Ice expanse growing in Antarctica as Arctic gets warmer

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

In the southern hemisphere winter, when emperor penguins huddle together against the 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 end of the northern summer. That trend is 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 to 2006, said Donald Cavalieri, a senior research scientist at the NASA Goddard Space Flight Center.

At 7.3 million square miles, the ice accumulation is still slightly below the record level of the early 1970s, he said. The average year-round level has risen, too.

Some global warming skeptics point to the differing trends at the poles as a sign that worries about climate change are exaggerated. However, scientists 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 UN Climate Panel has said it is at least 90 percent sure that people are contributing to global warming, mainly by burning fossil fuels. But it said 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.

Cavalieri said some computer models indicate that a reduction in the amount of heat rising from the ocean around Antarctica is one possible explanation for growing ice. Another theory is that warmer air absorbs more moisture, leading to more snow and rainfall, he said. That could mean more fresh water at the sea surface around Antarctica. Fresh water freezes at a higher temperature than salt water.

Maksym predicted that global warming would eventually warm the southern oceans, and shrink the sea ice around Antarctica.