Climate Science

Heating the Poles

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Science  12 Jul 2002:
Vol. 297, Issue 5579, pp. 159
DOI: 10.1126/science.297.5579.159d

Paleoclimate data indicate that during the Eocene epoch [55 to 38 million years ago (Ma)] and the Cretaceous period (135 to 65 Ma), land and surface ocean temperatures at high latitudes were much higher than they are at present, and tropical flora and fauna extended into much higher latitudes than they do now. Tropical temperatures, however, were similar to or only slightly higher than they are today. Global climate models with Eocene-like boundary conditions predict much lower polar temperatures than those inferred from the geological record and do not reproduce the warm winters seen in continental interiors. This suggests that the models have neglected a strong warming mechanism and that climate predictions for a warmer future might also underestimate temperatures at high latitudes and in continental regions.

Kirk-Davidoff et al. propose that this discrepancy may be due to a failure of the models to reproduce the development of the polar stratospheric clouds (PSCs) that form in response to changes in stratospheric circulation and water content. In their model, which invokes polar stratospheric cooling and tropical stratospheric warming caused by a reduced equator-to-pole temperature (from higher atmospheric CO2 concentrations), an optically thick layer of PSCs forms owing to cooler temperatures and increased moisture in the polar stratosphere. The additional heat trapped by these clouds further increases high-latitude surface temperatures, leading to continued high CO2 concentrations and low equator-to-pole temperature gradients in a positive-feedback loop. — HJS

Geophys. Res. Lett.29, 10.1029/2002GL014659 (2002).

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