Unfrozen north

Natural History, Oct, 2005 by Avis Lang

For at least a million years, summertime north of the Arctic Circle has meant two months of partial melt. Unbroken expanses of sea ice fracture into ice floes. Polar bears dive off the sturdy floes into the temporarily open seawater. Myriad birds nest along exposed shorelines.

But all that could soon change, say Jonathan T. Overpeck, a geophysicist at the University of Arizona in Tucson, and twenty colleagues from across North America. Within less than a century, they calculate, the Arctic Ocean may well be ice free in summer, and its shorelines permanently submerged.

For the past thirty years, the extent of Arctic snow, glaciers, permafrost, and sea ice has been diminishing. The loss of sea ice is striking: the September averages have declined by about 8 percent per decade. With less and less surface covered for progressively shorter periods by white, highly reflective ice, the melting rate is on the rise. Soon, according to Overpeck and his colleagues, the interrelations among the factors that jointly sustain the Arctic as a system--the thickness, coverage, and reflectivity of the ice; the amounts of precipitation and evaporation; the saltiness of the seawater; the kinds and activities of resident organisms--will break down. The system will become simpler, and the Arctic Ocean liquid year-round. (Eos 86:309-16, 2005)