Later On

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The scientific consensus on global warming

with 2 comments

From the American Association for the Advancement of Science (AAAS), the preeminent scientific organization in the US. Note that this article is not based on a mere count of articles, but rather looks at statements from various scientific organizations.

Science 3 December 2004:
Vol. 306. no. 5702, p. 1686
DOI: 10.1126/science.1103618

BEYOND THE IVORY TOWER:
The Scientific Consensus on Climate Change

Naomi Oreskes*

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.
  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.

Written by LeisureGuy

4 September 2007 at 7:51 pm

2 Responses

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  1. This is the older study that was referenced in my previous post. And the article referenced in my previous post updates Oreskes’ 2004 study to conclude that the apparent consensus is unraveling as more and more scientists either refuse to hop onto the global warming bandwagon or actively challenge it. What is happening is global warming is what basic economics would predict — the pool of applicants for scientific grants to study (and confirm) global warming has grown because of the vast resources being funnelled to such studies by legislatures. This attracts greater numbers of scholars to the point that the competition weakens the quality of the product and/or saturates the market for grant money to prove global warming. Other scholars seeking to differentiate themselves for the purpose of justifying new grants can do so by maintaining sharp neutrality or challenging the prevailing global warming hypothesis. The latter activity is exactly what scientists, as opposed to politicians, are supposed to do–challenge, question, test, and alter hypotheses to fit existing facts, not existing political opinions.

    Overall, I’m relatively thankful to Al Gore for providing global warming with its “jumping the shark” moment. On the other hand, in 20 years we’ll have forgotten global warming as we all shiver and wait for the next ice age. Or if global warming is real–anthropogenic or not–we’ll be sitting pretty in a world that is far better suited to feeding the projected 9 billion people in 2050 because, as past warming periods have demonstrated, greater warmth equals more food.

    Dan

    5 September 2007 at 6:06 am

  2. The study you referenced has not been published in any peer-reviewed journal, and so far as I can tell is an article-count, nothing more. Orekes’s study includes statements made by leading scientific organizations that global warming is happening and is anthropogenic. That is, it includes conclusions of the major scientific organizations.

    Whether global warming is anthropogenic (as is the consensus) or not, BTW, is a scientific opinion, not political.

    Not sure where the “next ice age” comment comes from. According to a recent article in New Scientist:

    THE fossil fuels we burn today may leave an atmospheric “hangover” lasting hundreds of thousands of years, which may cause enough residual warming to prevent the onset of the next ice age. This is the most far-reaching disruption of long-term planetary processes yet suggested for human activity.

    The UN’s Intergovernmental Panel on Climate Change describes carbon dioxide as having a lifetime in the atmosphere of between five and 200 years before it is ultimately absorbed by the oceans. In fact, as much as one-tenth of the CO2 we are emitting now will linger in the air for at least 100,000 years, and perhaps much longer, says Toby Tyrrell of the UK’s National Oceanography Centre in Southampton.

    “It is often assumed that the Earth will always recover from perturbations. But our research shows that it doesn’t necessarily behave like this,” says Tyrrell. “It isn’t always inherently self-rectifying.”

    If global warming turns the American Midwest in another dust bowl through disruption of rain cycles, I think that the increased food supply you are suggesting may not occur. Not to mention other natural disasters such as the loss of all low-lying land, the growth of desert areas, loss of species (particularly fauna), and the like.

    I don’t think past warming periods will hold a candle to what we’re going to experience—those did not lead to the melting of the Greenland icecap and (if it happens) to the thawing of Antarctica.

    LeisureGuy

    5 September 2007 at 9:10 am


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