This article by Michael Mann is an interesting example of something that has gone wrong with the climate change debate. For what we're getting is people who claim expertise in one part of the problem insisting that said expertise gives them power to determine what should be the answers to other parts of said problem.

As ever, let's not get into the shouting match about the science being all wrong. Let us just, for the moment, accept what the IPCC tells us. Yes, even including Mann's hockey stick:

I have made my position on the Keystone XL pipeline quite clear. Approving this hotly debated pipeline would send America down the wrong path. The science tells us now is the time that we should be throwing everything we have into creating a clean 21st century energy economy, not doubling down on the dirty energy that is imperiling our planet. Now that the State Department has just released a final environmental impact report on Keystone XL, which appears to downplay the threat, and greatly increases the odds that the Obama administration will approve the project, I feel I must weigh in once again.

Erm, why must you weigh in again? You're a climate scientist. You work on temperature reconstructions. What on earth do you know about the economics of the oil industry?

And that's what our problem is here. Again, leave aside whether you believe Mann's science or not. Let us just, for the sake of argument, accept it for the moment. Excellent: so he's identified a problem, one that we should think carefully about. The same could be true of all sorts of people who have contributed to the IPCC reports. But the climate scientists are not the people we should be listening to on what we do next. For they've no expertise, not even any knowledge, of the subject that is crucial to what we do actually do next.

Economists know a great deal about what we should do next: Stern, Nordhaus, Greg Mankiw, in fact a goodly portion of the entire profession, would say that you whack on a carbon tax and you're done. Things like pipelines will then be controlled by whether they can carry the cost of that tax or not. As it should be: we've stuck our oar into the price system over an externality and can leave the market to sort out the impications. Even James Hansen has got this message.

OK, you might not like that answer either: but it is at least coming from people with qualifications in the relevant field. Asking Mann what we should do about climate change is as odd as asking an economist to do paleobiology: not just a waste of time but something highly likely to come up with the wrong answer.

And I do insist that this is a particular example of a larger problem. Being able to decipher what cloud cover does to temperature does not make one an expert in how to change the behaviour of human beings. That how cloud cover changes temperature is a building block of our knowledge of whether climate change is a serious problem or not is entirely true. But that simply doesn't mean that being able to pronounce with confidence on the one subject offers any insight at all into the second.

As you all know I'm perfectly happy to leave science to the scientists (and yes, I know many of you disagree). But I do insist that whether there is a problem is a different question than what we do about it if it is. And it requires entirely different skill sets to answer that second.

The people we ought to be listening to about what we do are the economists: assuming we believe what the climate scientists are telling us in the first place.

By the way, the economists and the engineers have spoken on Keystone XL now. It's not going to make any noticeable difference to emissions because those Canadian sands are going to be developed anyway.