[Vision2020] "Science" Journal: Evidence For Consensus Re: Global Warming

[Ted Moffett]

BEYOND THE IVORY TOWER:
The Scientific Consensus on Climate Change*Naomi Oreskes*
*<http://www.sciencemag.org/cgi/content/full/306/5702/1686#affiliation>

*P*olicy-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 <http://www.sciencemag.org/cgi/content/full/306/5702/1686#ref1>).
Some corporations whose revenues might be adversely affected by controls on
carbon dioxide emissions have also alleged major uncertainties in the
science ( 2 <http://www.sciencemag.org/cgi/content/full/306/5702/1686#ref2>).
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<http://www.sciencemag.org/cgi/content/full/306/5702/1686#ref3>).
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<http://www.sciencemag.org/cgi/content/full/306/5702/1686#ref4>)].


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<http://www.sciencemag.org/cgi/content/full/306/5702/1686#ref5>)].
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 <http://www.sciencemag.org/cgi/content/full/306/5702/1686#ref5>)].

Others agree. The American Meteorological Society
(6<http://www.sciencemag.org/cgi/content/full/306/5702/1686#ref6>),
the American Geophysical Union (
7<http://www.sciencemag.org/cgi/content/full/306/5702/1686#ref7>),
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<http://www.sciencemag.org/cgi/content/full/306/5702/1686#ref8>).


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<http://www.sciencemag.org/cgi/content/full/306/5702/1686#ref9>).


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.
   10. 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. I am grateful to AAAS and the
   History of Science Society for their support of this lectureship; to my
   research assistants S. Luis and G. Law; and to D. C. Agnew, K. Belitz, J. R.
   Fleming, M. T. Greene, H. Leifert, and R. C. J. Somerville for helpful
   discussions.

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Vision2020 Post: Ted Moffett
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