Melting ice at the world's rooftop stirs concern

US researchers called this weekfor a long-term international scientific assault on the "top of the world," where climate, ice cover, and plant and marine life are undergoing fundamental changes many scientists attribute to global warming.

Of greatest concern to researchers, the polar ice cap has been shrinking and the tundra's crust of permafrost has been softening. These occurrences, they say, are likely to set in motion changes that could affect everything from southern rain and snowfall patterns to trade routes across the northern seas.

"These changes are not reversible. They will propagate and continue," cautions Matthew Sturm, a scientist with the US Army Corps of Engineers' Cold Regions Research and Engineering Laboratory (CRREL) lab in Fairbanks, Alaska. The key question, he and others say, is how to get a better handle on the possible strength and duration of the shifts they see.

It's unclear how much of the change is due to natural swings in climate or to the impact of human activities on climate. "We really don't know that," acknowledges Mark Serreze, a researcher at the University of Colorado in Boulder. He and others add their observations are generally consistent with projections from many global-climate models when those models take human-generated carbon-dioxide emissions into account. "We need to recognize that change is here, and we have to adapt to that," he says.

The call for a broader Arctic monitoring and research effort comes as more than 400 scientists from around the world met this week in Seattle to try to outline approaches for tracking and forecasting long-term Arctic conditions.

It also comes at a time when tight budgets are forcing Canada and Russia to close or curtail activities at the relatively small number of weather stations that dot the far north. These stations provided critical records of Arctic weather conditions throughout most of the 20th century.

The most immediate concerns center on sea ice and permafrost. Using more than 20 years' worth of satellite data, Josefino Comiso, a researcher at the Goddard Space Flight Institute in Greenbelt, Md., notes that the thick cap of ice that covers much of the Arctic Ocean has decreased nearly 20 percent over the past 20 years. "This was a big surprise," he says.

Seasonal ice comes and goes. This leaves perennial ice to screen much of the Arctic Ocean from solar warming. The ice also reduces the warmth the ocean provides to the overlying atmosphere.

Researchers note that if the Arctic Ocean failed to freeze in winter, surface temperatures in the winter there would be 4.5 degrees Fahrenheit warmer. As the permanent ice pack shrinks, and more open water and dark melt ponds on seasonal ice absorb more heat, the warming that is already occurring will accelerate.

A recent example: Over the past two years, a large 3,000-year-old ice shelf over northernmost Canada has broken up.

The loss of ice would open northern sea routes between Asia, North America, and Europe, triggering a growth in commerce, observes David Rind, a researcher with the Goddard Institute for Space Studies in New York. This could, in turn, open disputes over which country controls these routes and whether they should be declared international maritime passages freely open to all. More broadly, Dr. Rind says, as the overlying atmosphere warms, altering large circulation patterns governing storm tracks could bring rain and snow into lower latitudes.

One of these patterns is known as the polar vortex, a river of high-altitude winds that circle the globe at high latitudes. James Morison, a polar scientist at the University of Washington, notes that the polar vortex "spun up" during much of the 1990s, although it eased up after 1997.

"This represents the kind of thing we might expect" from global warming, he says.

The loss of permafrost, is troubling for several reasons, researchers say. As the permanently frozen ground turns mushy, homes, pipelines, bridges, and buildings tailored to sitting atop permafrost face serious damage.

From a climate perspective, the frozen portions of tundra lock up some 30 percent of the globe's carbon. As it gradually thaws, carbon will be released into the atmosphere as CO2. The thaw will also release methane, a more potent greenhouse gas than carbon dioxide.

Researchers are urgently trying to assess how much of that released carbon is likely to be recaptured by shrubs and trees, whose habitat range already is shifting north as the Arctic warms.

The loss of ice also would affect subsistence patterns among the indigenous people in the far north, who hunt wildlife that live among the ice sheets. Yet even here the picture is mixed, because some of these groups also are noting increases in caribou herds and shifts in their migration patterns as the climate warms.

The challenge of designing and deploying the instruments and computer models to address these issues "is unprecedented," says Peter Schlosser, a researcher at the Lamont-Doherty Earth Observatory at Columbia University.

"The Arctic is a sensitive region for climate change" and change up there "is happening now," Rind says.