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The True Scientific Consensus on
Anthropogenic Global Warming

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The article below, under review by Environmental Research Letters and submitted Jan. 9, 2015, appears with the consent of the journal’s editor. It critiques an article by Cook et al. [CEA] which describes the results of their survey of the peer-reviewed literature on anthropogenic global warming (AGW). Their article is the basis for the widely believed “97% consensus” on AGW.

If the consensus were 97%, then if you read, say, 300 peer-reviewed articles you should find on average 9 that reject AGW. Instead, to find even a single rejecting article, you must read nearly 5,000. Try your hand at reviewing articles using a random selection of 300 here. You will quickly confirm that the true consensus on AGW cannot possibly be as low as 97%.

Below is a summary of my critique of the CEA article. The quotes, except for the first, are from the article:

1. The Oxford English Dictionary (2014) defines consensus as “Agreement in opinion; the collective unanimous opinion of a number of persons.” CEA redefined consensus to mean not merely to have an opinion, but to “express an opinion. ” It is obvious that many more scientists accept a theory than may happen to directly express their acceptance in their articles (see 5). Thus the CEA method is bound to underestimate the consensus of acceptance.

2. CEA ruled out "66.4%" of the published literature, 7,930 of 11,944 articles, because they took "no position." But because the consensus as defined and commonly understood is what the majority accept, it is logically impossible to rule out a two-thirds majority and still measure the consensus.

3. CEA ruled those 7,930 articles out of the consensus because they did not “address or mention the cause of global warming,” labeling them as taking “no position.” But if two-thirds of authors truly have no position, then ipso facto AGW cannot be the consensus position of climate scientists.

4. The articles that CEA reviewed are about global warming—that is why they came up in the CEA search. Obviously, the authors of the “no position” articles do have an opinion on global warming—they are writing about it. I argue that virtually all of them accept AGW and are part of the consensus.

5. Publishing scientists almost never directly endorse the ruling paradigm of their discipline. Not one author of 500 recent articles on plate tectonics did so (see the article below), nor did the authors of 261 articles on evolution or 100 articles on lunar craters. Before we can believe that a publishing biologist accepts Darwinian evolution, does the biologist have to say so explicitly? Of course not. The literature of science itself falsifies the use of explicit endorsement, the sine qua non of the CEA method, as the criterion of consensus.

6. The premise of the CEA method is that only authors who directly attribute global warming to human activities can count in the consensus (“address or mention the cause of global warming”). But authors who write about some aspect of global warming other than its cause have no particular reason to make such an attributive statement. The CEA method thus has do not with the scientific consensus on AGW, but with language and whether the subject of an article lends itself to a statement on attribution.

7. CEA ruled out of the consensus many articles by distinguished climate scientists whose acceptance of AGW is not in question, placing them in the "no position" category. These included (with number of omitted articles) R. Bradley (3), K. Briffa (2), E. Cook (5), J. Hansen (6), M. Hughes (2), P. Jones (3), T. Karl (5), M. Mann (2), M. Oppenheimer (3), B. Santer (2), G. Schmidt (3), the late S. Schneider (3), S. Solomon (5), K. Trenberth (7), and T. Wigley (3). (From the CEA Supplemental Materials.) Can a method that omits from the consensus articles by such eminent scientists possibly be right?

8. Most of the above authors in the “no position” category, and many others, also had articles in one or more of the three CEA endorsing categories. James Hansen, for example, has 4 articles in CEA category 1 (Explicit Endorsement with Quantification), 6 in category 2 (Explicit Endorsement without Quantification), and 6 in category 3 (Implicit Endorsement), as well as the 6 in category 4 (no position), as noted. That articles by a single author can appear in several different CEA categories is critical to understanding exactly what CEA measured and did not measure. Hansen, for example, has articles in CEA category 1, establishing that he fully accepts that humans are the primary cause of observed global warming. This is what we want to know: whether James Hansen is part of the scientific consensus on AGW, and he is. That he also has articles in other CEA categories has nothing to do with whether he accepts AGW. Rather it has to do with the subject of those articles and whether they lent themselves to the explicit endorsement that CEA required.

CEA classified articles. They did not measure the scientific consensus on anthropogenic global warming.

The only sound and practical way to judge the extent of a scientific consensus is to search for articles that reject the prevailing theory. For 2013 and 2014, I found that only 5 of 24,210 articles and 4 of 69,406 authors rejected anthropogenic global warming, showing that the consensus on AGW is above 99.9% and likely verges on unanimity.

See here for my methodology. Enter your comments on the Forum. If no PDF file appears below, download it here.

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