Policy decisions should be based on a judgment concerning the maximum tolerable increase in temperature and/or carbon dioxide levels given the state of scientific understanding. The appropriate role for economists would then be to determine the least-cost global strategy to achieve that target. While this remains a demanding and complex problem, it is far more tractable and epistemically defensible than the cost-benefit comparisons attempted by most IAMs.I agree wholeheartedly.
Indeed, that is why we have a 2 C target. It’s not just that the economics of the problem is hopelessly intractable, though it is.
We have delayed long enough that economics does not meaningfully enter into target-setting. See this article by me and a more detailed analysis by Dana Nuccitelli at Skeptical Science.
The strategy may have been an interesting economic question once, but it is not so any longer. We have delayed so much that the optimum rate of decarbonization is simply "as quickly as is feasible", that is, we need to achieve the absolute minimum cumulative net CO2 emissions that we can without the decarbonization kicking off destabilizing damage to society in itself.
So the question we can put to economists - how fast can we put the brakes on without spinning out of control economically or politically - may actually fall within the range of the sorts of analysis that, at least purportedly, they can do. Since it’s on a short time scale and by assumption avoids tipping points, maybe their methodologies will help.
Of course, as with any policy/expertise interface, distinguishing the real experts from the charlatans is also a crucial issue.
I am not entirely happy with David's opening for the article, though, and it raises a cluster of ideas that I have been meaning to write about for a while. I hope to explain shortly.