The potential influence of tropical sea surface temperature on global climate sensitivity to a doubling of CO2 concentration is found using an atmospheric general circulation model coupled to a slab mixed layer ocean. Sensitivity is significantly reduced when sea surface temperature in the eastern equatorial Pacific between latitudes 2.25° N and 2.25° N are held at their control simulation values. Sensitivity of the global mean temperature is reduced from 2.4° C in the unconstrained case to 1.9° C when the sea surface temperature constraint is applied. The mechanism for the global response to regional influences appears to be related to both convective forcing of tropospheric temperature and the water vapor greenhouse feedback. The results emphasize the importance of correctly modeling the dynamical processes in the ocean and atmosphere which help determine the SST in the equatorial eastern Pacific, in addition to the thermodynamical processes, in projecting global warming.
The technique of calculating climate sensitivity with regionally fixed surface temperatures is also used to show that the potential extratropical effect of errors in the model simulation of water vapor feedback in the tropics is substantial.
last update: 8 March 1996
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