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Tuesday, October 07, 2008

The climate crisis is worse than we think.

The problem is that conventional projections for how warm things will get come out of a calculation everyone knows is wrong. Called the Charney sensitivity, it estimates how much the global mean temperature will rise if atmospheric CO2 is doubled from its preindustrial levels, before people began burning coal and oil on a grand scale. In the mid-1800s carbon dioxide concentrations stood at about 280 ppm. Double that to 560 ppm, and the Charney sensitivity calculation tells you that temperatures should rise about three degrees C.

But the Charney sensitivity, though not quite as stripped down as the billiard ball model, is still an oversimplification. The calculation does take into account some feedback mechanisms that can modify the effects of increasing temperatures on short time­scales—changes in water vapor, clouds and sea ice, for example. But for the sake of simplicity, it assumes no change in other, longer-term factors, including changes in glaciation and vegetation; in particulates, such as dust; and in the ability of the ocean to absorb carbon dioxide, which diminishes as sea temperature rises.