Five countries that created a treaty nearly four decades ago to protect polar bears through limits on hunting issued a joint statement on Thursday identifying climate change as "the most important long-term threat" to the bears.
The statement came at the end of a three-day meeting in Tromso, Norway, of scientists and officials from the United States, Norway, Canada, Russia and Denmark, all with territory abutting the Arctic Ocean that serves as habitat for the bears. (Denmark was represented through Greenland, which is moving toward becoming an independent country.)
Bear experts at the meeting said the treaty parties were committed to collaborating on programs aimed at limiting direct threats to bear populations from increasing 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 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 that 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," Dr. Meehan said. "The thing we need to do is look to the global community to seriously address and mitigate climate change." The Norwegian government posted background on the meeting on the Internet at polarbearmeeting.org.
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 goose eggs when they cannot hunt their preferred prey, bearded and ringed seals.
The bears were greatly depleted by unregulated hunting across much of the Arctic until the Soviet Union clamped down in 1956 and other countries followed, 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 United States 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, although about 700 bears a year are still shot in Canada, Alaska and Greenland, according to Norway's environment agency.
Not everyone from countries ringing the Arctic agrees that the bears need to be singled out for protection in the face of climate change. Fernando Ugarte, head of mammal and bird science at the Greenland Institute of Natural Resources, said the 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, Greenland's capital. "There's a long list of animals that will be affected. Why not the walrus, the narwhal, the ringed seal?" Mr. Ugarte said that scientists disagreed over why people around Baffin Bay and elsewhere had 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 icons 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. Their argument, pointing to studies by American government scientists and other groups, is that hunting restrictions have caused most of the populations of bears around the Arctic to grow in recent decades and that long-term forecasts of ice retreats are flawed.
Walter Gibbs contributed reporting from Oslo.