Scientific Consesus on Climate Change

[Guest guest]

Even though the following essay was written more than two years ago,

it led to op-ed pieces in the Washington Post, the San Francisco

Chronicle, and the Los Angeles Times and has been widely cited in

the mass media, including National Public Radio and in Al Gore's

movie, " An Inconvenient Truth. " The author also testified at a

hearing of the Senate Environment and Public Works Committee on

Climate Change and the Media.

 

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Beyond the Ivory Tower: The Scientific Consensus on Climate Change

By Naomi Oreskes, Science Magazine, Dec. 3, 2004...

 

Policy-makers and the media, particularly in the United States,

frequently assert that climate science is highly uncertain. Some

have used this as an argument against adopting strong measures to

reduce greenhouse gas emissions.

 

For example, while discussing a major U.S. Environmental Protection

Agency report on the risks of climate change, then-EPA administrator

Christine Whitman argued, " As [the report] went through review,

there was less consensus on the science and conclusions on climate

change " (1).

 

Some corporations whose revenues might be adversely affected by

controls on carbon dioxide emissions have also alleged major

uncertainties in the science (2). Such statements suggest that there

might be substantive disagreement in the scientific community about

the reality of anthropogenic climate change. This is not the case.

 

The scientific consensus is clearly expressed in the reports of the

Intergovernmental Panel on Climate Change (IPCC). Created in 1988 by

the World Meteorological Organization and the United Nations

Environmental Programme, IPCC's purpose is to evaluate the state of

climate science as a basis for informed policy action, primarily on

the basis of peer-reviewed and published scientific literature (3).

 

In its most recent assessment, IPCC states unequivocally that the

consensus of scientific opinion is that Earth's climate is being

affected by human activities: " Human activities ... are modifying

the concentration of atmospheric constituents ... that absorb or

scatter radiant energy. ... [M]ost of the observed warming over the

last 50 years is likely to have been due to the increase in

greenhouse gas concentrations " [p. 21 in (4)].

 

IPCC is not alone in its conclusions. In recent years, all major

scientific bodies in the United States whose members' expertise

bears directly on the matter have issued similar statements. For

example, the National Academy of Sciences report, Climate Change

Science: An Analysis of Some Key Questions, begins: " Greenhouse

gases are accumulating in Earth's atmosphere as a result of human

activities, causing surface air temperatures and subsurface ocean

temperatures to rise " [p. 1 in (5)].

 

The report explicitly asks whether the IPCC assessment is a fair

summary of professional scientific thinking, and answers yes: " 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 " [p. 3 in (5)].

 

Others agree. The American Meteorological Society (6), the American

Geophysical Union (7), and the American Association for the

Advancement of Science (AAAS) all have issued statements in recent

years concluding that the evidence for human modification of climate

is compelling (8).

 

The drafting of such reports and statements involves many

opportunities for comment, criticism, and revision, and it is not

likely that they would diverge greatly from the opinions of the

societies' members. Nevertheless, they might downplay legitimate

dissenting opinions. That hypothesis was tested by analyzing 928

abstracts, published in refereed scientific journals between 1993

and 2003, and listed in the ISI database with the keywords " climate

change " (9).

 

The 928 papers were divided into six categories: explicit

endorsement of the consensus position, evaluation of impacts,

mitigation proposals, methods, paleoclimate analysis, and rejection

of the consensus position. Of all the papers, 75% fell into the

first three categories, either explicitly or implicitly accepting

the consensus view; 25% dealt with methods or paleoclimate, taking

no position on current anthropogenic climate change. Remarkably,

none of the papers disagreed with the consensus position.

 

Admittedly, authors evaluating impacts, developing methods, or

studying paleoclimatic change might believe that current climate

change is natural. However, none of these papers argued that point.

 

This analysis shows that scientists publishing in the peer-reviewed

literature agree with IPCC, the National Academy of Sciences, and

the public statements of their professional societies. Politicians,

economists, journalists, and others may have the impression of

confusion, disagreement, or discord among climate scientists, but

that impression is incorrect.

 

The scientific consensus might, of course, be wrong. If the history

of science teaches anything, it is humility, and no one can be

faulted for failing to act on what is not known. But our

grandchildren will surely blame us if they find that we understood

the reality of anthropogenic climate change and failed to do

anything about it.

 

Many details about climate interactions are not well understood, and

there are ample grounds for continued research to provide a better

basis for understanding climate dynamics. The question of what to do

about climate change is also still open. But there is a scientific

consensus on the reality of anthropogenic climate change. Climate

scientists have repeatedly tried to make this clear. It is time for

the rest of us to listen.

 

-- References and Notes:

 

(1) A. C. Revkin, K. Q. Seelye, New York Times, 19 June 2003, A1.

(2) S. van den Hove, M. Le Menestrel, H.-C. de Bettignies, Climate

Policy 2 (1), 3 (2003).

(3) See www.ipcc.ch/about/about.htm.

(4) J. J. McCarthy et al., Eds., Climate Change 2001: Impacts,

Adaptation, and Vulnerability (Cambridge Univ. Press, Cambridge,

2001).

(5) National Academy of Sciences Committee on the Science of Climate

Change, Climate Change Science: An Analysis of Some Key Questions

(National Academy Press, Washington, DC, 2001).

(6) American Meteorological Society, Bull. Am. Meteorol. Soc. 84,

508 (2003).

(7) American Geophysical Union, Eos 84 (51), 574 (2003).

(8) See www.ourplanet.com/aaas/pages/atmos02.html.

(9) The first year for which the database consistently published

abstracts was 1993. Some abstracts were deleted from our analysis

because, although the authors had put " climate change " in their key

words, the paper was not about climate change.

 

-- This essay is excerpted from the 2004 George Sarton Memorial

Lecture, " Consensus in science: How do we know we're not wrong, "

presented at the AAAS meeting on 13 February 2004 by Naomi Oreskes,

a professor of history and science studies at the University of

California-San Diego.

 

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