Whom do you believe: The Cato Institute, or the Hadley Centre? Both cannot be right. Yet both claim to be backed by real scientists.

First, to get this out of the way, the latest ad from Cato has been thoroughly debunked by RealClimate, including a critical look at whether the papers that Cato cites offer any support for Cato’s position (hint: they don’t), and a quick tour through related literature. So I won’t waste my time repeating their analysis.

The Cato folks attempted to answer back, but it’s largely by attacking red herrings. However, one point from this article jumped out at me:

“The fact that a scientist does not undertake original research on subject x does not have any bearing on whether that scientist can intelligently assess the scientific evidence forwarded in a debate on subject x”.

The thrust of this argument is an attempt to bury the idea of expertise, so that the opinions of the Cato institute’s miscellaneous collection of people with PhDs can somehow be equated with those of actual experts. Now, of course it is true that a (good) scientist in another field ought to be able to understand the basics of climate science, and know how to judge the quality of the research, the methods used, and the strength of the evidence, at least at some level. But unfortunately, real expertise requires a great deal of time and effort to acquire, no matter how smart you are.

If you want to publish in a field, you have to submit yourself to the peer-review process. The process is not perfect (incorrect results often do get published, and, on occasion, fabricated results too). But one thing it does do very well is to check whether authors are keeping up to date with the literature. That means that anyone who regularly publishes in good quality journals has to keep up to date with all the latest evidence. They cannot cherry pick.

Those who don’t publish in a particular field (either because they work in an unrelated field, or because they’re not active scientists at all) don’t have this obligation. Which means when they form opinions on a field other than their own, they are likely to be based on a very patchy reading of the field, and mixed up with a lot of personal preconceptions. They can cherry pick. Unfortunately, the more respected the scientist, the worse the problem. The most venerated (e.g. prize winners) enter a world in which so many people stroke their egos, they lose touch with the boundaries of their ignorance. I know this first hand, because some members of my own department have fallen into this trap: they allow their brilliance in one field to fool them into thinking they know a lot about other fields.

Hence, given two scientists who disagree with one another, it’s a useful rule of thumb to trust the one who is publishing regularly on the topic. More importantly, if there are thousands of scientists publishing regularly in a particular field and not one of them supports a particular statement about that field, you can be damn sure it’s wrong. Which is why the IPCC reviews of the literature are right, and Cato’s adverts are bullshit.

Disclaimer: I don’t publish in the climate science literature either (it’s not my field). I’ve spent enough time hanging out with climate scientists to have a good feel for the science, but I’ll also get it wrong occasionally. If in doubt, check with a real expert.

I was recently asked (by a skeptic) whether I believed in global warming. It struck me that the very question is wrong-headed. Global warming isn’t a matter for belief. It’s not a religion. The real question is whether you understand the available evidence, and whether that evidence supports the theory. When we start talking about what we believe, we’re not doing science any more – we’re into ideology and pseudo-science.

Here’s the difference. Scientists proceed by analyzing all the available data, weighing it up, investigating its validity, and evaluating which theory best explains the evidence. It is a community endeavour, with checks and balances such as the peer review process. It is imperfect (because even scientists can make mistakes) but it is also self-correcting (although sometimes it takes a long time to discover mistakes).

Ideology starts with a belief, and then selects just that evidence that reinforces the belief. So if a blog post (or newspaper column) provides a few isolated data points to construct an entire argument about climate change, the chances are it’s ideology rather than science. Ideologists cherry-pick bits of evidence to reinforce an argument, rather than weighing up all the evidence. George Will’s recent column in the Washington Post is a classic example. When you look at all the data, his arguments just don’t stand up.

The deniers don’t do science. There is not one peer-reviewed publication in the field of climate science that sheds any doubt whatsoever on the theory of anthropogenic global warming. If the deniers were doing good science, they would be able to publish it. They don’t. They send it to the media. They are most definitely not scientists.

The key distinction between science and ideology is how you engage with the data.