Two springs ago, hunter friends lost their snowmobile when it fell through the ice.

And some Inuits are now wary of venturing to the floe edge - where ice gives way to open water - in late spring, giving them less time to hunt the polar bears and seals that have sustained their culture for generations.

"The ice is softer," said Mitsima, 50.

The Arctic provides a front-row seat for the phenomenon of global warming, as temperatures here have been rising almost twice as fast as in the rest of the world. Wildlife, native traditions, and the very foundations of buildings are at risk, experts said at an April conference here on Canada's snowy Baffin Island, 600 miles above the tree line.

Higher temperatures are also changing the lives of people and animals in more temperate climes, a trend most climate scientists attribute - at least partly - to pollution from heat-trapping "greenhouse" gases.

Birds and plants are heralding the arrival of spring days and even weeks earlier than they once did, from pink azaleas in Washington to eastern bluebirds in Michigan. In May, Stanford University researchers reported a statistical link between these shifts and human impacts on climate.

Man-made pollution also has been cited as a factor in everything from rising ocean levels at the Jersey Shore to the decline in U.S. maple-syrup production.

But the change is especially dramatic here in the land of ice and snow.

Average Arctic temperatures have increased by about 2 degrees Fahrenheit in the last century, with most of the increase coming in the last four decades, according to a major report on Arctic climate released in the fall. Data in some areas are spotty, but the change is more than twice as great in the western Arctic, including Alaska.

In the next century, the report said, average temperatures here are expected to increase by 9 to 13 degrees Fahrenheit - twice as fast as in the world at large. Polar bears, according to the gloomiest predictions, could become extinct by 2100, because each year their hunting grounds - the ice - are melting sooner.

A key reason the Arctic warms faster than elsewhere is that ice and snow do a good job of reflecting sunlight, said oceanographer Robert Corell, head of an international team that issued the Arctic climate report.

But as temperatures increase, more ice and snow melt, and the Arctic loses more of its ability to reflect the sun's energy back into the atmosphere. In effect, warmth leads to more warmth, Corell said at the April conference.

Snow and ice reflect up to 85 percent of the sunlight that hits them; open water, on the other hand, reflects 15 percent, absorbing the rest. The average amount of ice covering the open ocean has been declining by 3 percent per decade since measurements were first taken by satellite in 1978, said Greg Flato, a climate modeler for the Canadian government.

A warmer Arctic could in turn affect climate to the south. "The oceans are really the flywheel" that drives the world's climate, Corell said. "That's where the heat goes."

Most of the world's developed nations began taking steps this year to achieve modest reductions in their smokestack emissions of greenhouse gases, as called for in the treaty known as the Kyoto protocol.

The U.S. Senate has not ratified the pact; in 1997, senators voted 95-0 against doing so, unless developing nations such as China were also included.

And the Bush administration has decided that the Clean Air Act does not allow carbon dioxide to be regulated as a pollutant. That position sparked a lawsuit from environmental groups and 12 states, including New Jersey.

In the absence of federal action, nine Northeast and Mid-Atlantic states, again including New Jersey, met in April to consider regional restrictions on carbon dioxide emissions.

In the meantime, scientists say the decline in ice already has affected polar bears in the western Hudson Bay, in a well-studied population near the town of Churchill.

Winter is the bears' big chance to fatten up on seals, which breed on the ice. But in the western bay, sea ice has been melting three weeks earlier, on average, than it did in the 1970s, said Canadian Wildlife Service biologist Nick Lunn.

As a result, he said, the bears in the Churchill area are 12 percent to 15 percent smaller than in the early 1980s, as measured by a formula based on weight and length.

Smaller bears do not produce as many offspring. Lunn said the number of Churchill bears had declined from 1,200 to 1,000, according to preliminary estimates. If the ice continues to decline, the fortunes of seals and other ice-dependent creatures likely will suffer as well, he said.

Inuits already are making subtle changes in their way of life.

Some hunters on Canada's Baffin Island are uncomfortable about ice conditions this time of year, saying they no longer trust the traditional knowledge handed down for centuries.

One longtime hunter, Pitseolak Alainga, declined to take a visitor to the floe edge in April, calling the conditions "unpredictable." Late April would have been fine 15 years ago, he said.

"You have to watch out," Mitsima said.

Less ice means a shorter period to hunt for what the Inuits call "country food" - seal, polar bear and walrus. Hunting is part of becoming a real man - angutimmarik - in the native language, said Jose Kusugak, president of the Inuit Tapiriit Kanatami, a political group that represents Inuit.

"It's part of growing up," said Mitsima, who got his first seal at age 9 and often provides food for community events.

Climatologist Heather Auld, who works for Environment Canada, the country's environmental-protection agency, told conference participants of other risks. Natural-gas pipelines and building foundations, anchored in permafrost in some places, are showing signs of instability, she said at the two-day seminar.

"They've been trying to do everything from keeping the ground frozen through air-conditioning types of technology ... to trying to put jacks under the buildings," Auld said afterward. "You can only keep that up for so long."

Paul Okalik, premier of the Nunavut territory, reminded conference attendees that one of Canada's national parks was called Auyuittuq - which, he said, means "the place that never melts."