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.
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.
By contrast, plankton – food for other marine creatures – are increasing as less ice means more light reaches the ocean's upper layer, stimulating their growth.
Gray whales are moving into the Arctic Ocean and staying longer to feed on the increased plankton populations.
And it may be family-reunion time for bowhead whales. With open waters along Canada's Northwest Passage during the summer, bowhead whales from the Arctic Pacific and Arctic Atlantic have been observed sharing space in the passage – the first time the two populations have been observed to overlap.
Along the coasts, warmed by the release of heat the Arctic Ocean captures as well as by warm air circulating up from lower latitudes, plant life in coastal areas is shifting from moss and lichens to tall shrubs. Researchers say it's still unclear what effect this might have on caribou and reindeer populations, which rely on the moss and lichen for winter forage. The concern is that the shrubs increasingly will shade the mosses and lichens, depriving them of light.
In addition, the report notes that throughout the Arctic, permafrost is warming, even to depths of 20 meters (65 feet) below the surface. Arctic permafrost represents an enormous reservoir of carbon, mainly as methane. Molecule for molecule, methane is a far more-potent greenhouse gas than carbon dioxide from burning fossil fuels and from land-use changes.
The full report, which runs 167 pages, documents a range of other changes in the region.
In the end, the Arctic remains the canary in the coal mine for global warming because warming's direct and indirect effects tend to amplify the changes taking place there more strongly than at lower latitudes, researchers say.
"Certainly with continued rising CO2 and temperatures, the changes in the Arctic will continue," says Jim Overland, a researcher at NOAA's Pacific Marine Environmental Laboratory in Seattle.
But, he adds, several recent studies indicate that runaway changes are not inevitable. "It takes the continued forcing by CO2-increased temperatures, as part of the overall system, to continue the changes" researchers are noting in the Arctic.
Some models suggest that if CO2 concentrations in the atmosphere are stabilized, "you stabilize the [Arctic] environment as well," he says.