The report by the international Arctic Monitoring and Assessment Program, or AMAP, is one of the most comprehensive updates on climate change in the Arctic, and builds on a similar assessment in 2005.
The full report will be delivered to foreign ministers of the eight Arctic nations next week, but an executive summary including the key findings was obtained by The Associated Press on Tuesday.
It says that Arctic temperatures in the past six years were the highest since measurements began in 1880, and that feedback mechanisms believed to accelerate warming in the climate system have now started kicking in.
It also shatters some of the forecasts made in 2007 by the U.N.'s expert panel on climate change.
The cover of sea ice on the Arctic Ocean, for example, is shrinking faster than projected by the U.N. panel. The level of summer ice coverage has been at or near record lows every year since 2001, AMAP said, predicting that the Arctic Ocean will be nearly ice free in summer within 30-40 years.
AMAP also said the U.N. panel was too conservative in estimating how much sea levels will rise – one of the most closely watched aspects of global warming because of the potentially catastrophic impact on coastal cities and island nations.
The melting of Arctic glaciers and ice caps, including Greenland's massive ice sheet, are projected to help raise global sea levels by 35 to 63 inches (90-160 centimeters) by 2100, AMAP said, though it noted that the estimate was highly uncertain.
That's up from a 2007 projection of 7 to 23 inches (19-59 centimeters) by the U.N. panel, which didn't consider the dynamics of ice caps in the Arctic and Antarctica.
"The observed changes in sea ice on the Arctic Ocean, in the mass of the Greenland ice sheet and Arctic ice caps and glaciers over the past 10 years are dramatic and represent an obvious departure from the long-term patterns," AMAP said in the executive summary.
The organization's main function is to advise the nations surrounding the Arctic – the U.S., Canada, Russia, Denmark, Norway, Sweden, Iceland and Finland – on threats to the Arctic environment.
The findings of its report – Snow, Water, Ice and Permafrost in the Arctic – will be discussed by some of the scientists who helped compile it at a conference starting Wednesday in the Danish capital, Copenhagen.