documents in existence.
Individual technical chapters are prepared by expert scientific teams
that consider the full range of published papers in a subject area.
This expert author team then solicits an initial peer review from a
large number of other scientists in the field, drawing on those
representing the full range of expert science. The reports next go
through a much wider review that is open to literally thousands of
scientists around the world. Finally countries, NGO's, and professional
groups (such as business groups) are provided the opportunity to send
in review comments. (and in the case of the U.S. government review, an
invitation to submit comments to be considered to be forwarded to the
IPCC is published in the Federal Register, enabling all to participate
in this review). With the comments available at each stage of the
review process, the authors consider each comment and document their
response. The meticulousness and fairness of the revision process by
the authors in response to reviewer comments is evaluated by an
independent pair of ``review editors'' who are themselves top
international climate scientists who are not authors of the report
itself. The National Academy of Sciences, at President George W. Bush's
request, and other national academies around the world have
independently reviewed the process and the validity of the scientific
findings of the IPCC and endorsed them.
Question 44. Did MBH98 and MBH99 use any proxy series, which were
either unpublished or which resulted from unpublished calculations,
which you carried out? If so, please identify, and detail how you
verified those unpublished results.
Response. MBH98 and MBH99, as many studies, made use of newly
available data that had not yet been published by the original authors
providing those data, and thus was provided to Mann and colleagues on a
provisional basis that they not release the data until the authors had
a chance to publish the records themselves. After all of the data used
had been published, the full dataset used by MBH98 and MBH99 was made
available in the public domain on the public website: ftp://
Question 45. Despite solar variability over the last two millennia,
your analysis concludes the Northern Hemisphere average temperature has
remained virtually constant. What mechanism or mechanisms are
responsible for negating the influence of the sun? Do climate models
(GCMs) exhibit the same lack of response to solar forcing that your
analysis implies? If not, why are model simulations at variance with
your conclusions and how does that limit their applicability for future
climate scenario assessments?
Response. The question is falsely premised on several levels. No
reasonable description of the reconstructions that we or others have
produced of temperature variations in past centuries would characterize
them as ``virtually constant''. The reconstructions performed by my
group and others indicate an amplitude of variability that consistent
with expectations from models driven with estimates of past radiative
forcing including solar and radiative forcing, and allowing for the
added role of internal unforced variability [see e.g. Crowley, T.J.,
Causes of Climate Change Over the Past 1000 Years, Science, 289, 270-
277, 2000]. Indeed, it has been shown that the model-predicted pattern
of surface temperature response to solar forcing in past centuries
closely resembles that estimated from the temperature reconstructions
that my colleagues and I have performed [Shindell, D.T., Schmidt, G.A.,
Mann, M.E., Rind, D., Waple, A., Solar forcing of regional climate
change during the Maunder Minimum, Science, 294, 2149-2152, 2001;
Waple, A., Mann, M.E., Bradley, R.S., Long-term Patterns of Solar
Irradiance Forcing in Model Experiments and Proxy-based Surface
Temperature Reconstructions, Climate Dynamics, 18, 563-578, 2002;
Shindell, D.T., Schmidt, G.A., Miller, R., Mann, M.E., Volcanic and
Solar forcing of Climate Change During the Pre-Industrial era, Journal
of Climate, in press, 2003].
Question 46. How did the temperatures of the mid-Holocene Optimum
Period (6000 to 9000 BP) compare with those observed today? Was it a
global or a local phenomenon? What was or were the cause or causes of
any temperature anomalies in that period? What is the cause of the 104
to 105 year timescale changes in deuterium, oxygen isotope, etc.,
concentrations in ice core records? Are such changes global or local?
Response. Paleoclimate experts have established that mid-Holocene
warmth centered roughly 5000 years ago was restricted to high latitudes
and certain seasons (summer in the Northern Hemisphere and winter in
the southern hemisphere). Because much of the early paleoclimate
evidence that was available (for example, fossil pollen assemblages)
came from the Northern Hemisphere extratropics, and is largely
reflective of summer conditions, decades ago some scientists believed
that this was a time of globally warmer conditions. It is now well
known that this is not the case. More abundant evidence now
demonstrates, for example, that the tropical regions were cooler over
much of the year. All of these changes are consistent with the expected
response of surface temperatures to the known changes in the Earth's
orbital geometry relative to the Sun during that time period and
associated climate feedbacks, as detailed in peer-reviewed scientific
publications [e.g., Hewitt, C.D., A Fully Coupled GCM Simulation of the
Climate of the Mid-Holocene, Geophysical Research Letters, 25 (3), 361-
364, 1998; Ganopolski, A., C. Kubatzki, M. Claussen, V. Brovkin, and V.
Petoukhov, The Influence of Vegetation-Atmosphere-Ocean Interaction on
Climate During the Mid-Holocene, Science, 280, 1916-1919, 1998].
Climate model simulations indicate quite good agreement with
paleoclimate evidence now available. These models calculate that global
annual average temperatures were probably about the same or a few
tenths of a degree C cooler than today (the late 20th century) during
this time period [Ganopolski, A., C. Kubatzki, M. Claussen, V. Brovkin,
and V. Petoukhov, The Influence of Vegetation-Atmosphere-Ocean
Interaction on Climate During the Mid-Holocene, Science, 280, 1916-
1919, 1998; Kitoh, A., and S. Murakami, Tropical Pacific Climate at the
mid-Holocene and the Last Glacial Maximum simulated by a coupled
oceanatmosphere general circulation model, Paleooceanography, 17 (3),
(19)1-13, 2002.]. That's a far cry from the very out-of-date claim made
by Dr. Legates in his testimony. Dr. Legates' comments regarding
climate changes over the past 1000 years reflect a similar lack of
familiarity with a whole body of paleoclimate research, especially with
the new insights gained through the augmented research program, during
the past decade.
Question 47. It has been observed that in the past, carbon dioxide
concentrations have sometimes lagged air temperature trends; that is,
changes in air temperature have subsequently sometimes resulted in
changes in carbon dioxide concentrations. Do you agree with those
results from expert researchers? Why or why not?
Response. The question mis-characterizes the evidence that has been
provided by paleoclimate researchers. The studies that the questioner
appears to be alluding to, demonstrate a phase relationship between ice
core CO2 estimates and *local* temperature variations at the
site of the ice core. Furthermore these local temperature estimates are
indirectly inferred from oxygen isotopes, based on quite uncertain
assumptions regarding oxygen isotope paleothermometary and neglecting
possible biases due to the variable seasonality of local accumulation.
As local temperature variations at the site of the ice core have an
unknown relationship with global mean temperature variations (which are
far more dominated by lower latitudes which occupy the majority of the
Earth's surface area), the phase relationships between past CO2
and global mean temperature variations are not known. In spite of these
qualifications, it is not at all implausible that the geologic record
indicates that at some times the CO2 increase may lag the
initial temperature increase; such a situation would be expected, for
example, if the change in climate was initiated by a change in the
orbital geometry that affected the distribution of solar radiation, and
then the slow warming drove CO2 from the warming ocean into
the atmosphere. It is because of the many possibilities for how
different processes can interact that it is essential to not simply
base a conclusion on an apparent correlation without evaluating the
underlying physical mechanisms for that particular period.
Question 48. Are there any time periods for which atmospheric
CO2 content has changed without a concomitant change in
global air temperature? Are there periods when the atmospheric CO2
content was relatively high butglobal air temperatures relatively low?
Response. In his testimony, Dr. Legates indicated that there were
historical cases where the temperature has gone up, but that CO2
has fallen. It may well be the case that this has happened in the past.
However, it is hardly surprising, and certainly not inconsistent with
our established understanding of the various factors that influence
surface temperatures. The warming response to increased greenhouse gas
concentrations lags the actual increase in greenhouse gas
concentrations in the atmosphere potentially by several decades, due to
the sluggish response of the oceans, which have an enormous thermal
capacity compared to the atmosphere, to increased surface radiative
forcing. So warming is not expected to be contemporaneous with changes
in CO2, but instead, to lag it by several decades. However,
greenhouse gases are certainly not the only factor affecting the
average surface temperature of the Earth. There are other anthropogenic
factors, such as increased sulphate aerosols, which can have a cooling
effect on the climate, and natural factors, such as volcanic activity,
modest natural variations in solar output, and internal dynamics
associated with climate events such as El Nino, which also influence
the average surface temperature of the globe. At any particular time,
these other factors may outweigh the warming effect due to increased
greenhouse gases. For example, the relative lack of warming during the
period 1940-1970 appears to be related to a combination of such
factors, as discussed in my response to an earlier question. But while
these other factors tend to cancel over time, the increased greenhouse
gases lead to a systematic warming that will not cancel out over a very
long time period. It is for precisely this reason that late 20th
century warming now appears to have risen above the range of the
natural variability of past centuries.
Question 49. Two independent and nearly direct measures of surface
temperature (deep borehole reconstructions) over the past several
millennia have been published for Greenland (Dahl-Jensen et al 1998)
and the Middle Urals (Demeshko and Shchapov 2001). The local surface
temperature at these locations is highly correlated with global
temperature on 10-year time scales and longer (r2 > 50 percent 10 yr
with agreement increasing for longer averaging periods). Both
reconstructions independently show their local surface temperatures
were at least a1 + C warmer for century-scale mean temperatures around
A.D. 900 than the latter half of the 20th century, translating into a
global anomaly of at least +0.2+ C relative to today.
This further implies that even higher global temperature anomalies
for shorter periods, such as half-century or decadal periods, were
observed about 1000 years ago. Why do these two robust measures of
local and global approximations differ greatly from Mann et al. 1999?
Response. The question is wrongly premised on multiple levels.
First, the correlations cited are completely wrong. No citation to the
peer-reviewed literature is provided, so it is difficult to determinate
how these numbers were arrived at. I therefore proceeded to analyzed
the appropriate surface air temperature gridpoint data from the
Climatic Research Unit of the University of East Anglia myself. I found
that only after 1922 is there adequate coverage (>50 percent areal
coverage) to estimate a meaningful Greenland areal-mean temperature.
For the period back to 1922, the linear correlation between the
Greenland and Northern Hemisphere mean temperature is r= -0.06
(negative!), nor is there a significant correlation at decadal or
longer timescales. In fact, the trends in the two series during the
latter 20th century are of opposite sign. So the numbers cited are
It is in fact well known by the climate community that there are
fundamental physical reasons why temperatures in Greenland are, in
general, poorly correlated with Northern Hemisphere mean temperature.
Owing to the strong overprint of processes, such as the North Atlantic
Oscillation, and changes in coupled ocean-atmosphere processes in the
North Atlantic that impart a large regional overprint of temperature
variation in this region, both negative and positive correlations with
Northern Hemisphere mean temperature can be found, depending on the
time period and region of Greenland analyzed.
The Dahl Jensen et al Greenland borehole data may indeed be useful
temperature proxy data for the regions they represent, and they have
been used in reconstructions of Northern Hemisphere mean temperature,
with caveats due to their extremely low temporal resolution (see Mann
and Jones, 2003). While the two Greenland borehole records show
significantly different histories over the past 1000 years (which is
expected since temperature trends vary markedly depending on the region
of Greenland in question), one of the two records does correlate well
with the instrumental Greenland record over the period of mutual
overlap. Its shows the mid-20th century warm peak, followed by the
latter 20th century cooling peak, just as the instrumental Greenland
annual mean temperature record does. However, instrumental Northern
Hemisphere mean temperature has, in contrast, warmed markedly during
the latter 20th century.
The Greenland borehole temperature reconstruction may tell us
something about temperatures in Greenland over the past few millennia
even though the two different Greenland borehole records show some
differences between them. But these results are unlikely to tell us
much, if anything, about Northern Hemisphere mean temperature trends.
Indeed, Dahl-Jensen et al have never, to my knowledge, claimed in their
studies that that temperature variations in the two regions of
Greenland reconstructed (which themselves show significantly different
histories over the past 1000 years) are representative of Northern
Hemisphere mean temperatures, and I would be surprised if the authors
were comfortable in having their data represented as such.
Question 50. In your view what should the Federal Government do in
response of rising concentrations of CO2? What would be the
climate impact of this effort?
Response. In my view, the Congress and the Federal Government
should be taking the scientific findings of the mainstream research
community very seriously and should stop focusing so much attention on
the poorly conducted and distracting nitpicking of the various
contrarian scientists. The IPCC assessments represent the most
authoritative reviews of the science and have been unanimously endorsed
by all of the participating nations of the world--it is time to pay
attention to their findings. Exactly what steps should be taken and how
fast this should be done are policy questions that members of this body
should be responsibly and thoughtfully addressing. The long residence
timescales of anthropogenic greenhouses gases, and the lags in the
response of the climate system (e.g. sea level rise) to already
realized increases in greenhouse gas concentrations dictate, however,
that there are potentially significant costs to delayed action.
Question 51. Approximately what percentage of the temperature
increase in the observational record over the last 100 years would you
attribute to anthropogenic causes? What percentage would you attribute
to increased urbanization? What percentage would you attribute to non-
urbanized land use changes? What percentage would you attribute to
natural (solar, volcanic, etc.) variability? What percentage would you
attribute to ``internal'' climate variability? What percentage would
you say results from other or unexplained sources? Give estimates for
the years 1900,1940, 1980 and 2000.
Response. A cursory review of the available evidence (see e.g.
Figure 2.1 of chapter 2 of the 2001 IPCC Scientific Working Group
report) indicates the following approximate attributes in the observed
record of global mean temperature changes over the past 100 years: a
warming of approximately 0.3+ C to 1940, a statistically insignificant
change (given the uncertainties) from 1940 to the mid-1970's, and then
an additional warming of approximately 0.5+ C from 1970 to 2000. This
pattern of behavior is reproduced closely by models driven with
estimates of both natural and anthropogenic forcing of the climate
during the 20th century. The period of relative stasis in global mean
temperatures from 1940 to 1970, in these model simulations, appears to
result from the cooling impact of anthropogenic aerosols (for which
there was a large increase during that time period) as well as a
potential cooling contribution from explosive volcanic eruptions that
occurred during that period, which tended to offset the warming
influence of increased greenhouse gas concentrations during that time
period (e.g. the 1957 eruption). However, much of the overall warming
of the globe during the 20th century (which is between 0.6+ C and 1.0+
C depending on the precise instrumental data set used, and the precise
endpoints of the interval examined) is clearly a result of increased
greenhouse gas concentrations, as established in these simulations,
consistent with the conclusions of the IPCC Third Assessment Report
that most of the warming of the past 50 years is attributable to human
Question 52. What was the earth's climate like the last time the
atmospheric concentration of carbon dioxide was near today's level of
about 370 parts per million (ppm) and what were past conditions like
when concentrations were at 550 ppm? Detail the factors that cause the
global carbon cycle to produce these high levels of atmospheric carbon
Response. It is not precisely known what the ``earth's climate''
was like the last time carbon dioxide levels were near 370 ppm (let
alone 550 ppm) because the available paleoclimate evidence available
this long ago are quite uncertain and incomplete. That having been
said, it is believed, based on the available proxy information and
faunal/floral evidence, that global temperatures were probably several
degrees higher than they are today when CO2 concentrations
neared 550 pm, roughly consistent with model simulation results. One
probably has to go back roughly 40-50 million years ago (see chapter 3
of the 2001 IPCC working group 1 report) to find a time when CO2
concentrations were in the range of 550 ppm (i.e., roughly double their
pre-industrial concentration) and approximately 80 million years ago
(i.e., the mid-Cretaceous period when Dinosaurs roamed the polar
regions) to find a time when CO2 levels were in excess of
1200 ppm (a level that will be reached, at current rates of CO2
increase, within 1 to 1\1/2\ centuries). Proxy evidence available for
this period, tenuous though it is, suggests deep ocean temperatures 8-
12+ C warmer than present. State of the art climate model simulations
performed by Bette Otto-Bleisner and colleagues using the National
Center for Atmospheric Research (NCAR) global climate model, which
incorporate such CO2 levels (and the continental
configuration corresponding to the mid-Cretaceous period), indicate
significantly warmer sea surface temperatures, with tropical sea
surface temperatures approximately 4+ C warmer and polar sea surface
temperatures approximately 6-14+ C warmer than present. The simulations
indicate an absence of perennial sea ice at even the most polar
Question 53. In your vitae, you indicate that you serve on the
panel for NOAA's Climate Change Data and Detection (CCDD) program,
while at the same time, you also have received large grants from this
program. Please explain your role on the panel, how grant submissions
are evaluated, and why there is no conflict of interest or impropriety
associated with members of a panel receiving large grants from the
program for which they serve.
Response. I am not a spokesperson for NOAA, and would suggest that
the questioner contact the appropriate NOAA agency officials for
further information on their conflict of interest and disclosure
policies. That notwithstanding, however, I would note the following
points. Government funding agencies seek to draw upon the leading
experts of the field in their panels. Inevitably, this means that
specific science programs within NSF and NOAA invite to their review
panels scientists who typically submit proposals themselves to those
panels. Scientists are also asked to disclose any conflicts of interest
they might have in reviewing a proposal, and are asked to recuse
themselves from any participation in discussions related to proposals
that they might have even peripheral involvement with. In my
involvement in both NSF and NOAA panel reviews, I have on many
occasions recused myself from reviewing or discussing a proposal based
on such considerations.
Question 54. Do you receive any income or reimbursement (travel,
speaking fees, etc.) from any sources, which have taken advocacy
positions with respect to the Kyoto Protocol, the U.N. Framework
Convention on Climate Change, or legislation before the U.S. Congress
that would affect greenhouse gas emissions? If so, please identify
those sources and the approximate amount of money that they represent.
Response. All income or travel expense reimbursement funds that I
have received to my recollection have come from academic institutions,
government funding agencies such as NSF, NOAA, NASA, DOE, and
scientific organizations such as the American Geophysical Union and
University Corporation for Atmospheric Research (UCAR). I am not
familiar with any advocacy positions that have been taken by any of
these institutions or organizations regarding the U.N. Framework
Convention on Climate change, or legislation before the U.S. Congress
that would affect greenhouse gas emissions.
Responses by Michael Mann to Additional Questions from Senator Jeffords
Question 1. Is it your understanding that during the mid-Holocene
optimum period (the period from 4000-7000 B.C.) that annual mean global
temperatures were more than a degree C warmer than the present day?
Response. This is an oft-repeated but patently false claim. Dr.
Legates, who has no established expertise in the relevant field of
paleoclimatology, indeed asserts that temperatures were warmer at this
time. In fact, not only is that not the consensus of the paleoclimate
research community, but just the opposite is believed to be true of
global annual mean temperatures at this time. Paleoclimate experts know
that the mid-Holocene warmth centered roughly 5000 years ago was
restricted to high latitudes and certain seasons (summer in the
Northern Hemisphere and winter in the southern hemisphere). Because
much of the early paleoclimate evidence that was available (for
example, fossil pollen assemblages) came from the Northern Hemisphere
extratropics, and is largely reflective of summer conditions, decades
ago some scientists believed that this was a time of globally warmer
conditions. It is now well known that this is not the case. More
abundant evidence now demonstrates, for example, that the tropical
regions were cooler over much of the year. All of these changes are
consistent with the expected response of surface temperatures to the
known changes in the Earth's orbital geometry relative to the Sun
during that time period and associated climate feedbacks, as detailed
in peer-reviewed scientific publications [e.g., Hewitt, C.D., A Fully
Coupled GCM Simulation of the Climate of the Mid-Holocene, Geophysical
Research Letters, 25 (3), 361-364, 1998; Ganopolski, A., C. Kubatzki,
M. Claussen, V. Brovkin, and V. Petoukhov, The Influence of Vegetation-
Atmosphere-Ocean Interaction on Climate During the Mid-Holocene,
Science, 280, 1916-1919, 1998].
Climate model simulations indicate quite good agreement with
paleoclimate evidence now available. These models calculate that global
annual average temperatures were probably a few tenths of a degree C
cooler than today during this time period [Kitoh, A., and S. Murakami,
Tropical Pacific Climate at the mid-Holocene and the Last Glacial
Maximum simulated by a coupled ocean-atmosphere general circulation
model, Paleooceanography, 17 (3), (19)1-13, 2002.]. That's a far cry
from the very out-of-date claim made by Legates. Legates' comments
regarding climate changes over the past 1000 years reflect a similar
lack of familiarity with a whole body of paleoclimate research,
especially with the new insights gained through the augmented research
program, during the past decade.
Question 2. Why only focus on the past 1000 or 2000 years and not
Response. Large changes in climate certainly occurred in the
distant past. If we look million years back in time, dinosaurs were
roaming the polar regions of the Earth, and the globe was several
degrees wanner than today. Carbon dioxide levels were probably several
times their current level, slowly having attained such high levels due
to changes in the arrangements of the continents (`plate tectonics')
which influence the volcanic outgassing of carbon dioxide from the
solid Earth. These changes occurred on timescales of tens of millions
of years. Going back 10,000 years ago, large ice sheets existed over
North America due to natural changes that occur in the Earth's orbit
around the Sun on timescales of tens of thousands of years. Trying to
study distant past climates for insights into modern natural climate
variability is hampered by the fact that the basic external constraints
on the system (the continental arrangement, the geometry of the Earth's
astronomical orbit, the presence of continental ice sheets--what we
call the `boundary conditions') were significantly, different from
today. Focusing on the evolution of climate in the centuries leading up
to the 20th century (i.e., the past 1000 to 2000 years) provides a
perspective on the natural variability of the climate prior to the
period during which large-scale human influence is likely to have
occurred, yet modern enough that the basic boundary conditions on the
climate system were otherwise the same. This provides us, in essence,
`control' for diagnosing whether or not recent changes in climate are
indeed unusual. Moreover, only during the past 1000-2000 years do we
have adequate networks of proxy climate data with the required (annual)
resolution in time to compare and validate against modern instrumental
records; Reliable quantitative reconstructions of large-scale surface
temperature patterns further back in time are thus not, at present,
Question 3. One of the Northern Hemisphere temperature
reconstructions in your Figure 1 (the green curve from a paper by Esper
and colleagues from Science in 2001) shows larger swings in past
centuries, marginally outside the uncertainty bounds of the other
reconstructions and model simulations. Does this indicate internal
inconsistency in our knowledge?
Response. There is no inconsistency. Esper et al noted, in their
paper, that their estimate, unlike that of my colleagues and mine (the
Mann/Bradley/Hughes or ``MBH'' reconstruction), was not representative
of the entire Northern Hemisphere. They explicitly noted this in their
paper, where they pointed out the likely reason for differences is that
the MBH reconstruction represents the full Northern Hemisphere
(tropics, subtropics, and extratropics) while the Esper et al
reconstruction only represents the restricted extratropical continents.
In fact, in a Science article that appeared in the same issue as the
Esper et al paper [Briffa, K.R. and T.J. Osborn, Science, Blowing Hot
and Cold, 295, 2227-2228, 2002] Briffa and Osborn noted that much of
the difference was due to an arguably inappropriate scaling that Esper
et al used, and an inappropriate comparison of summer vs. annual
temperatures; ``when we regressed the record of Esper et al. against
non-smoothed data (see the figure), this difference (with MBHJ was
reduced to about 0.4+ C. Recalibrating both curves against year-by-year
warm season temperatures reduces this difference further to about 0.35+
As shown in the ``Eos''article discussed in my testimony, which
represents a consensus of the leading researchers in the field [Mann,
ME, Ammann, C.M., Bradley, R.S., Briffa; K.R., Crowley, T.J., Hughes,
M.K.; Jones, P.D., Oppenheimer, M., Osbom, T.J., Overpeck, J.T.,
Rutherford, S., Trenberth, K.E., Wigley, T.M.L., On Past Temperatures
and Anomalous Late 20th Century Warmth, Eos, 84, 256-258, 2003], a
proper scaling of Esper et al record prior to comparison with other
estimates, shows it only marginally outside the error estimates of the
MBH reconstruction and the many other estimates that are in agreement
with it. As noted in two articles in Science that shortly followed the
Esper et al paper [Mann, M.E., Hughes, M.K., Tree-Ring Chronologies and
Climate Variability, Science, 296, 848, 2002; Mann, ME, The Value of
Multiple Proxies, Science, 297, 1481-1482, 2002], it is likely that the
emphasis of the Esper et al reconstruction on only the summer season
and the extratropical continental regions, provides a biased estimate
of the true pattern of annual, hemisphere-wide temperatures in past
centuries, explaining the small differences between this estimate and
other estimates. This conclusion has been verified in recent modeling
studies [Shindell, D.T., Schmidt, G.A., Miller, R., Mann, M.E.,
Volcanic and Solar forcing of Climate Change During the Pre-Industrial
era, Journal of Climate, in press, 2003 ]. It is thus clearly
disingenuous when contrarians make the argument that the Esper et al
result is in conflict with the mainstream conclusions of the climate
research community with regard to the history of Northern Hemisphere
mean annual temperature variations over the past millennium as
embodied, for example, in the Eos article.
Question 4. As climatologist, can you explain what kind of
quantitative analysis it takes to determine whether or not the last 50
years has been unusually warm compared to the last 1000 years?
Response. Well, such an analysis requires the careful use of proxy
data, because we don't have widespread instrumental temperature records
prior to the mid-19th century. By `careful use': I mean that one must
first establish that the records actually resolve the changes of the
past 50 years. This typically requires annually resolved proxy records
or the very circumspect use of records with decadal resolution. One
must not, as in the Soon and Baliunas' studies, use records that do not
resolve the trends of the past few decades. One must also establish the
existence of an actual temperature signal in the available proxy data
before using them to reconstruct past temperature patterns, and one
must properly synthesize regional data, which typically all show
different tendencies at any given time, into an estimate of the average
temperature over the entire hemisphere or globe. There area number of
ways of performing such a synthesis, from the sophisticated pattern
reconstruction approaches my colleagues and I have described in the
technical literature, to the relatively straightforward compositing
approach that many other paleoclimatologists, (including myself) have
also used. In all cases, the estimates based on the proxy data must be
calibrated against modern instrumental temperature measurements, to
allow, for a quantitative estimate of past temperatures. The estimate
must then be independently verified or, what we call, `cross-
validated,' by showing that it independently reproduces earlier
instrumental data that were not used to calibrate the estimates.
Finally, uncertainties must be diagnosed based on how well the
reconstruction describes actual available instrumental measurements.
Once such steps have been taken, it is possible to compare the recent
instrumental record to the reconstruction within the context of the
uncertainties of the reconstruction. This latter comparison allows us
to gauge whether or not late 20th century temperatures are anomalous or
not in a long-term context. The conclusion from legitimate such studies
that late 20th century warmth is indeed anomalous in a millennial or
longer-term context has been shown to be quite robust with respect to
the details of the data set used, or the methodology used (as shown in
exhibit 1 in my testimony, the first figure of the ``Eos'' piece). It
is noteworthy that the Soon and Baliunas paper satisfies none of the
required standards for a `careful use of proxy data' specified above.
Question 5. Do you claim that appropriate statistical methods do
not exist for calibrating statistical predictors, including climate
proxy records, against a target variable, such as the modern
instrumental temperature record?
Response. No. The statement belies a centuries-old field of
statistics known as ``multivariate linear regression'' in which a set
of candidate ``predictors'' (such as proxy data) are statistically
related to a target variable or ``predictand'' (such as the
instrumental temperature record) during a common interval of overlap
(e.g., the 20th century). If done properly, this statistical method
isolates the temperature information that is contained within the proxy
data, and uses that information to reconstruct past temperature
patterns from the proxy data. It is also well known to those properly
trained in statistics that the ``regression model'' must be
independently ``validated'' by showing that it successfully reproduces
independent data (e.g. longer-term instrumental temperature records)
that were not used in constructing the statistical model itself. The
estimates by Mann and colleagues embrace each of these fundamental
Legates in his testimony seemed to claim that a composite estimate
(e.g. of Northern Hemisphere mean temperature) should somehow resemble
each of the individual predictors (e.g. the various regional
temperature estimates). Such a result is, in general, a statistical
impossibility. There is a basic theorem in statistics known as the
``central limit theorem'' which indicates a general tendency for a
composite (i.e. average) of a large number of different individual
estimates to cancel out in terms of the pattern variation and amplitude
of variability evident in the individual estimates. If Legates were
indeed (as he claims to be) familiar with the instrumental surface
temperature record, he would know, for example, that individual
instrumental thermometer records available for particular locations
over the globe during the 20th century show very little in common with
the `composite' series constructed by averaging all of the individual
records into a hemispheric or global estimates. Because season-to-
season and year-to year fluctuations in the climate at regional scales
often result from shifts in the atmospheric circulation, not every
location experiences the same variation in any given year; for example,
this summer, the western United States and Europe are anomalously warm,
while the East Coast is anomalously cool. The average series reflects a
tendency for a cancellation of the various ``ups'' and ``downs'' in the
different individual series that often occur at different times. This
is simply a statement about the instrumental record itself, and
requires no use of proxy data at all. It is discouraging that Legates
and colleagues haven't performed even such simple analyses with
available instrumental data that would expose the fundamental flaws in
their supposed `statistical' reasoning.
In this context, it should be noted that Legates testimony
seriously misrepresents the statistical analyses used by Mann and co-
workers. In his testimony, Legates claimed that my collaborators and I
replaced the proxy data for the 1900's by the instrumental. The
assertion is simply factually incorrect. Any reader of our published
work knows full well that our proxy-based temperature reconstruction
extends well into the late 20th century, through 1980 (the vast
majority of published high-resolution climate proxy data are not
available at later times than this). It is shown in our work that the
reconstruction independently reproduces estimates from the instrumental
surface temperature data record back through the mid-19th century and,
in certain regions, back through the mid-18th century (i.e., our
regression model is ``validated'' in the manner discussed above). Our
Northern Hemisphere average temperature series reconstructed from proxy
data is shown to agree with the instrumental Northern Hemisphere
average record over the entire interval available for comparison (1856-
1980). This successful validation of the reconstruction, furthermore,
allows us to compare the proxy-based reconstruction to the entire
instrumental record (available through 1999 at the time of our
publication), taking into account the uncertainties in the
Legates further claim that we present the instrumental record
without uncertainty is disingenuous. If Legates, for example, were
familiar with studies of the instrumental surface temperature record,
he would understand that the uncertainties in this record using the
20th century are minimal compared to the uncertainties shown for our
reconstruction [see e.g. Figure 2.1b in Folland, C.K., Karl, T.R.,
Christy, J.R., Clarke, R. A.,Gruza, G.V., Jouzel, J., Mann, M.E.,
Oerlemans, J., Salinger, M.J.;, Wang, S.-W., Observed Climate
Variability arid: Change, in Climate Change 2001: The Scientific Basis,
Houghton, J.T., et al. (eds.), Cambridge Univ. Press, Cambridge, 99-
181, 2001.]. Furthermore, all scientists with a proper training in
statistics know that uncertainties add ``in quadrature'', In other
words, you have to square them before adding them. This means that the
relatively small uncertainty in the instrumental record makes a
relatively small contribution to the total uncertainty. Legates claimed
in his testimony that including the uncertainty in the instrumental
record, which he estimates as 0.1+ C would change the conclusions
expressed by us and other mainstream climate scientists that the 1990's
are the warmest decade in at least the past 1000 years within estimated
uncertainties. This claim is very misleading for several reasons,
First, the standard error in Northern Hemisphere mean annual
temperatures during the 1990's is far smaller than the amount cited, by
Legates [see again Folland et al, 2001 cited above]. Even more
problematic, however, Legates claim indicates a fundamental
misunderstanding of the statistical concepts of standard error and
uncertainty,. The shaded region shown along with the Mann et al
reconstruction (and other similar plots shown in recent articles such
as the aforementioned ``Eos'' article, and the IPCC report) indicate
two standard error intervals. The decade of the 1990's is roughly two
standard errors warmer (i.e., about 0.4+ C) than any decade prior to
the 20th century in the reconstruction. Based on a one-sided test for
anomalous warmth, this translates to a roughly 97.5 percent level of
significance. Modifying the uncertainties to include the small
additional contribution due to uncertainties in the instrumental record
itself would modify this only slightly, and would not lower the
significance level below the 95 percent level. Though there is no such
thing as an absolute estimate of uncertainty, despite Legate's
implications to the contrary, a 95 percent confidence is often adopted
as an appropriate criterion for significance. Legates statement that
including instrumental contributions to the uncertainty would change
the conclusions is thus clearly false.
Question 6. In determining whether the temperature of the
``Medieval Warm Period'' was warmer than the 20th century, does your
work analyze whether a 50-year period is either warmer or wetter or
drier than the 20th century? Is it appropriate to use indicators of
drought and precipitation directly to draw inferences of past
Response. No, the work of me and my colleagues does not follow the
flawed approach used by Soon and Baliunas. It is fundamentally unsound
to infer past temperature changes directly from records of drought or
precipitation. The analysis methods used by my various collaborators
and I (e.g. the 13 authors of the recent article in Eos) employ
standard statistical methods for identifying the surface temperature
signal contained in proxy climate records, and using only that
temperature signal in reconstructing past temperature patterns. By
contrast, Soon and Baliunas simply infer evidence for warm ``Medieval
Warm Period'' or cold ``Little Ice Age'' conditions from the relative
changes in proxy records often reflective of changes in precipitation
or drought, rather than temperature. It is difficult to imagine amore
basic mistake than misinterpreting hydrological evidence in terms of
temperature evidence. This fundamental shortcoming in their approach is
identified in the Eos article referred to in my testimony that was
written by 13 leading climate and paleoclimate scientists.
Incidentally, the Eos piece was peer-reviewed, despite the claim by
Legates otherwise in his testimony--an associate editor with training
in the particular field corresponding to the submitted piece
(``Atmospheric Science'' in this case); reviews the content of Eos
forum pieces prior to acceptance.
Question 7. Can you compare the quantitative analysis that supports
your conclusion that the climate is warming faster in recent years than
at any time in the recent past with the analysis done in the Soon
Response. Technically speaking, there is no actual ``analysis'' in
the Soon and Baliunas review, in that they don't appear to have
performed a single numerical or statistical operation upon a single
time series at all. They do not provide any quantitative estimates of
temperature changes, let alone any estimate of uncertainties, Instead,
they claim to interpret the results of past studies mainly by counting
the number of studies coming to some conclusion; no matter how they got
there and whether there have been later interpretations. Science
requires analysis--not just counting studies. Climate scientists whose
records they analyzed have gone on record as indicating that Soon and
Baliunas misinterpreted their studies (e.g., the article by David
Appell in the August 2003 issue of Scientific American) and numerous
climate scientists have indicated (see same article) that Soon and
Baliunas misinterpreted evidence of drought or precipitation as
evidence of temperature changes, did not use records that resolve the
climate changes of the late 20th century, and did not take into account
whether or not variations in different regions were coincident or not.
Soon and Baliunas also neglect undeniable evidence of substantial
warming of hemispheric and global surface temperatures during the past
few decades. So the Soon and Baliunas analysis fails just about every
meaningful criterion that might be applied to determining the validity
of an analysis that purports to evaluate current warming in the context
of past temperature trends. This deeply flawed study thus contrasts
sharply with other rigorous quantitative studies (as discussed in the
Eos article) performed by numerous other scientists with appropriate
training in the fields of climatology and paleoclimatology, which use
proper statistical methods for inferring past temperature changes from
proxy data, provide uncertainty estimates, and employ appropriate
comparisons of current and past trends.
Question 8. What was the earth's climate like the last time that
atmospheric concentrations of carbon dioxide were at today's levels or
about 370 parts per million (ppm) and what were conditions like when
concentrations were at 550 ppm, which will occur around 2060 or so?
Response. We have to go back far into the past to find carbon
dioxide levels approaching today's levels. Ice core studies indicate
that modern carbon dioxide levels are unprecedented for at least four
glacial/inter-glacial cycles: in other words, for more than 400,000
years. Other evidence suggests that carbon dioxide levels are now
higher than they have been for at least 10 million years. One probably
has to go back roughly 40-50 million years ago (see chapter 3 of the
2001 IPCC working group 1 report) to find CO2 concentrations
were in the range of 550 ppm (i.e., roughly double their preindustrial
concentration) and approximately 80 million years ago (i.e., the mid-
Cretaceous period when Dinosaurs roamed the polar regions) to find
CO2 levels in excess of 1200 ppm (a level that will be
reached, at current rates of CO2 increase, within one to
one-and-a-half centuries). Proxy evidence available for this period,
tenuous though it is, suggests deep ocean temperatures 8-12+ C warmer
than present. State of the art climate model simulations performed by
Bette Otto-Bleisner and colleagues using the National Center for
Atmospheric Research (NCAR) global climate model, which incorporate
such CO2 levels (and the continental configuration
corresponding to the mid-Cretaceous period), indicate significantly
warmer sea surface temperatures, with tropical sea surface temperatures
approximately 4+ C warmer and polar sea surface temperatures
approximately 6-14+ C warmer than present. The simulations indicate an
absence of perennial sea ice at even the most polar latitudes.
Question 9. Are you aware of any scientists beside the authors of
the Soon et al article who support using ``wetness'' or ``dryness'' as
indicators of past temperatures, instead of actual temperatures or
proxy data that reflects temperatures?
Response. I am not aware of any other scientist who has made the
mistake of interpreting paleoclimatic information in this way. As
discussed above, trained paleoclimatologists typically use statistical
methods to identify the strength of the temperature signal in a proxy
record prior to using it in reconstructing past temperature patterns.
Question 10. Is there any known geologic precedent for large
increases of atmospheric CO2 without simultaneous changes in
other components of the carbon cycle and the climate system?
Response. There is not, to my knowledge, such an example. As
discussed above, the geological record shows a clear relationship
between periods of high CO2 and relatively high global mean
temperatures. The study of the relationship between changes in CO2
and climate in the paleoclimate record is sometimes complicated by the
fact that these relationships can be relatively complex during rapid
transitions between glacial and interglacial climates such as those
that occurred with the coming and going of ice ages that occurs on a
roughly 100 thousand year timescale over the past nearly one million
years. However, one can turn to periods of time when the climate and
CO2 were not varying rapidly, and thus the climate was
approximately in an ``equilibrium'' state, for insights into the
relationship between CO2 and climate, A perfect such example
is the height of the last ice age, the so-called ``Last Glacial
Maximum'' or ``LGM'' centered roughly 25 thousand years ago. At this
time, CO2 was substantially lower than today (just below 200
ppm) and global mean surface temperatures were several degrees (about
4C or so) cooler than today. Such relationships between past CO2
changes and global temperature changes typically, suggest a
``sensitivity'' of the climate system to enhanced CO2 of 1,
5 to 4.5 C warming for each doubling of CO2 concentrations
from their pre-industrial levels, similar to the range of sensitivities
found in various climate models.
Question 11. According to a study published in Science magazine
recently [B. D. Santer; M. F. Wehner, T. M. L. Wigley, R. Sausen; G. A.
Meehl, K. E. Taylor, C. Ammann, J. Arblaster, W. M. Washington, J. S.
Boyle, and W. Bruggemann Science 2003 July 25; 301; 479-483], manmade
emissions are partly to blame for pushing outward the boundary between
the lower atmosphere and the upper atmosphere. How does that fit with
the long-term climate history and what are the implications?
Response. This is yet another independent piece of evidence
confirming a detectable anthropogenic influence on climate during the
late 20th century. This evidence is consistent with evidence for
unprecedented surface warming during the past few decades--warming that
indeed appears unprecedented for as long as we have records (i.e., for
at least a thousand, and probably two thousand years). These changes,
moreover, are consistent with predictions from climate models driven by
known anthropogenic (human) forcing of the climate.
Question 12. At this hearing, there were a number of calls for
``sound science.'' Could you please explain what it is about the IPCC
process that justifies respecting the IPCC results as the very soundest
representation of the science of climate change?
Response. The IPCC carries out a process for developing its
summarization of the understanding of science that leads to one of the
most rigorously peer-reviewed scientific documents in existence,
Individual technical chapters are prepared by expert scientific teams
that consider the full range of published papers in a subject area.
This expert author team then solicits an initial peer review from a
large number of other scientists in the field, drawing on those with
the full range of views. The reports next go through a much wider
review that is open to literally thousands of scientists around the
world. Finally countries, NGOs, and professional groups (such as
business groups) are provided the opportunity to send in review
comments. At each stage, authors consider each comment and document
their response. The meticulousness and fairness of the revision process
by the authors in response to reviewer comments is evaluated by an
independent pair of ``review editors'' who are themselves top
international climate scientists who are not authors of the report
itself. The National Academy of Sciences, at President George W. Bush's
request, and other national academies around the world have
independently reviewed the process and the validity of the scientific
findings of the IPCC and endorsed them. To question the IPCC and the
IPCC process, as does Dr. Legates thus not only does a disservice to
thousands of the world's top scientists; but to the exceptional care
and rigor of the process that has led to the unanimous adoption of all
of the IPCC's assessments by representatives of the over 150 nations
that participate in the IPCC process. The documents are very finely
honed and carefully phrased. The scientific studies of those such as
or, Legates are considered, as are their review comments, and it is
terribly disingenuous, not to mention totally unacceptable to the
international community, after all of the care and consideration put
into these efforts to try to so cavalierly dismiss them.
In his testimony Legate's alleges that the IPCC report
misrepresents what is known about climate change in past centuries and
that it somehow replaces conventional wisdom with dramatically new
conclusions. One must conclude that Legates either did not read the
report, or if he did, he did not understand what he read; for if he had
he would certainly have to recognize factually incorrect nature of his
comments. The IPCC chapter dealing with paleoclimatic evidence
discussed the full range of regional evidence described in the peer-
reviewed as well as evidence from hemispheric composites that average
the information from different regions. The paper by Soon and Baliunas
is a dramatic throwback to the State of our knowledge many decades ago,
while the IPCC report provides a far more upto-date assessment of all
of the available knowledge regarding past climate change. The Soon and
Baliunas papers provide a glaring example of the very ``unsound''
science that Senator Inhofe claims to be concerned about, as numerous
mainstream climate researchers have now opined in the media, and in the
peer-reviewed scientific literature.
Question 13. In your opinion, how do the processes used by the IPCC
and the National Academy of Sciences compare to the process used in the
publication of the Soon and Baliunas paper and other papers by so-
called ``contrarians''? In the next IPCC assessment, would you expect
that the Soon and Baliunas paper will be considered and cited, putting
it into the context of other papers and findings and explaining why it
has differences or similarities?
Response. As discussed above, the IPCC is one of most rigorously
peer-reviewed scientific documents in existence. By contrast, the
contrarians rarely publish in the peer-reviewed literature and when
they do, it is not uncommon to discover, as in the case of the Soon and
Baliunas paper, irregularities in the peer-review process. Publisher
Otto Kinne indeed indicated that the review process at Climate Research
``failed to detect methodological flaws'' in the Soon and Baliunas
paper. I would indeed expect that in the next IPCC assessment, the Soon
and Baliunas paper will be discussed and evaluated in the context of
other available evidence and in the context of how it is faring in the
literature when the IPCC review takes place (e.g., if there are as many
criticisms about their work as at present, and they have not been
seriously addressed by more careful followup studies by the authors. I
would think their conclusions will be rejected as scientifically
unsound. I would not presume to know in detail what the result of the
assessment will be, but I believe it fair to assume that the rigorous
review provided by the IPCC assessment process will not fail to
identify the methodological flaws that appear to have slipped through
the cracks in their publication in the journal ``Climate Research''.
Question 14. Could you explain the IPCC's lexicon for indicating
relative levels of confidence and how you would suggest this relates to
the information being ``real'' and ``probable''? When IPCC says
something is ``very likely,'' just what do they mean?
Response. To avoid the type of misunderstanding that often results
from when scientists seek to convey scientific results to a non-
technical audience, the IPCC specifically sought to employ a lexicon in
which terms such as ``likely'' or ``probable'' or ``very likely'' had
specific statistical meanings attached to them. A fairly conservative
standard was typically employed in this process. Consider the
conclusion in the IPCC report that the 1990's are the warmest decade in
at least the past 1000 years for the Northern hemisphere average
temperature. This conclusion is based on the fact that the average
warmth of the 1990's exceeds that for any reconstructed decade in the
reconstructed Northern Hemisphere series. To be more specific, the
1990's warmth exceeds any past decade by two standard errors. This
corresponds to a roughly 97.5 percent probability based on standard
statistical assumptions. Probabilities of 90 percent-99 percent are
termed ``very likely'' in lexicon typically adopted by the IPCC report.
However, this conclusion was offered as only ``likely'' (corresponding
to a 66 percent-90 percent level of probability) rather than the more
stringent ``very likely'' because it was based on only a small number
of independent studies at the time. Since that time, of course, several
more studies have affirmed this conclusion, and one might imagine that
a more stringent conclusion will be offered in the future. This example
nonetheless illustrates the manner by which IPCC adopted conservative
standards in their use of terms such as ``likely'' or ``very likely''.
It is instructive to contrast that standard with the one taken in the
Soon and Baliunas paper. The Soon and Baliunas paper does not provide a
quantitative estimate of any quantity (such as average Northern
Hemisphere temperature), or any assessment of uncertainty. It is thus
not possible for the authors to attach any meaningful statement of
likelihood or probability to any of their conclusions. They thus
provide no basis for judging the validity of any of the claims made in
their paper, in striking contrast to the rigorous standards adopted by
IPCC, and by the work of my collaborators and me.
Question 15. In his questioning, Senator Inhofe cited results
regarding the potential costs of implementing the Kyoto Protocol from
the Wharton Econometric Forecasting Association (WEFA). I realize that
you are not an economist, but would you please comment as a scientist
on the following two points:
(a) Senator Inhofe cited economic projections (e.g., 14 percent
increase in medical costs; real income drop of $2,700 per household)
going out a decade or so into the future and without any indication of
uncertainty on these estimates implying an accuracy of two-significant
figures. Senator Voinovich cited numbers to similar claimed accuracy
going out 20-25 years; again without any indication of uncertainty.
Could you please comment on what you think are the relative strengths
and weaknesses of making climate projections based on use of physical
laws versus economic extrapolations and what sorts of relative
uncertainty should likely be associated with each type of estimate so
that they can be interpreted in a comparative way by decisionmakers?
Response. Indeed, it is somewhat remarkable that politicians who
reject the validity, for example, of climate model simulations, which
are based on solution of the laws of physics, can so uncritically
accept precise economic projections based on economic forecasts based
on untestable and unverifiable assumptions governing human
decisionmaking, and speculative future scenarios that depend on the
unfolding of the political process. Specific numbers of ``14 percent''
or ``$2,700'' are of course entirely dependent on the assumptions that
go into such forecasts. Because assumptions about future economic
growth and about future government policies are necessarily uncertain,
estimates of changes in costs or income from such models must also be
quite uncertain, and so should have large uncertainties (or ranges)
associated with them. The faith expressed in such poorly constrained
economics estimates by the same individuals who express strong
skepticism of results from far more physically based and testable
climate simulation models, strikes me as a remarkable inconsistency.
(b) Because you may be familiar with the 1997 study by the World
Resources Institute entitled ``The costs of climate protection: A guide
for the perplexed,'' which explains the important role of assumptions
in leading to very different cost estimates from even one economic
model, much less among different models, could you explain in a
comparative fashion how robust the findings regarding the ``hockey
stick'' behavior of the climate in the various studies carried out: by
you and fellow investigators may be to variations in the assumptions
made. It's clear that varying the assumptions among reasonable
possibilities in the economic models can change what is calculated to
be a few percent impact on the economy to a small gain; would changes
in the assumptions you are making change the indication of strong
anthropogenic warming to an indication of human-induced cooling?
Response. The millennial temperature reconstruction (or ``hockey
stick'' as it was termed by former GFDL head Dr. Jerry Mahlman) is
based on a rigorously validated statistical model with demonstrated
predictive skill based on comparisons with independent data. The
primary conclusions drawn from the reconstruction (e.g. the anomalous
nature of late 20th century warmth) are based on a conservative
appraisal of the uncertainties in the reconstruction, and are not
strongly dependent on the assumptions made. The same--conclusions have
been affirmed now by several other independent empirical and-model-
based estimates. As discussed above, this contrasts with economic
predictions which are necessarily far more sensitive to the assumptions
that go into them.
Question 16. In his opening statement, Senator Inhofe concluded
that the Soon and Baliunas paper is ``credible; well-documented; and
scientifically defensible.'' By contrast, your testimony indicated that
the experts in the field do not consider this to be the case. Does one
have to be an expert in the field to understand the apparent problems
with this paper? If not, could you summarize in terms for non-
scientists what the key problems with the paper are?
Response. The mainstream scientific research community has indeed
rejected the approach, interpretation, and conclusions advanced by Soon
and Baliunas as fundamentally unsound. The major flaws in the analysis,
as described in earlier comments in more detail, are basic enough that
they can be understood by a non-specialist. In short, the analysis by
Soon and Baliunas is unsound because (a) they inappropriately
interpreted indicators of past precipitation as evidence of past
temperature changes, (b) they did not use an approach which takes into
account the simultaneity and lack of simultaneity of variations in
different regions, and (c) they did not employ a proper standard for
evaluating recent changes (i.e., changes during the past few decades)
in the context of past variations. Indeed, they also misinterpreted
past published work, and did not provide any quantitative estimates,
let alone estimates of uncertainty. It is difficult to find anything of
scientific merit at all in their published work.
Question 17. As I understand it, the data that both you and Soon
and Baliunas draw from is the same, and it is not a question of the
data being the problem. Instead, it is apparently the processing of the
data that you are indicating has been done in a substandard way by Soon
and Baliunas. Is this correct?
Response. Keep in mind that Soon and Baliunas, unlike my
collaborators and I, don't actually analyze any data at all. They
simply claim to have `interpreted' past studies (often incorrectly).
Soon and Baliunas refer to a number of proxy data studies that describe
data which we employed in our analysis. There are also many proxy data
that we used in our study that the Soon and Baliunas do not discuss.
However, as alluded to in the question, the real issue isn't what data
were used. Numerous independent now-published studies employing widely
different assemblages of proxy climate data sets have demonstrated
(e.g, as in the Eos article discussed earlier) a similar pattern of
past variations in hemispheric mean temperature. The real issue with
Soon and Baliunas is indeed not the set of studies that they claim to
have interpreted, but rather the approach that they took to
interpreting those studies. As indicated in previous comments, Soon and
Baliunas, unlike mainstream climate researchers, did not employ a
method for isolating the actual temperature signal in the proxy records
before using the records to draw conclusions regarding past temperature
changes. Unlike mainstream researchers, they did not aggregate
information in a way that addresses whether or not variations in
different regions are simultaneous. Unlike mainstream researchers, they
did not analyze the actual modern (late 20th century) warmth in the
context of past variations. And finally, they did not even produce a
quantitative estimate of past temperature variations, let alone an
estimate of uncertainty.
Question 18. The Soon et al literature review has been described as
shifting the paradigm away from the ``hockey stick'' description of
global warming. It seems that that review simply attempted to revive an
older theory of climate change that has been discarded by NOAA, the
USGCRP, the NAS, the IPCC, etc. Please comment.
Response. The mainstream scientific community has clearly and
decisively rejected the Soon and Baliunas papers as scientifically
unsound which undermines any claims made by industry-funded special
interest groups or politicians, that the papers provide any valid
scientific conclusions, let alone the basis for a shift of the
``paradigm''. Indeed, the Soon and Baliunas papers simply promote a
number of long-discredited myths which have been replaced, in recent
decades by far more rigorous and quantitative analyses as described by
the IPCC, USGCRP, NAS, and other mainstream scientific organizations
and funding agencies. In short, the Soon & Baliunas papers simply
repackage myths that were discredited more than a decade ago.
Question 19. In an opinion-editorial by former Secretary of Energy
James Schlesinger, he suggested that ``we have only a limited grasp of
the overall forces at work, . . .'' in terms of global climate change.
Could you please summarize for us what the scientific community
considers the key forces at work over the past 1000 years, how well
these estimates are understood, and whether there is a general
consistency or inconsistency between the various forcings and the
climate estimates that you and colleagues have developed for the last
Response. Mr. Schlesinger's assertions entirely mischaracterize the
nature of our scientific knowledge, which has advanced tremendously
during the past several decades. In fact, a very large number of peer-
reviewed scientific studies have been published in the leading
scientific, journals such as Nature and Science in the past two decades
elucidating the role of natural and anthropogenic factors in observed
climate changes. Physically based models have been developed and
validated against observations, and these models reproduce complex
climate phenomena such as El Nino. These same models have been driven
with the primary ``external'' factors that are believed to govern
climate variations on timescales of decades and centuries. These
external factors include natural factors, such as the modest estimated
variations in radiative output of the Sun, which varies by a fraction
of a percent over time, variations in the frequency and intensity of
explosive volcanic eruptions, which have a several-year cooling effect
on the climate through the injection of reflective volcanic aerosols
into the stratosphere, and very small changes in the Earth's orbit
relative to the Sun that occur on multi-century timescales. These
external factors also include the ``anthropogenic'' influences of
increased greenhouse gas concentrations due to fossil fuel burning,
changes in the reflective properties of the land surface due to human
land use alterations, and the regional cooling effect of anthropogenic
sulphate aerosols in certain industrial regions. When driven with these
factors, these climate models have demonstrated a striking ability to
reproduce observed global and hemispheric temperature trends during the
20th century, as well as longer-term trends in past centuries as
reconstructed from proxy data. Such results are nicely summarized in
the 2001 IPCC scientific working group report. Mr. Schlesinger would
have benefited from a reading of this report, or the follow-up National
Academy of Sciences report that endorsed the key IPCC conclusions,
prior to writing his oped piece, which reflects a decades-old
understanding of the State of the science.
Question 20. In Dr. Soon's testimony, he speaks about there being
``warming'' and ``cooling'' for different periods. If he did not
construct an integral across the hemisphere or a real timeline; can he
say anything other than that there were some warm periods and cool
Response. Aside from not adequately distinguishing temperature
changes from hydrological changes, Dr. Soon and his collaborators
indeed did not even attempt to estimate contemporaneous patterns of
past temperature change, let alone an integral across the hemispheric
domain to assess hemispheric mean temperature changes. It is unclear
what, if any, meaningful conclusions can be drawn from the Soon and
Question 21. Dr. Soon indicates that ``local and regional, rather
than global average changes are the most relevant and practical measure
of climate change and its impact.'' Could you please comment on this,
including the relative likelihood of identifying a signal of climate
change amidst the local fluctuations? In what sense might local changes
be the most practical measure? In that the primary forcings of the
climate are global in scale, does it not make most sense to first
determine how the large-scale rather than the regional climate might be
Response. Dr. Soon's comments are truly misguided. Firstly, the
surface temperature reconstructions published by my colleagues and I
explicitly resolve regional patterns of surface temperature, so it is
entirely unclear why Dr. Soon believes that we don't address regional
climate changes. Had Dr. Soon understood our papers, he would be aware
that we do. However, unlike the study that Dr. Soon published, our
reconstructions explicitly take into account the issue of the relative
timing and simultaneity of surface temperature changes in different
regions. Only through doing this it possible to form an integrated
measure of temperature changes such as hemispheric mean temperature.
Scientists with training in climatology, statistics; and other areas of
research required in the study of paleoclimate reconstruction know that
the signal-to-noise ratio of any surface response to global radiative
climate forcing increases as the scale of spatial averaging increases,
In discussions of climate change it is thus the integral of the surface
temperature field over an entire hemisphere or globe, which constitutes
the most useful single variable for detecting, and attributing causal
factors to observed changes. The spatial signature of the surface
temperature signal (both with respect to position on the surface of the
Earth, and altitude in the atmosphere) can nonetheless help to
distinguish one source of climate forcing (e.g. solar) from another
(e.g. enhanced greenhouse gases). My colleagues and I have indeed used
the spatial patterns of surface temperature changes in past centuries
to identify the role of natural external forcing of climate [Shindell,
D.T., Schmidt, G.A., Mann, M.E, Rind, D., Waple, A., Solar forcing of
regional climate change during the Maunder Minimum, Science, 294, 2149-
2152, 2001; Waple, A., Mann, M.E., Bradley, R.S., Long-term Patterns of
Solar Irradiance Forcing in Model Experiments and Proxy-based Surface
Temperature Reconstructions, Climate Dynamics, 18, 563-578, 2002;
Shindell, D.T., Schmidt, G.A., Miller, R., Mann, M.E., Volcanic and
Solar forcing of Climate Change During the Pre-Industrial era, Journal
of Climate, in press, 2003]. Both Dr. Soon and Dr. Legates advocate in
their testimony a primary role of solar forcing in recent climate
change, though they provide no quantitative justification for this
assertion at all. In fact, nearly a dozen detailed ``detection'' and
``attribution'' studies published during the past decade by leading
climate researchers in the premier international scientific peer-
reviewed journals such as Science and Nature, have shown that the
vertical and horizontal pattern of observed warming is inconsistent
with the response of the climate to solar forcing, but is consistent,
with the response of the climate to anthropogenic forcing. Thus a
prudent use of spatial information, as described in various studies by
leading climatologists, including my collaborators and I, can
potentially help elucidate the roles of natural and anthropogenic
factors. However, Dr. Soon's studies are deficient in their use of any
such information, and provide no insights into the factors governing
past climate change.
Question 22. This year, the western United States is anomalously
hot and dry. The eastern United States is wetter than it has been since
approximately 1891 and cool. Europe is hotter and drier than it has
been in about 150 years. If we assume for the moment that these types
of anomalies would persist for 50 years, are these the types of
anomalies that Soon and Baliunas would consider as being indicative of
there being an equivalent to the Medieval Warming in the western United
States and Europe while at the same time there is the equivalent of the
Little Ice Age in eastern North America? How would your type of
approach vary in its analysis of the year 2003 compared to the
apparently contradictory results that Soon and Baliunas would have?
Response. Indeed, as my colleagues and I discussed in our peer-
reviewed articles in ``Eos'' and more recently ``Geophysical Research
Letters'' [Mann, M.E., Jones, P.D., Global Surface Temperatures over
the Past two Millennia, Geophysical Research Letters, 30 (15), 1820,
doi: 10.1029/2003GL017814, 2003] the Soon and Baliunas approach is
indeed internally contradictory in that it would separately identify
anomalies for even a given year, such as 2003, as simultaneously
supportive of conditions they would classify as associated with a
``Little Ice Age'' and a ``Medieval Warm Period'' anomaly. As outlined
in the question, this year's pattern of climate anomalies is a perfect
example. Trained climatologists and paleoclimatologists know that one
must independently evaluate precipitation or drought information from
temperature information in reconstructing past climate patterns. For
example, colleagues of mine and I have developed reconstructions of
patterns of drought over the continental U.S. in past centuries from
droughtsensitive tree-ring data [Cook, E.R., D.M. Meko, D.W. Stahle,
and M.K. Cleaveland, Drought Reconstructions for the Continental United
States, Journal of Climate, 12, 1145-1162, 1999; Zhang, Z., Mann, M.E.,
Cook, E.R., Alternative Methods of Proxy-Based Climate Field
Reconstruction: Application to the Reconstruction of Summer Drought
Over the Conterminous United States back to 1700 From Drought-Sensitive
Tree Ring Data, Holocene, in press, 2003]. The drought reconstructions
display a quite different pattern of behavior over time from
reconstructions of Northern Hemisphere mean temperatures, just as
patterns of drought over the continental U.S. during the 20th century
as recorded from instrumental data show relatively little in common
with instrumental Northern Hemisphere mean temperature estimates (for
example, the most prominent drought episode was the `dust bowl' of the
1930's, while the most prominent anomaly in the Northern Hemisphere
temperature record is the late 20th century warming). Drought and
temperature are essentially independent climate variables. The papers
by Soon and Baliunas seem not to recognize this fundamental fact.
Finally, there is an irony in the testimonies of Soon and Legates in
that they seem to be criticizing my colleagues and me for supposedly
only focusing on the reconstruction of temperature patterns, when in
fact we, and not they, have published work reconstructing past patterns
of drought, precipitation, and atmospheric circulation from proxy
climate data. However, we have made careful use of the information
contained in proxy data in independently reconstructing patterns of
temperature and patterns of drought. By contrast, Soon and colleagues
hopelessly convolute such information in their interpretations of past
Question 23. Could you provide a more detailed explanation for the
apparent Northern Hemisphere, cooling from the 1940's to 1970's? What
is the general expectation of what would have happened to the climate
in the absence of any human influences, so just continuing on from the
trend for the last 1000 years prior to human intervention?
Response. In fact, this issue has been studied by quite a number of
climate scientists for well over a decade. As I mentioned in my
testimony, a statistically significant cooling trend from 1940's to the
1970's is not evident for the globe, but only, for the Northern
Hemisphere. Dr Legates testimony on this matter is incorrect in that
regard. The observed record of global-mean temperature changes over the
past 100 years indicates a warming to about 1940; little change from
1940 to the mid-1970's, and then further warming, Legates implies in
his comments that these changes are inconsistent with our current
understanding of the factors governing climate change. This is also
incorrect. In order to understand these observed changes it is
necessary to consider all likely causal factors, both anthropogenic and
natural, Anthropogenic factors include the warming effects of
greenhouse gases and the cooling effects of sulfate aerosols. Natural
factors include changes. in the output of the Sun and the effects of
explosive volcanic eruptions (such as the El Chichon eruption in 1982
and the Mt. Pinatubo eruption in 1991). and internal variability
associated with natural climate oscillations in the ocean circulation
and various modes of coupled ocean-atmosphere variability (such as El
Nino). When all of these factors are considered, models give an
expected pattern of 20th century temperature changes that is in
remarkable agreement with the observations--and the models clearly show
the three phases noted above. In particular, the leveling off of the
warming trend over 1940-1975 turns out to be explained largely by the
relatively rapid increase in cooling effects of sulfate aerosols as the
world emerged from the Depression and WWII (and perhaps a small
contribution from natural, internal variations in ocean currents). This
cooling temporarily offset the warming due to increasing concentrations
of greenhouse gases. This was first pointed out in a paper by Dr. Tom
Wigley of the National Center for Atmospheric Research (NCAR) in Nature
in 1989 and has been verified by numerous additional studies since.
This agreement between models and observations shows quite clearly that
human factors have been the dominant cause of global-scale climate
change over the past 50 years, contrary to the repeated assertions by
Soon and Legates that they are a manifestation of natural climate
variability. In the absence of anthropogenic factors, model simulations
indicate that natural factors alone would have lead to a slight cooling
trend of global temperatures over the 20th century [Crowley, T.J.,
Causes of Climate Change Over the Past 1000 Years, Science, 289, 270-
277, 2000], in stark contrast to the dramatic warming that has been
Question 24. It was suggested at the hearing that increased
CO2 could enhance plant life, and that since plants produce
oxygen, this could lead to more O2 and less CO2.
Could you please comment on the likelihood of this and how large the
percentage changes could possibly be, recognizing that as the CO2
decreased, this would presumably mean the plants would do less well and
conditions would cool?
Response. Those suggestions (for example, Legates testimony with
regard to the role of the `CO2 fertilization' effect)
represent a misunderstanding of the factors governing carbon cycle
dynamics and their interaction with climate. In fact, careful studies
that have been performed with coupled climate/terrestrial carbon cycle
models that take into account the internal coupled interactions between
climate and carbon dioxide, accounting for multiple potential factors
such as (a) the potential `CO2 fertilization' effect in
which productivity of plants increases in a higher CO2
environment, (b) the impact of climate on productivity in which higher
surface temperatures favor enhanced plant growth, and (c) the feedback
of CO2 back on surface temperature alluded to in the
question [see chapter 3 of the 2001 IPCC working group 1 report]. Such
studies show that changes in surface temperature, through their impact
on biological productivity, have led to, at most, changes of 5 to 10
ppm in CO2--levels over the past 1000 years [see Gerber, S,
Joos, F., Bruegger, P.P., Stocker, T.F., Mann, M.E.; Sitch, S.,
Constraining Temperature Variations over the last Millennium by
Comparing Simulated and Observed Atmospheric CO2; Climate
Dynamics, 20, 281-299,2003]. Such changes are minimal in comparison
with the dramatic increases in CO2 concentrations of more
than 80 ppm associated with human activity, suggesting that the
`CO2 fertilization' effect advanced by Legates in his
testimony in reality has a minimal role, at best, in the modern changes
taking place in CO2 concentrations and climate.
Question 25. Could you please clarify your remarks regarding the
FACE experiments? When you say that increased CO2 leads to
more uptake and that they will rot, do you mean that all plants will
grow and eventually die and decay, and that increased CO2
really only ties up a bit more carbon in the process?
Response. The sequence of questions and time allotted did not allow
me to adequately explain this basic, but important point. The point I
was making in my testimony is that the supposed increase in the
terrestrial carbon reservoir due to enhanced plant growth that is
argued to occur in a higher CO2 concentration atmosphere
(the so-called `CO2 fertilization' effect) is not a long-
term, sustained effect, It is only a short-term effect that lasts only
over the generational timescales of forest stands. Any depletion of the
atmospheric carbon reservoir due to enhanced growth or productivity of
plants argued to arise from higher CO2 concentrations is
short lived, because the plant or tree eventually dies and gives its
carbon back to the atmosphere either through microbial activity
(rotting) or burning. In other words, when plants, with any potential
additional organic carbon storage that might arise from enhanced
biological activity eventually die, they don't simply pile up in place
with their carbon reservoir intact (which is what is implicitly assumed
by those who argue that `CO2 fertilization' represents a
potential long-term offset to anthropogenic CO2 increases).
Instead, this carbon is acted upon by biological, chemical, or
physical processes which serve to add the carbon back to the
atmosphere. Thus, the so-called ``CO2 fertilization''
effect, cannot serve as a permanent offset to anthropogenic increases
in the atmospheric carbon budget (i.e., atmospheric CO2
concentrations), as implied by Legates in his testimony. It may simply
act to slow, slightly, the rate of CO2 increase in the
atmosphere by slightly increasing the storage rate (but not the
residence time) of carbon in the terrestrial biosphere.
Another way to estimate the potential influence is by considering
the total amounts of carbon presently stored in vegetation. Present,
about 600 billion tons of carbon are tied up in the aboveground
vegetation. About 2-3 times this much is tied up in roots and below
ground carbon, which is a more difficult carbon pool to augment. By
comparison, scenarios for fossil fuel emissions for the 21st century
range from about 600 billion tons (if we can keep total global
emissions at current levels, which implies controls well beyond the
Kyoto Protocol calls for) to over 2500 billion tons if the world
increases its reliance on combustion of coal as economic growth and
population increase dramatically. These numbers clearly indicate that
sequestering a significant fraction of projected emissions in
vegetation is likely to be very difficult, especially as forests are
cleared to make way for agriculture and communities. While there are
possibilities of storage in wells and deep in the ocean, stabilizing
the atmospheric CO2 concentration would require gathering up
the equivalent of 1 to 2 times the world's existing above ground
vegetation and putting it down abandoned oil wells or deep in the
ocean. While CO2 fertilization will help to increase above
ground vegetation a bit, storing more than a few tens of percent of the
existing carbon would be quite surprising, and this is likely to be
more like a few percent of global carbon emissions projected for the
Question 26. Senator Thomas stated that ``[t)he rise in temperature
during the 20th century occurred between 1900 and 1940.'' Could you
please provide an indication of how much change occurred during this
period based on internationally accepted observations, and compare this
to the total change during the 20th century? Also please comment on
whether it is scientifically representative to calculate a change
starting with a cold period due to volcanic eruptions and end it during
a period devoid of volcanic eruptions and then compare it to the
century long period, which had major volcanic eruptions in both the
first and last decades of the century.
Response. A cursory review of the actual evidence (see e.g. Figure
2.1 of chapter 2 of the 2001 IPCC Scientific Working Group report)
indicates the following approximate attributes in the observed record
of global-mean temperature changes over the past 100 years: a warming
of approximately 0.3+ C to 1940, a statistically insignificant change
(given the uncertainties) from 1940 to the mid-1970's, and then an
additional warming of approximately 0.5+ C from 1970 to 2000. Senator
Thomas' claim is thus clearly mistaken. As discussed in my answer to an
earlier question, this pattern of behavior is reproduced closely by
models driven with estimates of both natural and anthropogenic forcing
of the climate during the 20th century. The period of relative stasis
in global mean temperatures from 1940 to 1970, in these model
simulations, appears to result from the cooling impact of anthropogenic
aerosols (for which there was a large increase during that time period)
as well as a cooling contribution from explosive volcanic eruptions
that occurred during that period, which tended to offset the warming
influence of increased greenhouse gas concentrations during that time
period. However, much of the overall warming of the globe during the
20th century (which is between 0.6+ C and 1.0+ C depending on the
precise instrumental data set used, and the precise endpoints of the
interval examined) is clearly a result of increased greenhouse gas
concentrations, as established in these simulations.
Question 27. Senator Thomas stated that ``there is no real
evidence'' that the greenhouse gases are affecting the climate. Could
you please summarize the available evidence explaining their probable
effect? Please include in your answer a specific example of a proxy
indicator such as tree rings and explain the various subtleties in
deriving a temperature.
Response. As discussed in my answers to previous questions, the
fact that increased greenhouse gas concentrations have a role in 20th
century warming is no longer considered as being in doubt by mainstream
researchers. Even noted contrarians such as Patrick Michaels of the
Cato Institute now agree with this conclusion. The only room for
legitimate scientific debate concerns the relative role of greenhouse
gas concentrations vs. other factors, and the rate of future warming
that may occur. Evidence establishing the role of anthropogenic
greenhouse gas increases in 20th, century warming includes the
agreement with the full spatial (horizontal and vertical) pattern of
warming with predictions from model simulations, and the fact that only
model simulations which include anthropogenic forcing can match the
observations, as discussed earlier. Evidence for an anthropogenic
influence on climate also comes from evidence of the anomalous nature
of late 20th century warmth in a very long-term context (i.e., in at
least the past millennium, and potentially the past several millennia
or longer). One such source of evidence for this conclusion comes from
proxy climate records (such as tree rings, corals, and ice cores) that
can be used to reconstruct long-term temperature patterns based on a
careful consideration of the temperature signal in those data, as
discussed in my response to earlier questions. But other evidence of
anomalous late 20th century warmth comes from indications of
unprecedented melting of mountain glaciers the world over (including
meltback in the Alps so dramatic that it recently revealed the now-
famous ``Ice Man'' who had been trapped in ice for more than 5000
years), and evidence of unusual phenological changes (e.g. the timing
of flowering of plants) during the late 20th century.
Question 28. Senator Carper asked the other two witnesses if they
thought it ``possible to emit unlimited amounts of CO2 into
our atmosphere without having any impact on climate or temperature?''
What is your expectation of what would occur? That is, how much change
in the CO2 concentration would cause how much of a response?
Response. The response of global mean surface temperature to
increased CO2 varies roughly as the logarithm of the
CO2 concentration (meaning that increments in temperature
scale with the percentage change in CO2 rather than the
change in amount itself). This is a very well known, and long
established result that follows both from basic theoretical
considerations of radiative transfer theory, and is embodied in
experiments using global climate models with varying levels of CO2
concentrations. The statistical relationship between estimated
concentrations of CO2 and the admittedly crude estimates of
global mean temperatures at various periods in the geological past or
during past glacial intervals, conform relatively well to this
theoretical relationship within estimated uncertainties [see e.g. the
textbook, ``Earth's Climate Past and Future'', by W.F. Ruddiman (WR
Freeman and Co), 2001]. I was extremely surprised when Dr. Soon
indicated that he did not know how to answer Senator Carper's question,
suggesting that he is not familiar with this fairly basic scientific
This result implies, in the absence of any other factors, a linear
increase in temperature over time in response to an exponential
increase in CO2 (which is not a bad description of the
character of the CO2 trend associated with exponentially
increasing anthropogenic activity over the past two centuries). Climate
models tell us that the ``slope'' of that linear increase is between
1.5+ C to 4.5+ C for each doubling of the CO2 concentration.
In this context, the testimony Dr. Legates that an arbitrary increase
in greenhouse gases would lead only to a ``slight'' increase in
termperature, seems especially disingenuous. Dr. Legates seems to be
suggesting that the warming would be small despite the magnitude of the
CO2 increase. Yet, both model-based studies and analyses of
how climates changes in the past may have been influenced by changes in
atmospheric composition suggest that a 1.5+ C to 4.5+ C increase in
temperature is likely for each doubling of the CO2
concentration. Thus, a quadrupling of the CO2 concentration,
which is plausible if the world chooses to derive most of its future
energy from coal, would be expected to be associated with a roughly 3+
C to 9+ C increase in global mean temperature. Does Dr, Legates
consider this a ``slightly'' increased temperature?
Question 29. In his testimony, Dr. Legates indicated that there
were historical cases where the temperature has gone up; but the
CO2 has fallen. Do you agree there were such periods and how
would you explain this?
Response. It is certainly the case that this has happened in the
past. However, it is hardly surprising, and certainly not inconsistent
with our established understanding of the various factors that
influence surface temperatures. The warming response to increased
greenhouse gas concentrations lags the actual increase in greenhouse
gas concentrations in the atmosphere potentially by several decades,
due to the sluggish response of the oceans, which have an enormous
thermal capacity compared to the atmosphere, to increased surface
radiative forcing. So warming is not expected to be contemporaneous
with changes in CO2, but instead, to lag it by several
decades. In addition, greenhouse gases are certainly not the only
factor affecting the average surface temperature of the Earth. There
are other anthropogenic factors, such as increased sulphate aerosols,
which can have a cooling effect on the climate, and natural factors,
such as volcanic activity, modest natural variations in solar output,
and internal dynamics associated with climate events such as El Nino,
which also influence the average surface temperature of the globe. At
any particular time, these other factors may outweigh the warming
effect due to increased greenhouse gases. For example, the relative
lack of warming during the period 1940-1970 appears to be related to a
combination of such factors, as discussed in my response to an earlier
question. But while these other factors tend to cancel over time, the
increased greenhouse gases lead to a systematic warming that will not
cancel out over time. It is for precisely this reason that late 20th
century warming now appears to have risen above the range of the
natural variability of past centuries.
There are two myths commonly perpetuated by climate change
contrarians with regard to the relationship between historical CO2
and temperature variations that are worth addressing in particular:
(1) Contrarians sometimes argue that the fact that the seasonal
cycle in atmospheric CO2, which is opposite of the seasonal
cycle in temperature in the Northern Hemisphere (maximum atmospheric
CO2 levels over the course of the year occur during the
Northern Hemisphere winter) implies a negative feedback of temperature
on CO2 concentration. Such an argument is based on a most
profound misunderstanding of the basic principles governing atmospheric
chemistry. Properly trained atmospheric chemists know that the seasonal
cycle in global atmospheric CO2 concentration is governed by
the breathing of the terrestrial biosphere, which exhibits a
hemispheric (and thus seasonal) asymmetry: there is a net uptake of
atmospheric CO2 (and thus a drawdown of atmospheric CO2
concentrations) by terrestrial plants during the Northern Hemisphere
summer growing season, owing to the vastly greater proportion of land
in the Northern Hemisphere. This simple fact, and nothing else,
dictates the relationship between Northern Hemisphere surface
temperatures and CO2 concentrations on seasonal timescales.
(2) Contrarians sometimes argue that the relationship between
atmospheric CO2 concentrations and temperature variations
associated with glacial/interglacial variations over the past several
hundred thousand years, as deduced from ice core measurements shows
that CO2 is an effect, rather than cause, of climate
variability. This reasoning is unsound for at least two fundamental
(a) Detailed measurements show that global atmospheric CO2
concentrations lead estimated polar temperature variations (as deduced
from ice core oxygen isotope ratios) during the long phase of increased
glaciation, consistent with greenhouse gas forcing of the atmosphere.
There is some evidence that CO2 concentrations, however, lag
estimated polar temperature variations during the rapid phase of
deglaciation (melting of the terrestrial ice sheets at the termination
of an ice age). This observation is the basis of the flawed argument
summarized below. During this more rapid `deglacial' phase, the climate
system if far from being in an equilibrium state, and the dynamics of
the climate system must be considered as representative of the a
coupled interaction between surface temperature, atmospheric
CO2, ocean circulation, and glacial mass. It is well known
by glaciologists who study this problem that the relationship between
CO2 and temperatures in such a scenario cannot be
interpreted in terms of a simple causeeffect relationship.
(b) Even during the rapid deglaciation, the oxygen isotopes from
the ice cores only provide an estimate of surface temperature
variations in the proximity of the ice core (and a very imperfect one,
owing to possible seasonal deposition biases and non-temperature
influences on isotope fractionation). They certainly do not provide an
estimate of hemispheric, let alone global, temperature variations.
Thus, a comparison of ice core estimates of CO2 and oxygen
o18 ratios cannot be used to confidently infer the relationship between
CO2 concentrations and global mean temperatures
Question 30. During the hearing, there was some contention over the
issue of the effect of surface cover changes and urban influences on
the climate? Could you please restate your position on the likely sign
and magnitude of the influence of both factors?
Response. Unfortunately misleading comments by Soon and Legates,
and the complexity of the issues involved, made it difficult for me to
convey, in the brief time allotted, the established science dealing
with the various influences on Earth's surface radiation balance and
changes therein in recent decades. Legates in his testimony confused
and misstated the nature of both natural and anthropogenic influences
on the Earth's surface energy budget and on the measurement of surface
temperatures from surface-based stations. There are several different
issues involved here, which I will attempt to clarify one at a time
(1) The claim made by Legates that the location of thermometer
measurements in urban centers biases estimates of global mean
temperature from the available meteorological observations would be
correct were this effect not already carefully accounted for. In
particular, possible urban heat island effects on global temperature
estimates have been studiously accounted for in estimates that have
been produced for more than a decade, See e.g. the 2001 IPCC report.
This is unrelated to the issue of the influence of land-use changes on
the surface radiation budget, though Legates testimony blurs the
distinction between the two issues:
(2) The implication by Legates that land-use changes (such as
urbanization) are the dominant influence on changes in the absorptive
properties of the Earth as a whole in recent decades is completely
wrong for at least two reasons:
(a) The primary factor impacting changes in the absorption of solar
insolation by the Earth's surface in modern decades is the decrease in
reflective snow and ice cover due to the warming of the Earth's
surface. This represents a well-known positive feedback (the `ice-
albedo' feedback) associated with global warming in which warming leads
to melting of snow and ice, which decreases the reflective properties
of the surface, increasing surface absorption of radiation, and: thus
increased the surface temperatures themselves. This crucial positive
feedback, which enhances the impact of greenhouse gas concentrations on
the warming of the surface, is fully accounted for in the climate model
simulations that I have referred to above and in my testimony.
(b) While urbanization, as suggested by Legates, may lead to
increased absorption of solar insolation in some urban areas, this is
the more minor of the human land use changes impacting climate. There
are far more extensive regions of the Earth where other changes in land
use, such as conversion of forested land to agricultural land, have,
instead, increased the reflective properties of the Earth's surface
[Ramankutty, N., and J. A. Foley Estimating historical changes in
global land cover: croplands from 1700 to 992, Global Biogeochemical
Cycles, 13, 997-1027, 1999.], tending to cool the surface, as I
explained in my testimony. Scientists who have studied the influences
of these effects have found that the latter cooling effect is the
dominant of these two anthropogenic land-use influences on the Earth's
surface properties. Thus, climate model simulations investigating the
influence of land-use changes on hemispheric or global mean
temperatures indicate that they have imposed a modest cooling influence
[Govindasamy, B., P.B. Duffy, and K. Caldeira, Land use changes and
Northern Hemisphere cooling, Geophysical Research Letters, 28, 291-294,
2001; Bauer, E, M. Claussen, and V. Brovkin, Assessing climate forcings
of the Earth system for the past millennium, Geophys. Res. Lett., 30,
doi: 10.1029/2002GL016639, 2003] that partially offsets even greater
warming that would have been realized during the 20th century due to
anthropogenic greenhouse gas influences, Evidence, therefore, does not
support the case, as argued by Legates, that the full range of human
land use changes have had a net warming effect on the climate. They
have had a modest cooling influence on the climate.
Question 31. Do you receive any income from any sources which have
taken advocacy positions with respect to the Kyoto Protocol, the U.N.
Framework Convention on Climate Change, or legislation before the U.S.
Congress that would affect greenhouse gas emissions? If so, please
identify those sources and the relevant advocacy position taken.
Response. I do not, nor have I ever, received any such income.
Statement of David R. Legates, Director, Center for Climatic Research,
University of Delaware
Distinguished Senators, panelists, and members of the audience: I
would like to thank the Committee for inviting my commentary on this
important topic of climate history and its implications. My name is
David R. Legates and I am an Associate Professor and Director of the
Center for Climatic Research at the University of Delaware in Newark,
Delaware. My research interests have focused on hydroclimatology--the
study of water in the atmosphere and on the land--and on the
application of statistical methods in climatological research.
I am familiar with the testimony presented here by Dr. Soon. I
agree with his statements and I will not reiterate his arguments. My
contributions to Dr. Soon's research stemmed from my grappling with the
apparent technology between the long-standing historical record and the
time-series recently presented by Dr. Mann and his colleagues. It also
stems from my own experiences in compiling and merging global estimates
of air temperature and precipitation from a variety of disparate
My Ph.D. dissertation resulted in the compilation of high-
resolution climatologies of global air temperature and precipitation.
From that experience, I have become acutely aware of the issues
associated with merging data from a variety of sources and containing
various biases and uncertainties. By its very nature, climatological
data exhibit a number of spatial and temporal biases that must be taken
into account. Instrumental records exist only for the last century or
so and thus proxy records can only be used to glean information about
the climate for earlier time periods. But it must be noted that proxy
records are not observations and strong caveats must be considered when
they are used. It too must be noted that observational data are not
without bias either.
THE HISTORICAL RECORD OF THE LAST MILLENNIUM
Much research has described both the written and oral histories of
the climate as well as the proxy climate records (e.g., ice cores, tree
rings, and sedimentations) that have been derived for the last
millennium. It is recognized that such records are not without their
biases--for example, historical accounts often are tainted with the
preconceived beliefs and limited experiences of explorers and
historians while trees and vegetation respond not just to air
temperature fluctuations, but to the entire hydrologic cycle of water
supply (precipitation) and demand (which is, in part, driven by air
temperature). Nevertheless, such accounts indicate that the climate of
the last millennium has been characterized by considerable variability
and that extended periods of cold and warmth existed. It has been
generally agreed that during the early periods of the last millennium,
air temperatures were warmer and that temperatures became cooler toward
the middle of the millennium. This gave rise to the terms the
``Medieval Warm Period'' and the ``Little Ice Age'', respectively.
However, as these periods were not always consistently warm or cold nor
were the extremes geographically commensurate in time, such terms must
be used with care.
A BIASED RECORD PRESENTED BY THE IPCC AND NATIONAL ASSESSMENT
In a change from its earlier report, however, the Third Assessment
Report of the Intergovernmental Panel on Climate Change (IPCC), and now
the U.S. National Assessment of Climate Change, both indicate that
hemispheric or global air temperatures followed a curve developed by
Dr. Mann and his colleagues in 1999. This curve exhibits two notable
features. First is a relatively flat and somewhat decreasing trend in
air temperature that extends from 1000AD to about 1900AD and is
associated with a relatively high degree of uncertainty. This is
followed by an abrupt rise in air temperature during the 1900's that
culminates in 1998 with the highest temperature on the graph. Virtually
no uncertainty is shown for the data of the last century. The
conclusion reached by the IPCC and the National Assessment is that the
1990's are the warmest decade with 1998 being the warmest year of the
Despite the large uncertainty, the surprising lack of variability
in the record gives the impression that climate remained relatively
unchanged through most of the last millennium--at least until human
influences began to cause an abrupt increase in temperatures during the
last century. Interestingly, Mann et al. replace the proxy data for the
1900's by the instrumental record and no uncertainty characterization
is provided. This too yields a false impression that the instrumental
record is consistent with the proxy data and that it is `error free'.
It is neither. The instrumental record contains numerous uncertainties,
resulting from a lack of coverage over the world's oceans, an under-
representation of mountainous and polar regions as well as under-
developed nations, and the presence of urbanization effects resulting
from the growth of cities. Even if a modest uncertainty of a
0.1+ C were imposed on the instrumental record, the claim
of the 1990's being the warmest decade would immediately become
questionable, as the uncertainty window would overlap with the
uncertainty associated with earlier time periods. Note that if the
satellite temperature record--where little warming has been observed
over the last 20 years--had been inserted instead of the instrumental
record, it would be impossible to argue that the 1990's are the warmest
RATIONALE FOR THE SOON ET AL. INVESTIGATION
So we were left to question why the Mann et al. curve seems to be
at variance with the previous historical characterization of climatic
variability. Investigating more than several hundred studies that have
developed proxy records, we came to the conclusion that nearly all of
these records show considerable fluctuations in air temperature over
the last millennium. Please note that we did not reanalyze the proxy
data--the original analysis from the various researchers was left
intact. Most records show the coldest period is commensurate with at
least a portion of what is termed the ``Little Ice Age'' and the
warmest conditions are concomitant with at least a portion of what is
termed the ``Medieval Warm Period''.
But our conclusion is entirely consistent with conclusions reached
by Drs. Bradley and Jones that not all locations on the globe
experienced cold or warm conditions simultaneously. Moreover, we chose
not to append the instrumental record, but to compare apples-with-
apples and determine if the proxy records themselves indeed confirm the
claim of the 1990's being the warmest decade of the last millennium.
That claim is not borne out by the individual proxy records.
However, the IPCC report, in the chapter with Dr. Mann as a lead
author and his colleagues as contributing authors, also concludes that
research by Drs. Mann, Jones, and their colleagues ``support the idea
that the 15th to 19th centuries were the coldest of the millennium over
the Northern Hemisphere overall.'' Moreover, the IPCC report also
concludes that the Mann and Jones research ``show[s] temperatures from
the 11th to 14th centuries to be about 0.2+ C warmer than those from
the 15th to 19th centuries.'' This again is entirely consistent with
our findings. Where we differ with Dr. Mann and his colleagues is in
their construction of the hemispheric averaged time-series, their
assertion that the 1990's are the warmest decade of the last
millennium, and that human influences appear to be the only significant
factor on globally averaged air temperature. Reasons why the Mann et
al. curve fails to retain the fidelity of the individual proxy records
are detailed statistical issues into which I will not delve. But our
real difference of opinion focuses solely on the Mann et al. curve and
how we have concluded it misrepresents the individual proxy records. In
a very real sense, this is an important issue that scientists must
address before the Mann et al. curve is taken as fact.
Our work has been met with much consternation from a variety of
sources and we welcome healthy scientific debate. After all, it is
disagreements among scientists that often lead to new theories and
discoveries. However, I am aware that the editors of the two journals
that published the Soon et al. articles have been vilified and the
discussion has even gone so far as to suggest that Drs. Soon and
Baliunas be barred from publishing in the journal Climate Research.
Such tactics have no place in scientific debate and they inhibit the
free exchange of ideas that is the hallmark of scientific inquiry.
CLIMATE IS MORE THAN MEAN GLOBAL AIR TEMPERATURE
In closing, let me state that climate is more than simply annually-
averaged global air temperature. Too much focus has been placed on
divining air temperature time-series and such emphasis obscures the
true issue in understanding climate change and variability. If we are
truly to understand climate and its impacts and driving forces, we must
push beyond the tendency to distill it to a single annual number. Proxy
records, which provide our only possible link to the past, are
incomplete at best. But when these records are carefully and
individually examined, one reaches the conclusion that climate
variability has been a natural occurrence, and especially so over the
last millennium. And given the uncertainties in the proxy and
instrumental records, an assertion of any decade as being the warmest
in the last millennium is premature.
I'm sorry that a discussion that is best conducted among scientists
has made its way to a U.S. Senate committee. But hopefully a healthy
scientific debate will not be compromised and we can push on toward a
better understanding of climate change.
I again thank you for the privilege of speaking before you today.
Prepared Statement of Leonard Levin, Ph.D., Technical Leader, EPRI,
Palo Alto, California
I am Leonard Levin, technical leader at EPRI, which is a non-
profit, collaborative organization conducting energy-related R&D in the
public interest. Our members are public and private organizations in
the electricity and energy fields, and we now serve more than 1000
energy and governmental organizations in more than 40 countries. These
remarks constitute a synthesis of current research on environmental
mercury, and are not a representation of official EPRI position.
As a global pollutant, the impact of mercury on the human
environment is a critical issue that EPRI and the scientific community
have been examining for many years. As the scientific understanding of
where mercury originates nationally and globally, combined with the new
health data, continues to be refined, it can help inform decisions
regarding its management. I would like to address three key questions
where new findings have emerged. First, where does mercury found in the
U.S. environment originate? Second, how much has mercury in fish
changed in the last few decades? And third, how do potential mercury
management steps change the amount of mercury depositing to the earth's
surface in the U.S.?
WHERE DOES MERCURY IN THE U.S. ENVIRONMENT ORIGINATE?
Mercury is clearly a global issue. Recent estimates are that, in
1998, some 2340 tons of mercury were emitted globally through
industrial activity; of these, more than half, or 1230 tons, came from
Asian countries, primarily China\1\. These findings are similar to
those of other global inventories\2\. In addition, it is estimated that
another 1300 tons of mercury emanates from land-based natural sources
globally, including abandoned mining sites and exposed geological
formations. Another 1100 tons or so issues from the world's oceans,
representing both new mercury emitted by undersea vents and volcanoes,
and mercury cycled through the ocean from the atmosphere previously.
Recent findings from the large United States-Canadian METAALICUS field
study in Ontario, Canada showed that a fairly small amount of deposited
mercury, no more than 20 percent or so, re-emits to the atmosphere,
even over a 2-year period. The implications of this are profound:
mercury may be less mobile in the environment than we previously
thought; once it is removed from the atmosphere, it may play less of a
role in the so-called ``grasshopper effect\3\ '' where persistent
global pollutants are believed to successively deposit and re-emit for
many years and over thousands of miles.
\1\ Christian Seigneur, C., K. Vijayaraghavan, K. Lohman, Pr.
Karamchandani, C. Scott, Global Source Attribution for Mercury
Deposition in the United States, submitted to Environ. Sci. Technol.,
\2\ Jozef M. Pacyna, Elisabeth G. Pacyna, Frits Steenhuisen and
Simon Wilson, Mapping 1995 global anthropogenic emissions of mercury,
Atmospheric Environment 37 (S1) (2003) pp. 109-117.
\3\ Environment Canada, The Grasshopper Effect and Tracking
Hazardous Air Pollutants, The Science and the Environment Bulletin,
Recent studies by EPRI have shown that the mercury depositing into
the U.S. from the atmosphere may originate at very distant points.
Model assessments show that, for \3/4\ of the area of the continental
United States, more than 60 percent of the mercury received originates
outside U.S. borders, from other countries or even other continents.
Only 8 percent of U.S. territory receives \2/3\ or more of its mercury
from U.S. domestic sources, and less than 1 percent of U.S. territory
gets 80 percent or more of its mercury from sources within the U.S. One
implication of this dichotomy between mercury sources and the U.S.
areas impacted is that there may be a ``management floor'' for U.S.
mercury, a level below which the amount of mercury depositing to the
surface cannot be reduced.
Additional evidence for the external origins of much of the mercury
in the U.S. environment was gathered over the last 2 years by aircraft
experiments carried out by EPRI, the National Center for Atmospheric
Research, and a number of U.S., Asian, and Australian investigators.
One set of flights measured significant mercury in winds entering the
Pacific Ocean from Shanghai; China; researchers tracked the Chinese
mercury plume over the Pacific for 400 miles toward America. A second
set of flights from Monterey, California, found that same plume from
China crossing the California coast, and a second, higher plume of
enriched mercury originating in Central Asia also moving into the U.S.
The global nature of mercury in the U.S. has been clearly demonstrated.
WHAT ARE THE PRIMARY SOURCES OF MERCURY IN FISH AND THE ENVIRONMENT?
For much of the twentieth century, mercury was an essential part of
industrial products, such as batteries and switches, or a key
ingredient in such other products as house paints. These industrial
uses of the element declined significantly in the latter half of the
century, and are now less than 10 percent of their use of fifty years
ago.\4\ Professor Francois Morel of Princeton University and colleagues
recently analyzed newly caught Pacific tuna for mercury\5\, and
compared those results to the mercury content of similar tuna caught in
the 1970's. Despite changes in mercury emissions to the atmosphere in
those thirty years\6\, and a matching increase in the mercury
depositing; from the atmosphere to rivers and oceans below, Prof Morel
found that mercury levels in tuna have not changed over that time. One
conclusion is that the mercury taken up by such marine fish as tuna is
not coming from sources on land, such as utility power plants, but from
natural submarine sources of mercury, including deep sea volcanoes and
ocean floor vents. The implications are that changes in mercury sources
on the continents will not affect the mercury levels found in open
ocean foodfish like tuna.
\4\ Engstrom, D.R., E.B. Swain, Recent Declines in Atmospheric
Mercury Deposition in the Upper Midwest, Environ. Sci. Technol. 1997,
\5\ Kraepiel, A.M.L., K. Keller, H.B. Chin, E.G. Malcolm, F.M.M.
Morel, Sources and Variations of Mercury in Tuna, Meeting of American
Society for Limnology and Oceanography, Salt Lake City, Utah: January
\6\ Slemr, F., E-G. Brunke, R. Ebinghaus, C. Temme, J. Munthe, I.
Wangberg, W. Schroeder, A. Stgeffen, T. Berg, Worldwide trend of
atmospheric mercury since 1977, Geophys. Res. Ltrs., 30 (10), 23-1 to
An estimate in 2001 by scientists of the Geological Survey of
Canada and others\7\ estimated that geological emissions of mercury, as
well as emissions from inactive industrial sites on land, are five to
seven times as large as had been estimated earlier. Recent measurements
in the stratosphere by EPRI researchers show a rapid removal of mercury
in the upper atmosphere, allowing for additional sources at the surface
while still maintaining the measured rates of deposition and removal
needed for a global balance of sources and sinks. As a result, it is
now possible to attribute a greater fraction of the mercury entering
U.S. waters to background natural sources rather than industrial
emissions from the U.S. or elsewhere globally.
\7\ Richardson G. M., R. Garrett, I. Mitchell, M. Mah-Paulson, T.
Hackbarth, Critical Review On Natural Global And Regional Emissions Of
Six Trace Metals To The Atmosphere, International Lead Zinc Research
Organization, International Copper Association, Nickel Producers
Environmental Research Association.
HOW COULD POTENTIAL MERCURY REDUCTIONS CHANGE MERCURY DEPOSITION?
EPRI recently completed work to assess the consequences, of further
mercury emissions reductions for mercury in the atmosphere, U.S.
waterways, and fish\8\. The approach used linked models of atmospheric
mercury chemistry and physics with analyses of Federal data on mercury
in fish in the U.S. diet, along with a model of costs needed to attain
a given reduction level.
\8\ EPRI Technical Report 1005224, ``A Framework for Assessing the
Cost-Effectiveness of Electric Power Sector Mercury Control Policies,''
EPRI, Palo Alto, CA, May 2003.
Current U.S. utility emissions of mercury are about 46 tons per
year. At the same time, a total of about 179 tons of mercury deposit
each year in the U.S., from all sources global and domestic. One
proposed management scenario examined cutting these utility emissions
by 47 percent, to 24 tons per year. The analysis showed that this cut
results in an average 3 percent drop in mercury deposition into the
U.S. Some isolated areas totaling about 1 percent of U.S. land area
experience drops of up to 30 percent in mercury deposited. The cost
model used in association with these calculations showed utility costs
to reach these emission control levels would amount to between $2
billion and $5 billion per year over 12 years. This demonstrated that
U.S. mercury patterns are relatively insensitive to the effects of this
single category of sources.
In addition, most of the fish consumed in the U.S. comes from ocean
sources, which would be only marginally affected by a global reduction
of 24 tons of mercury per year due solely to U.S. controls. Wild fresh
water fish in the U.S. would be expected to show a greater reduction in
mercury content, but are a relatively small part of the U.S. diet
compared to ocean or farmed fish. When these changes were translated
into how much less mercury enters the U.S. diet, we found that 0.064
percent fewer children would be born ``at risk'' due to their mothers
taking in less mercury from consumed fish. These results were based on
the Federal dietary fish consumption data. So, a drop of nearly half in
utility mercury emissions results in a drop of 3 percent (on average)
in mercury depositing to the ground, and a drop of less than one-tenth
of a percent in the number of children ``at risk.''
DECISIONMAKING UNDER UNCERTAINTY
These recent findings on mercury sources, dynamics, and management
are a small part of the massive international research effort to
understand mercury and its impacts on the human environment. EPRI and
others, including the U.S. Environmental Protection Agency and the U.S.
Department of Energy, are racing to clarify the complex interactions of
mercury with geochemical and biological systems, vital to understanding
mercury's route to human exposure and potential health effects. With
this improved understanding, informed decisions can be made on the best
ways to manage mercury.
Thank you for the opportunity to deliver these remarks to the
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Statement of Deborah C. Rice, Ph.D., Maine Department of
Environmental Protection, Augusta, Maine
I would like to thank the Committee for this opportunity to
present information on the adverse health consequences of exposure to
methylmercury in the United States. Until 3 months ago, I was a senior
toxicologist in the National Center for Environmental Assessment in the
Office of Research and Development at the Environmental Protection
Agency. I am a co-author of the document that reviewed the scientific
evidence on the health effects of methylmercury for EPA, and which
included the derivation of the acceptable daily intake level for
I would like to focus my presentation on four points that are key
to understanding the health-related consequences of environmental
mercury exposure. One: there is unequivocal evidence that methylmercury
harms the developing human brain. Two: the Environmental Protection
Agency used analyses of three large studies in its derivation of an
acceptable daily intake level, including the study in the Seychelles
Islands which found no adverse effects. Three: 8 percent of women of
child-bearing age in the United States have levels of methylmercury in
their bodies above this acceptable level. And four: cardiovascular
disease in men related to low levels of methylmercury has been
documented, suggesting that a potentially large segment of the
population may be at risk for adverse health effects.
The adverse health consequences to the nervous system of
methylmercury exposure in humans were recognized in the 1950's with the
tragic episode of poisoning in Minamata Bay in Japan, in which it also
became clear that the fetus was more sensitive to the neurotoxic
effects of methylmercury than was the adult. A similar pattern of
damage was apparent in subsequent episodes of poisoning in Japan and
Iraq. These observations focused the research community on the question
of whether exposure to concentrations of methylmercury present in the
environment might be producing neurotoxic effects that were not
As a result, over half a dozen studies have been performed around
the world to explore the effects of environmental methylmercury intake
on the development of the child. Studies in the Philippines (Ramirez et
al., 2003), the Canadian Arctic (McKeown-Eyssen et al., 1983), Ecuador
(Counter et al., 1998), Brazil (Grandjean et al., 1999), French Guiana
(Cordier et al., 1999) and Madeira (Murata et al., 1999) all found
adverse effects related to the methylmercury levels in the children's
bodies. These included auditory and visual effects, memory deficits,
deficits in visuospatial ability, and changes in motor function.
In addition to the above studies, there have been three major
longitudinal studies on the effects of exposure to the mother on the
neuropsychological function of the child: in the Faroe Islands in the
North Atlantic (Grandjean et al., 1997), in the Seychelles Islands in
the Indian Ocean (Myers et al., 1995), and in New Zealand (Kjellstrom
et al., 1989). Two of these studies identified adverse effects
associated with methylmercury exposure, whereas the Seychelles Islands
study did not. Impairment included decreased IQ and deficits in memory,
language processing, attention, and fine motor coordination. A National
Research Council (NRC) National Academy of Sciences panel evaluated all
three studies in their expert review, concluding that all three studies
were well designed and executed (NRC, 2000). They modeled the
relationship between the amount of methylmercury in the mother's body
and the performance of the child on a number of neuropsychological
tests. From this analysis, they calculated a defined adverse effect
level from several types of behavior in each of the three studies.
These adverse effect levels represent a doubling of the number of
children that would perform in the abnormally low range of function.
The National Academy of Sciences panel also calculated an overall
adverse effect level of methylmercury in the mother's body for all
three of the studies combined, including the negative Seychelles study.
Thus the results of all three studies were included in a quantitative
manner by the NRC.
The Environmental Protection Agency (EPA) used the analyses of the
NRC in the derivation of the reference dose, or RfD, for methylmercury.
The RfD is a daily intake level designed to be without deleterious
effects over a lifetime. The EPA divided the defined deleterious effect
levels calculated by the NRC by a factor of 10 in its RfD derivation.
There are two points that need to be made in this regard. First, the
factor of 10 does not represent a safety factor of 10, since the
starting point was a level that doubled the number of low-performing
children. Second, the EPA performed the relevant calculations for a
number of measurements for each of the two studies that found
deleterious effects as well as the integrative analysis that included
all three studies modeled by the NRC, including the negative Seychelles
study. The RfD is 0.10 g/kg/day based on the Faroe Islands study alone
or the integrative analysis of all three studies. The RfD would be
lower than 0.10 g/kg/day if only the New Zealand study had been
considered. Only if the negative Seychelles Islands study were used
exclusively for the derivation of the RfD, while ignoring the values
calculated for the Faroe Islands and New Zealand studies, would the RfD
be higher than the current value of 0.10 g/kg/day. EPA believes that
to do so would be scientifically unsound, and would provide
insufficient protection to the U.S. population.
A substantial portion of U.S. women of reproductive age have
methylmercury in their bodies that is above the level that corresponds
to the EPA's RfD. Data collected over the last 2 years as part of the
National Health and Nutritional Examination Survey (NHANES 99+)
designed to represent the U.S. population (CDC, Web) revealed that
about 8 percent of women of child-bearing age had blood levels of
methylmercury above the level that the U.S. EPA believes is ``safe''
(Schober et al., 2003). This translates into over 300,000 newborns per
year potentially at risk for adverse effects on intelligence and
memory, ability to pay attention, ability to use language, and other
skills that are important for success in our highly technological
I would like to further comment here on the use of a factor of 10
by EPA to derive the allowable daily intake level (RfD) for
methylmercury from the defined effect levels calculated by the National
Research Council. The RfD corresponds to roughly 1 part per million
(ppm) of methylmercury in maternal hair, from the defined effect level
of about 11 ppm calculated by the NRC. But we know that there is no
evidence of a threshold below which there are no adverse effects down
to about 2-3 ppm in hair, the lowest levels in the Faroe Islands study.
In fact, there is evidence from both the Faroe Islands (Budtz-Jorgensen
et al., 2000) and New Zealand (Louise Ryan, Harvard University,
personal communication) studies that the change in adverse effect in
the child as a function of maternal methylmercury level may be greater
at lower maternal methylmercury levels than at higher ones. Therefore,
the so-called safety factor almost certainly is less than 10, and may
be closer to non-existent. Babies born to women above the RfD may be at
actual risk, and not exposed to a level 10 times below a risk level.
There is an additional concern regarding the potential for adverse
health consequences as a result of environmental exposure to
methylmercury. Several years ago, a study in Finnish men who ate fish
found an association between increased methylmercury levels in hair and
atherosclerosis, heart attacks, and death (Salonen et al., 1995, 2000).
Two new studies in the U.S. and Europe found similar associations
between increased methylmercury levels in the bodies of men and
cardiovascular disease (Guallar et al., 2002; Yoshizawa et al., 2002).
Effects have been identified at hair mercury levels below 3 ppm. It is
not known whether there is a level of methylmercury exposure that will
not cause adverse effects. It is important to understand that the
cardiovascular effects associated with methylmercury may put an
additional, very large proportion of the population at risk for adverse
health consequences as a result of exposure to methylmercury from
In summary, there are four points that I would like the Committee
to keep in mind. First, at least eight studies have found an
association between methylmercury levels and impaired
neuropsychological performance in the child. The Seychelles Islands
study is anomalous in not finding associations between methylmercury
exposure and adverse effects. Second, both the National Research
Council and the Environmental Protection Agency included the Seychelles
Islands study in their analyses. The only way the acceptable level of
methylmercury could be higher would be to ignore the two major positive
studies that were modeled by the NRC, as well as six smaller studies,
and rely solely on the single study showing no negative effects of
methylmercury. Third, there is a substantial percentage of women of
reproductive age in the United States with levels of methylmercury in
their bodies above what EPA considers a safe level. As a result of
this, over 300,000 newborns each year are exposed to methylmercury
above levels U.S. EPA believes to be ``safe''. Fourth, increased
exposure to methylmercury may result in atherosclerosis, heart attack,
and even death from heart attack in men, suggesting that an additional
large segment of the population may be at risk as a result of
environmental methylmercury exposure.
Thank you for your time and attention.
Responses by Deborah Rice to Additional Questions from Senator Jeffords
Question 1. In testimony, you indicated that ``there might be
virtually no safety factor at all'' with respect to the effect level
for mercury exposure. Does that mean that the reference dose should be
lowered further? If so, what would be a safer and more protective
Response. The current reference dose (RfD) is based on a cord blood
mercury concentration associated with a defined risk: a doubling of the
number of children performing in the abnormally low range. A total
uncertainty factor of 10 was applied to account for inter-individual
variability. There are several decisions made by EPA that, if
different, would have resulted in a lower RfD.
(a) It was assumed that the ratio of cord-to-maternal blood mercury
was one. Subsequent analyses of 10 studies revealed that cord blood has
more mercury compared to maternal blood. The average ratio is 1.7:1.0,
with the upper 5 percent of women having a ratio of 3.3:1.0. Based on
just the average ratio, if no other decisions were changed, the RfD
would be reduced from 1.0 g/kg/day to 0.6 g/kg/day.
(b) As was recommended by the NAS expert committee, EPA assumed
that there was a linear relationship between adverse effects on a
number of neuropsychological endpoints and the level of mercury in cord
blood or maternal hair. In fact, the data from the Faroe Island study
best fit a supra-linear model: i.e., the slope was actually greater at
lower body burdens (see figure below). It turns out that this was also
true for the New Zealand study. Recently, a study was published
reporting a supra-linear shape to the relationship between adverse
behavioral performance and blood lead levels in children. So this
phenomenon, while somewhat counter-intuitive, may be real. Using the
``best fit'' model rather than forcing a linear relationship would
result in a lower estimate of the defined adverse starting point (a
doubling of the number of children performing in the abnormally low
range), and thereby a lower RfD.
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(c) EPA used a total uncertainty factor (UF) of 10 to derive the
RfD, which is designed to provide a margin of safety against adverse
effects. EPA typically applies an UF of 10 for inter-individual
variability if the starting point is a no-observable-adverse-effect-
level (NOAEL). If the starting point is the lowest level that has been
demonstrated to produce an effect, with a NOAEL not identified, the EPA
applies an additional UF, usually 10. In the case of methylmercury,
even though the starting point was a level associated with an effect,
only a total factor of 10 was applied, rather than the more typical
100. In addition, the UF of 10 for inter-individual variability is
presumed to account for differences in both metabolism and response of
the target organ (sensitivity) between individuals. The variability in
metabolism of methylmercury between women has been demonstrated to be
about 3. The variation in cord-maternal blood levels between women may
be also about 3. These would be multiplied together to equal about 10.
That allows no room for any variation in response of the fetal brain to
methylmercury, which is undoubtedly not the case. Therefore a total UF
of 10 is almost certainly inadequate to protect the most sensitive
portion of the population.
The issue of whether the reference dose should be lowered, and if
so, the appropriate value, requires thorough evaluation by a group of
expert risk assessors and other scientists. Any new evaluation of the
RfD should also include evaluation of the levels of methylmercury that
produce adverse cardiovascular effects documented in several studies of
adult males. It is currently unknown whether these effects occur at
lower or higher levels than those that produce developmental
Question 2. What is a reasonable estimate of the approximate
average mercury concentrations in non-commercial fish in the U.S.?
Response. EPA keeps an extensive data base of fish tissue
contaminant levels from inland water bodies compiled by individual
states (http://www.epa.gov/ost/fish/mercurydata.html). Data for average
levels of mercury for 1987-2000 are in the attached figure. Average
tissue levels vary significantly depending on species, such that
deriving an ``average'' for all species is not particularly
informative. Averages for different species range from 0.1 ppm for
herring and whitefish to 0.9 ppm for bowfin. As can be seen from the
figure, the average level for many species is below the 0.3 ppm level
recommended by EPA (Water Quality Criterion for the Protection of Human
Health: Methylmercury, OST, Office of Water, 2001, EPA-823-R-01-001).
Approximately one third of species have average concentrations above
this. Even for species with averages below 0.3 ppm, some samples will
exceed this level. For species with averages about 0.5 ppm, more than
half the samples will exceed the EPA recommended limit, whereas half
the samples will exceed the 0.5 ppm action limit set by many European
countries and Canada. Ocean fish and sharks can have levels that are
considerably higher. For example, blue marlin average 3.08 ppm, with
the highest level for an individual at 6.8 ppm (Florida Marine Research
Institute Technical Reports' Mercury Levels in Marine and Estuarine
Fishes of Florida. 1989-2001: FMRI Technical Report TR-9, Second
Edition, Revised, 2003). Sharks such as white shark averaged over 5
ppm, with the highest value for a shark at 10 ppm (ibid.) These are
non-commercial sport-caught species.
Question 3. You indicated that the NHANES data does not adequately
capture the individuals or subpopulations that are likely to be the
most exposed to non-commercial fish mercury concentrations above the
reference dose. Are you aware of any work underway to collect this kind
of data and hopefully protect these people from overexposure?
Response. There have been a number of relatively small studies
focusing on fish intake by groups that consume large amounts of fish,
specifically sports fishers and subsistence fishing communities. Most
of these efforts have been by individual states or tribes. EPA is
developing a data base of these studies, most of which are unpublished
and not in the public domain, a project which I managed before leaving
the agency. The data base currently includes about 70 studies (contact
project officer Cheryl Itkin, EPA/ORD/National Center for Environmental
Assessment, Washington, D.C. at email@example.com).
There are also several published studies: Bellanger, T.M., Caesar,
E.M., Trachtman, L. 2000. Blood mercury levels and fish consumption. J.
La. Med. Soc, 152:64-73; Burge, P., Evans, S. 1994. Mercury
contamination in Arkansas gamefish. A public health perspective. J.
Ark. Med. Soc. 90:542-544; Hightower, J.M., Moore, D. 2003. Mercury
levels in high-end consumers offish. Environ. Health Perspect. 111:604-
608; and Knobeloch, L.M., Ziamik, M., Anderson, H.A., Dodson, V.N.
1995. Imported seabass as a source of mercury exposure: A Wisconsin
case study. Environ. Health Perspect. 103:604-606.
Protecting individuals who may be at greater risk from over-
exposure to methylmercury presents significant challenges. Forty states
have fish advisories for inland waters, based largely on levels of
mercury in fish. Some states have levels that are specific to
particular water bodies, others have statewide advisories for all water
bodies. Advisories typically are set with regard to species of fish,
designating them as e.g. ``no restriction'', ``eat no more than once a
week'', or ``eat no more than once a month''. If a person eats a fish
from one restricted category they are meant not to eat fish from
another restricted category in that month. Signs are posted by some
states at specific water bodies, and most if not all states distribute
literature related to fish advisories with fishing licenses. Some
tribes have also performed significant outreach related to issues of
contaminants in wild foods. Immigrant communities are often the most
difficult to inform, as a result of language and cultural barriers.
Minnesota, for example, has made a substantial effort to work with
immigrant communities, publishing appropriate information in relevant
languages, as well as performing extensive outreach activities. A few
other states have made efforts in this regard as well. Some communities
rely on fish as a significant protein source for both cultural and
economic reasons. It is unfortunate indeed that these communities are
risking adverse health outcomes by consuming what should be a very
Question 4. Please describe the purposes and intended uses of the
various Federal agencies' exposure limits for methyl mercury.
Response. EPA, FDA, and ATSDR have set exposure limits for
methylmercury. The reference dose (RfD) set by EPA is designed to
represent an ``estimate of a daily exposure to the human population
(including sensitive subgroups) that is likely to be without
appreciable risk of deleterious [non-cancer] effects during a
The minimal risk level (MRL) of ATSDR is ``an estimate of the daily
human exposure to a hazardous substance that is likely to be without
appreciable risk of adverse noncancer health effects over a specified
duration of exposure''. MRLs may be derived for acute (1-14 days),
intermediate (15-364 days) or chronic durations (over 364 days). ATSDR
states that ``[t]hese substance-specific estimates, which are intended
to serve as screening levels, are used by ATSDR health assessors and
other responders to identify health effects that may be of concern at
hazardous waste sites. It is important to note that MRLs are not
intended to define clean-up or action levels for ATSDR or other
Agencies.'' [bold original] (http://www.atsdr.cdc.gov/mrls.html) It is
critical to understand that ATSDR is involved in clean-up activities.
The MRLs are designed to identify chemicals that are important for
clean-up decisions. They are not intended as health-protective levels
for the general population, or for a lifetime.
The FDA acceptable daily intakes (ADI) is ``the amount of a
substance that can be consumed daily over a long period of time without
appreciable risk'' (http://www.fda.gov; http://www.cfsan.fda.gov/-
acrobat/hgstud16.pdf). For contaminants in food, FDA uses the ADI to
derive an Action Level, ``which defines the maximum allowable
concentration of the contaminant in commercial food.'' In other words,
the Action Level is supposed to be health-based.
The RfD and the ADI are designed to protect the general population
from adverse effects from contaminants in food over a lifetime of
exposure, including protection of sensitive populations. In contrast,
the MRL is designed for a different purpose: identifying contaminants
that may be important in making decisions regarding clean-up of
The exposure limits from U.S. agencies are as follows:
EPA RfD: 0.1 g/kg/day
ATSDR MRL: 0.3 g/kg/day
FDA ADI: 0.4 g/kg/day
Question 5. What is the preferred measurement methodology for most
reliably determining and predicting the effect on children's
developmental health of methyl mercury exposure?
Response. There has been considerable discussion within the
academic and regulatory communities regarding what might be a ``best''
test or test battery for determining adverse neuropsychological
function in children exposed to methylmercury. There are two basic
strategies that have been used to assess methylmercury neurotoxicity.
The first is the use of standard clinical instruments such as measures
of IQ. These have the advantage of being standardized for the
population, as well as assessing a wide range of functional domains.
However, because they may be measuring a number of functions that are
not affected in addition to those that are, the results can be
``diluted'', and therefore these tests may be less sensitive than a
more focused approach. The second approach is to choose domain-specific
tests based on the known effects of higher levels of the toxic
chemical, if such effects are known. This strategy has the advantage of
being potentially more sensitive than using broad-based clinical
instruments. On the other hand, using domainspecific tasks runs the
risk of looking at the wrong functions.
The investigators of the Faroe Islands study used a number of
domain-specific tasks, based on the effects of high-level methylmercury
exposure as well as the pathological changes in specific brain areas
produced by methylmercury. The Faroe Island study found deficits in
these' tasks. The investigators of the Seychelles study used standard
clinical instruments that assessed a little bit of a lot of functions,
which were standardized for a U.S. population rather than the
Seychellois population. They found no effect of methylmercury. In
contrast, the investigators of the New Zealand study, also using
standard clinical instruments, did identify mercury-related deficits.
The consensus of the research community seems to be that a
combination of both approaches should be used, The standard clinical
instruments (e.g. full-scale IQ) are comprised of subscales (e.g.
verbal, visuospatial) that can be used to explore more specific
functional domains. Researchers should also use what is known about the
behavioral and neuropathological effects of methylmercury to design
domainspecific tests, with the hope that these will be maximally
sensitive. To date, deficits in memory, language processing,
visuospatial ability, motor function, and attention have been
identified to be adversely affected by in utero methylmercury exposure.
Hearing may also be adversely affected. New studies, or continued
testing of current cohorts, should build on this knowledge to hone in
even further on specific behavioral functions.
Question 6. In 1974, the FDA established a mercury action limit of
.5 parts per million in fish. This was changed in 1979 to 1 part per
million. What was the basis for this change?
Response. FDA set an action level of 0.5 ppm for mercury in fish in
1969,' in response to the recognition. of the devastating consequences
of fetal exposure to methylmercury in the poisoning episodes in
Minamata and Niigata, Japan. This level was reaffirmed in 1974, citing
concerns about damage to the fetus at lower exposures than are harmful
to the adult. The level was changed in 1979 as a result of a lawsuit by
the fishing industry that resulted in a court ruling based on
socioeconomic impacts presented by the National Marine Fisheries
Service (NMFS). They argued that raising the action level would expand
the number of fisheries available for exploitation and expand the
profits of the fishing industry (Fed. Reg. 3990, 3992, 1979). The
notice was a withdrawal of the proposed rulemaking and terminated a
rulemaking procedure to codify the (then) existing action level
limiting the amount of unavoidable mercury residues permitted in fish
and shellfish of 0.5 ppm. The FR notice also indicates that ``[t]he
Food and Drug Administration will continue to monitor mercury levels in
fish so that if there is any change in mercury residue levels as a
result of raising the action level, or if there is any other change in
the information regarding mercury in fish, the action level can be
revised accordingly.'' Thus, the action limit is not health-based, but
was established for economic considerations.
Question 7. What, if anything, should consumers of fish in the
Great Lakes region and other areas that are downwind of major mercury
emission sources such as coal-fired power plants, chlor-alkali
manufacturing facilities and; waste incinerators, be advised to do with
respect to limiting their methyl mercury exposure?
Response. Unfortunately, the majority of inland lakes and rivers
are contaminated with mercury. Methylmercury is created from mercury by
microorganisms in the water. Methylmercury is bioconcentrated as it is
passed up the food chain, with older and larger fish at the top of the
food chain containing more methylmercury than smaller fish or fish that
are lower on the food chain. Methylmercury exposure in humans is
exclusively from eating contaminated fish. Forty states have explicit
fish advisories as a result of mercury contamination for consumption of
fish based on species, size, and in some states specific water bodies.
There were 2,242 advisories in 2000, up 8 percent o from 1999 and up
149 percent from 1993. By far the greatest number of fish advisories
for mercury are around the Great Lakes and in the Northeastern states.
Consumers are advised to carefully follow State fishing advisories for
inland fish. There is an increasing recognition that commercial and/or
ocean fish may represent a significant source of methylmercury
exposure. Currently, FDA advises pregnant women, nursing mothers and
young children against eating any shark, swordfish, tilefish, or king
mackerel. Recent data indicate that canned white (albacore) tuna may
have substantial levels of methylmercury, and so should be consumed
seldom, especially by children. Other species such as fresh tuna and
halibut may also have significant levels of methylmercury. Intake of
purchased fish that are potentially high in methylmercury should be
included by individuals in determining safe fish intake over a specific
time period. In other words, consumers need to have detailed
information on fish species from both commercial and non-commercial
sources to keep track of their potential methylmercury intake.
This is an unsatisfactory solution, since fish should be a very
healthful food. Moreover, sport fishing is an important economic
resource in many areas, and some individuals rely on fishing for a
substantial portion of their protein, particularly in certain immigrant
communities. The ultimate solution is of course to decrease
environmental deposition of mercury.
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Statement of Dr. Gary Myers, Pediatric Neurologist
and Professor, University of Rochester
Thank you for the opportunity to present the views of our research
group on the health effects of methylmercury (MeHg) exposure. My name
is Gary Myers. I am a pediatric neurologist and professor at the
University of Rochester in Rochester, New York and one member of a
large team that has been studying the human health effects of MeHg for
nearly 30 years. For nearly 20 years our group has specifically studied
the effects of prenatal MeHg exposure from fish consumption on child
In the 1950's, massive industrial pollution for over two decades in
Japan resulted in high levels of MeHg in ocean fish. Several thousand
cases of human poisoning from consuming the contaminated fish were
reported. The precise level of human exposure causing these health
problems was never determined, but was thought to be high. During that
epidemic pregnant women who themselves had minimal or no clinical
symptoms of MeHg poisoning delivered babies with severe brain damage
manifested by cerebral palsy, seizures and severe mental retardation.
This suggested that MeHg crosses the placenta from the mother to the
fetus and that the developing nervous system is especially sensitive to
its toxic effects.
In 1971-1972 there was an epidemic of MeHg poisoning in Iraq.
Unlike the Japanese poisonings, the source of exposure in Iraq was
maternal consumption of seed grain coated with a MeHg fungicide. Our
research team studied the children of about 80 women who were pregnant
during this outbreak. We measured mercury exposure to the fetus using
maternal hair, the biomarker that best corresponds to MeHg brain level,
and examined the children. We concluded that there was a possibility
that exposure as low as 10 ppm in maternal hair might be associated
with adverse effects on the fetus, although there was considerable
uncertainty in this estimate. This value is over 10 times the average
in the United States, but individuals consuming large quantities of
fish can achieve this level.
MERCURY FOUND NATURALLY IN THE ENVIRONMENT
Mercury is a natural element in the earth's crust. In aquatic
environments, bacteria can convert inorganic mercury to MeHg. Once MeHg
enters the food chain, it is bioaccummulated and bioconcentrated. All
fish contain small amounts, and predatory fish or mammals such as
whales have larger amounts. Most commercial oceanic fish in the United
States has < 0.5 ppm MeHg in the muscle, but some freshwater fish have
> 1 ppm. In comparison, contaminated fish in Japan that caused
poisoning had up to 40 ppm.
Everyone who consumes fish is exposed to MeHg, and regular fish
consumption can lead to hair mercury levels as high as 10 ppm or more.
The average hair mercury level in the United States is < 1 ppm. If MeHg
does affect the developing brain at such low levels, mothers who
consume large amounts of fish would be exposing their babies to this
The hypothesis of our study in the Seychelles was that prenatal
MeHg from fish consumption might affect child development. Since
millions of people around the world consume fish as their primary
source of protein, we decided to investigate the question directly. We
initiated the Seychelles Child Development Study in 1983 and began
enrolling subjects in a pilot study in 1987. We selected the Seychelles
as a sentinel population for the United States for two reasons. First,
they consume large amounts of fish. The average mother in our main
cohort ate fish with 12 meals per week or over 10 times that of U.S.
women. Second, the fish consumed in Seychelles (average mercury content
0.3 ppm) has approximately the same mercury concentration as commercial
fish in the United States.
THE SEYCHELLES CHILD DEVELOPMENT STUDY (SCDS)
The SCDS is a collaborative study carried on by researchers at the
University of Rochester Medical Center in Rochester, NY and the
Ministries of Health and Education in the Republic of the Seychelles.
Funding has come from the National Institute of Environmental Health
Sciences, the Food and Drug Administration, and the governments of
Seychelles and Sweden. The Republic of the Seychelles is an island
Nation in the Indian Ocean off the East Coast of Africa.
Our original hypothesis was that prenatal MeHg exposure at levels
achieved by regular maternal consumption of fish would be associated
with adverse effects on child development that could be detected by
clinical examination, or by the use of developmental tests that have
previously been used to study the effects of environmental exposures on
The Seychelles was chosen partly because there is no mercury
pollution and many factors that complicate epidemiological studies of
low-level exposure are not present. Health care is free, universal and
readily available. Prenatal care is nearly 100 percent, the birth rate
is high, and the general health of mothers and children is good.
Education is free, universal, and starts at age 3.5 years. There is
limited emigration and both the people and the government were
cooperative and supportive.
Before starting a carefully controlled main study, we carried out a
pilot study. We expected to find only subtle effects on children at
these levels of exposure. Consequently, it was important to minimize
any possibility of bias, so a number of decisions were made before the
study began. First, no one in Seychelles including researchers visiting
the island would know the exposure level of any child or mother, unless
our results indicated that children were at risk from prenatal mercury
exposure. Second, children with a known cause of developmental delay
(meningitis, very low birth weight, or brain trauma) would not be
studied. Third, the tests administered would include tests previously
reported to show associations with MeHg exposure, tests used with other
toxic exposures, and other tests that might detect subtle changes.
Fourth, all testing would be performed within specific age windows to
minimize the effect of age on test interpretation. Fifth, results would
be adjusted for multiple confounding factors (covariates), including
things like socioeconomic status, maternal intelligence and birth
weight, which are known to have independent effects on child
development and if not accounted for, could bias the results. Sixth,
the data analysis plan would be determined before the data were
collected to minimize the possibility that the data would be repeatedly
analyzed until the anticipated effect was eventually found.
In 1989-90, we enrolled over 700 mothers and children in the SCDS
main study. These children were evaluated on five occasions (6, 19, 29,
66 and 107 months of age) during the past 9 years. When the children
were about 4 years old their homes were visited and evaluated. The
study focused on prenatal exposure. This was measured in the mothers'
hair growing during pregnancy. Postnatal exposure was also periodically
measured in the children's hair. The exposure of both mothers and
children ranged from 1 to 27 ppm, the range of concern. The testing was
extensive with over 57 endpoints being evaluated to date.
Through 107 months (9 years) and over 57 primary endpoints, the
study has found only three statistical associations with prenatal MeHg
exposure. One of these associations was adverse, one was beneficial and
one was indeterminate. These results might be expected to occur by
chance and do not support the hypothesis that adverse developmental
effects result from prenatal MeHg exposure in the range commonly
achieved by consuming large amounts of fish. The test results do show
associations with factors known to affect child development such as
maternal IQ and home environment so there is evidence that the tests
are functioning well.
OUR INTERPRETATION OF THE FINDINGS
We do not believe that there is presently good scientific evidence
that moderate fish consumption is harmful to the fetus. However, fish
is an important source of protein in many countries and large numbers
of mothers around the world rely on fish for proper nutrition. Good
maternal nutrition is essential to the baby's health. Additionally,
there is increasing evidence that the nutrients in fish are important
for brain development and perhaps for cardiac and brain function in
The SCDS is ongoing and we will continue to report our results.
Presently we are examining a new cohort to determine specific nutrients
that might influence the effects of MeHg.
Appendix--Not read before the committee, but included in the
Because of the public health importance of the question being
studied by the SCDS, the potential exists for differing opinions of
scientific findings to become highly politicized. The SCDS has received
only one published criticism (JAMA, 280:737, 1998), but other points
have been raised at conferences. These questions are addressed here
Why did the SCDS measure mercury in the hair rather than
in the cord blood? Hair mercury was used because it is the standard
measure used in nearly all other studies of this question. Mercury is
thought to enter the hair and brain in a similar fashion. Hair was also
chosen because hair has been shown to follow blood concentrations
longitudinally, and samples of hair can recapitulate the entire period
of exposure, in this case the period of gestation. As part of our
research we have shown that hair levels reflect levels in the target
tissue, brain. Measuring mercury in blood requires correction for the
red blood cell volume (hematocrit) since the mercury is primarily in
red blood cells and reflects only very recent exposure. It can also
vary if recent meals with high mercury content are consumed.
Did the SCDS use subjects whose mercury values were too
low to detect an association? No, the study's goal was to see if the
children of women who consume fish regularly were at risk for adverse
developmental effects from MeHg. Women in Seychelles eat fish daily and
represent a sentinel population with MeHg levels 10 times higher than
U.S. women. Because of higher levels of exposure, their children should
be more likely to show adverse effects if they are present. These
children show no adverse effects through 9 years of age suggesting that
eating ocean fish, when there is no local pollution, is safe. However,
we cannot rule out an adverse effect above 12-15 ppm since we had too
few cases to substantiate a statistical association if one really
Did the SCDS use the best tests available to detect
developmental problems? Yes, the SCDS used many of the same
neurodevelopmental and neuropsychological tests used in other
developmental studies. These tests are deemed to be excellent measures
for determining development at the ages studied. The tests examined
specific domains of children's learning and were increasingly
sophisticated as the children become older.
Did the SCDS find expected associations between
development and birth weight, socioeconomic factors, and other
covariates? Yes, expected relationships with many covariates such as
maternal IQ, family socioeconomic status and the home environment were
found, indicating that our tests were sensitive to developmental
Did the removal of statistical outliers in the analysis
bias the study? No. It is standard practice among statisticians to
remove statistical outliers. Outliers are values that are inconsistent
with the statistical model employed to analyze the data. Every
statistical analysis depends on a model, and every statistical model
makes assumptions about the statistical (distributional) properties of
the data that must be satisfied if the results of the analysis are to
be interpreted correctly. Sound statistical practice requires that the
necessary assumptions be checked as part of the statistical analysis.
Examination of outliers constitutes one of these checks. Statistical
outliers are defined by the difference between the actual test score
for a child and the value predicted by the statistical model. Small
numbers of such outliers occurred in test scores for children with
widely varying MeHg exposures. The results of all analysis were
examined both before as well as after the removal of outliers. For
analyses in the main study the removal of statistical outliers did not
change the conclusions.
What about the Faroe Islands study where prenatal MeHg
exposure was reported to adversely affect developmental outcomes? There
are substantial differences between the Faroe Islands and Seychelles
studies. The exposure in the Faroe Islands is from consuming whale meat
and there is also concomitant exposure to PCBs and other neurotoxins.
There are also differences in the measurement of exposure and the
approach to statistical analysis. The Faroe Islands study reported
associations between cord blood mercury levels and several tests. After
statistical analysis they attributed the associations to prenatal MeHg
exposure. Scientific studies are frequently open to different
interpretations and some scientists do not agree with the researchers'
interpretation. We believe the Seychelles study of individuals
consuming fish more closely approximates the U.S. situation.
Are the children in Seychelles too developmentally robust
to find the effects of MeHg if they are present? No, the children in
Seychelles tested similar to U.S. children on nearly all measures apart
from motor skills where they were more advanced. There is no reason to
think that they are too robust to show the effects of prenatal MeHg
exposure if any are present.
Are children in Seychelles exposed to PCBs or other food-
born toxins that might have confounded the results? No, sea mammals are
not consumed in Seychelles and measured PCBs in the children's blood
Should data from the Seychelles be considered interim?
Maybe. Among developmental studies, a 9-year followup is considered
very long and should be adequate to identify associations with most
toxic exposures. However, very subtle effects can be more readily
tested in older individuals and there is evidence from experimental
animals that some effects of early mercury exposure may not appear
until the animal ages.
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August 18, 2003.
Hon. James M. Inhofe, Chairman,
Committee on Environment and Public Works,
Dear Mr. Chairman: Thank you for offering me the opportunity to
respond to certain comments that were made in the EPW committee hearing
on Tuesday, July 29, of this year. I hope I can clear up any confusion
that might have been caused by incomplete, misleading or erroneous
testimony that day.
The testimony in question by Dr. Michael Mann stated:
``It's unfortunate to hear comments about the supposed
inconsistencies of the satellite record voiced here years after
that has been pretty much debunked in the peer-reviewed
literature in Nature and Science. Both journals have, in recent
years, published . . . articles indicating that in fact, the
original statement that the satellite record showed cooling was
flawed because . . . the original author, John Christy, did not
take into account a drift in the orbit of that satellite, which
actually leads to a bias in the temperatures . . . Christy and
colleagues have claimed to have gone back and fixed that
problem. But just about every scientist who has looked at it
says that this fix isn't correct and that if you fix it
correctly then the satellite record actually agrees with the
surface record, indicating fairly dramatic rates of warming in
the past two decades.''
Virtually all of this testimony is misleading or incorrect. I will
touch on the major problems, point-by-point, and I will try to be
1. Certainly no one has ``debunked'' the accuracy of the global
climate dataset that we built at The University of Alabama in
Huntsville (UAH) using readings taken by microwave sensors aboard NOAA
satellites. This dataset has been thoroughly and rigorously evaluated,
and has been published in a series of peer-reviewed papers beginning in
Science (March 1990). The most recent version of the dataset was
published in May 2003 in the Journal of Atmospheric and Oceanic
Technology after undergoing a strenuous peer review process.
2. We, and others, are constantly scrutinizing our techniques to
find ways to better analyze the data. In every case except one we
discovered needed improvements ourselves, developed a method for
correcting the error, and published both the error and the correction
in peer-reviewed journals. When Wentz, et al. (1998) published their
research on the effects of orbital decay (the one exception) they
explained an effect we immediately recognized, but which was partially
counterbalanced by other factors we ourselves discovered. Since that
time we have applied the corrections for both orbital decay and other
factors, and have published the corrected data in peer-reviewed
3. The UAH satellite record does not show cooling in the lower
troposphere and hasn't shown a long-term cooling trend since the period
ending in January 1998. I cannot say where this chronic cooling
misconception originated. Our long-term data show a relatively modest
warming in the troposphere at the rate of 0.133+ Fahrenheit per decade
(or 1.33+ Fahrenheit per century) for the period of November 1978 to
4. There is no credible version of the satellite dataset that
``actually agrees'' with the surface temperature record for the past 25
years, nor one that shows ``fairly dramatic rates of warming.'' The as-
yet-unexplained differences between the surface and satellite data are
at the heart of the controversy over the accuracy of the satellite
While much of the surface data remains uncalibrated and
uncorroborated, we have evaluated our UAH satellite data against
independent, globally-distributed atmospheric data from the U.S. and
the U.K. (Hadley Centre) as shown in the figure (enclosure 1). We
published the results of those comparisons in numerous peer-reviewed
studies (enclosure 2). In each case we found excellent consistency
between the satellite data and the atmospheric data. One should note
that such independent corroboration has not been performed on the other
satellite temperature datasets alluded to in the quoted testimony.
This consistency between two independent datasets gathered using
very different techniques gives us a high level of confidence that the
UAH satellite dataset provides a reliable measure of global atmospheric
temperatures over more than 90 percent of the globe. (By comparison,
one of the most often quoted surface temperature datasets achieves
partial-global coverage only by claiming that certain isolated
thermometer sites provide representative temperatures for an area
roughly equaling two-thirds of the contiguous 48 states, an area that
would reach from about Brownsville, Texas, to Grand Forks, North
5. A final point relates to numerous comments elsewhere in the
testimony in which an appeal to a nebulous ``mainstream climate
community'' was made to support what was stated. First, the notion that
``thousands'' of climate scientists agreed on the IPCC 2001 text is an
illusion. I was a lead author of IPCC 2001, as was Dr. Mann. There were
841 lead authors and contributors, the majority of whom were not
climatologists and who provided input in the area in which they have
expertise only to their tiny portion of the 800+ page document. These
841 were not asked to approve nor where they given the opportunity to
give a stamp of approval on what was finally published.
Although I might be outside the ``mainstream,'' according to Dr.
Mann's perspective, I have never thought a scientist's goal was to
achieve membership in the ``mainstream.'' My goal is to produce the
most reliable climate datasets for use in scientific research. Whether
they show warming or cooling is less important to me than their
reliability and accuracy. That these datasets have been published in
numerous peer-reviewed venues is testimony to accomplishing this goal
and, by inference, would place me inside the mainstream climate
community. In addition to being an IPCC lead author, significant
achievement awards from NASA and the American Meteorological Society
along with my recent election as a Fellow of the AMS are evidence of my
impact on the community of scientists.
I hope this clears up any confusion you or your committee members
might have had about the UAH global temperature data. If you or any of
your committee members have any questions, I will be delighted to
answer them to the best of my ability.
Thank you again for offering me this opportunity. I remain,
John Christy, Ph.D.