Drier Tropics, Wetter Poles

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Science  10 Dec 2004:
Vol. 306, Issue 5703, pp. 1863
DOI: 10.1126/science.306.5703.1863a

Earth's climate was noticeably warm during the Late Cretaceous, a time when dinosaurs and plants were found at polar latitudes. Climate models with enhanced greenhouse gases—notably CO2 and water vapor—and increased poleward ocean circulation have not been able to simulate fully the high polar temperatures of that period. One possibility is that much more moisture generated by evaporation in the tropics may have been transported poleward than what occurs today. This process effectively transfers heat from the tropics to the poles, because evaporation consumes considerable heat whereas precipitation releases it. Ufnar et al. calculate the changes in precipitation and evaporation that could account for the anomalously warm climate and reproduce stable isotope data reflecting rainfall at that time. The data imply that, compared to today, the greenhouse climates of that time dried (decrease in precipitation minus evaporation) latitudes below 40° dramatically and increased precipitation at higher latitudes, resulting in a two- to threefold increase in latent heat tranport toward the poles. — BH

Geology 32, 1049 (2004).

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