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Sea Ice Loss Driving Arctic Warming Cycle, Scientists Confirm

By David Adam

30 April, 2010

Study identifies cycle of ice loss and temperature rise that could see Arctic's icy cover disappear sooner than expected

The Arctic is locked into a destructive cycle that could see its icy cover rapidly disappear, scientists have confirmed. A new analysis shows that dwindling levels of sea ice are responsible for unusual levels of global warming in the region. The findings reinforce suggestions that a positive feedback between ice loss and temperature rise has emerged in the Arctic, which increases the chances of further rapid ice loss and warming.

The study could re-ignite claims that the Arctic has passed a key tipping point, which could see ice disappear much sooner than expected. While most estimates say the summertime Arctic will not be ice-free until the middle of the century, some models suggest it could vanish within a decade.

James Screen, a researcher at the University of Melbourne, Australia, who led the study, said: "The concept of Arctic sea ice having a tipping point is still hotly debated. Our results cannot prove whether we have passed a tipping point or not. What we can say is that the emergence of these strong ice-temperature feedbacks can only increase the likelihood of further rapid warming and sea ice loss."

Temperatures in the Arctic have risen twice as fast as the rest of the world in recent decades, a phenomena known as Arctic amplification. Scientists have long suspected that loss of sea ice was responsible, but other factors such as changes in wind, clouds and ocean currents have also been blamed.

Writing in the journal Nature, Screen and his colleague Ian Simmonds, say they used new data to show that the projected ice-temperature feedbacks are now being observed. "Previous studies have been hampered by a lack of quality data for the Arctic," Screen said. "The ice temperature feedbacks have likely strengthened in the last decade or so due to the dramatic declines in sea ice. Prior to this, the signal may have been harder to detect."

Part of this change is down to the albedo effect, with white, reflective ice replaced by dark water, which absorbs more of the sun's heat. The removal of ice has also led to more summer evaporation of water, which acts as a powerful greenhouse gas in the atmosphere, and speeds temperature rise.

Screen said: "The albedo effect is very important here, but there are other factors related to the loss of sea ice that likely play a role."

guardian.co.uk © Guardian News and Media Limited 2010