Steven Kazlowski / Two curious young Polar bears (Ursus maritimus), Barter Island, off the 1002 area of the Arctic National Wildlife Refuge, North Slope of the Brooks Range, Alaska, October 2011

Steven Kazlowski / Young Polar bear (Ursus maritimus) standing and trying to balance in shallow water along the Bernard Spit, 1002 area of the Arctic National Wildlife Refuge, North Slope of the Brooks Range, Alaska, Oc...

Steven Kazlowski / Young Polar bear (Ursus maritimus) standing and trying to balance in shallow water along the Bernard Spit, 1002 area of the Arctic National Wildlife Refuge, North Slope of the Brooks Range, Alaska, Oc...

Steven Kazlowski / Young Polar bear (Ursus maritimus) standing and trying to balance in shallow water along the Bernard Spit, 1002 area of the Arctic National Wildlife Refuge, North Slope of the Brooks Range, Alaska, Oc...

Andy Rouse / Polar Bear (Ursus maritimus) portrait in sea-ice landscape. Wide angle / fish-eye shot. Svalbard, Norway, September.

Steven Kazlowski / Polar bear (Ursus maritimus) on sea ice, off the coast of Svalbard, Norway

Steven Kazlowski / Polar bear (Ursus maritimus) mother with cub, newly emerged from their den on the Arctic coast, eastern Arctic National Wildlife Refuge, Alaska

Terry Andrewartha / Polar bear walking {Ursus maritimus} Hudson Bay Canada

Sue Flood / Polar bear footprint in snow {Ursus maritimus} Churchill Canada

Staffan Widstrand / Polar bear resting at sunset {Ursus maritimus} Arctic

Martha Holmes / Polar bear swimming. Canada (Ursus maritimus) NW Territories

Sylvain Cordier / Polar bear (Ursus maritimus), female with two cubs, on a barrier island outside Kaktovik, Alaska, USA.

Andy Rouse / Polar bear (Ursus maritimus) standing on pack ice at the water's edge, Svalbard, Norway. June.

Ingo Arndt / Polar Bear (Ursus maritimus) on icefield with moon in late winter, Svalbard, Spitsbergen, Norway, April

Ingo Arndt / Polar Bear (Ursus maritimus) on icefield with moon in late winter, Svalbard, Spitsbergen, Norway, April

Ingo Arndt / Polar Bear (Ursus maritimus) on icefield with moon in late winter, Svalbard, Spitsbergen, Norway, April

Tony Wu / Polar bear (Ursus maritimus) female with a single young cub, only a few months old, northern Svalbard, Norway, June

Eric Baccega / Polar bear (Ursus maritimus) feeding on a Narwhal (Monodon monoceros), Arctic Bay, Baffin Island, Nunavut, Canada, June.

Eric Baccega / Polar bear (Ursus maritimus) swimming in front of an iceberg, Arctic Bay, Baffin Island, Nunavut, Canada, June.

Eric Baccega / Female Polar bear (Ursus maritimus) grooming, with two cubs playing nearby, Wapusk National Park, Manitoba, Canada, February.

Steven Kazlowski / Polar bear (Ursus maritimus) portrait against sky at sunset, Bernard Spit, off the 1002 Area, Arctic National Wildlife Refuge, North Slope, Alaska, USA, September. Vulnerable species.

Steven Kazlowski / Polar bear (Ursus maritimus) silhouetted against setting sun, Bernard Spit, off the 1002 Area, Arctic National Wildlife Refuge, North Slope, Alaska, USA, October. Vulnerable species.

Brent Stephenson / Polar bear (Ursus maritimus) mother and large second year cub swim across calm water, Scott Inlet, Baffin Island, Canadian Arctic, August. Vulnerable species.

Brent Stephenson / Young Polar bear (Ursus maritimus) walking across melting sea ice, Scott Inlet, Baffin Island, Canadian Arctic, August. Vulnerable species.

Brent Stephenson / Male Polar bear (Ursus maritimus) feeding on a first year Polar bear cub it has just killed, Scott Inlet, Baffin Island, Canadian Arctic, August. Vulnerable species.

Brent Stephenson / Male Polar bear (Ursus maritimus) feeding on a first year Polar bear cub it has just killed, Scott Inlet, Baffin Island, Canadian Arctic, August. Vulnerable species.

Klein & Hubert / Polar bear (Ursus maritimus) pair playing, with male on pack ice and female in water, Svalbard, Norway, July.

Danny Green / Polar bear (Ursus maritimus) cub playing with branch,Churchill, Canada, November

Klein & Hubert / Polar bear (Ursus maritimus) play fighting on ice male biting female on the neck, Svalbard, Norway.

Klein & Hubert / Polar bear (Ursus maritimus) play fighting on ice pair fighting, male on right and female on left, Svalbard, Norway.

Roy Mangersnes / Juvenile female Polar bear (Ursus maritimus) rolling, playing with ice in a fjord, Svalbard, Norway, March.

Roy Mangersnes / Juvenile female Polar bear (Ursus maritimus) hunting for seals at breathing holes in the ice, Svalbard, Norway, March.

Roy Mangersnes / Juvenile female Polar bear (Ursus maritimus) lying down protecting a seal carcass at sunset, Svalbard, Norway, March.

Ole Jorgen Liodden / Polar bear (Ursus maritimus) standing on ice floe, looking at camera. Svalbard, Norway. August.

Staffan Widstrand / Dead Polar bear (Ursus maritimus) starved to death, Zeipelodden, Svalbard, Norway, September.

Ole Jorgen Liodden / Ivory gull (Pagophila eburnea) behind Polar bear (Ursus maritimus) framed by its legs, Svalbard, Norway, July.

Ole Jorgen Liodden / Polar bear (Ursus maritimus) walking across vast ice floe, Spitsbergen, Svalbard, July 2013.

Ole Jorgen Liodden / Polar bear (Ursus maritimus) walking over blue ice, Nordaustlandet, Svalbard, Norway, July.

Ole Jorgen Liodden / Polar bear (Ursus maritimus) waving standing on hind legs with paws raised, Svalbard, Norway, September.

Todd Mintz / Polar bear (Ursus maritimus) cub at entrance to den, Manitoba, Canada. March.

Roy Mangersnes / Polar bears (Ursus maritimus) courting on ocean ice north of Spitsbergen, Svalbard, Norway, July.

Ole Jorgen Liodden / Ivory gull (Pagophila eburnea) behind Polar bear (Ursus maritimus), Svalbard, Norway, July.

Ole Jorgen Liodden / Polar bear (Ursus maritimus) pouncing, Svalbard, Norway, July.

Ole Jorgen Liodden / Polar bear (Ursus maritimus) footprints in snow, on cracked ice, Svalbard, Norway, September.

Ole Jorgen Liodden / Polar bear (Ursus maritimus) stranded on island, with full moon above, north of Nordaustlandet, Svalbard, Norway, September.

Steven Kazlowski / Polar bear (Ursus maritimus) mother with two juveniles walking along ice edge during autumn freeze up, Beaufort Sea, off Arctic coast, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow with two juveniles walk along the ice edge during autumn freeze up, Beaufort Sea, off Arctic coast, Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) curious young bear approaching camera, over newly forming pack ice during autumn freeze up, Beaufort Sea, off Arctic coast, Alaska