Global warming has brought a new normal to the Arctic, with warmer air and ocean temperatures, thinner and less expansive summer sea ice, and greener vegetation in coastal regions abutting the open water.

In addition, longer periods of open water during the annual sea-ice melt season is allowing the ocean to take up more carbon dioxide from the atmosphere, leading to seasonal bouts of ocean acidification in some areas.

These broad observations, along with more-detailed looks at some 32 environmental indicators, appear in the National Oceanic and Atmospheric Administration's 2011 Arctic Report Card, released Thursday.

The changes have wide implications, from opening new sources of offshore oil, gas, and minerals to speeding the release of heat-trapping methane into the atmosphere as permafrost melts.

Even on a continental level, changes in atmospheric circulation patterns at the top of the world can affect the intensity of winter weather well into the lower latitudes. Wind patterns that repeated during the past two winters – itself unusual, according to the report – brought relatively warm temperatures to regions of the Arctic, including Greenland, while subjecting the eastern US with cold temperatures and heavy snowfall.

Previous reports have been reluctant to pronounce a changed regime at the top of the world. But with nearly five years of additional observations and research in the region since the record-low summer sea-ice cover of 2007, the trends have become clearer, the researchers say.

"We've got a new normal," says Don Perovich, a polar scientist with the US Army Corps of Engineers' Cold Regions Research and Engineering Laboratory in Hanover, N.H. It's "a normal that has less ice, thinner ice, younger ice, a new normal where more light will be transmitted through the ice into the upper ocean. That has implications not just for the ice but for other components of the Arctic system."

Changes the report tracks "have long been predicted," notes Jonathan Overpeck, who is codirector of the Institute of the Environment at the University of Arizona in Tucson. "It is troubling how fast the change is proceeding. Of particular note is not just the sea-ice change, but the accelerating rate of Greenland Ice Sheet ice loss."

The Arctic's engine of change

The summer sea-ice extent and its impact on the ocean as the global climate warms are the regional engine driving the changes. 

Summer sea ice has been declining since satellites began tracking it in 1978. As a result, a region of the world that helps moderate global climate by reflecting sunlight back into space from its veneers of snow and ice is losing its reflective surface at a time when sunlight is strongest.

The summer sea-ice minimum in 2011 was the second lowest on record, nearly matching the record low set in 2007.

Some are as subtle as shifts in the shape of ice crystals in the snow covering high elevations on Greenland's Ice Cap, which can reduce the snow cover's ability to reflect sunlight back into space, explains Jason Box, a polar scientist at Ohio State University and a contributor to NOAA's report card.

For polar bears and walruses, the loss of summer ice can put them at a disadvantage. Out of 19 sub-populations of polar bears in the Arctic, seven are declining, with two of the seven declines linked to the loss of summer sea ice.