The amount of sea ice around Antarctica has grown in recent Septembers in what could be an unusual side-effect of global warming, experts said on Friday.

In the southern hemisphere winter, when emperor penguins huddle together against the biting cold, ice on the sea around Antarctica has been increasing since the late 1970s, perhaps because climate change means shifts in winds, sea currents or snowfall.

At the other end of the planet, Arctic sea ice is now close to matching a September 2007 record low at the tail end of the northern summer in a threat to the hunting lifestyles of indigenous peoples and creatures such as polar bears.

“The Antarctic wintertime ice extent increased…at a rate of 0.6 percent per decade” from 1979-2006, said Donald Cavalieri, a senior research scientist at the NASA Goddard Space Flight Center.

At 19 million sq kms (7.34 million sq mile), it is still slightly below records from the early 1970s of 20 million, he said. The average year-round ice extent has risen too.

Some climate skeptics point to the differing trends at the poles as a sign that worries about climate change are exaggerated. However, experts say they can explain the development.

“What’s happening is not unexpected…Climate modelers predicted a long time ago that the Arctic would warm fastest and the Antarctic would be stable for a long time,” said Ted Maksym, a sea ice specialist at the British Antarctic Survey.

The U.N. Climate Panel says it is at least 90 percent sure that people are stoking global warming — mainly by burning fossil fuels. But it says each region will react differently.

A key difference is that Arctic ice floats on an ocean and is warmed by shifting currents and winds from the south. By contrast, Antarctica is an isolated continent bigger than the United States that creates its own deep freeze.

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