The consensus explained: cats are difficult to herd, but apparently can agree with each other

Just a quick post on the Cook lecture yesterday. It was an interesting lecture and there seemed to be quite some skeptical voices present. For whatever reason, there were however a lot of seats still empty.

In general I didn’t hear anything new in the lecture. If one reads his paper and visited the skepticalscience blog it would all be very recognizable.

It started a bit odd however. Cook showed the statement that scientists rely on testable evidence and that they are like cats, difficult to herd. To be honest, I didn’t really expect such quotes. These are usually used by skeptics. It made me even more curious about what would come next. His research can not possibly follow from those … this promised this be an interesting lecture…

Then came a question to the public if someone could explain the process global warming. He said he asked it several times in other occasions, yet only one seemed to have answered it correctly until now. To him it was a two way process and most of the people who answered it, explained only one of them.

The two processes are: carbon dioxide is transparent for sunlight, but laying a blanket over the earth so less heat escapes to space. To him these were testable processes. Less heat escapes to space, more heat getting trapped, so a cooling of the upper atmosphere, hence shrinking, etcetera, etcetera. He says that the observations of these lines are consistent with carbon dioxide being the main culprit.

Then came the jump. The fact that scientists agree with each other (despite being cats which are difficult to herd) means there must be many lines of evidence. Otherwise it would been impossible to agree with each other…

Wow, I am not sure if I follow that one!

In school we learned about logical fallacies. The teacher explained us that a conclusion can only be reliable if all the premises are valid. In this case there are two premises. The first is: scientists are like cats, difficult to herd. One could of course debate everything, but this one I could accept.

The second premise is a bit more tricky. When history teaches us something, it is not necessarily true that scientists agree on something because of multiple lines of evidence. It can be true that some scientists agree with the theory of global warming because of multiple lines of evidence or the evidence they found their field. But this is not necessarily true for all the scientists who have an opinion on the issue. In the Cook survey most, if not all, papers were not on attribution, but the theory was their starting point. These authors believed in it, but it is not sure if they concluded that from the different lines of evidence or that they did it because they just had trust. In the Cook survey it was not analyzed WHY they endorsed it.

In short, there are several reasons possible why scientists agree with each other. Knowing the evidence could be one of them, but this is not certainly the only one.

Put a scientist in a place where his tenure or his income depends on adhering the consensus and that could change the game completely. Or consider a scientist in a very polarized debate where the respect of his peers comes into the line (see the peer pressure on Bengtsson). Then we have a different situation were contradicting the current theory is not that interesting anymore, yet adhering is. Also climate is a very complex system, involves different specialization, comes with huge uncertainties and very little reliable data before the 1980s. In such a system it would be a downright miracle if scientists agree with each other in such a high degree.

To me that is the Achilles heel of this survey. Sure they made a big effort in analyzing the title/abstracts of 12,000+ papers and I admire them for their persistence. Yet the basis of their conclusion is not holding much water.

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