Sea ice is melting and, if predictions hold true, here’s a grim bit of news from the U.S. Geological Survey:

By 2050 the world’s polar bear population could be largely gone:

Two-thirds of the world’s polar bear population could be gone by midcentury if predictions of melting sea ice hold true, the U.S. Geological Survey reported on Friday.

The fate of polar bears could be even bleaker than that estimate, because sea ice in the Arctic might be vanishing faster than the available computer models predict, the geological survey said in a report aimed at determining whether the big white bear should be listed as a threatened species.

“There is a definite link between changes in the sea ice and the welfare of polar bears,” said Steve Amstrup, who led the research team. Arctic sea ice is already at an all-time low this year and is expected to retreat farther this month, according to the U.S. National Snow and Ice Data Center.

That means that polar bears — some 16,000 of them — will disappear by 2050 from parts of the Arctic where sea ice is melting most rapidly, along the north coasts of Alaska and Russia, researchers said in a telephone briefing.

The AP story is even blunter than the Reuters piece quoted above. And it dares to cite a cause that some insist is strictly fiction and an idea promoted by “tree huggers.”

Two-thirds of the world’s polar bears will be killed off by 2050 — and the entire population gone from Alaska — because of thinning sea ice from global warming in the Arctic, government scientists forecast Friday.

Only in the northern Canadian Arctic islands and the west coast of Greenland are any of the world’s 16,000 polar bears expected to survive through the end of the century, said the U.S. Geological Survey, which is the scientific arm of the Interior Department.

USGS projects that polar bears during the next half-century will disappear along the north coasts of Alaska and Russia and lose 42 percent of the Arctic range they need to live in during summer in the Polar Basin when they hunt and breed. A polar bear’s life usually lasts about 30 years.

“Projected changes in future sea ice conditions, if realized, will result in loss of approximately two-thirds of the world’s current polar bear population by the mid 21st century,” the report says.

Polar bears depend on sea ice as a platform for hunting seals, which is their primary food. They rarely catch seals on land or in open water. Because the general decline of Arctic sea ice appears to be underestimated, scientists said their forecast of how much polar bear populations will shrink also may be on the low side.

“There is a definite link between changes in the sea ice and the welfare of polar bears,” said USGS scientist Steven Amstrup, the lead author of the new studies. “As the sea ice goes, so goes the polar bear.”

Despite a host of stories like this, there are some commentators who dismiss the whole concept of global warming. On an L.A. radio station yesterday, a rerun of a top conservative talk show host’s show contained a segment where he scornfully said global warming doesn’t exist and suggested it’s a myth perpetuated by liberals.

Here’s the lead of a story from December 2005 run in what therefore must be the liberal newspaper The Wall Street Journal:

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.

Further down in the apparently liberal newspaper’s piece it also noted that there is debate over global warming:

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.”

The National Resources Defense Council’s website on saving the polar bears has this:

Without federal protection, the polar bear could become the first mammal to lose 100 percent of its habitat to global warming. And global warming is the leading threat to our planet as a whole. During the past 200 years, our industrial economy has overloaded the earth’s atmosphere with carbon dioxide, trapping the sun’s heat and causing the planet to warm up. Today, the United States is the world’s leading source of global warming pollution, produced mostly by coal-burning power plants and automobiles.

A rise in global temperature of one degree Fahrenheit has already caused the polar ice cap to shrink, malaria and other illnesses to afflict more people, and heat waves, wildfires, droughts, and hurricanes to intensify. Allowing temperatures to rise more than another 2 degrees Fahrenheit threatens to trigger the irreversible melting of the Greenland ice sheet, a 20-foot rise in sea levels, and the extinction of species, including the polar bear. Our only chance to avert such catastrophic outcomes is to act now to reduce global warming pollution. Stabilizing the world’s climate demands that the United States cut its carbon emissions 25 percent by 2020 and 80 percent by 2050.

The UN Works website:

Muffled against the bitter artic cold by thick white fur and layers of fat, the polar bear lives and hunts in the snowbound lands and ice flows surrounding the North Pole. A strong swimmer and a lone predator, it is at home ice flows, which may carry it far from its original locality.

The polar bear is found on the arctic coasts and islands of the five countries around the North Pole, the United States (Alaska), Canada, Denmark (Greenland), Norway and Russia. It is the only species that still lives throughout its original range, with an estimated 20,000 still in the wild.

However, even in the seemingly pristine Arctic environment, polar bears are threatened by the spread of hormone-disrupting chemicals and global warming. This affects the polar ice edge ecosystem, the habitat of walrus, seals and penguins, as well as bears.

Global warming could already be having a negative impact on polar bears. In Canada’s Hudson Bay (see map), numbers have been declining according to a study by Canadian Wildlife Services. Ice on the bay is melting an average of three weeks earlier than in the mid-1970s. This forces polar bears to retreat further inland before they have been able to replenish their reserves of fat by feeding on seal pups, which live on the ice.

The National Wildlife Federation:

Though most people will probably never get the chance to see them in the wild, polar bears have become one of the most iconic wildlife species around. Unfortunately, they are fast becoming an icon of global warming–exemplifying just how a warming world will challenge wildlife in the coming years.

…..Polar bears are literally drowning from global warming, unable to swim the increasingly longer distances between land and receding sea ice. They depend on this sea ice to hunt their primary food source–seals. With ice forming later in the fall and breaking up sooner in the spring, the time period bears can forage for food is shrinking every year.

A recent study by the U.S. Geological Survey’s Alaska Science Center discovered a “very dramatic” change in cub survival and estimated that only about 43 percent of the polar bear cubs in Alaska’ Beaufort Sea are surviving their first year as a result of shrinking ice habitat. Cub survival is down from about 65 percent survival measured in the late 1980s and early 1990s.

In December the Seattle Times wrote, in part:

It took the threat to an iconic mammal from the coldest reaches of the north to get the Bush administration to entertain a serious debate about global warming.

The U.S. Interior Department filed a proposal Wednesday in the Federal Register to list polar bears as a threatened species under the Endangered Species Act. The filing triggers a 90-day comment period, during which the agency will hold hearings and collect written testimony. The agency has been studying stresses on the polar bear, partly under pressure from a lawsuit from three environmental groups.

The move is significant, because the Bush administration has been reluctant to engage debate about the mounting evidence the world is warming and posing potential harm to the environment, wildlife and humans. A growing scientific consensus says human-generated greenhouse gases are contributing to global warming.

While the administration has all but resisted the connection, many states and cities, including Seattle, have started to raise awareness about the looming threat.

Solving the challenges facing polar bears is where the rub is in federal policy. About 4,700 of the world’s polar-bear population, which might number as many as 25,000, live in Alaska and spend part of the year in Canada and Russia.

Some of global warming’s critics also point to THIS ARTICLE saying global warming has helped the bears thrive in some areas. But further down you’ll read that the study cited is controversial (the “study was commissioned by the Inuit-dominated government of Nunavit. Critics claim the government has an agenda to encourage polar bear hunting and keep the animals off the endangered species list.) The Huffington Post did a satire piece on this article.

And, indeed, the bulk of articles and websites addressing the issue and expressing concern far outweigh one that one article. In 2004, for instance, the Washington Post ran a story that began:

Global warming could cause polar bears to go extinct by the end of the century by eroding the sea ice that sustains them, according to the most comprehensive international assessment ever done of Arctic climate change.

The thinning of sea ice — which is projected to shrink by at least half by the end of the century and could disappear altogether, according to some computer models — could determine the fate of many other key Arctic species, said the Arctic Climate Impact Assessment, the product of four years of work by more than 300 scientists.

Bears are dependent on sea ice because they use it to hunt for seals, which periodically pop up through breathing holes in the ice. Because the ice has broken up earlier and earlier in the year over the past few decades, polar bears are deprived of crucial hunting opportunities.

The uncertain fate of the world’s largest non-aquatic carnivores — as well as the future of other animals and humans who live in the Arctic — was sketched in stark relief yesterday by the 139-page document.

The report offered a broad picture of the evidence that climate change has disproportionately affected far northern latitudes.

The researchers concluded that some areas in the Arctic have warmed 10 times as fast as the world as a whole, which has warmed an average of 1 degree Fahrenheit over the past century.

“The Arctic is really warming now,” said Robert Corell, a senior fellow at the American Meteorological Society who chaired the assessment. “These areas provide a bellwether of what’s coming to planet Earth.”

They’re all just a bunch of tree huggers?