The Scientific Consensus

Climate Consensus: by James Powell

 

 

As discussed in detail here, I searched the Web of Science for peer-reviewed scientific articles published between 1 January 1991 and 9 November 2012 that had the keyword phrases "global warming" or "global climate change." The search produced 13,950 articles. See methodology.
By my definition 24 of the 13,950 articles, 0.17% or 1 in 581, clearly reject human-caused global warming or endorse a cause other than CO2 emissions for observed warming. The articles have a total of 33,690 individual authors (rounded to 33,700 in the figure). The 24 rejecting papers have a total of 34 authors, about 1 in 1,000.

What can we conclude from this study?
1. In the scientific literature, there is virtually no disagreement that humans are causing global warming.
2. The authors of the handful of papers that reject human-caused global warming tend not to agree with, or even to cite, each other's work.
3. Other than those authors themselves, only a handful of other scientists cite the few rejecting articles. Those who do cite them do not themselves reject human-caused global warming.
4. The rejecting authors have no alternative theory to explain the observed warming.
5. Most of the most prominent global warming deniers (for example, Lindzen, Michaels, Monckton, Singer, and Watts) have never written a scientific paper in which they said explicitly that human-caused global warming is false. Why? Because then they would have to produce the evidence to back it up, and there is no such evidence. If there were, surely they would have told us by now.
6. The vast majority of climate scientists accept the theory that human emissions of greenhouse gases are causing the observed global warming. Here is how I arrive at this deduction.

When a new scientific theory is first proposed, scientists often go out of their way to state explicitly that they reject it, or that they accept it. This was the case with continental drift in the 1920s, with plate tectonics in the 1960s, and with the Alvarez theory of dinosaur extinction in the 1980s. One reading the literature in these fields can usually tell from the title of an article alone whether an author rejects the new theory. But after a theory achieves maturity and becomes the ruling paradigm, scientists no longer see any point in stating explicitly that they accept the now-no-longer-new theory. They take it as a given, often as an observational fact—like the measured movement of tectonic plates and the measured global temperature rise. To explicitly endorse the ruling theory would have the counter-effect of suggesting that the theory needs reinforcement. My literature survey shows that global warming has achieved the status of the ruling paradigm of climate science. Thus it is reasonable to assume that those who today reject human-caused global warming would make it clear that they do so, while those who accept it would not feel the need to say so explicitly. As a practical matter, virtually all of the global warming papers that Oreskes and I separately reviewed can be classified as about effects, mitigation, adaptation, methods of detecting, climate modeling, and paleoclimatology. Authors of these papers would hardly be likely to deny the existence of the very thing they are writing about. It is theoretically possible that a paper on paleoclimatology could be the exception, dealing with the lack of evidence for CO2-driven global warming in the geologic past, say, leading the author to question the seriousness of modern, human-caused global warming, but I did not find such papers. What we know for a fact is that among the authors of peer-reviewed articles, only a tiny fraction, which I estimate as about 1 author in 1,000, rejects human-caused global warming. In my opinion, based on my understanding of the history of science, it is reasonable to conclude that the vast majority of publishing climate scientists accept that human activities are causing the Earth to warm. Polls of scientists reinforce this conclusion, but polls are no substitute for the primary, peer-reviewed literature, the ground truth of science.

http://www.jamespowell.org/

______________________________________________________________________________
............................................................................................................................................................


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.

cite