GRL Article/James Hansen - Arctic Sea Ice "Beyond Point Of No Return" - Der Spiegel

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Thu Dec-04-08 01:12 PM
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GRL Article/James Hansen - Arctic Sea Ice "Beyond Point Of No Return" - Der Spiegel

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A new study completed by a team of US, Norwegian and German researchers may now provide some clues. Published in the scientific journal Geophysical Research Letters in November, the study posits that a dramatic change in atmospheric circulation patterns has taken place since the beginning of the decade, with centers of high pressure in winter shifting toward the north-east. The new pattern of sudden climate change is characterized by "poleward atmospheric and oceanic heat transport," the authors write in the study, a transport which drives temperature increases in the Arctic. The discovery was made using specialized filters that allow one to follow changes to high pressure centers over time.

Behind the complex language and impenetrable calculations upon which the study is based, however, is a frightening possibility: climate change in the Arctic could already have reached the point of no return. Climate researchers have long been warning of such "tipping points," and that crossing them could mean irreversible developments for eco-systems and humanity. In the case of the Arctic, that could mean a complete disappearance of ice in the region during the summer months. Such an eventuality would then further magnify global warming, due to the fact that bright white ice reflects sunlight back into the atmosphere whereas dark colored land and ocean absorbs heat. "In the case of Arctic Sea ice, we have already reached the point of no return," says the prominent American climate researcher James Hansen, director of the Goddard Institute for Space Studies at NASA.

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James Overland from the Pacific Marine Environmental Laboratory in Seattle agrees. In the scientific journal Tellus the oceanographer, together with colleagues, also points to the new north-south flow patterns in the Arctic. "If the current flows stay the way they are, then we will see the disappearance of Arctic sea ice 40 years earlier than we would as a result of greenhouse-gas emissions alone," Overland told SPIEGEL ONLINE. Even if the Arctic circulation were to return to normal and would switch to the "dipolar" pattern just once in a decade, the situation would look grim, he said. "Each time we would see a loss of so much ice that it would be impossible to return to the initial state." Overland says that the dramatic disappearance of Arctic ice observed in 2007 was no exception. The summer of 2008 was just as bad, he says. The progression is clear: sooner or later the ice cap will become so small that it will not be able to survive the warm summer months.

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The series of warm winters experienced in the Arctic this decade, it should be noted, is not the first time in recent history the region has been visited by mild weather. In the 1930s, there was a similar "dipolar" pattern that pushed warm air into the Arctic, as researchers now know. Back then, though, it was air from the North Atlantic and not from the North Pacific. Furthermore, says Gerdes, the warm air did not penetrate beyond 75 degrees north latitude, which roughly marks the previous limits of the ice cap. Today, the heat spreads through the entire Arctic. It could be that the new patterns of air circulation in the Arctic are caused by natural climate variations. But given the dramatic ice melt currently being observed, such an explanation is not enough to satisfy researchers. The American scientist Overland, for his part, has no doubts: the dramatic change in pressure systems in the Northern Hemisphere combined with Arctic warming is, he says, "a clear signal of warming."

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http://www.spiegel.de/international/world/0,1518,594461,00.html