CLIMATE SCIENCE: Melting Faster

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Science  18 May 2007:
Vol. 316, Issue 5827, pp. 957a
DOI: 10.1126/science.316.5827.957a

Observations of the extent of Arctic sea ice in September—at the end of the melt season, when ice coverage is at its annual minimum—have shown a large decline over the past several decades, consistent with current qualitative understanding of natural variability and the effects of a warming climate. Nearly all climate models predict that September Arctic sea ice extent will continue to decline through the 21st century, largely in response to rising concentrations of atmospheric greenhouse gases. How well do observations and models agree, though? To answer that question, Stroeve et al. compared the output of the more than a dozen models participating in the Intergovernmental Panel on Climate Change Fourth Assessment Report that calculated sea ice. They found that nearly all of the models overestimated annual minimum Arctic sea ice area, in many cases by large amounts. These findings have two important implications: first, that the effect of rising greenhouse gases may have been more important than has been believed; and second, that future loss of Arctic sea ice may be more rapid and extensive than predicted. — HJS

Geophys. Res. Lett. 34, L09501 (2007).

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