The rapid retreat of Arctic sea ice observed in recent summers could triple the rate of warming over northern Alaska, Canada and Russia, a new study suggests. Such intensive warming could endanger sensitive ecosystems and human infrastructure in those regions. It's the warm version of the snowball effect. "Our study suggests that, if sea-ice continues to contract rapidly over the next several years, Arctic land warming and permafrost thaw are likely to accelerate," said study leader David Lawrence of the National Center for Atmospheric Research in Boulder, Colo. The North Pole is a region of ice floating on the sea, an expanse of ice that in winter connects in some places with continental Arctic ice. The new research was spurred by the record melt of Arctic sea ice last summer, which shrank to more than 30 percent below its average. Around the peak in ice melt, which occurred in September, air temperatures over land in the western Arctic were also unusually warm from August to October, reaching more than 4 degrees Fahrenheit (2 degrees Celsius) above the 1978-2006 average. This raised the question of whether or not these phenomena were related. To answer that question, Lawrence and his team used simulations of sustained periods of rapid sea ice loss. The simulations showed that during such episodes, the rate of Arctic land warming is 3.5 times greater than the average 21st century warming predicted in global climate models. While the warming was largest over the ocean, the simulations suggested that it could penetrate as far as 900 miles (1,450 kilometers) inland. They also indicated that this warming is particularly pronounced in the autumn months; a decade that sees rapid sea-ice loss could also see autumn temperatures rise by as much as 9 F (5 C) along Arctic coastlines. Such accelerated warming could lead to rapid thaw of permafrost, the frozen soil that covers larger portions of the Arctic, especially in areas where the permafrost is already at risk from warming. Thawing permafrost could further exacerbate global warming, because Arctic soils are believed to hold 30 percent or more of all the carbon stored in soils worldwide. Though researchers are unsure what would happen to this carbon when the soil thawed, it is possible that significant amounts of carbon dioxide or methane could be released into the already greenhouse-gas-enriched atmosphere. As the permafrost thaws, it could also buckled highways, destabilize houses, and cause trees to lean at wild angles. "An important unresolved question is how the delicate balance of life in the Arctic will respond to such a rapid warming," Lawrence says. "Will we see, for example, accelerated coastal erosion, or increased methane emissions, or faster shrub encroachment into tundra regions if sea ice continues to retreat rapidly?" The study is detailed in the June 13 issue of the journal Geophysical Research Letters, and was funded by the U.S. Department of Energy and the National Science Foundation.
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