The claim that “97% of climate experts agree humans are causing global warming” is all over the internet. The most common study cited to support this claim is Doran 2009. However, I wrote an article about that paper which I believe shows it is fundamentally flawed. Even “skeptical” climate scientists answered the survey in such as a way as to be included in the consensus group.
Doran 09 is flawed, but it is not the only paper cited to make the 97% claim. There is one other, Anderegg 2010. This study breaks down climate scientists into two groups, those who are convinced by the evidence (CE) on anthropogenic climate change, and those who are unconvinced by the evidence (UE). Here is the abstract (emphasis mine):
Although preliminary estimates from published literature and expert surveys suggest striking agreement among climate scientists on the tenets of anthropogenic climate change (ACC), the American public expresses substantial doubt about both the anthropogenic cause and the level of scientific agreement underpinning ACC. A broad analysis of the climate scientist community itself, the distribution of credibility of dissenting researchers relative to agreeing researchers, and the level of agreement among top climate experts has not been conducted and would inform future ACC discussions. Here, we use an extensive dataset of 1,372 climate researchers and their publication and citation data to show that (i) 97–98%of the climate researchers most actively publishing in the field surveyed here support the tenets of ACC outlined by the Intergovernmental Panel on Climate Change, and (ii) the relative climate expertise and scientific prominence of the researchers unconvinced of ACC are substantially below that of the convinced researchers.
There is the 97% claim. Someone reading this might agree it supports the claim that 97% of climate scientists agree about anthropogenic climate change (ACC). They mention a dataset of 1,372 climate researchers and then give the 97% number. You might think this mean 1331 researchers believe in ACC, and only 41 researchers reject it.
You’d be wrong. The actual numbers are 903 who accept AGW, and 472 who reject it. That gives us a percentage of researchers who believe in ACC of about 66%.
How did I come up with these figures? If you look closely in the paper, you’ll find them, but it’s much easier to see them in the SI. Take a look. Here is the CE number:
We compiled a database of 1,372 climate researchers and classified each researcher as either convinced by the evidence (CE) for anthropogenic climate change or unconvinced by the evidence (UE) for ACC. We compiled these CE researchers comprehensively (i.e., all names listed) from the following lists: [List of lists here] After removing duplicate names across these lists, we had a total of 903 names.
Here is the UE number:
We define UE researchers as those who have signed reputable statements strongly dissenting from the views of the IPCC. We compiled UE names comprehensively from the following 12 lists: [List of lists here] After removing duplicate names across these lists, we had a total of 472 names.
There you have it. The 66% number doesn’t appear anywhere in Anderegg 2010. Is this dishonest?
No, and let’s look at the introduction again to see why:
Here, we use an extensive dataset of 1,372 climate researchers and their publication and citation data to show that (i) 97–98%of the climate researchers most actively publishing in the field surveyed here support the tenets of ACC outlined by the Intergovernmental Panel on Climate Change
That’s the qualifying statement that makes this possible. They define who the most active scientists are, and then it is 97% of that group that believes in ACC.
I questioned Anderegg about this and he was nice enough to reply. He acknowledges that his paper doesn’t look at all climate scientists, only at the most active publishers. However, he wants to make clear that the 1,372 number is not representative of the total number of scientists (and so the 66% number isn’t correct). Here is part of his response:
my groups are NOT representative of the total number of scientists because 1) we went out of our way to get all major skeptic’s declarations and only a few mainstream declarations, 2) mainstream scientists have been much more reticent to sign declarations, and 3) many scientists, regardless of camp, have not signed these declarations – thus the survey/polling methods of these other two studies are more appropriate for assessing the total numbers of scientists
He’s right on the first point. They used twelve lists for the UE, and only five for the CE. This makes it likely that UE are over-represented. As for the second point, I don’t know if that is true or not. The third point is undoubtedly true, but doesn’t mean the composition of CE versus UE is different. And the “other two studies” refer to Doran 09 (which I’ve already mentioned), and Rosenberg et al 2010. As an aside, Rosenberg et al 2010 does not agree with the 97% claim. It’s more like 88%.
I believe that Anderegg is right in cautioning us not to use the 66% figure. However, others are wrong in using Anderegg 2010 as evidence for the claim that 97% of climate scientists believe in AGW. The study does not claim that, it clearly is only referring to only those scientists who are most actively publishing. Of course, this definition is subjective, and many other scientists have been critical of Anderegg 2010 for this reason. Marc Morano has a list of websites which challenge Anderegg 2010. (Note: Morano calls it “the black list paper” because it creates two categories which he believes are ‘the good guys’ and ‘the bad guys’, and presumably the bad guys will be blacklisted. Pielke Sr. and Jr. both have written about this, and both seem to agree. I’m not so sure this paper will have that effect, but I understand their concern about such a black and white approach.)
Could the 97% claim still be true? It certainly could be, but it looks like quite a high estimate. As I said before, Rosenberg 2010 found more like 88% believed in AGW. I expect the number is higher than 66% and lower than 97%.
Does the percent really matter all that much? It doesn’t affect the science one iota, but it does form the basis of the claim that there is a consensus among climate scientists about AGW. To me, it seems difficult to claim a consensus exists about something when over 400 scientists sign statements explicitly saying that a consensus doesn’t exist.
It seems undoubtedly true that the majority of climate scientists do believe in AGW, but it also seems untrue that a consensus exists. Majority doesn’t mean consensus.