Sadly, a large percentage of Americans are under the impression that climate scientists do not agree on the reality of anthropogenic global warming (AGW). A lot of people are simply wrong about this. They think that there is a great deal of controversy among the scientists who study the Earth’s climate. But there isn’t. One way we know this is from a study done by John Cook, Dana Nuccitelli, Sarah A Green, Mark Richardson, Bärbel Winkler, Rob Painting, Robert Way, Peter Jacobs, and Andrew Skuce, called “Quantifying the consensus on anthropogenic global warming in the scientific literature”

In that study, the authors analyzed “the evolution of the scientific consensus on anthropogenic global warming (AGW) in the peer-reviewed scientific literature, examining 11,944 climate abstracts from 1991–2011 matching the topics ‘global climate change’ or ‘global warming’.” They learned that “66.4% of abstracts expressed no position on AGW, 32.6% endorsed AGW, 0.7% rejected AGW and 0.3% were uncertain about the cause of global warming.” Among the papers that expressed a scientific position on the topic, “97.1% endorsed the consensus position that humans are causing global warming.”

The study was actually a bit conservative, as in order to be counted as part of that ~3% not supporting the consensus position on AGW a paper did not really have to be fully against the idea. Also, since the study was done, the consensus has increased. I asked study author Dana Nuccitelli about more recent changes in consensus, and he told me, “The consensus is growing over time, and reached 98% in 2011 (the last year included in our survey). So by now the minimizers/deniers are probably in the 1-2% range in the peer-reviewed literature (contrary to the ‘crumbling consensus’ claims).”

The other day I was giving talks at a local high school, and between classes, found myself chatting with a science teacher who had just completed a module on climate change and AGW. She asked me, “Isn’t there now research that shows that the consensus isn’t really as high as previously thought? Or is that bogus? Sounds bogus to me.”

Yes. Bogus.

I’m not sure what research the teacher was referring to (it was just something she had heard about) but there is a paper just published in “Energy Policy” by economist Richard Tol, who as far as I can tell has been a naysayer of climate science for some time now. Tol’s abstract says:

A claim has been that 97% of the scientific literature endorses anthropogenic climate change… This claim, frequently repeated in debates about climate policy, does not stand. A trend in composition is mistaken for a trend in endorsement. Reported results are inconsistent and biased. The sample is not representative and contains many irrelevant papers. Overall, data quality is low. Cook’s validation test shows that the data are invalid. Data disclosure is incomplete so that key results cannot be reproduced or tested.

Nuccitelli has responded to Tol’s paper, in a post at Skeptical Science called “Richard Tol accidentally confirms the 97% global warming consensus.”

Concern Tol-ing

Tol is practicing a special kind of science denialism here, sometimes called “seeding doubt” or as I prefer it, “casting seeds of doubt on infertile ground.” In other contexts this is called “concern trolling” or the “You’re not helping” gambit. The first of two paragraphs of the Conclusion section of Tol’s paper reads (emphasis added),

The conclusions of Cook et al. are thus unfounded. There is no doubt in my mind that the literature on climate change overwhelmingly supports the hypothesis that climate change is caused by humans. I have very little reason to doubt that the consensus is indeed correct. Cook et al., however, failed to demonstrate this. Instead, they gave further cause to those who believe that climate researchers are secretive (as data were held back) and incompetent (as the analysis is flawed).

Let’s get straight that Cook et al is not flawed, despite Tol’s complaints.

Tol’s main complaint is in the coding of the abstracts. He claims that it is imperfect. Well, duh. This is, essentially, social science research, and coding of text is imperfect. Tol makes the claim that the imperfections, if corrected, might bring the consensus down to a dismal 91%. I’m pretty sure he’s wrong about that, but if he is right, we are not impressed.

Tol’s key point is that the papers that are coded as not making a claim include some that do. He then incorrectly calculates how many of of those, if coded “correctly” there would be, and using this, downgrades the consensus to 91%

Nuccitelli explains in detail, in his post, how Tol’s re-analysis is badly done (see the amazing graphic at the top of this post) (go read it) and notes:

In reality, as our response to Tol’s critique (accepted by Energy Policy but not yet published) shows, there simply aren’t very many peer-reviewed papers that minimize or reject human-caused global warming. Most of the papers that were reconciled ‘towards stronger rejection’ went from explicit to implicit endorsement, or from implicit endorsement to no position. For abstracts initially rated as ‘no position,’ 98% of the changes were to endorsement categories; only 2% were changed to rejections.

Nuccitelli also notes that a separate study indicates that Tol’s method is flawed in the sense that no matter what data are used, the consensus will be decreased as an artifact of the methodology. Nuccitelli notes “…by making this mistake, Tol effectively conjured approximately 300 papers rejecting or minimizing human-caused global warming out of thin air, with no evidence that those papers exist in reality. As a result, his consensus estimate falls apart under cursory examination.”

Amazingly, when the Consensus research team fixed Tol’s methodology but applied the same question about coding papers in the no-position category, and re-calculated the percent consensus, it went up by 0.1%. Also, as Nuccitelli points out the Cook et al paper is not alone, and there have been a number of other studies that show essentially the same level of consensus among papers and/or scientists.

So, the consensus is real and isn’t going away. As is also the case with Anthropogenic Global Warming.