Some 80 percent of Arctic ice may disappear in 30 years, not 90 as scientists had previously estimated, according to a new study on the impact of global warming.

"The amount of the Arctic Ocean covered by ice at the end of summer by then could be only about 1 million square kilometres, or about 620,000 square miles," said US researchers who authored the study publishedThursday. "That's compared to today's ice extent of 4.6 million square kilometres, or 2.8 million square miles," they added, warning the development "raises the question of ecosystem upheaval."

The scientists made their projections based on models that took accounted for changes in Arctic ice, which saw "dramatic declines" at the end of summer in 2007 and 2008, when the ice surface dropped to 4.3 and 4.6 million square kilometres (1.7 and 1.8

million square miles), respectively.

The models pointed to a "'nearly ice-free" Arctic in just 32 years, with some of the models making the same prediction for 11 years from now.

"In recent years, the combination of unusual warm temperatures from natural causes and the global warming signal have worked together to provide an earlier summer sea-ice loss than was predicted," said James Overland of the National Oceanic and Atmospheric Administration (NOAA).

Overland and co-author Muyin Wang of the University of Washington said earlier models had predicted the event would not take place before the end of the 21st century.

Maps illustrating Overland and Wang's models showed a nearly ice-free Arctic Ocean, although some ice would remain along northern Canada and Greenland, whmp; powerful winds make for very-thick layers of ice.

The researchers noted one benefit of less ice in the Arctic: "a boon for shipping and for extracting minerals and oil from the seabed."