Monday, June 9, 2014

Deniers Confirm Consensus

One of the false claims deniers make is that there is no consensus among scientists. This, despite the fact that studies have shown 97% of scientist that have published papers on climate science agree that man made climate change is real. Now, there is some new evidence of the consensus among scientists and, ironically, it comes from the deniers, the same people who claim there is no consensus.

An English denialist organization, the Global Warming Policy Foundation, set out to disprove the study that showed the 97% consensus. There is a very nice article written by two of the researchers in the original study (delving quite deeply into statistical analysis) about the results of the GWPF study. The bottom line is a quote directly from the individual doing the denialist study, Richard Tol:

There is no doubt in my mind that the literature on climate change overwhelmingly supports the hypothesis that climate change is caused by humans. I have very little reason to doubt that the consensus is indeed correct.”
The individuals that did the original paper also established a webpage revealing their methods and the abstracts they studied. Tol came to the conclusion that there was a 91% consensus among climate scientists and this figure is very consistent with the previous study. But, Tol made a big mistake in his methods that resulted in a lower figure. He said the people doing the study and categorizing the abstracts were humans and subject to error (no problem so far). But, then he went on to use improper statistical methods.

In the original study, they had two separate individual look at the abstracts and categorize them. If they both agreed then there was no problem. In the cases where they disagreed, they first reexamined the abstracts to see if they could reconcile their results. In the case where a difference of opinion still existed, a third person was called in the settle it. After all of this, there was still about 6.7% of the papers categorized as being miscategorized. He looked at the initial grades and noted that about 55% of the disputed papers were moved to the denial category while 45% were moved to the support category. So, he used that same percentage on the 6.7% that may be in the wrong category and that is how he ended up with the 91%.

I would say that this completely proves the point that there is a very strong consensus among scientists. But, there is more to the story.

Tol incorrectly included changes where the paper remained in the same category, but was shifted between a stronger and weaker stand. This is not the same as shifting between supporting climate change and rejecting it. When these kinds of errors were corrected, Tol's study actually showed a consensus of 97.2% and compared to 97.1% in the original study.

In other words, an individual that wanted to discredit the consensus study actually obtained a result that showed an even slightly stronger consensus.

So, equipped with the 91% consensus of his own published work, and not withstanding his statement that is quoted at the top of this page, what did Tol do? He went before Congress and stated,
" far as I can see, this estimate just crumbles when you touch it ... this 97% is essentially pulled from thin air."
 Is there any doubt at all that the deniers are liars and deceivers?


  1. Hi Chris,

    Thanks for taking the time to read our response, but I think we confused you slightly.

    We rated abstracts on a score of 1-7, where 1 was strongest acceptance, 4 was no position and 7 strongest rejection of the consensus that most of the recent warming is man-made. As you go up the scores you get 'closer' to rejection, but that doesn't mean you go from endorse to reject. Moving from 1 to 2 is still an endorsement, it's just less explicit!

    55% of disagreements ended up with the paper's score going up, and 45% with it going down. But lots of those were just papers moving around inside endorsement, or between endorsement and no position.

    If you look at papers where one rater went for 'no position' but it was ultimately decided that the paper was 'endorse' or 'reject', 98% of the time it was endorse, and 2% of the time it was reject. Instead of moving 2% of the remaining uncertain 'no position' abstracts to rejection, Professor Tol decides to move 55%.

    We redid the sums, using 2 = 2 instead of 2 = 55 and that's where we found out that the consensus actually goes up, but only by a tiny amount. For all intents and purposes it's still 97%, and I'm sure that Professor Tol will publish a correction once he's checked his sums.

    1. Thank you for your clarification. It would be a good thing if Professor Tol printed a retraction, but will he make a retraction for his statement to Congress?