Scientists see dramatic drop in Arctic sea ice

By Will Dunham

WASHINGTON (Reuters) - Arctic sea ice declined this year to the lowest levels registered since satellite assessments started in the 1970s, extending a trend fuelled by human-caused global warming, scientists said on Monday.

Sea ice declined by so much this year that the typically ice-clogged Northwest Passage, allowing vessels to sail from the Atlantic to the Pacific, completely opened for the first time anyone can recall, the researchers said.

Scientists at the U.S. National Snow and Ice Data Centre, part of the University of Colorado at Boulder, measure Arctic sea ice during the annual melt season beginning in March and ending in September.

The average sea ice extent for September, when ice is at its lowest quantities, slipped to 1.65 million square miles (4.28 million square km), breaking by nearly a quarter the previous record low for the month set two years ago, the scientists said.

"Overall there's been a steep and significant downward trend since we've been getting good satellite data starting in 1979," Walt Meier, one of the scientists studying Arctic sea ice for the data Centre, said in a telephone interview.

"We've got the final numbers now for this September, and it's a really dramatic record low. It didn't just break the record, it shattered the record. This year just obliterated everything else."

Sea ice last month was 39 percent below the long-term average from 1979 to 2000, the scientists said.

Meanwhile, a NASA-led study documented a 23 percent loss during the past two winters in the extent of the Arctic's thick, year-round sea ice cover.