Wednesday, February 26, 2014

A Climate Falsehood You Can Check for Yourself

One problem in arguments about climate (and many other things) is that most of the information is obtained at second, third, or fourth hand, with the result that what you believe depends largely on what sources of information you trust. One result is that people on either side of the argument can honestly believe that the evidence strongly supports their view. They trust different sources; different sources report different evidence. It is thus particularly interesting when on some point, even a fairly minor one, you can actually check a claim for yourself. I believe I have found an example of such a claim.

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."
To check that claim, look at Cook et. al. 2013. Table 2 shows three categories of endorsement of global warming reflected in the abstracts of articles. Category 1, explicit endorsement with quantification, is described as "Explicitly states that humans are the primary cause of recent global warming." Category 2 is explicit endorsement without quantification. The description, "Explicitly states humans are causing global warming or refers to anthropogenic global warming/climate change as a known fact" is ambiguous, since neither "causing" nor "anthropogenic global warming" specifies how large a part of warming humans are responsible for. But the example for the category is clearer: 'Emissions of a broad range of greenhouse gases of varying lifetimes contribute to global climate change.' If human action produces ten percent of warming, it contributes to it, hence category 2, as implied by its label, does not specify how large a fraction of the warming humans are responsible for. Category 3, implicit endorsement, again uses the ambiguous "are causing," but the example is '...carbon sequestration in soil is important for mitigating global climate change,' which again would be consistent with holding that CO2 was responsible for some but less than half of the warming. It follows that only papers in category 1 imply that "human emissions of greenhouse gases are the main cause." Authors of papers in categories 2 and 3 might believe that, they might believe that human emissions of greenhouse gases were one cause among several.
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.

That Cook misrepresents the result of his own research does not tell us whether AGW or CAGW is true. It does not tell us if it is true that most climate scientists endorse AGW or CAGW. It is nonetheless interesting, for two related reasons.

In recent online exchanges on climate, I repeatedly encountered the claim that 97% of climate scientists believed humans were the main cause of global warming. That included an exchange with one of the very few reasonable and civil supporters of the CAGW claim that I encountered in the online arguments, where most participants on either side are neither. So far as I know, the paper says nothing that is not true. But it appears designed to encourage the misreading that actually occurred. It does so by lumping together categories 1-3 and reporting only the sum and by repeatedly referring to "the consensus" but never stating clearly what that consensus is. 

The closest it came to defining the consensus is as the "position that humans are causing global warming," which leaves it unclear whether "causing" means "are one cause of," "are the chief cause of," or "are the sole cause of." To discover that it meant only the former, a reader had to pay sufficiently careful attention to the details of the paper to notice "contribute to" in the example of category 2 in Table 2, which few readers would do. The fact that Cook chose, in a second paper, to misrepresent the result of the first is pretty good evidence that the presentation of his results was deliberately designed to mislead.

There is a second, and more important, reason why all of this matters. Beliefs on either side depend largely on what sources of information you trust. I have now provided unambiguous evidence, evidence that anyone on either side willing to carefully read Cook (2013) and check what it says against what Bedford and Cook claims it says can verify for himself, that John Cook cannot be trusted. The blog Skeptical Science lists John Cook as its maintainer, hence all claims on that blog ought to be viewed with suspicion and accepted only if independently verified. Since, as a prominent supporter of the position that warming is primarily due to humans and a very serious threat, Cook is taken seriously and quoted by other supporters of that position, one should reduce one's trust in those others as well. Either they too are dishonest or they are over willing to believe false claims that support their position.

The fact that one prominent supporter of a position is dishonest does not prove that the position is wrong. For all I know, there may be people on the other side who could be shown to be dishonest by a similar analysis. But it is a reason why those who support that side because they trust its proponents to tell them the truth should be at least somewhat less willing to do so.

P.S. A commenter has located the data file for Cook et. al. (2013). By his count, the number of articles classified into each category was:

Level 1 = 64
Level 2 = 922
Level 3 = 2910
Level 4 = 7970
Level 5 = 54
Level 6 = 15
Level 7 = 9

The 97% figure was the sum of levels 1-3. Assuming the count is correct—readers can check it for themselves—that 97% breaks down as:

Level 1: 1.6%
Level 2: 23%
Level 3: 72%

Only Level 1 corresponds to "the Earth is warming up and human emissions of greenhouse gases are the main cause." (emphasis mine) Hence when John Cook attributed that view to 97% on the basis of his Cook et. al. (2013) he was misrepresenting 1.6% as 97%. Adding up his categories 5-7, the levels of rejecting of AGW, we find that more papers explicitly or implicitly rejected the claim that human action was responsible for half or more of warming than accepted it. According to Cook's own data.

Would anybody now like to claim that lumping levels 1, 2, and 3 together and only reporting the sum was not a deliberate attempt to mislead?

P.S. John Cook eventually responded to my criticism, not here but on the comment thread of another blog that linked to this one. See his response and my comments on it here.

38 Comments:

At 3:33 AM, February 27, 2014, Anonymous Anonymous said...

Good post. The other source of the (questionable) 97% support statistic was a survey done in 2009 by the University of Illinois.( Here's a gated version- http://onlinelibrary.wiley.com/doi/10.1029/2009EO030002/abstract).

The final number was based on 75 out of 77 respondents (of significant eminence) who answered two questions, the first utterly uncontroversial even to a climate skeptic and the second very vague. A breakdown of the poverty of this widely-cited fact can be found here- http://wattsupwiththat.com/2012/07/18/about-that-overwhelming-98-number-of-scientists-consensus/

 
At 3:41 AM, February 27, 2014, Anonymous Anonymous said...

(Same anonymous)

Another link I discovered was a handful of academics who claim their work was wrongly classified in the original Cook paper as showing strong support for CAGW. I don't have the time to cross check anything but it would be appreciated if anyone else has heard things like this- I imagine these people would not have kept quiet if they felt their work was being misinterpreted in such a politicised context.

http://sppiblog.org/news/97-study-falsely-classifies-scientists-papers-according-to-the-scientists-that-published-them#more-9391

 
At 6:22 AM, February 27, 2014, Blogger Charlie O said...

Based on your findings, Cook obviously mis-characterized the results of his first paper.

But calling it a deliberate lie seems a bit strong. I think it more likely that Cook fooled himself into believing that his first paper does in fact show what his second paper claims (97% think humans are main cause).

Not that this quibble changes your analysis of Cook's reliability. He is either a deliberate lair or not a careful objective thinker. Both options make him less reliable.

 
At 6:28 AM, February 27, 2014, Blogger Fred Mangels said...

My guess is he's simply a Believer. One who came up with his conclusion at the beginning, then formed the evidence to lead to that conclusion.

 
At 6:43 AM, February 27, 2014, Anonymous Anonymous said...

Doesn't the statement "a conventional Principal Component Analysis (PCA) is performed" in MBH98 qualify as a flat-out lie?

 
At 8:02 AM, February 27, 2014, Blogger Eric Rasmusen said...

This is a very nicely written post. I might use it in my class, as an example of how to evaluate sources, and how objective data can be misused.

One always must consider the possibility that someone is stupid rather than evil, forgetting his own results rather than lying about them. But that seems implausible here. The original paper does, after all, carefully distinguish the 3 categories. It's like an author who first showed the percentages of blacks, blacks plus hispanics, and blacks plus whites plus hispanics in America and then said, "As I have just shown, 97% of Americans are black."

 
At 8:02 AM, February 27, 2014, Blogger Eric Rasmusen said...

This is a very nicely written post. I might use it in my class, as an example of how to evaluate sources, and how objective data can be misused.

One always must consider the possibility that someone is stupid rather than evil, forgetting his own results rather than lying about them. But that seems implausible here. The original paper does, after all, carefully distinguish the 3 categories. It's like an author who first showed the percentages of blacks, blacks plus hispanics, and blacks plus whites plus hispanics in America and then said, "As I have just shown, 97% of Americans are black."

 
At 8:22 AM, February 27, 2014, Blogger David Friedman said...

Anonymous asks whether Mann's hockey stick paper (MBH98) contains a flat-out lie in its claim to use conventional principal component analysis.

Possibly it does, but it isn't one that an ordinary reader with no expertise in statistics can check for himself.

 
At 10:23 AM, February 27, 2014, Blogger Tibor Mach said...

I think this is an issue in a lot of topics other than global warming as well...the more political the topic is, the more it is an issue.

One very important "life lesson" that was repeatedly told me at the faculty of mathematics and physics in Prague and that which also the mathematicians at the Institute for Mathematical stochastics in Göttingen seem to adhere to is Never trust authorities. In other sense, think for yourself, don't believe something automatically just because this guy is an esteemed author with a lot of reputation. One professor (in a bachelor level course) even put it like this:"I could be your grandfather and you should trust your grandfathers...but don't trust me on anything" :) I even learned it first hand during the writing of my MS thesis. I compared some of my and my advisors work to a book by two esteemed English mathematicians...and we found out a mistake in one of their statements which we then managed to correct so that the statement held under slightly less general conditions (the way it was stated it was false).

On the other hand....

I had the misfortune of having to attend a "diversity competence" lecture today, which is mandatory for all PhD students in Germany and while the lecturer kept covering a wide array of unrelated (and very very left wing) opinions (e.g. she showed us a video of a former Clinton advisor from Davos who spoke about how the state is weak and the big business is very powerful and consists of just "old white men" and how we need to increase the power of the state), all of her arguments were mentions of authorities. "This is true, because this person says that and she has won a Nobel prize". When I tried to mention opposing arguments, she basically cut me out and did not allow any disturbance in her entirely one sided talk (and since I could not stand it and sighed from time to time she then called me offensive and threatened me not to award me credits for the course...I told her I did not like this being so preachy with no chance at a discussion, which I would have probably even enjoyed, while having to be there as it was a mandatory course, but agreed not to show apparent disagreement during the course of her talk and so we at least agreed that the idea that this was mandatory was a bad thing for all of us). It was particularly funny as she kept talking about the importance in diversity, but seemingly she meant superficial diversity of ethnicities and gender and could not stand a diversity of opinions.

Nothing like this has ever happened to me at a university before. If this is what most US liberal arts colleges are like, then that is rather worrying.

Here, at least, 3 people (including me) told her that they would have spent the time differently had the course not been mandatory when she asked for our evaluation and some people at least criticized it to a point...On the other hand a lot of people did criticize it much more during the lunch break but they simply did not want to enter a conflict, which makes me a little bid sad (even though I admit that whatever my reaction to her had been, it would have not changed anything and so perhaps one could say I was only doing it for my ego and could have simply sat through that without any arguments...still, this was too close to a political indoctrination for me to stay above the whole thing).

 
At 10:38 AM, February 27, 2014, Blogger Eric Rasmusen said...

It's important to remember that though academics talk a lot about freedom of thought, a big reason we need to talk about it is because we're very timid people, easily cowed into silence. That's predictable, actually. Mad dog warriors don't become professors (with the possible exception of the former oldest active warrior in the Middle Kingdom). As a result, even tenured professors are remarkably frightened of harsh words and of administrators.

So don't feel too disappointed in your fellow academics--- society does contain braver men; it's just we ought not to trust to bookish scholars for society's freedom.

 
At 10:53 AM, February 27, 2014, Blogger Tibor Mach said...

Eric Rasmusen: I don't think bravery necessarily consists of waving a sword above your head or shooting people. You can be brave in a very different way...that is not being afraid to honestly (but politely if you can) explain your opinion even if all others see you as "an outcast". Even it if means you are shunned to a certain point (by the way, I don't consider myself to be "brave" by confronting that lecturer...I knew a lot of people shared at least partly my opinion of the course even if they were not willing to express it...it could be considered brave if everyone in the room or even everyone at the university was just like the lecturer). And there are even much much more extreme scenarios like the Nazi Germany or Soviet Russia where still people emerged from the academia to criticize the regime...and they probably knew very well what was to follow. That takes at least as much courage as fighting in a battle...or well, that is my guess. Luckily I have never been forced to do either and hopefully I never will be.

Also, that lecturer was definitely really worried. She believed (she told me) that if these ideas do not spread across the world, then we will face a war, a conflict much worse than what Stalin or Hitler or Mao have ever done. If you are truly convinced about such a grave importance of what you are doing then it is easy to become very very preachy. I don't think she is evil and probably not even stupid. I think it is rather sad what an ideology can do to you if you subscribe to it without question. And my (for the lack of a better word I have to say libertarian) opinions can work that way just as well (and I have talked to libertarians with attitudes to other viewpoints perhaps even worse than hers)...so in a way it was very educational for me to see how important it is to try to be actually open minded (while she talked about open-mindedness a lot, she did not exhibit it very much).

 
At 2:55 PM, February 27, 2014, Blogger Ramiro said...

Thanks for calling me reasonable and civil ;)

I'll point out a few issues with your post:
1) You mention there may only be two papers supporting the 97% consensus. Actually there are more than just two. For example, here's another one:
http://www.pnas.org/content/early/2010/06/04/1003187107.abstract
I remember finding a fourth one, but can't seem to find it now. If I do, I will link it.

2) You ignore the "self-rating" section of Cook's paper, whereby scientists were asked to provide their own opinion of their viewpoint. The responses show a 96.4% agreeing with the consensus. Unfortunately, I can't seem to find the exact question that was asked, so it's difficult to determine whether they referred to humans as "main", "significant", or whatever word you can think of.

3) Cook himself in his paper stated:
"Lastly, some subjectivity is inherent in the abstract rating
process. While criteria for determining ratings were defined
prior to the rating period, some clarifications and amendments
were required as specific situations presented themselves. Two
sources of rating bias can be cited: first, given that the raters
themselves endorsed the scientific consensus on AGW, they
may have been more likely to classify papers as sharing
that endorsement. Second, scientific reticence (Hansen 2007)
or ‘erring on the side of least drama’ (ESLD; Brysse et al
2012) may have exerted an opposite effect by biasing raters
towards a ‘no position’ classification. These sources of bias
were partially addressed by the use of multiple independent
raters and by comparing abstract rating results to author
self-ratings"

So he is not deliberately misleading, in fact he stated directly in the paper that there may be some bias introduced in the result. He also stated that the self-ratings were a guard against that, in that the numbers were the same when the authors actually provided their own opinion directly

4) Regarding the comment about the three people who disagreed with how their papers were rated, if only three people had this problem out of 12500, I call that a good result. These may have been mischaracterised because the Cook paper only looked at the abstracts, not the entire paper. One even said that he didn't write his conclusion explicitly in the paper but that they should be able to get the idea from it. Cook never claimed to do a detailed analysis of 12,500 papers.
As I mentioned before, the author self-rating provides backup for the consensus claim, by showing a close match to the 97% number.

I'd like to extend my "make a model" challenge to "study the real consensus". AGW skeptics (and note I will still use AGW as the term here since the paper does not talk about the effects of warming, just the cause) still do not produce a model which explains the current warming trend, and if they really think there is not a 97% consensus, they are more than welcome to perform their own study to determine the result. At the moment, these papers are the best meta-analyses we have, and they all claim numbers at around the same level.

There may be small flaws in each of these studies (no one could claim that they are flawless), but to maintain that they are dishonest or inadmissible as a result is quite unfair.

 
At 4:22 PM, February 27, 2014, Blogger David Friedman said...

Ramiro:

Thanks for joining the conversation.

Your first point is irrelevant to the point of my post, since the question is not whether the 97% statement is true but whether Cook lied about the results of the first paper, which is the source he specified in the second paper for his claimed fact.

"So he is not deliberately misleading"

You are not responding to either piece of evidence I offered that he is--the fact that only the pooled category 1-3 number was reported or the use of "consensus" without defining it in a way that would distinguish between his category 1 and his categories 2 and 3.

"but to maintain that they are dishonest or inadmissible as a result is quite unfair."

I do not think you are responding to what I am arguing is the smoking gun.

Do you agree that, in the second paper, Cook explicitly says that the result of the first paper showed 97% endorsing the view that human action was the *main* cause--as I quoted? (emphasis mine)

Do you agree that neither category 2 nor category 3 in the first paper justifies that description? Again, the clearest evidence is the example for category 2, but the label for category 2, "without quantification," has the same implication.

Do you agree that the 97% figure is for the sum of the three categories?

If you disagree with any of those, explain why. If not, I do not see how you avoid the conclusion that Cook, in the second paper, deliberately lied about the result of the first paper.

My conclusion that the first paper was designed to mislead doesn't have a correspondingly clear proof, but I think the evidence I offered, combined with the misrepresentation in the second paper, provides adequate support for it.

Do you agree that Cook lied? If not why?

If yes, do you agree that is a reason not to trust him?

If you do, do you agree that is a reason to reduce your trust of other people who agree with him and support and rely on him?

Do you agree that your views on climate issues are in large part due to your trusting sources of information, most of which you have not yourself checked?

Hence do you agree that, on the basis of this blog post, you should reduce your confidence in those views?

 
At 6:37 PM, February 27, 2014, Anonymous Mark Bahner said...

Hi David,

Good post! Have you considered asking the John Cook or anyone else at Skeptical Science to comment on your analysis?

I view the whole paper as pretty much a joke. The figures are pretty much worthless. One might, on first glance at the first figure, think that more and more people are "endors(ing) AGW". But the value is only going up because there were more abstracts reviewed in the later years.

What would be useful would be the ratio over the years of the number of abstracts that "endorse AGW" versus those that "reject AGW."

And even more important and useful would be a breakdown into the three separate categories of "endorse AGW." If the percentage in categories 2 and 3 increased, while the percentage in category 1 went down, that would actually not be good for the point Cook et al. were trying to make.

Last, but certainly not least, there is the basic approach of the paper, which *defines* what the "consensus" is, rather than to investigate what the "consensus" is.

 
At 7:11 AM, February 28, 2014, Blogger Eric Rasmusen said...

Tibor Mach: I quite agree that bravery doesn't have to be shown by waving a sword. Or, at least, that in modern times we have to rescale what we mean by "brave", or we're like someone who calls kindergarteners stupid because none of them know calculus. My point is that few academics have even the level of bravery you showed: being willing to speak openly against political correctness in the presence of one of its priests.
Did academics really speak out against the Nazis or Communists? I think the Nazi expulsion of Jewish professors might be a good example of cowardice, though I don't know details, so I might be wrong. I have wondered if there would be significant objection if the US expelled all conservative professors. My prediction is that most remaining faculty would be appalled, would express their condolences privately, and would keep very quiet in public.

 
At 10:22 AM, February 28, 2014, Blogger Tibor Mach said...

Eric: Not many of them, undoubtedly. Then again, the same could be said of anyone else in the third reich or soviet union. It was quite a futile attempt anyway. If bravery does not achieve anything but causes several damage, it might be even called stupid. Do you know the film Life of Brian? And the "Judean people's front crack suicide squad"? That is a perfect example - a bunch of guys being undoubtedly brave...but in an extremely stupid manner that causes more harm to them and their cause than to anyone else. You can be brave in a much more useful way (e.g. hiding jews in your cellar while putting up a facade of a loyal national socialist), it of course depends a lot on the situation you are in and what you can make of it.

I attended the second (it was a two day course) part of the course today. It seems the lecturer thought a bit about what was said to her by those three of us who claimed that this was mostly political opinions. She even admitted she could have skipped certain bits even though she kept going on about that it is definitely entirely political as there is a lot of research behind it (who says political means there are no good arguments? But she did not present any, she was just citing her authorities). Still, the second part seemed to be toned down on these things quite a bit and was far more bearable. Also, it was in some ways closer to a dicussion than the previous day. That is not to say that I am disturbed that what is still 80% political (and one sided atop of that) is given as a mandatory course, but maybe our effort did help make a slight change at least in the way it was presented today.

One thing that amazed me though is that she agreed that bureaucracy caused a lot of problems in many countries, somehow she believed that EU bureaucracy was (mostly) for the good as it made "things more organized and efficient". We did not have a chance to discuss that further, but it struck me as the same kind of wishful thinking I hear from communists who say "well, these past X times those institution failed horribly and lead to something none of their original proponents intended...but this X+1st time it will surely work."

Also, she talked about things such as peer pressure and other stuff that I sometimes agreed was really important. But it struck me as very odd that she did not realize she was in effect excercising (some of) the very same things she mentioned. I guess it goes to what you believe is right...if you believe strongly enough that something is right and without it there will be a huge amount of trouble, not being entirely ethical about it (or what else should I call it?) is well justifiable...much to the annoyance of those who do not share this sentiment or even think that it is those ideas you propose that are a possible danger. That is why this requires a discussion and not a "lecture"...and either way, it should not be mandatory.

Last notion - what she identified as mainstream is quite the opposite of what I see it as. For her, the current mainstream is "reaganomics" or "friedmanism" (and a couple of other labels I forgot), decreasing taxes and the power of the state and decreasing the influence of Academia and especially its social sciences part...I saw most of what she was talking about as the right ways to change that as the most mainstream as you can get in today's EU and (probably from what I can tell from across the pond) North America.

I also wanted to mention Michael Haidt, the US psychologist who I mentioned here and who noticed how extremely one sided his profession is politically (with I think about 80% attendants at a major conference being of a liberal persuation) and how can then such science be considered as objective facts. But there was no opportunity for me to mention that.

 
At 10:23 AM, February 28, 2014, Blogger Tibor Mach said...

Eric: In fact, I don't see how one can talk about the opposite of his ideas being the mainstream with a straight face when he is holding a lecture on those which is made mandatory for all students.

 
At 11:47 AM, February 28, 2014, Blogger Eric Rasmusen said...

Interesting. People do talk differently if they know that one person in the audience disagrees.

 
At 11:52 AM, February 28, 2014, Blogger Busa Blade said...

This comment has been removed by the author.

 
At 11:55 AM, February 28, 2014, Blogger Busa Blade said...

I understand the importance of having trustworthy and verifiable claims. It is extremely important in that ultimately money is spent in the direction of doing something if the claim is correct.
I don't believe anyone is a fan of throwing money at a problem that doesn't exist. What this analysis seems to be is a willingness to toss out a claim over splitting hairs. It is absolutely fair to question biases as they can drive the results and ultimately policy/money.

But, I think you are holding the research to an unfair standard.
I think rather than be concerned with the specific wording, we should be concerned with the data and what does it say? Does it say that the planet is warming? The analysis is not perfect because it is performed by humans. I think requiring it to be perfect before attempting to tackle problems that could ultimately doom us all is in my opinion, short-sighted. I do believe we need to know as much as possible about the problem, but the concern is that we run out of time to correct it while we are hand-wringing over whether it is mostly true or completely true.

 
At 2:58 PM, February 28, 2014, Anonymous Mark Bahner said...

"What this analysis seems to be is a willingness to toss out a claim over splitting hairs."

It's not "splitting hairs" to point out that the paper had 3 categories with respect to endorsement of AGW (anthropogenic global warming) but the author misrepresents all the views as belonging to the first category.

As David Friedman notes, the author must know what was in his own paper, so the author is simply lying about what his paper said. (Or else the author has suffered some sort of brain injury and forgot what his paper said, or something like that.)

 
At 4:44 PM, February 28, 2014, Anonymous Mark Bahner said...

Hi David,

I downloaded data file for this paper into an Excel file:

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

...and did a "countif" for the 7 levels of "endorsement."

These were the results:

Level 1 = 64
Level 2 = 922
Level 3 = 2910
Level 4 = 7970
Level 5 = 54
Level 6 = 15
Level 7 = 9

I wonder why the combined the first three bins? Oh right...to "simplify the analysis." (Heh, heh, heh! Good to see a little humor in a peer-reviewed journal...)

 
At 5:10 AM, March 01, 2014, Anonymous Anonymous said...

David Friedman, I posted a link to this blog post in a Facebook group. One of the members commented, and I'd like your response. Here's his comment:

"Let's put this in context. There have been many claims in the media that there is substantial disagreement among climate scientists that the climate change is driven by human activity. Climate scientists dispute this, but the response is "Ah, you're just giving your own opinions. You can't speak for all climate scientists." So Cook et al went through thousands of abstracts to look for signs of a disagreement on the main argument - that human activity drives climate change. Results: Hardly any papers which deny that humans are the cause. The vast majority accept it, either explicitly or by implication.

The David Friedman blog points out that only a few abstract actually quantify the degree of human impact, suggesting that there is no evidence that the rest of the scientists felt human activity was the main cause.

This is a weak argument for two reasons.

First, most of the 4000 abstracts studied were not attempting to assign proportions of blame to human activities, so it's hardly surprising that most did not quantify the amount.

Second, if there was an alternate cause of global warming which was a bigger cause than human release of greenhouse gases, we might reasonably expect it to show up in the abstracts. We might also expect some scientists to focus on that cause and deny the impact of human activity. It should still show up in the studies. It doesn't. The analysis of abstracts confirms the subjective experience of climate scientists and contradicts the claims by the fossil fuel PR people that there "the science is not settled" or that there is substantial disagreement among scientists about whether human activity causes climate change. That's untrue. There is consensus. It's just one more piece of disinformation in a deliberate disinformation campaign. Don't be a sucker for PR."

 
At 5:16 AM, March 01, 2014, Blogger Tibor Mach said...

Uff...I looked back at what I wrote earlier and I guess I should read it after myself before I click on "publish your comment". There are several unintentionally omitted words that change the meaning of a sentence (like "not") and sometimes the phrasing is very confusing...so sorry for that.

 
At 6:42 AM, March 01, 2014, Blogger David Friedman said...

Anonymous:

Cook's data don't tell us what fraction believe humans are the main cause. They do tell us that, of those who expressed an opinion, a large majority thought humans contributed to warming.

But that's not enough to get the conclusion being argued for. The claim repeatedly made is that 97% agree that humans are the main cause--that is the claim Cook himself makes in the second paper. You can't support that by showing that, of those who express an opinion, 1.6% say humans are the main cause, 95% say that humans are a cause.

The fact that Cook so wildly misrepresented his own data and that the same misrepresentation is made by many others, including the President of the U.S., means that the claim of consensus as it is routinely made is bogus.

"Don't be a sucker for PR" is a relevant comment, but your commenter is applying it in the wrong direction.

 
At 10:24 AM, March 01, 2014, Anonymous Andrew said...

Anonymous:

"The analysis of abstracts confirms the subjective experience of climate scientists and contradicts the claims by the fossil fuel PR people that there "the science is not settled" or that there is substantial disagreement among scientists about whether human activity causes climate change."

I don't think your commenter understands the position of climate skeptics (shills for Big Oil or the poor fools who do it for free). I can't think of anyone who believes that human civilisation has no impact at all on climate. The big question is how much.

If there was a consensus, one would also hope they could be more accurate- between 50 and 100% caused by man is still uncertain. Is there a consensus about how much it is, any more accurate than that?

 
At 10:40 AM, March 01, 2014, Blogger Eric Rasmusen said...

I expect there are a lot of people who think that human CO2 either explains a small part of warming (say, 10%) or explains a lot of past warming but won't cause any future warning because of negative feedback effects, or think there is some probability (say, 10%) that human CO2 is the cause of global warming. None of those people would dismiss the idea human CO2 causes global warming, even though they don't believe it is much of problem.

 
At 11:30 AM, March 01, 2014, Blogger Ma'aji Caleb Zonkwa said...

All arguement propond and proposals put foreward looks reasonable. Unfortunately, the energy misused by we human and ecological upset we subject this our planet in the name of development are bases of climate Change that we should prepare for David.

 
At 3:26 PM, March 01, 2014, Blogger David Friedman said...

Andrew writes:

..."whether human activity causes climate change."

The trouble with wording the question that way is the ambiguity of "causes." It could mean "is a cause of" or it could mean "is the cause of." In my view, Cook deliberately takes advantage of that ambiguity to make it look as though the claim is the latter when it is actually the former.

The difference matters. Human activity as 90% of the cause has different implications than human activity as 10% of the cause.

 
At 4:08 PM, March 01, 2014, Anonymous Andrew said...

David:

You've misread my comment, I was making the same point. The first paragraph was a quote from the anonymous you had just replied to.

 
At 6:23 PM, March 01, 2014, Blogger David Friedman said...

Andrew: My mistake.

 
At 6:56 PM, March 01, 2014, Blogger Douglas said...

Prof. Friedman,

Here's another data point. In a 2013 survey of the members of the American Meteorological Society, the authors concluded that 22% of the respondents with the most expertise "do not subscribe to the position that global warming is mostly human caused." http://journals.ametsoc.org/doi/pdf/10.1175/BAMS-D-13-00091.1. The authors also found that views on the AGW hypothesis also correlated with political leanings - demonstrating that scientists, like all other men, are not immune to prejudice and predisposition.

- Douglas Levene

 
At 6:44 AM, March 20, 2014, Blogger Mike Hammock said...

The 97% number is apparently getting a big publicity campaign.

 
At 3:32 PM, March 29, 2014, Blogger Michael Hartl said...

Super-anal nitpick: the "et" in "et alia" ("and others") is a full word, so "et alia" should be abbreviated as "et al.", not as "et. al."

 
At 2:45 AM, March 30, 2014, Anonymous Anonymous said...

The rabbit hole is very deep. Here is Michael Mann doing a Snoopy dance about a Harvard vindication of his life's work, published in top journal Science, in which the authors took old Ph.D. data that showed no hockey stick blade and bizarrely re-dated low lying input data to afford a pure artifact hockey stick blade by data drop off at the end!

http://s6.postimg.org/jb6qe15rl/Marcott_2013_Eye_Candy.jpg

-=NikFromNYC=-

 
At 8:00 AM, April 02, 2014, Anonymous Anonymous said...

Relevant peer-reviewed paper:
http://www.ncbi.nlm.nih.gov/pubmed/20566872

 
At 10:20 AM, April 08, 2014, Blogger Eric Rasmusen said...

For someone who has some time, here's a fun project. Consider the question: "Are increasing carbon emissions the main explanation for the lack of change in the world temperature from 2000 to 2014?"

 
At 10:37 AM, April 08, 2014, Blogger David Friedman said...

Anonymous provides a link to Anderegg et. al. I think if you read it closely, what it shows is not that 97% of climate scientists agree with the "consensus" but that climate scientists who disagree get fewer articles published than those who agree.

You will note that their sample starts with about a third disagreeing. It's only when they rank scientists by how many articles they publish and only look at the top 50, 100, or 200 that they get overwhelming agreement.

I've emailed the principal author to check a couple of details, plan to do a blog post on the article when I either get a response or conclude I'm not going to.

 

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