ain't over till the fat tail sings

They argue that current policies are leading to a substantial chance (perhaps one in ten) that global temperatures will rise by at least six degrees centigrade. This will be..."the end of the human adventure on this planet as we know it."

--Nordhuas in the NYRB. 

Have to say here that Weitzman is recognized as a leading thinker on uncertainty and climate change. Nordhaus (and Weitzman, for different reasons) have criticized my old teacher, Stern, for his estimates of the discount rate (and/or the way in which it is derived). Based on the low discount rate (which means giving relatively more weight to future generations) Stern calls for a more immediate response. The discount rate is-at least in part-an "ethical parameter" and something that can not just be proxied by the market interest rate. 

Also, as far as I understand it, these are global averages. If so, some countries may see in the intervening period (i.e. before stabilization) much higher temperatures. 

The main point, though, is clear. A one in ten chance of acatastrophic increases in temperatures! (Also note the word 'perhaps'). I'm not a betting man, but I don't like those odds.  

(From memory). In an earlier paper Weitzman says there is a 5% chance that temperatures will stabilize at ten degrees warmer; and a 1% chance that it will be twenty degrees hotter. The "tails" of the distribution are "fat"-which mans that the chances of an extreme or catastrophic change occurring are not insignificant. If someone said to you: there's a 1/20 chance this plane will crash would you board it?

~~