Monday, November 26, 2007

This Climate Goes to Eleven

This Climate Goes to Eleven: Gerard H. Roe and Marcia B. Baker, "Why Is Climate Sensitivity So Unpredictable?", Science 318 (2007): 629--632 [...] Roe and Baker's argument is simple but ingenious and compelling. The climate system contains a lot of feedback loops. This means that the ultimate response to any perturbation or forcing (say, pumping 20 million years of accumulated fossil fuels into the air) depends not just on the initial reaction, but also how much of that gets fed back into the system, which leads to more change, and so on. [...] Suppose, just for the sake of things being tractable, that the feedback is linear, and the fraction fed back is f. [...] What happens, Roe and Baker ask, if we do not know the feedback exactly? Suppose, for example, that our measurements are corrupted by noise --- or even, with something like the climate, that f is itself stochastically fluctuating. The distribution of values for f might be symmetric and reasonably well-peaked around a typical value, but what about the distribution for G? Well, it's nothing of the kind. Increasing f just a little increases G by a lot, so starting with a symmetric, not-too-spread distribution of f gives us a skewed distribution for G with a heavy right tail. (Via Three-Toed Sloth.)

Interesting study. Besides the scary aspects of this finding relative to climate change, there's the more academic question of whether these types of processes can explain skew distributions we find in other fields.

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