ANCHORAGE, Alaska – Rapid global warming has sped up the movement of sea ice off Alaska's coasts, and already at-risk polar bears are paying a price, a new U.S. study says.
Most sea ice moves throughout the year, and the iconic white bears are on a perpetual walk to stay within their preferred habitat, said U.S. Geological Survey research ecologist George Durner, lead author of the study.
He compares it to living on a treadmill that has picked up speed because ice is thinner, more brittle and moving faster because of wind and ocean currents.
“Increased sea ice drift rates likely exacerbate the physiological stress due to reduced foraging opportunity already experienced by many polar bears in the warming Arctic, adding yet another 'straw to the camel's back,' ” Durner said.
Polar bears were listed as threatened under the Endangered Species Act in 2008 amid the alarming loss of summer sea ice in recent decades and climate models indicating the trend would persist. However, the government said the act would not be used to regulate greenhouse gas emissions.
Researchers made a conservative estimate that bears will have to kill one to three more seals a year to compensate for faster-moving ice, a challenge for bears already facing fewer hunting opportunities.
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, and polar bears sniff out their lairs.
Diminished sea ice has reduced access to prey in the southern Beaufort Sea off Alaska's north coast. Researchers have documented polar bears' declining body condition, reproduction, survival and abundance.
In the new study, researchers looked at data from radio-collared female polar bears in the Beaufort and the Chukchi Seas during two periods: 1987-1998 and 1999-2013.
Sea ice changed in amount, thickness and composition in the second period as melting seasons lengthened.
Bears in the Chukchi Sea, off Alaska's northwest coast, had to walk farther and burn more calories than south Beaufort bears but are in better shape because more food is available, Durner said.
Researchers concluded that the bears must kill 2 to 6 percent more seals per year to make up for burning more calories on faster-moving ice. The study did not address whether they walk faster or spend more time moving to keep up with the ice.
Durner compared their plight to people living in a town hit by both inflation and rising unemployment.
“For the polar bear, the Arctic is becoming more expensive to live in,” he said.