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Arctic Ocean ice shrinks abruptly

ATLANTA — The year-round layer of ice that covers the Arctic Ocean even during the warmest months has shrunk dramatically in the last two years, scientists reported Wednesday.

NASA researchers say since 2004, the 10-foot thick layer of perennial sea ice has decreased in size by 280,000 square miles, an area roughly the size of Texas — an abrupt change from recent decades, which were marked by modest declines.

"The recent changes in the ice are both rapid and dramatic," NASA researcher Son Nghiem reported in the journal Geophysical Research Letters.

Although researchers have witnessed a steady decline in the Arctic's summer ice cover, shrinking by about 8 percent a decade since satellite surveys began in 1979, the new report is the first to suggest that the thicker, permanent, year-round ice is also vulnerable to the gradual warming of the Arctic Ocean.

"The amount of Arctic sea ice reduction in the past two winters has not taken place before during the 27 years that satellite data has been available," says Josefino Comiso, a senior scientist at NASA's Goddard Space Flight Center.

Although winter temperatures in the Arctic average 30 degrees below zero, Nghiem says earlier thawing in the spring, and later freezing in the autumn, have combined to reduce the extent of perennial ice as well.

Average temperatures around the globe have increased over the past 30 years, and the changes in the Arctic have been even greater. Computer models have predicted that continued warming could, within a few decades, open a 21st century Northwest Passage that would make the Arctic navigable year-round.

But researchers say such a change could also have dramatic, and largely unpredictable consequences for wildlife and the rich fisheries of the Arctic. "We are now seeing declines in ice during all seasons, winter, summer spring and fall," says NASA/Goddard researcher Claire Parkinson. And she says that's particularly bad news for polar bears.

"The sea ice surface provides polar bears with a platform from which to hunt seals and other marine mammals," she says. "If the sea ice season continues to decrease, it poses a clear danger to their health and, in the long term, possibly to the species."

Parkinson and the Canadian Wildlife Service have reported a 20 percent decline in polar bear populations in the Hudson Bay area that closely matches the decline in the extent of ice there over the last 20 years. NASA scientists say the continued decrease in the Arctic ice cover may also be feeding on itself.

Because open water absorbs more heat from the sun than highly reflective snow and ice, they say the ocean is now warming even faster. Researchers say the area of the Arctic covered by summer ice reached a record low last year — and, as summer nears its end this month — may come close to matching the record this year.

They say there were surprised this year to discover a vast, "Maryland sized" expanse of open water in the midst of the pack ice, a feature known as a polynya , north of Alaska.

"We've seen polynyas before, but in 30 years of ice studies, we've never see one this large in this location before," says Mark Serreze, senior research at the National Snow and Ice Data Center.

Mike Toner writes for The Atlanta Journal-Constitution.