Global warming is heating the Arctic at a rapid pace - with impacts that could range from the disappearance of polar bears' summer habitat by the century's end to a damaging rise in sea levels worldwide.
That assessment, released Monday by a group of international climate experts, amounts to one of the most urgent warnings on climate change to date, and could put new pressure on the US and other nations to curb fossil-fuel emissions.
This comes at a time of growing concern about the effects of global warming, which scientists generally agree is increasingly driven by rising carbon-dioxide levels in the atmosphere from human industrial activity and changing land-use patterns.
Monday's report called for "strong near-term action" to reduce output of gases that, when they rise into the atmosphere, trap heat in what is called the greenhouse effect.
The trends cited in the Arctic Climate Impact Assessment are stark:
• Rapid melting of Arctic glaciers, including the vast sheet of ice that covers Greenland. The sheet locks up enough fresh water to raise sea levels by as much as 27 feet over the course of several centuries. The group calculates that during this century, Greenland temperatures are likely to exceed the threshold for triggering the long-term meltdown of the island's ice sheet.
• Arctic temperatures rising up to twice as fast as the global average. Over the past 50 years, average winter temperatures in Alaska, western Canada, and eastern Russia have risen as much as 7 degrees F. Over the next century, temperatures are projected to rise by up to 13 degrees F.
• A dramatic reduction in the extent of the summer ice pack in the Arctic Ocean. Late-summer ice coverage already has declined by as much as 20 percent over the past three decades. The summer ice pack is projected to shrink by another 10 to 50 percent by the end of the century. Some climate models show the summer ice vanishing by 2040.
Either change could accelerate warming by allowing the ocean to absorb solar heat. The change could threaten species such as polar bears and some seals with extinction. Researchers also worry that an influx of fresh water into the North Atlantic could disrupt large-scale ocean currents worldwide, altering weather patterns and the locations where nutrients rise from the depths to support regional fisheries.
"The Arctic is warming now, at a faster rate than the rest of the planet. It's affecting people, and its effects are global," says Robert Corell, a senior fellow with the American Meteorological Society who chaired the team that pulled the study together.
Assembled over 4-1/2 years, the study came at the request of the Arctic Council and the International Arctic Science Committee. The council includes top-level government officials from the United States, Canada, Denmark, Finland, Iceland, Norway, Russia, and Sweden, as well as from six organizations representing indigenous groups who live in the Arctic region. Some 300 scientists from the world's top polar-research centers were involved.
The report details current and projected changes that could affect everything from shipping, agriculture, and the livelihoods of indigenous people to breeding grounds for migratory birds, many of which are considered endangered. One aspect on which researchers are keeping their eye: the release of methane and carbon dioxide as permafrost thaws and tundra decomposes. Even if the advance of forests to higher latitudes soaks up some of this released CO2, this still leaves methane - a much more potent greenhouse gas - free to enter the atmosphere.
Monday, the Pew Center on Global Climate Change issued its own study of global warming's effect on the US. The report largely focuses on warming's impact on ecology and biodiversity.
The Arctic study also comes at a time of growing momentum internationally to address the climate change.
Last week, Russian President Vladimir Putin signed a bill passed by parliament that ratified the 1997 Kyoto Protocol. His signature was the final act required for the pact to take effect. The accord requires industrial countries party to the pact to reduce their CO2 emissions by an average of 5.5 percent between 2008 and 2012. While climate researchers agree that the pact's target will have little effect on atmospheric CO2, the agreement establishes mechanisms for achieving emissions targets, such as emissions trading, that may be a foundation for future agreements.
Perhaps just as important, supporters say, once the protocol takes force, it requires countries to begin looking ahead to follow-on agreements that would have a more significant impact on emissions.
In a statement released following Mr. Putin's signing, Eileen Claussen of the Pew Center on Climate Change noted that talks are set to begin next year on a post-Kyoto agreement. Now that the protocol is in effect, it "sets the stage for a new round of negotiations that can produce a broader, more durable agreement," she said. "New approaches will be needed to better engage the United States and major developing countries in the ... effort."
The new report is likely to add to pressure building on the Bush administration to take firmer actions to curb America's carbon emissions. British Prime Minister Tony Blair has signaled that climate will be one of his top priorities when he takes over as president of the G-8 group of industrial nations in January.
In a recent interview with Reuters, David King, Britain's chief science adviser, noted that during the summer, White House policymakers "fully accepted the scientific arguments for climate change and are keen to play a leadership role. So far we've been focusing on Russia. Clearly now the spotlight is going to move."
President Bush withdrew the US from the Kyoto treaty in 2001. The administration has said it views global warming as a serious threat, but that the Kyoto approach puts too much of the carbon-reduction burden on the US and other industrial countries, putting millions of jobs at risk.
The administration is spending several billion dollars each year to research technologies such as clean-burning coal and hydrogen-fueled cars. And while Bush hasn't signed on to the Kyoto goals, the administration talks of reducing the economy's "carbon-intensity" - the amount of carbon needed to produce each dollar of economic output.
"It is of importance to the president that we continue to make progress" on climate change, EPA administrator Mike Leavitt told the Associated Press Friday.