A polar bear watches her cubs on the Hudson Bay in Manitoba, Canada. The bay is famous for polar bears, but their population is in decline.
According to Steven C. Amstrup, chief scientist for Polar Bears International (PBI), rising temperatures have extended the duration of summer, melting ice in the Hudson Bay and forcing polar bears to live on shore for longer stretches of time.
"They live on the sea ice, and they catch their food from the surface of the sea ice," he said. "When they're on the shore, they lose about two pounds of body weight a day. They've adapted to being food-deprived for quite a while, but there are limits as to how far they can go."
As their habitat melts, polar bears are forced to forage elsewhere for food. In Svalbard, Norway, where melting sea ice is retreating from the archipelago's shore, hungry polar bears have gotten into trouble by wandering inland.
"Because there are more bears who are going longer without having anything to eat, often bears that are hungry and interact with humans end up getting shot," he said.
Amstrup says that the solution is to stop the rise in global temperatures.
"The threat to polar bears from global warming turns conservation as we've known it on its head," he said. "In the past, when a species is threatened, we could build a fence around it. But you can't build a fence to protect the sea ice. The only thing that will really make a difference is to stop the rise of global temperature."
Today, on International Polar Bear Day, PBI hopes to promote public awareness about the need to address the advancing detrimental effects of climate change.
—By Becky Little, photo gallery by Sherry L. Brukbacher