BOSTON — To spot the most pronounced signs of human-triggered climate change, supercomputers simulating the earth's weather have issued the same advice: Look to the far north, where retreating snow, ice, and permafrost would magnify the effects.
Ten Arctic scientists have reviewed nearly 40 years of polar research in what may be the largest focused survey yet of environmental change in the far north. Their new survey paints a picture broadly consistent with climate-model forecasts.
"I've been a fence-sitter for a long time" on human-induced climate change, says Mark Serreze, a polar scientist at the University of Colorado at Boulder and the survey's lead author. "Now, I'm definitely leaning very hard" toward accepting the notion, "although I haven't toppled yet."
Polar studies the team surveyed found a range of effects. Among them:
*Temperatures have been rising since at least 1961. Tree-ring data suggests that Arctic warming in the mid-20th century is the most pronounced in 400 years.
*Since the late 1950s, changes in atmospheric circulation patterns have brought more storms to the region in winter, spring, and summer and more-intense storms during all seasons.
*Since 1900, rain and snowfall have increased in a band running from latitude 55 degrees north to 85 degrees north. Northern Canada has seen a marked rise in precipitation during the past 40 years.
*Snow cover has dropped by about 10 percent since 1972, largely in the spring and summer as residual snow fields have shrunk. Sea ice has been declining in thickness and extent, dropping to record lows in the western Arctic Ocean two years ago.
*Melting of small glaciers in the Arctic may be responsible for about 20 percent of the estimated 7.4 centimeter rise in global sea levels since 1961.
Dr. Serreze and his colleagues note some important shortcomings in the data they surveyed. Records often span short time periods, limited territory, or the data's quality is suspect. Moreover, computer models and observations disagree over details.
Serreze notes addressing these shortcomings may be difficult. Although the US is putting money into limited data-gathering projects, key long-term monitoring stations in Russia and Canada have been shut down for budget reasons.
"We really need to restore these stations and gather more oceanographic observations," he says.
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