Will The Real AGW Skeptic Please Stand Up?
Normally, I don’t debate random bloggers on Anthropogenic Global Warming (AGW). However, I made an exception for Robin Hanson. For those who don’t already know of him, he was both an early proponent of decision markets and has a reasonably well known journal article on why two Bayesian rationalists can’t agree to disagree. I’m a fan of his work and have been reading his blog for years.
Yesterday, he put up a post titled CO2 Warming Looks Real. He’s not an expert. Like me, he has an economics background and did some detailed research. Yet from the title and body of the post, I though he must have reached a very different conclusion than I did. So I thought I’d try to engage him to find out where we differ. The results were interesting.
Obviously, and as Robin knows, the best way to elicit a person’s true beliefs is to observe where he puts his money. So I offered to negotiate a bet of up to $1,000. As you can see from reading the comments, he eventually offered an even-odds bet than the temperature would rise 0.1 deg C in 20 years. Yes, you read that correctly: 0.1 deg C.
So he’s as much of a skeptic as I am! I think a doubling of CO2 concentration would lead to about 1 deg C of warming. I think, it’s going to take about 200 years (from 1900-2100) to do that. So I believe that we should see warming of about .05 deg C per decade. In 20 years, that’s about… 0.1 deg C. (Yes, I know I’m linearly approximating a logarithmic function, but the amount of precision in all the input values is low enough that I don’t think it matters).
Now, as I pointed out to Robin, the official IPCC estimates are much higher. If you go to the latest Summary for Policy Makers and look at Table SPM.3, you see the rate of warming in the lowest impact scenario B1 is 2x to 5x higher. So Robin’s price reveals that he is quite skeptical of the IPCC estimates.
Moreover, if you believe that the over-under on temperature in 2100 is .45 deg C higher than today, why would you think that justifies any significant mitigation effort? To the extent that there are any costs, we could certainly pay them at a fraction of the economic cost of a carbon tax or cap-and-trade. Moreover, you’re saying that GHG emissions account for only a small part of the variance in future temperature. So it could get a lot cooler as well as a lot warmer. Seems like that implies we should save our money for adapting to whichever way the thermometer swings.
Personally, I’m pleased to know that Robin Hanson did not reach different conclusions from me and that, by my definition, he is a fellow member of the “well-informed skeptic” club.