Climate Science

Unlucky Seven

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Science  14 May 2010:
Vol. 328, Issue 5980, pp. 793-795
DOI: 10.1126/science.328.5980.793-d

Based on what we know about how atmospheric CO2 affects Earth's energy balance, how heat is distributed in the climate system, and how the concentration of CO2 in the atmosphere is likely to change over the next century, the global average surface air temperature in the year 2100 is projected to be 3° to 4°C higher than it is today. That is just a best estimate, however, and the temperature increase could be lower, if we are lucky, or higher—even much higher—if we are not so lucky. How could a larger than expected increase in temperature affect humans? Sherwood and Huber consider how much heat stress human metabolism can withstand. They contend that prolonged exposure to temperatures of 35°C would be intolerable, even fatal, and determine with a climate model that a global mean surface temperature increase of only 7°C would create certain zones in which temperatures would routinely rise above the tolerable threshold; with more time, or the misfortune of the climate's proving more sensitive to rising CO2 than we realize, temperature increases of 10°C or more could make much of the populated area of the planet uninhabitable. Though such large temperature increases may not be likely, still they are possible, and the potential consequences should not be ignored.

Proc. Natl. Acad. Sci. U.S.A. 107, 10.1073/pnas.0913352107 (2010).

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