The "97% consensus" on anthropogenic global warming: wrong assumptions, wrong method, wrong result. The true consensus of acceptance of AGW among publishing scientists is above 99.9%: virtual unanimity. The peer-reviewed literature contains no convincing evidence against AGW.

See my article debunking the "97%" consensus" in the November-December issue of Skeptical Inquirer, Vol. 39, 42. And this online article in Patheos by Hemant Mehta. This quote from Mehta's article nails it: "There are literally more Republicans in Congress who deny climate science than there are published scientists who feel the same way." In fact, combining an article by Tiffany Germain on with my results, the House of Representatives holds 40 times as many global warming rejecters as are found among the authors of scientific articles. If you want to find global warming deniers, don't start reading scientific articles: that will take way too long, believe me. Instead visit the House Science, Space, and Technology Committee.

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The True Scientific Consensus on
Anthropogenic Global Warming

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Cook et al. (Environmental Research Letters, 2013) describe the results of a 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%.

Cook et al. made several errors that invalidate their method and their result:

1. The Oxford English Dictionary (2014) defines consensus as “Agreement in opinion; the collective unanimous opinion of a number of persons.” Cook et al. redefined consensus to mean not merely to have an opinion, but to “express an opinion” and in writing. 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 Cook et al. method is bound to underestimate the consensus of acceptance.

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

3. Cook et al. 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. Conversely, if AGW is the consensus position, then Cook et al. have demonstrated that a majority of authors accept the theory but do not “express an opinion” on it in their articles, thus falsifying the Cook et al. method.

4. The articles that Cook et al. reviewed are about global warming—that is why they came up in their 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. I make that argument because 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. Only 2 of 619 authors of articles on global warming and climate change in Environmental Research Letters in 2013 endorsed AGW. Before we can know whether a publishing biologist accepts Darwinian evolution, to take one example, does the biologist really 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 Cook et al. method, as the criterion of consensus.

6. The premise of their 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 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. Cook et al. 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 Cook et al. 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 Cook et al. endorsing categories. James Hansen, for example, has 4 articles in Cook et al. 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 Cook et al. categories is critical to understanding exactly what Cook et al. measured and did not measure. Hansen, for example, has articles in Cook et al. 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 Cook et al. 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 Cook et al. required.

Cook et al. 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.