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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
Photograph by Tom Murphy, National Geographic
Thanks to a camera trap, a polar bear unwittingly makes a self-portrait in Svalbard.
(Read "Watching Polar Bears Eat Goose Eggs in Warmer Arctic.")
Photograph by Paul Nicklen, National Geographic
A polar bear jumps between ice floes near the island of Spitsbergen in Norway in 2010. Between 1979 and 2008, the ice pack in the Barents Sea, which borders Norway, shrank by nearly 30 percent.
(Read "Is Pollution Weakening Polar Bears' Ability to Mate?")
Photograph by Ralph Lee Hopkins, National Geographic
A red fox rubs noses with a polar bear on the Hudson Bay in Manitoba.
Johansen Krause, National Geographic
A polar bear and her cubs are stranded on an iceless shoreline in Svalbard. The photo appeared in the 2009 National Geographic magazine article "Ice Paradise," which reported on the consequences of the melting ice pack in Svalbard.
(Read "As Sea Ice Shrinks, Can Polar Bears Survive on Land?")
Photograph by Paul Nicklen, National Geographic
A polar bear sleeps on ice in Svalbard.
Photograph by Ralph Lee Hopkins, National Geographic
A polar bear swims in the Admiralty Inlet in Nunavut, Canada.
(Read "Polar Bear Numbers Plummeting in Alaska, Canada—What About the Rest?")
Photograph by Paul Nicklen, National Geographic
Two polar bears face off against each other in Churchill, Manitoba, in northern Canada.
Photograph by Paul Nicklen, National Geographic
A polar bear sleeps with his paws folded underneath.
Photograph by Norbert Rosing, National Geographic
A polar bear stands over a partially eaten whale carcass in Kaktovik, Alaska.
(See "Pictures: 80 Polar Bears Throng Village in Search of Whale.")
Photograph by Joel Sartore, National Geographic
A polar bear inspects photographer Paul Nicklen's cabin, his home while on assignment for National Geographic's 2009 article, "Ice Paradise." Nicklen called the icy strip outside his window a "bear superhighway."
Photograph by Paul Nicklen, National Geographic
A polar bear and cubs walk away from the camera in Manitoba.
(Read "Annual Polar Bear Migration Under Way: How It Works and How Climate Change Could Be Impacting It.")
Photograph by Norbert Rosing, National Geographic
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