Scientists tracking a dramatic shrinkage in Arctic sea ice over the past few years have come to a worrisome conclusion: If the trend continues, it could speed up the melting of Arctic permafrost as well. The environmental consequences of such a development are uncertain, but they could spell trouble for plants, animals, and humans in those regions that depend on solid ground underfoot.
As global temperatures climb, the extent of sea ice that persists in the Arctic until the end of summer has hit record lows. Between August and October 2007, for example, the area covered by sea ice shrank more than 30% below its average for that part of the year. At the same time, air temperatures in western Canada and Alaska jumped more than 2°C over the 1978-2006 average for late summer and early autumn. Researchers from the National Center for Atmospheric Research (NCAR) and the National Snow and Ice Data Center (NSIDC), both in Boulder, Colorado, realized that they had seen a similar relationship between Arctic ice melt and land warming in their climate computer model. So atmospheric scientist David Lawrence of NCAR and co-author Andrew Slater of NSIDC plugged the data they had collected--from satellites and ground- and sea-based monitoring stations in the Arctic--into the simulation to see what a continuing pattern would produce.
The simulation showed "that the rate of [air] warming increases substantially during rapid ice loss, especially during autumn," Lawrence says. The surprise is not in the relationship, he adds, but in the size of the land area impacted by the sea-ice change. If the rate of summer sea-ice loss persists, it could boost the rate of warming across permafrost areas by up to 3.5 times, the team will report Friday in Geophysical Research Letters. Such an increase could be enough to turn concrete-hard ground into muck and begin to release billions of metric tons of carbon dioxide and methane--an even more potent greenhouse gas--that had been locked up in the soil for millennia.
The results provide "yet another indication of the impact of sea-ice reduction on the polar climate systems," says atmospheric scientist Claire Parkinson of NASA's Goddard Space Flight Center in Greenbelt, Maryland. Although the consequences of degrading the permafrost remain unknown, she says, "they could be significant, both on the climate through release of greenhouse gases and on the local communities through damage to roads and buildings as the frozen ground underneath thaws and destabilizes."