WASHINGTON -- Scientists say changes in the earth's climate from human influences are occurring particularly intensely in the Arctic region, evidenced by the widespread melting of glaciers, thinning sea ice, and rising permafrost temperatures.
A study released yesterday said the annual average amount of sea ice in the Arctic has decreased by about 8 percent in the past 30 years, resulting in the loss of 386,100 square miles of sea ice, an area bigger than Texas and Arizona combined.
''The polar regions are essentially the earth's air conditioner," Michael McCracken, president of the International Association of Meteorology and Atmospheric Sciences, said at a news conference yesterday. ''Imagine the earth having a less efficient air conditioner."
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.
''The bottom line is that the Arctic is warming now, much more rapidly than the rest of the globe, and it's impacting people directly," Robert Corell, chairman of the scientists' study panel and a senior fellow with the American Meteorological Society, said Sunday.
The process is only likely to accelerate in the Arctic. That would wreak havoc on polar bears, ice-dependent seals, caribou, and reindeer herds, as well as the local people whose main food source comes from hunting those animals. Some endangered migratory birds are projected to lose more than half their breeding areas.
The study projects that in the next 100 years, the yearly average temperatures will increase by 7 to 13 degrees Fahrenheit over land and 13 to 18 degrees over the ocean. Forests would expand into the Arctic tundra, which would expand into the polar ice deserts, because rising temperatures would favor taller, denser vegetation. Sea levels globally already are expected to rise between another 4 inches to 3 feet or more this century.