David R. Henderson  

David Friedman on the 97% Consensus on Global Warming

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As David Friedman points out, it is hard for us who are not climate scientists to know what is true or false about global warming. But one thing we can sometimes do is check what various writers on climate science say and see what their statements are based on. David has found a major contradiction in the writing of John Cook. He writes:

Cook et. al. (2013) is the paper, possibly one of two papers, on which the often repeated claim that 97% of climate scientists support global warming is based. Legates et. al. (2013) is a paper which criticizes Cook et. al. (2013). Bedford and Cook (2013) is a response to Legates et. al. All three papers (the last a pre-publication version) are webbed, although Legates et. al. is unfortunately behind a pay wall.

Bedford and Cook (2013) contains the following sentence: "Cook et al. (2013) found that over 97% endorsed the view that the Earth is warming up and human emissions of greenhouse gases are the main cause."

Cook, by the way, is John Cook and here's what his bio on the web site, Skeptical Science, says:
John Cook, the Climate Communication Fellow for the Global Change Institute at the University of Queensland. He studied physics at the University of Queensland, Australia. After graduating, he majored in solar physics in his post-grad honours year. He is not a climate scientist. Consequently, the science presented on Skeptical Science is not his own but taken directly from the peer reviewed scientific literature.

David goes on to show that the very papers that Cook cites do not show that "97% endorsed the view that the Earth is warming up and human emissions of greenhouse gases are the main cause."

David writes:

Reading down in Cook et. al., we find "To simplify the analysis, ratings were consolidated into three groups: endorsements (including implicit and explicit; categories 1-3 in table 2)." It is that combined group, ("endorse AGW" on Table 4) that the 97.1% figure refers to. Hence that is the number of papers that, according to Cook et. al., implied that humans at least contribute to global warming. The number that imply that humans are the primary cause (category 1) is some smaller percentage which Cook et. al. do not report.

It follows that the sentence I quoted from Bedford and Cook is false. Cook et. al. did not find that "over 97% endorsed the view that the Earth is warming up and human emissions of greenhouse gases are the main cause." (emphasis mine). Any interested reader can check that it is false by simply comparing the two papers of which Cook is a co-author. John Cook surely knows the contents of his own paper. Hence the sentence in question is a deliberate lie.


I had pointed this out in a Facebook discussion a few months ago. In retrospect, it would have been worth a blog post. But David has done that well.

I did notice, though, another part of the Cook et al paper that further undercuts the 97% claim and a strange way of writing the piece that, although it does not undercut the claim, does undercut the authors' objectivity.

First, the part that undercuts the 97% claim. In the abstract to their article, the authors write:

We find 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 abstracts expressing a position on AGW, 97.1% endorsed the consensus position that humans are causing global warming.

In short, they got their 97 percent by considering only those abstracts that expressed a position on anthropogenic global warming (AGW). I find it interesting that 2/3 of the abstracts did not take a position. So, taking into account David Friedman's criticism above, and mine, Cook and Bedford, in summarizing their findings, should have said, "Of the approximately one third of climate scientists writing on global warming who stated a position on the role of humans, 97% thought humans contribute somewhat to global warming." That doesn't quite have the same ring, does it?

The strange thing I noticed in the abstract of Cook et al that undercuts their objectivity is the authors' use of the word "consensus." If neither David Friedman's nor my criticism were correct, it would still be the case that the authors use the word in a strange way. Had our criticisms not been correct, then they could justifiably have found a consensus. But take a look at the above sentence in which they use the word. It's the fact (if it were a fact) that 97% agree with a view that makes it a consensus. Had the authors' goal not been to bias the discussion, they would have left out the word "consensus" in the sentence quoted above. And, in case you missed it the first time, later in the abstract, they write, "Our analysis indicates that the number of papers rejecting the consensus on AGW is a vanishingly small proportion of the published research."

David has also added the usual caveats. The fact that Cook has stated a falsehood does not tell us that global warming is not caused by humans. (By the way, I'm not quite as positive as David is that Cook lied. There are only two possibilities, though: either he lied or he doesn't know what the word "main" means. I report: You decide.) What it does tell us is that the claim that 97 percent of climate scientists agree that humans are the main cause is not based on the studies that Cook purported to base it on.

This should, obviously, make us skeptical of other Cook claims, giving the name of his web site, Skeptical Science, an unintended double meaning.


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COMMENTS (40 to date)
Mark Bahner writes:

"The fact that Cook has stated a falsehood does not tell us that global warming is not caused by humans."

I'm just going to pick at that sentence, to expose some of the many subtleties in the issue.

"Caused by humans"-->The warming from the last ice age to the present interglacial was definitely not caused by humans. I think most scientists who study the matter would agree that *all* of the warming from the 1880s to the 1940s wasn't "caused by humans."

"global warming is not caused by humans"-->Even if 100% of global warming from the mid 1970s to the present was caused by humans, it would still not necessarily say something definitive about greenhouse gases. Black carbon has been found to have a larger role than previously thought:

The role of black carbon in global warming

Peter G. Klein writes:

Climate science seems to be one of those scientific fields in which the usual rules and practices of scientific discourse don't apply. No tentative hypotheses offered here, to be tested against the data; just bold, confident assertions and denouncement of heretics. I tried to make this point in blog post and was (predictably) slammed by the commentariat: http://organizationsandmarkets.com/2013/07/31/climate-science-and-the-scientific-method/

MikeP writes:

I'm somewhat astonished at the sheer hubris of believing that the conclusion "97% of X believe Y" is at all likely to be true. That seems to surpass so many statistical tests that it is almost certainly false unless X has been highly preselected to believe Y.

The fact that this putatively generalized result was determined from peer reviewed articles and then was peer reviewed itself only adds to the tragic comedy.

Seriously, this isn't even "97% of the people in a Baptist church on Sunday believe in God." This is "97% of the people in a Baptist church who have convinced the elders and deacons that they believe in God and state an opinion on believing in God believe in God."

Andrew_FL writes:

Having studied the issue extensively in the past...I want to say about five years? I would just like to point out that it is probably true that almost no one would say humans have no effect on climate. In that sense you could perhaps claim a "consensus" exists. That's totally innocuous, though. It is equally innocuous for humans to be responsible for even "most" of the change "since 1950" or whatever it is they 105% certain of this time. Although I suspect that there are many more people who would dispute the second statement than the first, even supposing said second group represents a small minority (which has not been demonstrated in any of these rather bogus sociology exercises), there is no reason to suppose that such is not merely a point of academic curiosity. An effect we can (allegedly) measure, but whose consequences are not of concern for human beings in general. These "studies" don't really address that at all.

And yet, it is telling that in trumping up their findings, Cook and his colleagues claim that one should leap directly from their "findings" to political action. This seems like a cheap way to avoid a lot of important steps that could potentially not go their way.

MikeP writes:

By the way, I believe in anthropogenic global warming.

I do not, however, believe that the economic case is anywhere close to being proven. Far to the contrary, the economics pretty clearly shows that foregoing wealth now to save warming later is simply wasting our progeny's inheritance.

The science is only step 1 of 3. Proponents of addressing global warming with government policy must also prove the economics -- is the future harm greater than the cost of preventing the harm? -- and the politics -- is the future harm greater than the cost of giving new levers of control to governments both liberal and hellish? -- before humanity should at all step down the road of using government to prevent climate change.

Just as one example, global warming proselytizers always consider the chance of catastrophic runaway warming, but they never seem to consider the chance of catastrophic runaway carbon bloc trade wars.

Dave Anthony writes:

What an odd way to get at the opinion of climate scientists. Why not just ASK THEM what they think?

AaronD writes:

"In short, they got their 97 percent by considering only those abstracts that expressed a I find it interesting that 2/3 of the abstracts did not take a position. So, taking into account David Friedman's criticism above, and mine, Cook and Bedford, in summarizing their findings, should have said, "Of the approximately one third of climate scientists writing on global warming who stated a position on the role of humans, 97% thought humans contribute somewhat to global warming." That doesn't quite have the same ring, does it?"

Maybe. But in the current political climate, I am surprised the percentage of those that deny AGW is not higher. Political articles may be the reason why 2/3 of GS don't comment on the issue. Besides, it may be settled science already, and hence repeating the cause seems futile. One would have to look at the timeline of published articles to see "why" 2/3 GS don't comment on cause that they may believe is already proven. The conclusion OP draws is disingenuous as well.

Daniel Kuehn writes:

I am with you on the problems with claiming "main cause" completely, but I'm having a little trouble with understanding your concerns about excluding the 2/3rds (if the paper doesn't discuss the point, how is it relevant to include in the estimate?) and the use of "consensus".

David R. Henderson writes:

@AaronD,
Who is OP?

drobviousso writes:

David - OP is internet jargon for "Original Poster" or perhaps "Opening Poster." AKA, you.

MikeP writes:

Daniel Kuehn,

"Consensus" has a meaning. It means that the great majority positively agrees.

If 2/3rds do not state an opinion, they do not positively agree.

What if the fraction of papers stating an opinion was 3%? Would the takeaway conclusion -- the "fact" that gets reported by newspapers and parroted by the James Hanson's and Al Gore's of the world -- that "97% of climate scientists believe in AGW" still hold?

Daniel Kuehn writes:

MikeP - That seems confused. I published a paper a couple months ago. It was about financial services, but I didn't comment at all on demand deposits. If someone were doing a survey of papers I would be in the 2/3rds that didn't speak to it. That hardly means I'm not in the consensus.

Note that for the one third remaining they did have a category "uncertain about the cause". That seems to me to be the relevant "expressed no opinion" category, because they discussed it but did not declare an opinion. The other two thirds just didn't discuss it! That's hardly grounds for denying a consensus.

Dan Pangburn writes:

The warming trend since the depths of the Little Ice Age and why the warming stopped in 2001 are accurately (95% correlation since before 1900) explained by only two drivers.

CO2 is not one of them.

Search AGWunveiled to see what they are.

David R. Henderson writes:

@AaronD,
Assuming that drobviousso is right about what OP means, are you willing to say why you have accused me of dishonesty?

David R. Henderson writes:

@Daniel Kuehn,
The other two thirds just didn't discuss it! That's hardly grounds for denying a consensus.
You’re right. That’s not grounds for denying a consensus. It IS grounds for their saying it the way I phrased it--so people know there is a huge percent that did not address the issue.

RPLong writes:

The "97%" claim need not be false in order to be objectionable. What is the purpose of pointing out a scientific consensus, except to apply negative peer pressure on the remaining n% of dissidents?

Science does not function by consensus. Physics is not a democracy. Either "97%" are correct or "97%" are wrong. If we are interested in knowing something about climate change, then we should not assign any weight to the prevalence of beliefs.

There is a place for conjecture in science, of course, but we should treat that conjecture the same whether it was made by one scientist or many.

nl7 writes:

It's not terribly controversial to say the Earth is warming, that greenhouse gases are a factor, or that humans contribute greenhouse gases to the atmosphere. But none of that, by itself, requires any real intervention. What's controversial is whether there's a substantial risk of a positive feedback loop such that moderate increases in warming will beget further warming, thus achieving possibly dangerous average temperature and climate points.

You can agree that a car is driving on a road, and that the driver is pressing the gas causing the car to accelerate, but that doesn't mean you must agree that the car is going to accelerate enormously beyond all control and wipe out.

Scientific facts also don't provide conclusive political or philosophical answers.

Daniel Kuehn writes:

I suspect they drew a sample using search terms and found out two thirds weren't relevant to consider. It's a Pelosi thing right - we don't know what's in it till we select it and read it.

I think how you phrased it is just fine but I don't think it's strictly necessary. When people do lit reviews they don't mention how many papers they downloaded but didn't end up mentioning.

MikeP writes:

Daniel Kuehn,

Can you suggest any experiment you can possibly do that polls human beings that would yield this 97% result? One approach is to suggest how tightly you must constrain the category "climate scientist" to come to this conclusion.

Note that you cannot exclude any human beings because they do not state a position.

Thomas Sewell writes:

The other issue with the 97% number, which has been mentioned elsewhere, is that the study was done with particular search terms.

For example, if you search for papers that mention "anthropomorphic warning", then the term itself will tend to be used more by people who believe in it. While people who don't will tend to use a different set of terminology.

To put it into economic terms, if you're looking for the "consensus" on the money supply's relationship to inflation, the terms you choose to search on may give significantly different results if they tend to be phrases used more by Austrians, or Keynesians or another group.

Scott Freelander writes:

What's funny is, that over 97% of those who expressed an opinion said they believe in AGW. That's still a staggering consensus among those expressing an opinion.

Daniel Kuehn writes:

MikeP -
I assume it's 97% because AGW is - as David points out here - not a particularly strong claim. The strong claim is that humans are the "main" cause, and that is precisely what the 97% does not represent.

Ed writes:

@Daniel Kuehn

I think there are couple of reasons to be interested in the percentage of papers that do not express a position on the topic of AGW. The main reason is that it might convey information about some kind of selection bias that's going on. The selection bias could be happening at the review level, or at the level of the researcher deciding what to research.

For example, suppose you're not as gung-ho on AGW, and while you might be interested in it, you don't want to risk going down a possibly cumbersome road (politically). As a result, you do research in related areas that do not express a position on the topic.

So I would be interested to know whether a number like 66% is pretty typical within a sub-field of this "nature". It would be neat to look at the distribution across sub-fields of the fraction of papers that do not express an opinion. I personally don't really have a feeling about whether that 66% is typical or not. I was trying to think of what that number is for something like the stimulus debate but I honestly have no clue.


MikeP writes:

Daniel Kuehn,

From the Cook, et al., Introduction:

We examined a large sample of the scientific literature on global CC, published over a 21 year period, in order to determine the level of scientific consensus that human activity is very likely causing most of the current GW (anthropogenic global warming, or AGW).

This goes back to David Friedman's original complaint that the authors are smuggling two weaker sets of papers into this very strong implicit consensus statement in order to come up with 97%.

Mark Bahner writes:
The strong claim is that humans are the "main" cause, and that is precisely what the 97% does not represent.

And then there needs to be further clarification of the "main cause" of warming from when to when? Because I'd guess than 97+% would agree that human beings were not the main cause of warming from the end of the last ice age to the start of the Industrial Revolution.

And there would probably be considerable debate (with less than 90% on either side) on whether human beings were the "main cause" of warming from the end of the "Little Ice Age" to the 1940s.

Mark Bahner writes:
And yet, it is telling that in trumping up their findings, Cook and his colleagues claim that one should leap directly from their "findings" to political action. This seems like a cheap way to avoid a lot of important steps that could potentially not go their way.

Indeed! I generally try to operate on the assumption that people who disagree with me are simply wrong, and not bad people. But I have troubling evidence that contradicts that premise, specifically with regard to the people at the Skeptical Science website.

They made a blog post with a blatantly false headline: "Global warming: Not reversible, but stoppable."

I repeatedly pointed out that global warming was indeed reversible, and I linked to a post on my blog which shows that for every single IPCC scenario it would be possible for the people of the 22nd century to spend ~10% of their GDP on removing CO2 from the atmosphere, and get down to an atmospheric concentration of 350 ppm CO2 within a few decades:

Global warming *is* clearly "reversible"

They repeatedly censored my comments as "sloganeering," which they define as "Comments consisting of simple assertion of a myth already debunked by one of the main articles..." That's remarkable, since I was actually debunking a myth in their headline.

But even more telling, in my mind, is that I repeatedly asked anyone at the site to provide their guesses for what the world would look like in the 22nd century. I referred them to my guesses posted on my blog:

What is the Morality of the Less-Well-Off Sacrificing for the Better-Off?

Not a single person did post their guesses. To me, that's evidence that they agree with me that people in the 22nd century are likely to be much better off than the people of today, but that they still want the less-well-off of today to sacrifice for the much-better-off of the 22nd century. I think they share my opinion that such a position is immoral, but they simply won't acknowledge it. To me, that makes them bad people.

Pajser writes:

The libertarians should advocate restriction of the pollution, because it is violence against people and their property. I'm flabbergasted that libertarians actually support pollution.

Harold Cockerill writes:

I don't care if 100% of scientists alive today join in the consensus. The idea that a bunch of yahoos in DC will formulate a policy that will have a positive affect on climate is laughable. They would get together and pass a huge law filled with things having nothing to do with climate. They would spend huge amounts of money, put us deeper in debt, slow the economy even more, put more people out of work and in the end probably make the planet hotter. The more they do the worse it all gets. You have noticed that haven't you?

John Cook writes:

As lead author of the Cook et al consensus paper, I can demonstrate how David Friendman ginned up a false contradiction by quoting me out of context. Here is the full line from the Bedford & Cook paper:

Of the 4,014 abstracts that expressed a position on the issue of human-induced climate change, Cook et al. (2013) found that over 97 % endorsed the view that the Earth is warming up and human emissions of greenhouse gases are the main cause.

To generate the 'contradiction', Friedman omits the first portion of the sentence:

Cook et al. (2013) found that over 97 % endorsed the view that the Earth is warming up and human emissions of greenhouse gases are the main cause.

I agree entirely with the OP's assertion of checking what writers say and see what their statements are based on. In this case, Friedman's criticism is based on misrepresentation of my original text. I find it extraordinary that Friedman accuses me of a deliberate lie while misquoting my work (deliberately? You decide). It is also ironic that a theme of this post is checking writing for falsehoods while uncritically repeating his misrepresentation.

Mark Bahner writes:
As lead author of the Cook et al consensus paper, I can demonstrate how David Friendman ginned up a false contradiction by quoting me out of context. Here is the full line from the Bedford & Cook paper:

"Of the 4,014 abstracts that expressed a position on the issue of human-induced climate change, Cook et al. (2013) found that over 97 % endorsed the view that the Earth is warming up and human emissions of greenhouse gases are the main cause."

You don't understand David Friedman's criticism. He says your characterization of your own paper is false, because the 97% includes three different bins of "endorse AGW." Two of those three bins--by your own paper's assessment--can not be characterized as saying "human emissions of greenhouse gases are the main cause."

The best thing for you to do would to go to David Friedman's blog and respond directly to his criticisms.

David R. Henderson writes:

@John Cook,
You admit that you wrote:
Of the 4,014 abstracts that expressed a position on the issue of human-induced climate change, Cook et al. (2013) found that over 97 % endorsed the view that the Earth is warming up and human emissions of greenhouse gases are the main cause.
Yet the paper you cite, Cook et al, did NOT come to this conclusion. Here’s a rewrite of your sentence above that is consistent with your evidence in Cook et al. (1993):
Of the 4,014 abstracts that expressed a position on the issue of human-induced climate change, Cook et al. (2013) found that over 97 % endorsed the view that the Earth is warming up and human emissions of greenhouse gases are one of the causes.
Do you see the difference, John?

Apolloswabbie writes:

A. Consensus is part of one part of the scientific method - forming conjectures and refining them. It has no role in proof or disproof. If the argument is about who's opinion is what, we are not talking about scientific anything. We're talking about opinions.
B. If the data was sufficiently robust, no one would be asking anyone's opinion of whether or not the earth is warming.
C. It seems pretty clear to me that "peer reviewed literature" is easily filtered and has been filtered to reduce the number of publications by those with a non-compliant perspective. If my perception is correct, the definition of "scientist" is "people successful at being published in peer reviewed journals."
D. Warming of the earth may or may not be good for humans. Those who speculate about the consequences, whether they be scientists or armchair AGW quarterbacks like I am, are at most competent at speculation.
E. The sum total of the AGW statement is "we think the sky is falling." "Our" collective response to that has little to do with science and everything to do with politics, fear, and a lack of understanding about what the scientific method is - mixed in with a cultural deference to "experts" which has not served us well in science, politics, religion, or anything else important.
F. Many people seem willing to cede their liberty on the basis of warnings by "experts" or "scientists", and their speculations about future events. It is an effort of will, or a wish for grace, not to feel contempt for them.
G. The 97% statistic, even if it meant what some state it means, is insignificant outside of a political perspective.

Brian writes:

"As David Friedman points out, it is hard for us who are not climate scientists to know what is true or false about global warming."

David,

Why not do a bleg? I suspect that more than a few readers, while not necessarily climate scientists, have a competence in this area and would be able to give you a knowledgeable perspective on any detail you want. The advantage is that you would be getting the perspective of people who tend to be libertarian minded, thereby getting a better sense of what YOU would think if you were more knowledgeable about the science.

Deva writes:

@Pajser - CO2 is naturally exhaled by animals (including us). It is required for plants to live. Plants then give off Oxygen which we need to live. Almost anything is a pollutant in sufficient quantities.


I have seen no one suggesting we don't fight pollution. This is about politics, power grab, etc. If we want to target pollution that is harming people then CO2 would not be where we would be aiming. There are far more pollutants harming people, and the environment. Check out fracking and what it is doing to people and the environment. Yet, we do not see some international motion to create an unelected board to rule all member nations to address fracking.


The first thing you must realize is that CO2 is no more polluting than Oxygen, or Dihydrogen Monoxide (AKA water). Water vapor is actually the more abundant factor in the greenhouse effect.


I responded to you hoping that you had not considered these things. I hope that is the case.

TallDave writes:

"Of the approximately one third of climate scientists writing on global warming who stated a position on the role of humans, 97% thought humans contribute somewhat to global warming."

The large majority of those called "skeptics" or "denialists" (or sometimes "flat-earthers") believe the same thing.

In any case opinion is irrelevant to the workings of the universe -- to paraphrase Einstein, if they were right one would be enough.

Theories are tested by their predictions. The AGW models do not predict climate. The most bizarre aspect of this "debate" is that the notion scientists could predict climate was never evidenced.

Scott Scheule writes:

John,

Do you have any response to Bahner and Henderson's point?

Kendall Ponder writes:
It's not terribly controversial to say the Earth is warming, that greenhouse gases are a factor, or that humans contribute greenhouse gases to the atmosphere. But none of that, by itself, requires any real intervention. What's controversial is whether there's a substantial risk of a positive feedback loop such that moderate increases in warming will beget further warming, thus achieving possibly dangerous average temperature and climate points

Nl7's point raises a question I have asked at different sites without a response. My understanding is the positive feedback is due to warming, not just CO2 induced warming. If that is true and there were no negative feedbacks to counter-act the positive feedback the warming in the first half of the 1900's should have accelerated out of control. Am I missing something they are saying?

Mark Bahner writes:

In case anyone was wondering what the exact breakdown was of 11,944 abstracts, answers can be found in the data file. (With the exception that the data file does NOT separate between "4a" and "4b"...and instead groups them together.)

http://iopscience.iop.org/1748-9326/8/2/024024/media/erl460291datafile.txt

The breakdown was:

(1) Explicit endorsement with quantification = 64 abstracts.

(2) Explicit endorsement without quantification = 922 abstracts.

(3) Implicit endorsement = 2910 abstracts.

4a) No position: Does not address or mention the cause of global warming

4b) Uncertain: Expresses position that human's role on recent global warming is uncertain/undefined

...the total for 4a and 4b combined was 7970.

(5) Implicit rejection = 54 abstracts.

(6) Explicit rejection without quantification = 15 abstracts.

(7) Explicit rejection with quantification = 9 abstracts.

I wonder why they combined #1 (64 abstracts) with #2 (922 abstracts) and #3 (2910 abstracts)?

Oh right...to "simplify the analysis." Good one.

Adam writes:

I'm curious as to why no one has mentioned that the plan by Cook, et al to game the numbers was created before the paper was even researched, written, or released. This was discovered around the middle of last year when private forum posts from Cook's web site were leaked to the public. Here's one place it was written up:

http://www.populartechnology.net/2013/06/cooks-97-consensus-study-game-plan.html

I'm honestly surprised we're still talking about this. The paper by Cook, et al has been so thoroughly debunked, shouldn't it be over by now?

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