Scientists say changes in the earth's climate from human influences are occurring particularly intensely in the Arctic region, evidenced by widespread melting of glaciers, thinning sea ice and rising permafrost temperatures.
A study released Monday 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.
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 three 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 as the result of greenhouse gases released into the atmosphere from 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. Nations participating in the study besides the United States are Canada, Denmark, Finland, Iceland, Norway, Russia and Sweden.
"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, a region that provides important resources such as oil, gas and fish, the study finds.
That would wreak havoc on polar bears, ice-dependent seals, caribou and reindeer herds — and local people such as Inuit 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, mainly because the water absorbs more heat.
Forests would expand into the Arctic tundra, which in turn would expand into the polar ice deserts, because rising temperatures would favor taller, denser vegetation. The areas of Arctic tundra would shrink to their smallest extent since 21,000 years ago when, humans began emerging from the last Ice Age.
"It's happening much more quickly than we had anticipated as recently as five years ago, and it has global implications due to the opening of the Arctic sea ice, providing for new marine transportation routes," said Corell, who from 1986 to 2000 headed a roughly $2 billion-a-year U.S. research program into climate and other global environmental changes.
Since it takes decades if not centuries to reverse warming from carbon dioxide, methane and other greenhouse gases, some damage is inevitable, though longer-term impacts could be "reduced significantly" by cutting emissions globally this century, the study says.
Sea levels globally already are expected to rise between another four inches to three feet or more this century. Longer term, if temperatures continue to rise unabated, in the range of 5 degrees to 11 degrees Fahrenheit over the next several centuries, sea levels would rise alarmingly.
In that scenario, the study projects "a virtually complete melting of the Greenland Ice Sheet," which would contribute as much as 23 feet to the world's sea level rise.