By Deborah Zabarenko, Environment Correspondent

WASHINGTON | Thu Oct 21, 2010 3:17pm EDT

WASHINGTON (Reuters) - The signs of climate change were all over the Arctic this year -- warmer air, less sea ice, melting glaciers -- which probably means this weather-making region will not return to its former, colder state, scientists reported on Thursday.

In an international assessment of the Arctic, scientists from the United States, Canada, Russia, Denmark and other countries said, "Return to previous Arctic conditions is unlikely."

Conditions in the Arctic are important because of their powerful impact on weather in the heavily populated middle latitudes of the Northern Hemisphere.

The heavy snows in the United States, northern Europe and western Asia last winter are linked to higher air temperatures over the Arctic, the scientists found.

"Winter 2009-2010 showed a new connectivity between mid-latitude extreme cold and snowy weather events and changes in the wind patterns of the Arctic, the so-called Warm Arctic-Cold Continents pattern," said the report, issued by the U.S. National Oceanic and Atmospheric Administration (NOAA).

The scientists found evidence of widespread Arctic warming, with surface air temperatures rising above global averages twice as quickly as the rate for lower latitudes, Jackie Richter-Menge of the U.S. Army Cold Regions Research and Engineering Laboratory.

Part of the reason for this is a process called polar amplification. Warming air melts the sun-reflecting white snow and ice of the Arctic, revealing darker, heat-absorbing water or land, spurring the effects of warming. This is further amplified by the action of the round-the-clock sunlight of Arctic summers, Richter-Menge said in a telephone briefing.

SNOWY PARADOX

Normally cold air is "bottled up" in the Arctic during winter months but in late 2009 and early 2010, powerful winds blew cold air from north to south instead of the more typical west to east pattern, said Jim Overland, an oceanographer at NOAA's Pacific Marine Environmental Laboratory in Seattle.

Overland saw this as a direct link between a warmer Arctic with less sea ice and weather in the middle latitudes, and he suggested it was likely to become more common as Arctic sea ice melts over the next 50 years.

This pattern has occurred only three times in the past 160 years, Overland said at the briefing.

"It's a bit of a paradox where you have overall global warming and warming in the atmosphere (that) actually can create some more of these winter storms," Overland said. "Global warming is not just warming everywhere. ... It creates these complexities."

Records tumbled in Greenland, where 2010 was the warmest year in 138 years in the island's capital city of Nuuk, and four big glaciers lost more than 10 square miles (25.90 sq km) each, said Jason Box of the Byrd Polar Research Center in Ohio.

"There's now really no doubt that glacier ice losses have not just increased but have accelerated," Box said. "Sea level rise projections for the future will again need to be revised upward."

The full report is available on the Internet here .

(Editing by Will Dunham)