SEA ice in the Arctic reached a record low this summer, a US government report said last week. But it could have been even worse were it not for a dramatic increase in summer clouds.
The report, by the US National Snow and Ice Data Center, based at the University of Colorado in Boulder, utilised NASA satellite data (see Graph). It says that higher temperatures are to blame, and that this effect is self-reinforcing, because white ice is being replaced by dark ocean that absorbs more heat from the sun.
鈥淚f passing changes in atmospheric circulation are creating extra clouds, ice loss could accelerate when these conditions reverse鈥�
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But in a paper published in the Journal of Climate in July (vol 18, p 2558), Jeff Key and Xuanji Wang of the University of Wisconsin, Madison, say extra summer clouds are reflecting solar heat as effectively as the ice they have replaced. 鈥淚f cloud cover had not increased in summer, the Arctic surface temperature would have risen even more,鈥� says Key.
He says it is too early to tell whether increased cloudiness is due more to evaporation from the newly exposed ocean or to temporary changes in atmospheric circulation in the Arctic. If the latter, ice loss could accelerate when these conditions reverse.
Last month, a team led by Igor Polyakov of the International Arctic Research Center in Fairbanks, Alaska, blamed the accelerated melting on a series of 鈥渋mmense pulses of warm water鈥� entering the Arctic in recent years from the Atlantic through the Fram Strait between Greenland and Svalbard. This year a 鈥減ulse鈥� wiped nearly all the ice from the Laptev Sea, north of Siberia.
