The future impact of global warming lies in the Arctic. There temperatures have risen almost twice as fast in recent decades as in the rest of the world. The Arctic Council, an intergovernmental organization comprising eight nations--the U.S., Canada, Iceland, Denmark, Norway, Sweden, Finland and Russia--plus several indigenous peoples' organizations, issued a sobering report last November. It estimates that by late in this century, average Arctic winter temperatures will rise roughly four to seven degrees Celsius over land and seven to 10 degrees C over oceans, leading to profound changes by the end of the century.

Although most of the sun's energy reaches the tropics, the atmosphere and oceans redistribute the equatorial energy toward the poles. Unlike the tropics, where a large proportion of the energy received at the surface goes into evaporation, more of the energy received at the Arctic surface goes into warming the atmosphere. For several complicated reasons, including greater absorption of solar radiation, the Arctic is likely to heat up more than the Antarctic.

This article was originally published with the title Melting at the Top.

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