CLIMATOLOGY

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Science  09 Nov 2001:
Vol. 294, Issue 5545, pp. 1245
DOI: 10.1126/science.294.5545.1245c

“Climate sensitivity” is a parameter used by climatologists to specify the increase in average global surface temperature in degrees celsius as a consequence of doubling the concentration of atmospheric carbon dioxide. This value is difficult to calculate, though, because there are large uncertainties in the responses of clouds and water vapor to the resulting warming, and in how those responses would modify Earth's radiation balance. The Intergovernmental Panel on Climate Change range of likely values for climate sensitivity is 1.4 to 5.8°C, although the full range varies from 0.1 to 10.0°C, and the derivations of these estimates make it hard to assign probabilities.

In order to construct a probabilistic estimate for climate sensitivity, Andronova and Schlesinger analyze 16 different radiative-forcing scenarios with a simple climate model using, in each case, a doubling of carbon dioxide, but with various combinations of additional factors such as tropospheric ozone, anthropogenic sulfate aerosol, the Sun, and volcanoes. They find that natural climate variability and uncertainties in the estimates of radiative forcing make 1.0 to 9.3°C the 90% confidence interval for climate sensitivity, implying that there is a roughly even chance that the best estimate lies outside the commonly accepted range.—HJS

J. Geophys. Res.106, 22605 (2001).

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