The ‘Fat Tail’ of climate change risk

(Michael Mann is someone to listen to on climate science, but notice the typical nod to “market mechanisms” as solution. Another illustration how positivist natural science almost always leads to conflation with mainstream economic/political views. Why the whole tradition of marxist analysis based in dialectics and systemic analysis is so important to be brought into the analysis of climate science and political change.)

Roughly 68 percent of the area falls within the region bounded by 1 standard deviation below (-1 sigma) and above (+1 sigma) the “mean” or “average”, and a substantially greater 96% of the area falls between two standard deviations below (-2 sigma) and above (+2 sigma) the mean. So given this statistical distribution, we would expect values to fall above the +2 sigma (two standard deviation) limit only about 2 percent of the time. Call that the positive “tail” of the distribution.

There are many phenomena that follow a normal distribution, from the heights of adult men in the U.S. to the day-to-day fluctuations in summer temperature in New York City. But the predicted warming due to increased greenhouse gas concentrations isn’t one of them.

Global warming instead displays what we call a “heavy-tailed” or “fat-tailed” distribution. There is more area under the far right extreme of the curve than we would expect for a normal distribution, a greater likelihood of warming that is well in excess of the average amount of warming predicted by climate models.

An important new book Climate Shock: The Economic Consequences of a Hotter Planet by Environmental Defense Fund senior economist Gernot Wagner and Harvard economist Martin Weitzman, explores the deep implications this has for the debate over climate policy.

Here’s the blurb I wrote for the book (a shortened version of which appears on the back cover):


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