Climate Science

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Science  07 Mar 2008:
Vol. 319, Issue 5868, pp. 1309
DOI: 10.1126/science.319.5868.1309b

Around 55 million years ago, at the height of the Paleocene-Eocene thermal maximum, the world was a much warmer place than today. Sea surface temperatures were higher everywhere than now, and the equator-to-pole thermal gradient was much shallower. Climate for much of the past 500 million years has been warmer than it is now, and during the warm periods the surface meridional temperature gradient generally appears to have been weak. Explaining how the climate system might have transferred heat from low to high latitudes to maintain such a shallow thermal gradient has been difficult, and many hypotheses have been advanced, including those involving effects from radiative forcing by high concentrations of atmospheric carbon dioxide, more intense ocean heat transport, differences in the amounts and locations of polar stratospheric clouds, and extratropical atmospheric convection. Korty et al., using a coupled model of intermediate complexity, investigate another possibility: that tropical cyclones could have caused enough ocean surface mixing in the tropics to cool the sea surface there and drive the strong poleward heat flux needed to produce the shallow thermal gradients that seem to have prevailed during warm climates. This solution, if correct, also has implications for how we might expect the climate system to respond to anthropogenic warming. — HJS

J. Clim. 21, 638 (2008).

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