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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. The original article by Cook et al. [CEA] 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 articles. (Try this yourself with a random selection of 300 peer-reviewed articles here.) The true consensus on AGW is bound to be much higher than 97%.

Here is a summary of my critique of the CEA article. Quotes are from the CEA article:

1. CEA ruled out "66.4%" of the published literature, 7,930 of 11,944 articles. But because the consensus is what the majority accept, it is logically impossible to rule out a two-thirds majority and still measure the consensus.

2. CEA ruled those 7,930 articles out of the consensus because they did not “express an opinion on AGW,” labeling them as taking “no position.” Consensus has to do with what people agree about—that is what the word means. But CEA re-defined "consensus" to mean not just agreement, but STATED agreement. Isn't it obvious that many more scientists accept a given theory than happen to say so explicitly in their writing?

3. There are two possible interpretations of the "no position" articles: (A) The authors of the 7,930 articles truly have no opinion on AGW, in which case there is no majority consensus in its favor. But no climate scientist writing about global warming could fail to have an opinion about it, so this interpretation defies credulity. (B) These authors do have an opinion about AGW—they accept it (see the article below for justification)—but they failed to say so explicitly. In that case, these authors must be counted in the consensus.

4. In fact, publishing scientists almost never state their opinion on the ruling paradigm. Not one author of 500 recent articles on plate tectonics did so (see 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, must the biologist say so explicitly? The scientific literature falsifies the use of explicit endorsement, the sine qua non of the CEA method, as the criterion of consensus.

5. To count an article, CEA required that it “address or mention the cause of global warming.” But authors who write about some aspect of global warming other than its cause have no reason to make such a declaration. They might, or they might not. The CEA method thus has to do with language and whether the subject of an article lends itself to a statement on attribution, not with whether the authors accept AGW, the true measure of consensus

6. CEA ruled out of the consensus a number of 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.) Most of these authors also had articles in one or more of the other endorsing categories, confirming that they do accept AGW. This is further evidence that the CEA method is not about what authors accept, but about the subject of their articles. How else could articles by a single author show up in three different endorsement categories and also in the "no position" category?

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.

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

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