专家讨论如何保护北极熊

专家称，可能造成北极熊死亡的全球暖化已经在这个物种身上留下记号，北极熊体型变得比较小，且活动力变小，且同类相食的情况有越来越严重的趋势。

冰雪溶化还意味着北极熊必须走得更远，才能到达狩猎场，那里的气温才够冷，才有猎物。

这让北极熊健康变差，影响他们的生育能力，及小熊生存的机率。气候变迁也似乎影响北极熊的行为模式。最近在阿拉斯加就发生数起北极熊吃掉同类的事件，令专家感到忧心。

国际研究网络“熊类专家群”主席安德鲁-德罗彻说：“我们没有气候变迁的确切证据，但是我们能证明气候变迁在北极熊身上造成的许多征兆。”

Five countries that created a treaty nearly four decades ago to protect polar bears through controlled hunting issued a statement Thursday that called climate change "the most important long-term threat" to the bears.

The statement came in Tromso, Norway, at the end of a three-day meeting of scientists and officials from Canada, Denmark, Norway, Russia and the United States, all with territory abutting the Arctic Ocean that serves as habitat for the bears.

Polar bear experts at the meeting said the treaty parties were committed to collaborating on programs aimed at limiting direct threats to bear populations from tourism, shipping and oil and gas drilling in the warming region.

But they said the countries bound by the 1973 bear agreement would be unable, without worldwide cooperation, to address the looming risk to the species: the prospect that global warming from accumulating emissions of greenhouse gases would continue to erode the sheath of Arctic sea ice that the half-ton bears roam in pursuit of seals.

In a telephone interview from Tromso, Rosa Meehan, the division chief in Alaska for marine mammals management of the United States Fish and Wildlife Service, said the agreement — among countries with a range of environmental views — signaled the strength of the science pointing to perils for the bears.

"Polar bears are facing a pretty rough road," Ms. Meehan said. "The thing we need to do is look to the global community to seriously address and mitigate climate change."

The species has probably existed across the Arctic for several hundred thousand years, researchers say. The animals are resilient, eating walrus, grasses and even snow-geese eggs when they cannot hunt their preferred prey, bearded and ringed seals.

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The bears were greatly depleted by ungoverned hunting across much of the Arctic until the Soviet Union clamped down in 1956 and other countries followed suit, with the 1973 treaty one result.

The current population across the Arctic has been estimated at 22,000 to 25,000 bears.

But last year the U.S. Interior Department granted the bears threatened status under the Endangered Species Act, citing the threat from retreating summertime sea ice.

Other countries have been ratcheting up protections, though about 700 bears are still shot each year in Canada, Alaska and Greenland, according to Norway.

Not everyone from countries ringing the Arctic agrees that the bears' fate is so closely tied to climate change.

Fernando Ugarte, head of mammal and bird science at the Greenland Institute of Natural Resources, said Greenland's government was concerned that the rising pressure to protect bears, particularly in the face of global warming, might prompt other countries to press Greenland to clamp down on hunting.

"I am not sure there is a scientific reason to appoint polar bears as the main icon of climate change," he said by telephone in Nuuk, the capital of Greenland. "There's a long list of animals that will be affected. Why not the walrus, the narwhal, the ringed seal?"

Mr. Ugarte said scientists disagree over why people in the settlements around Baffin Bay and elsewhere have reported an increase in polar bear sightings in recent years. One explanation may be that the local bear population is robust. Another, more likely in Mr. Ugarte's opinion, is that climate change is forcing the bears into new migration patterns.

The Tromso meeting was watched closely by environmental groups, which had warned that some countries might press to exclude strong language about global warming.

The bears have been enduring symbols in climate campaigns conducted by such groups, with at least three groups seeking contributions through "adopt a polar bear" programs. But the animals have also become a focal point for some elected officials and scientists who reject the need for cuts in the heat-trapping greenhouse gases, despite broad scientific consensus linking the gases to warming since 1950.