Is Global Warming Killing the Polar Bears?
by: JIM CARLTON 14 December 2005
It may be the latest evidence of global warming: Polar bears are drowning. Scientists for the first time have documented multiple deaths of polar bears off Alaska, where they likely drowned after swimming long distances in the ocean amid the melting of the Arctic ice shelf. The bears spend most of their time hunting and raising their young on ice floes.
In a quarter-century of aerial surveys of the Alaskan coastline before 2004, researchers from the U.S. Minerals Management Service said they typically spotted a lone polar bear swimming in the ocean far from ice about once every two years. Polar-bear drownings were so rare that they have never been documented in the surveys.
But in September 2004, when the polar ice cap had retreated a record 160 miles north of the northern coast of Alaska, researchers counted 10 polar bears swimming as far as 60 miles offshore. Polar bears can swim long distances but have evolved to mainly swim between sheets of ice, scientists say.
The researchers returned to the vicinity a few days after a fierce storm and found four dead bears floating in the water. Extrapolation of survey data suggests that on the order of 40 bears may have been swimming and that many of those probably drowned as a result of rough seas caused by high winds, the researchers say in a report set to be released today.
While the government researchers won't speculate on why a climate change is taking place in the Arctic, environmentalists unconnected to the survey say U.S. policies emphasizing oil and gas development are exacerbating global warming, which is accelerating the melting of the ice. For anyone who has wondered how global warming and reduced sea ice will affect polar bears, the answer is simple -- they die, said Richard Steiner, a marine-biology professor at the University of Alaska.
The environmental group Greenpeace began airing a 30-second commercial yesterday in New York, Los Angeles, Atlanta and other cities showing an animated adult polar bear and a cub on a cracking ice floe. The two bears, nowhere near land, slip underneath the water. Polar bears may soon be extinct because of global warming, the voice-over states. It ends with Global Warming: It's the Real Thing, a takeoff of a Coca-Cola Co. commercial featuring polar bears.
Some experts say that climate change may indeed be shrinking the ice pack, but they dispute that emissions are the main culprit or that significantly cutting greenhouse gases would really make a difference. Whether humans are responsible for some, most, or all of the current warming trend in the Arctic, there is no proposal on the table that would actually prevent continued warming or reverse present trends, said Sterling Burnett, a senior fellow at the National Center for Policy Analysis, a nongovernment organization based in Dallas. The question is how to adapt to future changes in climate, regardless of the direction or the cause.
In addition to documenting polar-bear deaths, the Minerals Management Service researchers, Chuck Monnett, Jeffrey Gleason and Lisa Rotterman, also found a striking shift in the bears' habits. From 1979 to 1991, 87% of the bears spotted were found mostly on sea ice. From 1992 to 2004, the percentage dropped to 33%. Most of the remaining bears have been found either in the ocean or on beaches, congregating around carcasses of whales butchered by hunters. In the past, polar bears were rarely seen at such kill sites, because they spent their time hunting their favorite meal -- seals -- on sea ice.
Marine experts consider the findings -- to be presented at a marine-mammal conference this week in San Diego -- an ominous sign. Some have warned for years that a rapid thawing of the Arctic from global warming could endanger species like the polar bear. Already, a warmer Alaska over the past half-century has been linked to increased erosion of rivers and streams, insect infestations and the undermining of pipelines and roads as the permafrost thaws.
Alarmed by the swift changes, the Alaska Inter-Tribal Council, a consortium of the state's tribes, earlier this month passed a resolution urging that the U.S. government enact a mandatory program to reduce global warming.
Some scientists predict polar bears could become extinct within the next century because they have adapted over the millennia to only hunting on ice. If they try to swim in disappearing ice conditions to catch seals, more are likely to tire and drown, scientists say. Polar bears that stay onshore aren't adapted to hunting land animals like caribou, which are preyed upon by more-aggressive grizzly bears. Polar bears also require more fat intake than most food on land offers them, experts say.
As the sea ice goes, that will direct to a very great extent what happens to polar bears, said Steven Amstrup, a polar-bear specialist with the U.S. Geological Survey in Anchorage, Alaska.
Another study set to be released at the marine-mammal conference shows what might happen to the Alaskan polar bears over time. Researchers from the USGS, the University of Wyoming and the Canadian Wildlife Service found that the population of polar bears in Canada's western Hudson Bay -- near the southernmost habitat for the bears in the world -- fell to 935 in 2004 from 1,194 in 1987, a 22% drop. Researchers said the decline -- the first recorded for these bears -- came in tandem with an extension by nearly a full month in the time it takes for Hudson Bay to ice over after the summer.
Our findings may foreshadow how more northerly populations will respond to projected warming in the Arctic ecosystem, wrote Mr. Amstrup, a co-author of the report.
Previous studies by the U.S. and Canadian governments support a link between the decline in sea ice in the Arctic and the ways polar bears try to adapt to their surroundings. For example, researchers say polar bears in the Beaufort Sea off Alaska and Canada used to spend most of their lives jumping from ice floe to ice floe in pursuit of seals. Only pregnant bears would occasionally wander onto the mainland, in search of a den.
But weekly aerial surveys by the U.S. Fish and Wildlife Service show that, over the past five years, an unusually large number of bears have congregated along the beaches. Between the coastal town of Barrow, Alaska and the Canadian border, about 300 miles east, researchers counted as many as 200 bears on land, said Scott Schliebe, director of the Fish and Wildlife's polar-bear project. Many bears could be seen gathered around whale carcasses near villages like Kaktovik, which lies in the Arctic National Wildlife Refuge where the Bush administration is pushing for drilling.
Scientists measured the distances from where the bears were gathered to the nearest ice sheets at sea and found this correlation: The farther the ice was from shore, the larger the number of bears were found on land.
Scientists estimate there are 20,000 to 25,000 polar bears world-wide, including about 2,000 that frequent the Beaufort Sea off Alaska. The latest population study by federal officials, in 1997, suggested the Alaskan bear population wasn't endangered. An update is expected by the end of next year.
Write to Jim Carlton at firstname.lastname@example.org