Jacques Descloitres/NASA/GSFC

Changing mix.
Warming temperatures are turning more Arctic ice (turquoise) into seawater (black) in summer, as in this satellite view of Hudson Bay.

Dwindling Days for Arctic Ice

If computer models are correct, by 2050 Arctic sea ice will shrink during late summer by more than twice as much as it does now. The results of a new study by researchers at the National Oceanic and Atmospheric Administration (NOAA) add weight to speculation that a northern sea route will open up from Europe to Asia for the first time in recorded history.

The Arctic ice cap remains one of the most variable features of our planet. For many millennia, the frozen areas of the Northern Hemisphere have advanced and retreated while a similar but smaller variation occurs on a seasonal basis. Now, between ice ages and in the midst of an upward trend in average temperatures, the Arctic Ocean's ice is showing signs of unprecedented summer shrinkage. That development could be a boon to international ship commerce but a potentially serious threat to the ecosystems that have emerged within polar environments. Furthermore, the transformation of the reflective white ice into heat-absorbing seawater could further accelerate the warming of the planet.

To carry out their study, oceanographer James Overland of NOAA's Pacific Marine Environmental Laboratory and meteorologist Muyin Wang of the agency's Joint Institute for the Study of the Atmosphere and Ocean at the University of Washington, both in Seattle, selected 11 climate models that closely predicted actual amounts of Arctic ice area from 1979 to 1999. Then they directed the computer programs to look ahead to 2050. The result, the team reports in the 8 September issue of Geophysical Research Letters, is that summer Arctic sea ice area could shrink by more than 40% and open waters off Alaska, Canada, and Russia that historically have remained icebound. That compares with about 18% summer shrinkage, on average, from 1979 to 1999. The models also project less ice formation during the winter in the Bering and Barents seas and in the Sea of Okhotsk, although not in Canada's Baffin Bay.

The 40% figure could be conservative, says ice scientist Waleed Abdalati of NASA's Goddard Space Flight Center in Greenbelt, Maryland, "as even the best models have historically underestimated the current rate of ice decline." But one thing is clear, he says: "The dramatic losses we are seeing in Arctic ice cover are not expected to slow down." Research scientist Jianli Chen of the University of Texas, Austin, thinks that the planet will experience a "snowball effect." Shrinking sea ice will increase the ocean's heat absorption, he says, which will in turn "further increase the melting of sea ice and contribute to global warming."

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