Climate Change: Broad Consensus
or "Scientific Cleansing"?
by Paul N. Edwards, Senior Research
Scholar, Program in Science, Technology & Society, Stanford University
and Stephen H. Schneider, Professor,
Institute for International Studies, Dept. of Biological Sciences, Stanford
Is the world getting warmer? And if it is
Since the 1980s, an inexorably rising tide
of evidence has strengthened scientific arguments that the Earth's surface
is heating up. By 1992, concerns were strong enough to produce a major
international agreement to study the issue. But the atmosphere is complex
and its science is young. While there is strong consensus about many
basic aspects of global warming, large uncertainties remain in others
- a perfect prescription for scientific and political contention. Nevertheless,
in December the world's nations will meet again, in Kyoto, to consider
a far-reaching treaty that might delay global warming by limiting emissions
of the so-called "greenhouse gases."
The stakes are very high. Reducing the human
contribution to climate change will be politically difficult. If done
clumsily, it could also be expensive - though perhaps not as costly
as the possible damage to ecosystems and economies across the globe
if nothing is done. Thus scientific studies of climate change have become
political battlegrounds. The credibility of climate science, and its
ability to pinpoint the causes of global warming, is critical to the
Kyoto treaty negotiations. Without a broad scientific consensus, there
can be no hope for strong and effective international measures.
It seems all but certain that the urgency
of the climate-change issue will only increase. Therefore, in hopes
of illuminating the nature of the media-based battles that will inevitably
accompany its growing visibility, we here report on one episode in the
scientific politics of global warming: an assault on the credibility
of the Intergovernmental Panel on Climate Change (IPCC), the most important
scientific body studying the climate change issue.1 We
hope this example will help lay readers to cut through the maze of confusion
around global warming - one that seems always to accompany science-based
political issues involving powerful stakeholders.
THE IPCC SECOND ASSESSMENT
In the spring of 1996, the IPCC released
its Second Assessment Report (SAR) on the question of human impacts
on the global climate system. The Global Climate Coalition (an energy
industry lobby group) and a number of self-proclaimed "contrarian" scientists
immediately launched a major, organized attack designed to discredit
the report's conclusions - especially those relating to the crucial
question of whether human activities are responsible for changes in
the world's climate. The attackers claimed that the IPCC had inappropriately
altered a key chapter for political reasons. They alleged that the IPCC
had "corrupted the peer review process" and violated its own procedural
These charges ignited a major debate - widely
reported in the press - lasting several months. Were they true?
The IPCC is an office of the United Nations
Environment Programme and the World Meteorological Organization. Its
purpose is to evaluate and synthesizes the scientific understanding
of global climate change for national governments and United Nations
agencies. The agency's goal is fairly to represent the full range of
credible scientific opinion and, if possible, to identify a consensus
view on the most likely scenario(s) within this range. IPCC reports
are intensively peer-reviewed. They are regarded by most scientists
and political leaders as the single most authoritative source of information
on climate change and its potential impacts on environment and society.
Like all IPCC assessments, the SAR contained
three "Summaries for Policymakers" (SPMs), one for each of the IPCC's
three Working Groups: climate science (Working Group I), impacts of
climate change (Working Group II), and economic and social dimensions
(Working Group III).2 Since the full SAR stretches to well
over 2,000 pages of mostly dense technical prose, few outside the scientific
community are likely either to read it in its entirety or to understand
most of its details. Therefore, these summaries tend to become the basis
for press reports and public debate. For this reason, the Working Groups
consider their exact wording with extreme care before they are published.
At the end of the IPCC report process, they are approved word for
word by national government representatives at a plenary meeting
attended by only a fraction of the lead authors.
The SPM for Working Group I, which assesses
the state of the art in the physical-science understanding of climate
change, contained the following paragraph:
Our ability to quantify the human influence
on global climate is currently limited because the expected signal
is still emerging from the noise of natural variability, and because
there are uncertainties in key factors. These include the magnitude
and patterns of long-term natural variability and the time-evolving
pattern of forcing by, and response to, changes in concentrations
of greenhouse gases and aerosols, and land surface changes. Nevertheless,
the balance of evidence suggests that there is a discernible human
influence on global climate. (Italics added.)3
Three-quarters of this paragraph consists
of caveats about uncertainties and limitations of current understanding.
Nonetheless, its now-famous closing sentence marked the first time the
IPCC had reached a consensus on two key points: first, that global warming
is probably occurring ("detection"), and second, that human activity
is more likely than not a significant cause ("attribution"). Like this
summary paragraph, the body of the report discussed - frequently and
at length - the large scientific uncertainties about attribution. The
Working Group carefully crafted the "balance of evidence" sentence in
the SPM to communicate the strong majority opinion that despite these
uncertainties, studies were beginning to converge on a more definitive
answer to the attribution question.
The SAR was fraught with political significance.
Official publication of the full report occurred in early June, 1996.
At that point the Second Conference of Parties (COP-2) to the 1992 Framework
Convention on Climate Change was about to meet in Geneva. A sea change
in American climate policy was widely rumored. Since the Reagan administration,
official U.S. policy had sanctioned only voluntary, non-binding emissions
targets and further scientific research. If the United States were to
abandon its resistance to binding emissions targets, a strong international
greenhouse policy would become much more likely. Since the more-research,
no-binding-targets position was officially based on assertions of high
scientific uncertainty, the SAR's expressions of increased scientific
confidence were viewed as critical.
The rumors proved correct. On July 17, 1996,
U.S. Under-Secretary of State for Global Affairs Tim Wirth formally
announced to COP-2 that the United States would now support "the adoption
of a realistic but binding target" for emissions. The exact degree to
which the IPCC SAR influenced this policy change cannot be known. But
Wirth certainly gave the impression that the report was its proximate
cause. He noted in his address that "the United States takes very seriously
the IPCC's recently issued Second Assessment Report." He then proceeded
to quote the SAR at length, proclaiming that "the science is convincing;
concern about global warming is real."4
"A MAJOR DECEPTION ON GLOBAL
On June 12, 1996, just days after formal
release of the IPCC SAR and scant weeks before the COP-2 meeting in
Geneva, the Wall Street Journal (WSJ) published an op-ed piece entitled
"A Major Deception on Global Warming." The article was written by Frederick
Seitz, President Emeritus of Rockefeller University. Seitz is not a
climate scientist but a physicist. Nevertheless, his scientific credentials
are formidable. He is a recipient of the National Medal of Science and
a past President of both the National Academy of Sciences and the American
In his article, Seitz accused some IPCC
scientists of the most "disturbing corruption of the peer-review process"
he had ever witnessed.5
Seitz's proclaimed distress stemmed from
the fact that the lead authors of the SAR's Chapter 8 - on detection
and attribution - had altered some of its text after the November, 1995
plenary meeting of Working Group I (WGI), in Madrid, at which time the
chapter was formally "accepted" by the Working Group. According to Seitz,
since the scientists and national governments who accepted Chapter 8
were never given the chance to review the truly final version, these
changes amounted to deliberate fraud and "corruption of the peer-review
process." Not only did this violate normal peer review procedure, Seitz
charged; it also violated the IPCC's own procedural rules.
Quoting several sentences deleted from the
final version of the chapter, Seitz argued that the changes and deletions
"remove[d] hints of the skepticism with which many scientists regard
claims that human activities are having a major impact on climate in
general and on global warming in particular." Without directly attributing
motives, Seitz implied that the changes had been made in the interests
of promoting a particular political agenda. Seitz said that Benjamin
D. Santer, lead author of Chapter 8, would have to shoulder the responsibility
for the "unauthorized" changes. Seitz was not present at the IPCC meetings.
He did not contact Santer or anyone else at the IPCC to verify that
the changes were indeed "unauthorized" before publishing his op-ed piece.
Responses from Santer and
Santer responded immediately, in a letter
co-signed by some 40 other IPCC officials and scientists (myself among
them - SHS). They said that Seitz had misinterpreted the IPCC rules
of procedure. Rather than being "unauthorized," they wrote, the post-Madrid
changes were in fact required by IPCC rules, under which authors must
respond to comments submitted during peer review or arising from discussions
at the meetings.6
Commentators at the Madrid meeting had advised
making changes to Chapter 8 for two reasons. First, they urged clarification
of the meaning and scientific content of some passages in accordance
with the recommendations of reviewers (including some criticisms introduced
at the Madrid meeting itself). Second, they thought the structure of
the chapter should be brought into conformity with that of other SAR
chapters. In particular, a "Concluding Summary" was removed from the
final version, since no other chapter contained a similar section. (Chapter
8, like all the rest, already had an "Executive Summary.") Sir John
Houghton, in his capacity as co-chairman of WGI, specifically authorized
that these changes be made (though he did not review their wording).
Santer, in consultation with other Chapter
8 authors, made the suggested changes in early December. The entire
SAR, including the newly revised Chapter 8, was "accepted" by the full
IPCC Plenary at Rome later than month.
Santer made the changes himself, and the
final version of the chapter was not reviewed again by others. However,
as he and his colleagues continually stressed, this procedure was the
normal and agreed IPCC process. Santer et al. pointed out that no one
within the IPCC objected (or had ever objected) to this way of handling
things. Replying separately in support of Santer and his colleagues,
IPCC Chairman Bert Bolin and WGI Co-Chairmen John Houghton and L. Gylvan
Meira Filho quoted the official U.S. government review of Chapter 8,
which stated explicitly that "it is essential that... the chapter authors
be prevailed upon to modify their text in an appropriate manner following
discussion in Madrid."7
The WSJ op-ed was not the first time charges
of suppression of scientific uncertainty in Chapter 8 had been aired.
On May 22, a few days before the Seitz op-ed appeared, the small journal
Energy Daily reported the same allegations in considerably greater detail.8
The Energy Daily article also reported their source: a widely circulated
press release of the Global Climate Coalition (GCC, an energy industry
In its June 13 issue, the prestigious science
magazine Nature also reported on the GCC allegations.9
The Nature report, unlike the Seitz and Energy Daily articles, included
explanations of the revision and review process from Santer and the
IPCC. Under the hot-button headline "Climate report 'subject to scientific
cleansing,'" an accompanying editorial argued that the GCC analysis
was politically motivated and generally false. But the editorial also
noted that the Chapter 8 changes may have resulted "in a subtle shift...
that... tended to favour arguments that aligned with [the SAR's] broad
The WSJ op-ed set off a lengthy chain of
exchanges lasting several months. The main participants in the public
controversy were Seitz, Santer, other Chapter 8 authors, the Chairmen
of the IPCC (Sir John Houghton and Bert Bolin), and climate-change skeptics
S. Fred Singer and Hugh Ellsaesser. Singer, in particular, made the
charges of political motivation explicit. In a letter to the Wall Street
Journal, he wrote that Chapter 8 had been "tampered with for political
purposes." The IPCC, he claimed, was engaged in a "crusade to provide
a scientific cover for political action."11
Semi-privately, in electronic mail exchanges
involving many additional participants (and widely copied to others),
the debate became intense and sometimes quite bitter. Santer, who felt
forced to defend himself, spent the majority of his summer time responding
to the charges. Previously a quiet, private man known to scientists
primarily as a proponent of the rigorous use of statistical methods,
Santer rapidly became a public figure, submitting to dozens of interviews.
The drain on his time and energy during this period kept him from his
scientific work, he said.12
Both the public and the private exchanges
themselves became objects of further press reports, widely disseminated
by the news wire services. As they went on, the debate spread from the
initial issues about peer review and IPCC procedure to include questions
about the validity of Chapter 8's scientific conclusions. Even before
the report was formally published, climate-change contrarians had claimed
that Chapter 8 dismissed or ignored important scientific results that
disconfirmed the global warming hypothesis. They argued that the allegedly
illegitimate changes to Chapter 8 made this problem even more acute.13
DID THE CHAPTER 8 AUTHORS
VIOLATE IPCC RULES?
Seitz, the GCC, and others accused the authors
of Chapter 8 of fraud on two counts. First, they alleged that the changes
made to Chapter 8 after the final IPCC plenary violated the IPCC's own
rules of procedure. Second, and more seriously, they charged them with
violating the fundamental standards of scientific peer review. In this
section, we argue that IPCC rules were not violated in the case of Chapter
8. In addition, we argue that in practice the process correctly reflects
the essential tenets of peer review. However, we also show that the
IPCC rules do not specify adequate closure mechanisms for the report
drafting process. We demonstrate that the two-level certification process
("acceptance" and "approval" of IPCC documents) is poorly specified
as well, and can even invite misinterpretation by determined critics.
In their responses to the Seitz/GCC charges,
the Chapter 8 authors claimed that IPCC rules required them to make
the changes advised immediately before and during the Madrid WGI Plenary.
Analysis of the IPCC rules suggests that the real situation is more
ambiguous. Yet they had three very good reasons for believing this to
be the case.
First, the rules require authors to respond
to commentary, to the best of their ability and as fully as possible.14
Working Group co-chairs have broad discretion to define this process
and set time limits for it. Nowhere do IPCC rules explicitly address
the question of when a report chapter becomes final (i.e., when all
changes must cease). Therefore, Santer et al. correctly understood that
the Working Group Chairs and the Plenary meeting itself would define
the endpoint of the revision process.
Second, report chapters are "accepted" rather
than "approved." Acceptance constitutes IPCC certification that the
drafting and review process has been successfully completed. It is an
expression of trust in the authors and the process, and is explicitly
distinguished from "approval," or detailed review on a line-by-line
basis. Operating under these definitions, the IPCC Plenary "approved"
the WGI Summary for Policymakers (SPM), but "accepted" Chapter 8. In
other words, Plenary acceptance did not imply word-for-word review of
the chapter. Instead, it indicated trust that the authors had responded
appropriately and sufficiently to the review process. Therefore, the
Chapter 8 authors believed that the rules permitted them to make changes
when explicitly requested to do so by the IPCC Plenary, or in response
to peer comments received at or immediately prior to the Plenary.
Third, no IPCC member nation has ever seconded
the Seitz/GCC objections.15 (Ninety-six countries were
represented at the Madrid plenary.) From this, above all, we can safely
infer that Santer et al. proceeded exactly as expected.
Santer et al. believed that they were following
IPCC rules, and this made perfect sense within the well-established
informal culture of the IPCC. However, a careful reading of the IPCC's
formal rules reveals that in fact the rules neither allow nor prohibit
changes to a report after its formal acceptance. The legalistic Seitz/GCC
reading of the rules is not, therefore, completely implausible - even
if it was, as we believe, primarily a smokescreen to divert attention
from the clear consensus that attribution could no longer be considered
Our analysis suggests a significant flaw
in the rules as currently written. While "approved" documents (the SPMs)
clearly must not be altered once approved, there is no precisely defined
closure mechanism for "accepted" documents (full-length Working Group
reports and their constituent chapters).16 The Seitz/GCC
attack has effectively demonstrated that a hybrid science/policy organization
like the IPCC needs better, more explicit rules of procedure. This minor
virtue aside, however, the Seitz/GCC reading violates the spirit and
intent of the IPCC process.
The IPCC is run by scientists. Its participants
think of it primarily as a scientific body. By the standards of many
political organizations, its formal rules are not very extensive. They
are also not very specific. They purposely leave undefined the meaning
of key terms such as "expert" and important processes such as "taking
into account" comments. Under the rules, Lead Authors carry full responsibility
for report chapters, and the IPCC leadership retains very broad discretion,
subject to Plenary "acceptance" and "approval" by national governments.
There are good reasons for this arrangement.
Formal procedures are relatively unimportant in scientific culture.
This is true because scientists belong to very small social groups endowed
with extremely strong and deeply entrenched (informal) norms. In addition,
since scientific methods and results are constantly changing, too much
focus on formal rules would inhibit progress. Likewise, formal rules
are not very important in the day-to-day functioning of the IPCC. Instead,
informal rules based on the everyday practices of scientific communities
guide the bulk of the work.
Maintaining this informality is quite important
for effective scientific work. Yet it is not without dangers, especially
in a situation where almost any scientific finding can have political
implications. Just as in any other politicized realm, without clear
procedures to ensure openness and full rights of participation, dissenters
may find - or believe they have found - their voices ignored. One of
the IPCC's most important features is its openness and inclusivity;
balancing this against scientific informality will require constant
vigilance, and perhaps a reconsideration of the formal review process.
From the point of view of political
legitimacy, then, acceptance of reports before final revision is clearly
a risky proposition. But from the viewpoint of scientific legitimacy,
ongoing revision is a normal feature of the research cycle. Even after
a multi-stage review process, minor flaws can be found and improvements
added. This is not unlike the common situation in which an author makes
minor changes to the galley proofs of a manuscript - changes not subject
to peer review. Thus, in the case of the IPCC, adding a final approval
stage to the already long and cumbersome review process would be unlikely
to add significantly to the scientific credibility of the final result.
While it needs to revise its rules to better protect itself from accusations
of political capture, the IPCC must also, at all costs, avoid becoming
a science-stifling, inflexible bureaucracy.
DID THE CHAPTER 8 REVISIONS
"CORRUPT" THE PEER REVIEW PROCESS?
One of the most important informal, everyday
practices of science is peer review. Seitz and the GCC accused the IPCC
of violating this standard, too. Were they right?
In a typical peer review procedure, scientists
write articles and submit them to a scientific journal. The journal
editor sends the article to several referees, all of them experts in
the authors' field ("peers"). Often peer review is "blind," meaning
that referees do not know the authors' identity. (Not all journals conform
to this standard, and it is actually rare in atmospheric science.) In
most cases, the referees' identity is kept secret from the author. However,
some journal editors, like myself (SHS), encourage referees to reveal
themselves. Since many scientific communities are quite small, referees
and authors can often guess each other's identity.
Referees may recommend acceptance, rejection,
or acceptance after certain specified changes are made ("revise and
resubmit"). The last of these responses is by far the most common. The
authors then rewrite their article in response to the reviewers, and
the editor serves as referee. The process usually goes back and forth
several times, with several rounds of revision, until a suitable compromise
is achieved among reviewers, authors and the editor. A similar process
is normally applied to grant proposals.17
To decide whether Chapter 8 "corrupted" this
process, let's look at how it worked in IPCC Working Group I (WGI).
In July of 1995, the third installment of the WGI drafting and review
process for the SAR took place in Asheville, North Carolina. This meeting,
like all other IPCC processes, was characterized by exceptional openness
to critique, review, and revision. About six dozen climate scientists
from dozens of countries took part. The meeting was designed to make
explicit the points of agreement and difference among the scientists
over exceedingly controversial and difficult issues, including Chapter
8 - the most controversial.
New lines of evidence had been brought to
bear by three climate modeling groups around the world, each suggesting
a much stronger possibility that a climate change signal has been observed
and that its pattern (or fingerprint) is matched to anthropogenic changes.
Ben Santer, as the Convening Lead Author of Chapter 8, had assembled
the results of a number of modeling groups. He presented the results
of his group's effort not just to Chapter 8's Lead Authors and contributors,
as is typical in IPCC meetings, but to the entire scientific group assembled
In this setting, Santer had to explain this
work not only to his most knowledgeable peers, but also to scores of
others from diverse scientific communities. These included stratospheric
ozone experts like Susan Solomon and Dan Albritton, satellite meteorologists
like John Christy, and biosphere dynamics experts such as Jerry Melillo.
Climatologists such as Tom Karl and I (SHS) were also present, along
with the heads of national weather services and other officials from
several countries who served on the IPCC's assessment team.
Not everybody was equally knowledgeable on
the technical details of the debate, of course. Perhaps only 25 percent
of those assembled had truly in-depth knowledge of the full range of
details being discussed. However, all understood the basic scientific
issues and most know how to recognize slipshod work -- to say nothing
of a fraud or a "scientific cleansing" -- when they see it. Even the
less familiar participants thus served an essential role: they acted
as technically-skilled witnesses to the process of honest, open debate.
This remarkable session lasted for hours.
(In fact, it was continued after dinner by roughly a dozen scientists,
who spent nearly three hours discussing the final paragraph of the "Detection
Section" of the Summary for Policymakers.)18 Though occasionally
intense, it was always cordial, never polemical. As a result, the wording
of Chapter 8 was changed. Ideas and concepts were somewhat altered,
but basic conclusions by and large remained unchanged - because the
vast bulk of those assembled were convinced that the carefully hedged
statements the lead authors proposed were, in fact, an accurate reflection
of the state of the science based upon all available knowledge, including
the new results.
This was peer review at ten times the normal
level of scrutiny! It would be practically inconceivable for the editor
of a peer-reviewed journal to duplicate this process. A few referees
and an editor can only hope to execute the reviewing role a fraction
as well as the remarkable, open process at Asheville. Moreover, after
the Asheville meeting, two more IPCC drafts were written and reviewed
by hundreds of additional scientists from all over the globe.
An Open Process of Scientific
Debate: Witnessing in Action
At Madrid, Santer presented Chapter 8's conclusions
to the national delegates of 96 IPCC member nations. The conclusions
were not presented alone, but followed a presentation to the plenary
session of the scientific evidence contained in Chapter 8. Nevertheless,
several countries objected to the Chapter 8 conclusions. Most of the
objections came from OPEC or less-developed nations. One delegate, from
Kenya, moved to have the chapter entirely dropped from the final report.
In response, the meeting's chair - following
procedures often used at IPCC Plenary meetings to resolve disputes -
called for a drafting group to revise the detection and attribution
section of the Summary for Policymakers and to inform the Chapter 8
lead authors of their concerns. Nations complaining about the Chapter
8 draft were invited, indeed expected, to meet with Lead Authors, first
to discuss the scientists' point of view and then to fashion new, mutually
This breakout group worked for the better
part of a day. Delegates from over half a dozen countries - including
the Kenyan who had publicly advocated dropping the chapter - met with
about half a dozen Chapter 8 authors, including Santer, co-Lead Author
Tom Wigley, and scientists Kevin Trenberth, Michael MacCracken, John
Mitchell, and me (SHS). The Kenyan sat next to me. Initially, he was
confused by the discussion and somewhat hostile. We had many side conversations
about what was being discussed: models, data, statistical tests and
various climate forcing scenarios. Although he was not a front-rank
climate researcher, this delegate was a trained scientist. He began
to grasp the nature of the Lead Authors' arguments, listening carefully
to about half of the breakout meeting.
Ironically, the Saudi Arabian delegation
sent no representative to this most controversial drafting group, even
though Saudi Arabia had led the opposition in the plenary meeting. During
the Chapter 8 debate, Saudi delegates often issued objections soon after
receiving notes from the Global Climate Coalition representative. (Non-governmental
organizations were also represented at Madrid. For example, S. Fred
Singer - President of the Science & Environmental Policy Project and
a self-proclaimed contrarian - raised a number of issues from the floor.)
Later in the plenary meeting, when Santer
presented the drafting group's revised text, the Saudi delegates once
again objected. Santer forcefully challenged them. Why, he asked, had
no Saudi attended the breakout group - if their objections had some
basis in science? The head Saudi delegate haughtily announced that he
didn't have to account for his decisions about which drafting group
to attend. Besides, he said, his was "only a small delegation" of a
At this point the Kenyan delegate rose to
speak. (I held my breath.) "I'm a member of a small delegation too,"
he said. (He was the only Kenyan representative.) "But somehow I managed
to attend this most important drafting session. As a result, I am convinced
that Chapter 8 is now well written and I have no objections to its inclusion
in the report." (I paraphrase his words from memory.) The impact of
his intervention was stunning, stopping with a few words what appeared
to be a mounting movement of OPEC and LDC opposition to Chapter 8 before
it could garner any further support.
Later on I privately congratulated the Kenyan
for having the courage to object publicly, observe privately, and then
re-evaluate his position before the entire plenary. He said he wasn't
sure his country would approve of his stance, but having witnessed the
debate process for several hours, he had become convinced it was honest
and open. That was all he needed to change his opinion from preconceived
skepticism to support of the Lead Authors' conclusions.
What this courageous delegate did was the
essence of good science. He allowed his initial hypothesis to be subjected
to new evidence, tested it, and found it wanting. He then listened to
arguments for a different point of view, subjected them to the tests
of evidence and debate, and reached a new conclusion.
Contrast this open IPCC process with that
of the critics led by Seitz and the Global Climate Coalition. The latter
first presented their technical counter-arguments in such "refereed
scientific literature" as the editorial pages of the Wall Street Journal.
Some even had the temerity to allege (falsely) that Chapter 8's conclusions
were based upon non-peer-reviewed articles.19 The Seitz/GCC
group charged that the minor changes made to Chapter 8 during the post-Madrid
revision process had somehow dramatically altered the report. Without
a shred of evidence, Singer and others asserted that the changes were
politically motivated "scientific cleansing."
These irresponsible claims were not reviewed
by a single independent, expert peer before being published - in the
opinion pages of a business daily and a few news magazines. We leave
it to readers to decide which are more credible: the reports of the
IPCC, submitted to many rounds of extremely public, intensive peer review,
or the op-ed pieces and pamphlets of Seitz, Singer, and the GCC.
WHAT ABOUT THE SCIENCE?
In a nutshell, the new evidence reported
to IPCC and later published in Nature was based not upon new empirical
or theoretical results, but on new ways of asking climate models the
right questions.20 In the past, critics such as the University
of Virginia's Pat Michaels had correctly argued that direct observational
evidence of global warming effects (i.e. "signals") in the climate record
were not very well matched to CO2-only model results. For example, CO2-only
models suggested that the Earth' surface should have warmed up 1°C rather
than the one-half degree C observed in the last century. Additionally,
CO2-only models suggested that the Northern Hemisphere would warm up
more than the Southern Hemisphere. Such models also, however, suggested
the stratosphere would cool as greenhouse gases increased. This clearly
was happening (although at least part of that cooling can be attributed
to stratospheric ozone depletion).21
The Earth's warming of a half degree C during
the 20th century could be explained simply by asserting the trend to
be a natural fluctuation in the climate. The IPCC scientists attempted
to estimate the likelihood that natural events were responsible for
the observed surface warming. They concluded that this was possible,
but improbable. Critics, meanwhile, simply asserted that the warming
was natural, without characterizing the probability that this was the
correct explanation. Even if it did go unchallenged in a number of op-ed
articles, this is a scientifically meaningless claim.
What is the probability that a half-degree
warming trend in this century is a natural accident? This cannot be
answered by looking at the thermometer record alone, since a globally
averaged record is not reliable for much more than a century, if that.
It is like trying to determine the probability of "heads" in a coin
flip by flipping it once. Instead, climate scientists look at proxy
records of climate change over long periods of time, such as fluctuating
time series of tree ring widths, the deposits left from the comings
and goings of glaciers, and the fluctuations of various chemical constituents
in ice cores. These records, while not direct measurements of global
temperatures, are nonetheless proportional to components of the climate
in different parts of the world, and provide a rich record of natural
This record (as summarized in Chapter 3 of
the SAR) suggests that the warming of the last century is not unprecedented.22
But it also is not common. Perhaps once in a millennium, such proxy
records suggest, a half-degree C global century-long trend could occur
naturally.23 In my judgment (SHS), this circumstantial
evidence implies that a global surface warming of half a degree has
about an 80 to 90 percent likelihood of not being caused by the natural
variability of the system.
Natural climatic forcing factors, such as
energy output changes on the sun or peculiar patterns of volcanic eruptions,
could cause the observed climate trend. However, each of these climate
forcings has a peculiar signature or fingerprint. For example, energy
increases from the sun would warm the surface, the lower atmosphere,
and the stratosphere all at the same time. On the other hand, greenhouse
gas forcing would cool the stratosphere while warming the lower troposphere.
Aerosols from human activities, particularly the sulfates generated
in coal- and oil-burning regions of the US Northeast, Europe, and China,
would cool the troposphere mostly during the day and not at night, and
would largely cool the Northern Hemisphere, especially in the summertime
when the sun is stronger.
This aerosol effect has turned out to be
very important. Indeed, adding sulfate aerosols to greenhouse gas increases
in the models led to a dramatic boost in the confidence that could be
attached to the circumstantial evidence associated with climatic fingerprints.
That is, when the models were driven by both greenhouse gases globally,
and sulfate aerosols regionally, no longer did the Northern Hemisphere
warm up more than the Southern Hemisphere, or all parts of the high
latitudes warm substantially more than the low latitudes. Instead, a
different fingerprint pattern emerged. Moreover, this pattern in the
models showed an increasing correlation with observations over time
- precisely what one would expect in a noisy system in which the human
forcing increases with time. By itself, the pattern still has roughly
a 10 percent chance of being a random event. However, when taken together
with good physical theory and knowledge of ice age-interglacial cycles,
seasonal cycles, volcanic eruptions, and now more consistent fingerprints,
the vast bulk of the scientific community felt it was not irresponsible
to assert that there was a higher likelihood that human climate signals
had been detected. Taken together, all this circumstantial evidence
was the basis for Chapter 8's now-famous claim that "the balance of
evidence suggests a discernible human influence on climate."
At this point in the evolution of knowledge
about the Earth's climate system, this is no longer a radical statement.
It reflects a lowest-common-denominator consensus view of the vast majority
of scientists. It does not say that a climate warming signal has been
detected beyond any doubt. Neither we nor any other responsible scientists
would make such a claim. But it does offer good reason to begin to plan,
responsibly, for the possibility - which we now see as more likely than
not - that the global climate will warm by at least one or two degrees
during the next 50 years.
HOW SHOULD SOCIETY RESPOND
TO CLIMATE-CHANGE CONTRARIANS?
To ignore contrarian critics would be inappropriate.
Occasionally, non-conventional outlier opinions revolutionize scientific
dogma (Galileo and Einstein being the most oft-cited examples). However,
we believe that news stories are grossly misleading and irresponsible
if they present the unrefereed opinions of contrarians as if they were
comparable in credibility to the hundred-scientists, thousand-reviewer
documents released by the IPCC. The general public cannot be relied
upon to determine for themselves how to weigh these conflicting opinions.
And to publish character-assassinating charges of "scientific cleansing"
without checking the facts is simply unethical - at least in any system
of ethics we respect.
The journalistic doctrine of "balance", while
perhaps appropriate in two-party political systems where the "other
side" must always get its equal coverage, is inappropriate if applied
literally to multifaceted scientific debates. In climate science, wide
ranges of probabilities are attached to a whole array of possible outcomes.24
Scientific controversy simply can't be trivialized into a false dichotomy
between those who assert that human effects are likely to produce a
catastrophic, "end of the world" crisis, "balanced" against those who
assert that at worst nothing will happen and at best it will all be
good for us. "The end of the world" and "no impact at all" are the two
This is not just a problem for journalists.
It also affects scientists. In communication with the public, we sometimes
tend to focus our attention on controversies at the cutting edge of
the art, rather than present clear perspectives on what is well understood
- separating what is truly known from what is merely probable and both
of these from what is highly speculative. This, combined with the propensity
of the media to focus on "dueling scientists" and extreme, outlier opinions,
leads to a miscommunication of the actual nature of the scientific consensus.25
This consensus is vital to the policy process.
In essence, the policy question is to decide how much of current resources
should be invested as a hedge against potential negative outcomes. This
clearly is a value judgment. It is precisely the kind of judgment that
the public and the policy establishment should make, but it can only
be made if the decisionmakers - who are not, and are not going to become,
experts - are aware of the best range-of-probability and range-of-consequences
estimates of the responsible scientific community.
Faxes sent by special interests to every
major journalist on the planet or every significant elected and unelected
official - what we like to call the "one fax, one vote" syndrome - are
not very good sources of truth. Vastly better is the work of groups
such as the IPCC and the National Research Council, which although slow,
deliberative, sometimes snobby, and occasionally dominated by strong
personalities, are nonetheless the best representation of the scientific
community's current general opinion.
This kind of scientific consensus is not
the same thing as "truth." Once in a while, the contrarians are right.
Indeed, we are certain that some aspects of the current vision of climate
change will turn out to be of minor impact, while others will prove
to be more serious than currently thought. That is why assessment needs
to be a continuous process, and why all policymaking requires "rolling
reassessment." The IPCC, or its progeny, need to be reconvened every
five years or so. Only with this input can the political process legitimately
decide, and re-decide, to crank up its efforts at mitigation - or to
crank them back down, depending upon what is learned in each new assessment
about the climate system, the impact of climate change on environment
and society, and the effectiveness and distribution of mitigation costs.
This ongoing and open process of refinement of knowledge is the only
way that a complex system can become adaptive. Only an adaptive system
can minimize the likelihood of making major mistakes, either by overinvesting
in environmental protection or by allowing nasty experiments to be performed
on Laboratory Earth without any attempt to anticipate or slow down the
potential negative, irreversible consequences.26
1 The authors wish to thank Simon Shackley,
Ben Santer, and Michael Oppenheimer for their helpful comments on a
draft of this article.
2 Houghton, J.J., Filho, L.G.M., et al.,
eds. 1996. Climate Change 1995: The Science of Climate Change. Cambridge,
UK, Cambridge University Press.
Watson, R.T., Zinyowera, M.C. & Moss, R.H.,
eds. 1996. Climate Change 1995: Impacts, Adaptations and Mitigation
of Climate Change: Scientific-Technical Analyses. Cambridge, UK, Cambridge
Bruce, J., Lee, H. & Haites, E., eds. 1996.
Climate Change 1995: Economic and Social Dimensions of Climate Change.
Cambridge, UK, Cambridge University Press.
3 Houghton, J.J., Filho, L.G.M., et al.,
eds. 1996. Climate Change 1995: The Science of Climate Change. Cambridge,
UK, Cambridge University Press: 5.
4 T. E. Wirth, U.S. Undersecretary for Global
Affairs. 1996. Statement on behalf of the United States of America to
the Second Conference of Parties. Geneva, Switzerland. July 17, 1996.
Provided by USGCRP office. Italics added.
5 Seitz, F. 1996. "A Major Deception on Global
Warming." Wall Street Journal. New York. June 12.
6 Santer, B., Wigley, T., et al. 1996. Response
to Wall Street Journal Editorial of June 12th, 1996 by Frederick Seitz.
Wall Street Journal. New York. June 25.
7 Bolin, B., Houghton, J. & Meira-Filho, L.G. 1996. Letter to the Editor. Wall Street Journal. New York. Original letter (quoted here) mailed June 15. A brief excerpt from the full letter was published by the Wall Street Journal on June 25.
8 Wamsted, D. 1996. "Doctoring the Documents?"
Energy Daily 24(98): 1-2.
9 Masood, E. 1996. "Climate Report `Subject
to Scientific Cleansing'." Nature 381(6583): 546.
10 Editorial. 1996. "Climate Debate Must
not Overheat." Nature 381(6583): 539.
11 Singer, S.F. 1996. Letter to the Editor.
Wall Street Journal. New York. July 11.
12 Personal communication.
13 Brown Jr., Rep. G.E. 1996. "Environmental
Science Under Siege: Fringe Science and the 104th Congress." Report
to the Democratic Caucus of the Committee on Science, U.S. House of
Representatives. Available at http://www.house.gov/science_democrats/envrpt96.htm.
14 Intergovernmental Panel on Climate Change.
1993. IPCC Procedures for Preparation, Review, Acceptance, Approval,
and Publication of its Reports. Approved by the IPCC June 30, 1993.
15 Bolin, B. 1996. Letter to Ben Santer.
16 IPCC Procedures, op. cit.
17 Peer review has not yet been studied extensively
by sociologists of science. One of the most thorough treatments is The
Second International Congress on Peer Review in Biomedical Publication.
1994. Special issue of the Journal of the American Medical Association.
July 13, 1994.
18 Ben Santer, personal communication.
19 See, for example, Singer, S.F. 1996. "Climate
Change and Consensus." Science 271(5249): 581.
20 Santer, B.D., Taylor, K.E., et al. 1996.
"A Search for Human Influences on the Thermal Structure of the Atmosphere."
Nature 382(6586): 39-46.
22 Houghton, J.J., Filho, L.G.M., et al.,
eds. 1996. Climate Change 1995: The Science of Climate Change. Cambridge,
UK, Cambridge University Press.
23 Schneider, S.H. 1994. "Detecting Climatic
Change Signals: Are There Any 'Fingerprints'?" Science. 263: 341-347.
24 Nordhaus, W.D. 1994. "Expert Opinion on
Climatic Change." American Scientist 82(1): 45-51.
Morgan, M.G. & Keith, D.W. 1995. "Subjective
Judgments by Climate Experts." Environmental Science and Technology
25 See the "Mediarology" chapter in S.H.
Schneider, 1989. Global Warming: Are We Entering the Greenhouse Century?
New York, Vintage Books. Schneider, S.H. 1997. Laboratory Earth: The
Planetary Gamble We Can't Afford To Lose. New York, Basic Books.
26 Schneider, S.H. 1997. Laboratory Earth:
The Planetary Gamble We Can't Afford To Lose. New York, Basic Books.