A Subtle Difference, Perhaps, But an Important One

Published at 09:36 on 12 May 2012

The ease at which information can easily be distorted by propagandists is illustrated by this article, which exhibits confusion about two distinct statements, which the author erroneously assumes are contradictory.

The first statement, made by MIT meteorologist Kerry Emanuel, is that it is not possible to point to global warming as the cause for any one outbreak of abnormally warm weather. The second, made by NASA climatologist James E. Hansen, is that there is statistical evidence that global warming is already making outbreaks of abnormally warm weather significantly more common than they used to be.

There is no contradiction between the two, because Emanuel’s claim is about specific events and Hansen’s is about overall trends. It’s just the sort of claims one would expect each to make: Emanuel specializes in studying short-term phenomena, while Hansen specializes in long-term ones. That’s the difference between meteorology and climatology.

It’s like a set of dice loaded to make snake eyes come up more frequently: when a roll comes up double ones, it is not possible to say if the loaded dice are responsible for this outcome or not. (Fair dice sometimes do come up snake eyes, after all.)

This is also why a record cold spell is by itself no evidence against global warming. Even loaded dice will occasionally land on sides not favored by the loading.

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