Arctic- Point of No Return?

By Volker Mrasek - www.spiegel

...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.

..."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.

The waters around the North Pole are heavily influenced by the currents coursing through the Atlantic and Pacific Oceans. Those currents are driven by conflicting pressure systems in each ocean: in the Pacific, the low pressure zone located near the Aleutian Islands extending west from Alaska is doing battle with a subtropical high pressure zone further south; in the Atlantic the currents are determined by the Azores High and the Icelandic Low.

Winter in the Arctic has long been determined by what researchers refer to as a "tri-polar" pattern. The interaction among the Icelandic Low, the Azores High and the subtropical high in the Pacific led to primarily east-west winds, a pattern which effectively blocked warmer air from moving northward into the Arctic region.

But since the beginning of the decade, the patterns have changed. Now, a "dipolar" (bipolar) pattern has developed in which a high pressure system over Canada and a low pressure system over Siberia have the say. The result has been that Artic winds now blow north-south, meaning that warmer air from the south has no problem making its way into the Arctic region. "It's like a short-circuit," says Rüdiger Gerdes, a scientist at the Alfred Webener Institute for Polar and Marine Research and one of the five authors of the study.

The influx of warm air from the south was especially intense during the winter of 2005-2006, the study says. During that period, 90 terawatts of energy flowed into the Artic Ocean from the North Pacific -- an amount that far exceeds the needs of the entire industrial world. Gerdes has no doubt that the ice will "quickly disappear if the new pressure patterns stay the way they are." He says that the Arctic Ocean would still freeze during the winter, but the ice pack would be too small to survive the warmer summer months.

...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.