Susan Joy Hassol, the report's lead author, said the Arctic probably would warm twice as much as the earth. A region of extreme light and temperature changes, the Arctic's surfaces of ice, ocean water, vegetation, and soil are important in reflecting the sun's heat.
Pointing to the report as a clear signal that global warming is real, Senators John McCain, Republican of Arizona, and Joseph I. Lieberman, Democrat of Connecticut, said yesterday the ''dire consequences" of warming in the Arctic underscore the need for their proposal to require US cuts in emissions of carbon dioxide and other heat-trapping greenhouse gases. President Bush has rejected that approach.
In the past half-century, average yearly temperatures in Alaska and Siberia rose by about 3.6 degrees to 5.4 degrees Fahrenheit, and winters in Alaska and western Canada warmed by an average of 5 degrees to 7 degrees Fahrenheit.
With ''some of the most rapid and severe climate change on earth," the Arctic regions' melting contributed to sea levels rising globally by an average of about 3 inches in the past 20 years, the report said.
''These changes in the Arctic provide an early indication of the environmental and societal significance of global warming," says the Arctic Climate Impact Assessment, a four-year study by 300 scientists in eight Arctic-bordering nations, including the United States.
This most comprehensive study of Arctic warming to date adds yet more impetus to the projections by many of the world's climate scientists that there will be a steady rise in global temperature, the result of greenhouse gases released by the burning of fossil fuels and other sources.
It is based on ice core samples and other evidence of climate conditions such as on-the-ground and satellite measurements of surface air temperatures.
