文章出处:Global warming makes life tough for already at-risk polar bears
ANCHORAGE, Alaska — Rapid global warming has increased the speed of sea ice moving off Alaska's coasts. Polar bears, which were already at risk, are paying a price, a new U.S. study says.
Most sea ice moves throughout the year and the white bears are on a perpetual walk to stay within their preferred living area, said U.S. Geological Survey research ecologist George Durner. He is the lead author of the study.
He compares it to living on a treadmill that has picked up speed. Change has come as ice is thinner, more brittle and moving faster because of wind and ocean currents, he said.
The bears are already stressed by fewer hunting opportunities in the warming Arctic, Durner said. Increased sea ice drift rates likely worsen the stress, he said. He compared it to adding "another 'straw to the camel's back.'"
Loss Of Summer Sea Ice Will Only Get Worse
Polar bears were listed as threatened under the Endangered Species Act in 2008 in the midst of the alarming loss of summer sea ice in recent decades. Climate models indicated the trend would persist. However, the government said the act would not be used to regulate greenhouse gas emissions.
The U.S. polar bear recovery plan says that without action to address climate change, it is unlikely that polar bears could be saved. Climate change is the primary cause of shrinking sea ice. The plan released in January noted positive signs such as emission goals in the Paris, France climate agreement.
President Donald Trump, however, withdrew from the international agreement last week. He argued that it had disadvantaged the U.S. to the benefit of other countries. His position is that it leaves American businesses and taxpayers to absorb the cost.
Trump also has called for expanded petroleum development in places where polar bears live. They include offshore Alaska waters and parts of the National Petroleum Reserve-Alaska and the Arctic National Wildlife Refuge.
Margaret Williams is Arctic program managing director for the World Wildlife Fund. She said withdrawal from the Paris agreement is frightening. However, she said private, state and local efforts to reduce carbon emissions and turn to wind or other energy are a positive sign.
"There's still a lot of hope," she said.
More Seal Meals
The political moves come as the Geological Survey and University of Wyoming published the study. It documented how polar bears use more energy to stay within their home range.
Researchers estimated that bears will have to kill 1 to 3 more seals a year to make up for faster-moving ice. It is a challenge for bears already facing fewer hunting opportunities.
Durner compared the bears' trouble to that of some people. It is like those living in a town hit by both higher prices and rising unemployment, he said.
"For the polar bear, the Arctic is becoming more expensive to live in," he said.
Polar bears can go for extended periods without eating but then gorge on ringed and bearded seals. Ringed seals give birth on sea ice in spring and early summer. Polar bears sniff out their lairs.
Burning More Calories On Faster Sea Ice
Decreased sea ice has reduced access to prey in the southern Beaufort Sea off Alaska's north coast. Researchers have documented the polar bear's declining body condition, survival and abundance.
In the new study, researchers looked at data from female polar bears wearing radio collars in the Beaufort and the Chukchi Seas. They looked at two time periods, 1987 to 1998 and 1999 to 2013.
Sea ice changed in amount and thickness in the second period as melting seasons lengthened.
Researchers concluded that the bears need to eat more to make up for burning more calories on faster-moving sea ice. They must kill 2 to 6 percent more seals per year, the study said. It did not address whether the bears walk faster or spend more time moving to **keep up with **the ice.
Exactly How Climate Change Affects Polar Bears
Bears in the Chukchi Sea, off Alaska's northwest coast, had to walk farther than south Beaufort bears, Durner said. So they burn more calories. However, they **are in better shape **because more food is available, he said.
Amy Cutting, animal curator at the Oregon Zoo, said in an email that the paper is important. The study is a key piece in the growing literature on challenges faced by polar bears, she said.
The Geological Survey has decades of location and movement data on bears, she said. **It is uniquely positioned to assess effects of **changes in sea ice, she said.
This kind of research is critical, Cutting said.** It is important for** understanding the specific ways in which climate change is affecting polar bears, she said.
