The ever-earlier spring breakup of sea ice is shortening the spring hunting season for female bears, which is probably why they getting thinner and less able to reproduce.
In the early 1980s an average female polar bear weighed in at around 650 pounds (295 kg). That’s recently dropped to less than 510 pounds (230 kg), "a significant weight loss," said Parkinson.
Studies of the timing of the ice break-up, which controls the hunting season for polar bears, show it arrives seven or eight days earlier each decade, Parkinson reported. That gradual loss of hunting and feeding time has accelerated in 2005 and 2006, as the Arctic sea ice has dropped to its lowest level ever.
Even the once-stable winter "perennial" ice, which seemed almost immune to global warming, has begun to lose ground.
"The winter ice extent was basically constant in the first 25 years of the approximately 30-year record," said Josefino Comiso, a NASA sea ice researcher. "But in 2005 and 2006 it’s much lower."
"If the winter ice retreat continues," he said, "the effect will be most profound, especially on Arctic mammals."
