Just a few posts ago I wrote about the accuracy of the consensus studies done by Zimmerman, Anderegg and Cook. It was inspired by a graphic with the agreement of scientists on global warming (see the image on the right). At that time I didn’t have the image itself and in this post I used a table with the results. Now, back at home, having a better internet connection than in the hotel, I found that graphic and updated that post with it.
But when looking a bit closer to that image a couple things caught my attention. The Anderegg pie chart says: “97.5% of climate scientists agree humans are causing global warming”. Well, that is not exactly true. As far as I know Anderegg classified climate researchers into two categories: those “who were convinced by the evidence” (903 scientists) and those “who were unconvinced by the evidence” (472 scientists). What the graph should mention is that 97% of the papers from the convinced scientists agreed, not 97% of the scientists. The proportion of unconvinced scientists was 34%, not 3% as presented here! Consensus-scientists tend to publish much more than those who are skeptical (who woulda thunk?), therefor coming to that 97.5% figure.
Over to the next chart, the Cook et al chart. It mentioned something really familiar: “97.1% of the relevant papers agree humans are causing global warming”. I already had a post on this “relevant” paper statement before, but at that time I thought this was just some one-time PR talk. I saw it before in the shapingtommorow website promoting the lecture, so I guess it came from there. But now it was repeated in the lecture. This is no coincidence anymore. They really seems to think that their study consists of “relevant” papers!
Another likely possibility is that they want the unaware viewer to think that their study consists of relevant papers. Just as it is possible that they want the viewer to think that those four pie charts compared the same thing.
It is all about the perception!
But relevant towards what? According to their paper that “human activity is very likely causing most of the current GW (anthropogenic global warming, or AGW)”.
So let us look at those relevant papers they found. As you probably know they were divided into seven endorsement levels from which level 1 was the most convinced (explicitly endorses and quantifies AGW as 50+%).
Category “Mitigation” and “Impacts” already assume global warming as a fact. Those studies didn’t investigate the issue, they just start from there. I wouldn’t call that relevant to the question whether global warming is human caused.
Category “Not climate related” has the same problem, it is not really relevant. Paleoclimate according to the methodology “examining climate during pre-industrial times”, so most likely not about human attribution from industrial times on.
Just by looking at those categories alone only 34% of the papers is left. Even in that remainder subjects like “The Actions Of The European Union For Environmental Protection”, “Consumption-based Accounting Of Co(2) Emissions” or “Cost-benefit Analysis Of Climate Change Dynamics”. The actions of the European Union and Cost-Benefit analysis, that sounds like a solid proof of anthropogenic global warming 😉
These were papers from endorsement level 1. Remember, this category is the top of the bill of the papers that indicate anthropogenic global warming is real. How much of the other papers are really studying “human” attribution?
The question about relevance of the papers was also a question that was posed in the Q&A session. The answer was that there were relevant papers in each category. That could be true, it would even be a nice project to check out how much really were about attribution. But this is not how these results are presented. You know, “most comprehensive study” and “97.1% of 12,000+ papers” or so.