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Is it 97% or 66% of climate scientists who believe in AGW?

27 Mar

The 97% claim on the "Skeptical Science" website

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.

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7 Comments

Posted by on March 27, 2011 in Uncategorized

 

7 responses to “Is it 97% or 66% of climate scientists who believe in AGW?

  1. Robert

    March 27, 2011 at 7:11 pm

    What is your definition of consensus? Compare, for example, the state of the “debate” over the theory of evolution, or the safety of vaccines, or the age of the earth. One might argue that when a political ideology finds a scientific truth very repugnant, they will always be able to enlist some educated people to their cause, and hence it makes more sense to look at the scientists with proven expertise as demonstrated by their publishing records.

     
  2. Sam

    March 27, 2011 at 8:10 pm

    Thanks for joining the conversation Robert.

    Are there hundreds of biologists who have signed statements saying that evolution isn’t true?

    Are there hundreds of biomedical engineers or pediatricians who have signed statements saying that vaccines cause autism?

    Are there hundreds of geologists who have signed statements saying that the earth is only 6,000 years old?

    These are good examples of pseudo-debates, where this is practically no real discussion in any literature and very very few reputable scientists willing to embrace the position.

    You are right in saying that every issue will have dissent, but look at the people who primarily dissent in the creation-evolution debate. They are religious figures with a poor scientific background.

    This is clearly not the case in climate science. The headlining dissenters, Lindzen, Christy, Spencer and the like, have all made serious contributions to the field and raise very legitimate questions.

    Another difference from your examples and climate science is a matter of degree. Either evolution is true or creation is. Either vaccines cause autism or they don’t. Either the earth is 6,000 years old or it isn’t.

    In climate change, saying that humans are going to warm the world by 1c over the next century puts you outside the consensus, but it is not a position so very different from someone expecting a 2.5c rise. It’s not black and white, the range of possible positions to hold on climate change is massive.

    This is important because the line between consensus and non-consensus opinions is blurred. In climate science, someone like Patrick Michaels is considered outside the consensus even though he accepts the low end of the IPCC range of warming. Why? Because he does not accept the solutions presented. Those should be two completely different arenas, but they are not.

    It’s a bit of a muddled mess and Anderegg 2010 doesn’t help by creating those two groups, CE and UE. It’s far too complicated for that.

     
  3. Robert

    March 27, 2011 at 10:11 pm

    “Are there hundreds of biologists who have signed statements saying that evolution isn’t true?”

    Yes. See, for example:

    http://www.answersingenesis.org/home/area/bios/

    http://www.discovery.org/scripts/viewDB/filesDB-download.php?command=download&id=660

    Hundreds and hundreds . . . with all the same questions and problems as the lists of supposedly anti-AGW scientists. Are their beliefs being accurately represented? Do they actually have any expertise in the field itself?

    “These are good examples of pseudo-debates, where this is practically no real discussion in any literature and very very few reputable scientists willing to embrace the position.”

    I’m glad we agree these are pseudo debates. Now, obviously the point on which we differ is whether the “debate” over the existence of AGW is, similarly, a pseudo-debate. I believe it is, while you believe it is not. What I am asking for is some set of objective criteria which you are using to tell the one from the other. As my links illustrate, the presence of long lists of “dissenting” “scientists” is a common one in the anti-science discourse, and not a good choice to separate the two.

    This practice of amassing lists is so popular among cranks that it has inspired parody:

    “NCSE’s “Project Steve” is a tongue-in-cheek parody of a long-standing creationist tradition of amassing lists of “scientists who doubt evolution” or “scientists who dissent from Darwinism.”

    Creationists draw up these lists to try to convince the public that evolution is somehow being rejected by scientists, that it is a “theory in crisis.” Not everyone realizes that this claim is unfounded. NCSE has been asked numerous times to compile a list of thousands of scientists affirming the validity of the theory of evolution. Although we easily could have done so, we have resisted. We did not wish to mislead the public into thinking that scientific issues are decided by who has the longer list of scientists! ”

    The anti-vaccine cranks have their lists too:

    http://www.generationrescue.org/recovery/doctors
    http://www.autism.com/pro_danlists_results.asp?list=US&type=1

    . . . and so on. So my question remains, how do you define consensus or, if you like, pseudo-debate vs actual debate?

    PS: As a note, this is not correct: “In climate change, saying that humans are going to warm the world by 1c over the next century puts you outside the consensus.”

    In fact, models whose lower band include 1C by 2100 are cited in the IPCC report and, thus, are part of the consensus. To truly leave the consensus, you need to either reject AGW completely, or assert in the face of the evidence that we can be confident that warming will be no more than, say, 1C.

    I agree that the lines are blurred, but I think you underestimate the flexibility of other psuedo-debates. The anti-vaccine crowd, for example, once blamed the vaccines themselves, and then thermasol, and now that thermasol is gone they have come up with some other theory. Some people say are vaccines are unsafe, some only have a problem with live-attenuated, and many people who will tolerate vaccines one at a time have come to believe that multiple vaccines at one visit are not. Some people think vaccines are fine for older children but dangerous for infants. And so on.

    So the lines in these debates are often blurred, not so much because it is hard to chose sides on the evidence as because people whose emotional need to cling to a position is strong will reposition themselves when the facts disprove the position in its original form.

     
  4. Sam

    March 28, 2011 at 1:01 pm

    Actually I asked if there were hundreds of biologists who challenged evolution. There were 107 in that list. It’s a higher number than I expected, but it still isn’t hundreds, and it’s drawn from a field much larger than climate science.

    Also, the use of the Autism lists is questionable. Those organizations are broader than simple resistance to vaccine. Actually the word vaccine doesn’t appear anywhere in those lists.

    In fact, models whose lower band include 1C by 2100 are cited in the IPCC report and, thus, are part of the consensus. To truly leave the consensus, you need to either reject AGW completely, or assert in the face of the evidence that we can be confident that warming will be no more than, say, 1C.

    The IPCC report states that is it “very unlikely” that climate sensitivity is lower than 1.5c, and I generally hear that as the lowest range considered to be “consensus”.

    You don’t have to reject AGW to be considered outside the consensus. I accept AGW as real, but substantially less than the IPCC claims, and not an issue that needs a governmental response. You may claim I am within the consensus, but it certainly doesn’t feel like it. The consensus implies action, whether it should or not.

    I agree that the lines are blurred, but I think you underestimate the flexibility of other psuedo-debates.

    You may be right on this. I was unaware of the tenacity of the anti-vaccines and others.

    So my question remains, how do you define consensus or, if you like, pseudo-debate vs actual debate?

    This is a question which requires more thought. While I have in intuitive answer, It’ll take some time to put it in words. I may devote an entire post to it.

    Thanks for the discussion.

     
  5. Lazarus

    April 3, 2011 at 6:16 am

    I must say that I agree with Robert.

    When I think of consensus in this issue it isn’t the number of individual scientists that make the issue compelling but the number of credible scientific organisations.

    As far as I’m aware there isn’t a single National academy or institute anywhere on the planet that has expressed any serious doubt about AGW. That makes it more 100% and since they represent their members there can’t be enough dissent with scientists in any country to currently suggest anything less than the science is considered sound.

    And to be fair when you cite evolution as an example where the decenters are poorly educated you miss the point that there are a fair numbers of cranks like Monckton or pure politicians who are commenting the loudest and well outside their area of credible expertise.

     
  6. Lachlan

    May 5, 2011 at 8:13 am

    Hey! I finally found some people with brains!

    As is usually the case; the truth is somewhere in the middle.

    A creator could have programmed evolution into out DNA, vaccinations could have (probably have had) massively negative impacts on select individuals and climate change…..?

    We’ll see…

     

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