The Real Climate guys have offered odds on future temperature changes, which is great because it gives us a sense of their confidence in predictions of future global average temperatures. Unfortunately, RCs foray into laying odds is not as useful as it might be.

The motivation for this bet is the recent Keenlyside et al. paper that has caused a set of mixed reactions among the commenters in the blogosphere. Some commenters here have stridently argued that the predictions in the Keelyside et al. paper are perfectly consistent with predictions of climate models in the IPCC. However, when one such commenter here was asked to show a single IPCC climate model run showing no temperature increase for the 2 decades following the late 1990s he submitted an irrelevant link and disappeared. Others have argued that the Keenlyside et al. projections (and this includes Keenlyside) are inconsistent with the IPCC predictions. Real Climate apparently falls into this latter camp.

The Real Climate Bet (and there is also one for a later period) is that the period 1994-2004 will have a higher average temperature than the period 2000-2010. Since the periods have in common 2000-2004, we can throw those out as irrelevant. Thus, the bet is really about whether the period 1994-1998 will be warmer than the period 2005-2010. And since we know the temperatures for 2005 to present, the bet is really about what will happen in 2009 and 2010. (Using UKMET temps here.)

It is strange to see the Real Climate guys wagering on 2-year climate trends when they already taught us a lesson that 8 years is far to short for trends to be meaningful. But perhaps there is some other reason why they offer this bet. That reason is that they are playing with a stacked deck, which is what you do when looking for suckers. The following figure shows why.

RcsBold.jpg

For the Real Climate guys to lose the bet global average temperatures for 2009 and 2010 would have to fall by about 0.30 from the period 2005-present (and I’ve assumed Jan-Mar as the 2008 value, 2008 obviously could wind up higher or lower). Real Climate has boldly offered 50-50 odds that this will happen. This is a bit like giving 50-50 odds that Wigan will come back from a 3-0 halftime deficit to Manchester United. Who would take that bet?

Another interpretation of the odds provided by RC is that they actually believe that there is a 50% chance that global temperatures will decrease by more than 0.30 over the next few years. Since I don’t think they actually believe that, it is safe to conclude that they’ve offered a suckers bet. Too bad. When Real Climate wants to offer a 50-50 bet in which the bettor gets to pick which side to take in the bet (i.e., the definition of 50-50) then we’ll know that they are serious.