The betting on climate change thing seems to have gone rather quiet. This post is prompted by a comment posted to an old entry on my old blog Probably not betting on climate with Lubos Motl (that post is still worth reading, I think, for the attempt to calculate what are “fair odds”. In some email discussion afterwards, I think I discovered that there isn’t really a good answer to that question). But if you haven’t seen the circuit before, look at James A’s stuff and Brian Schmidt’s. That last post offers a list of bets that GS is prepared to take.
My anonymus commenter said:
I have been making a regular, annual bet with my environmental science and biologist friends… every year from 1998 we would look at the earth average temp, if it was [down] from the previous year, I pay, if it were [up], they pay, I have not lost yet, 2005 was a push. Are you a betting man? No odds, just a simple bet that climate is not simple at all nor is it being driven directly by human CO2.
Well, I’m happy to accept that climate is not simple. “Directly” driven by CO2 would depend on the meaning of directly – clearly, the spike in 1998 was mostly an El Nino. Anyway, as I recall 2005 was about equal to 1998 – different datasets gave different answers. I’m not sure what “no odds” can mean – presumably, 1:1. Unless it means no stake, when it becomes less interesting.
At base, this is stuff thats been gone over before, in a different guise. Taking 1998 as a base year is cherry-picking. 1998 was exceptionally warm: its no surprise that the next few years were cooler. After 1973, the years until 1981 were cooler (see graph on old blog), so this is hardly unprecedented. If anyone had started anons bet in 1974, and continued to today, those betting on cooler would have lost heavily.
And so the answer is… betting on any given pair of years is a noisy statistic and won’t tell you much about climate. Doing it starting from a high year isn’t a good bet. Betting on 10 year trends is a better idea. Based on the HADCRU data, the trend from 1998 to 2005 (or 2003, or 4) is positive (albeit small), and I’d be prepared to bet on that staying true, given suitable odds.