Polar Bears
On Thin Ice
The  Arctic is warming so fast that by 2050 it may be largely ice free in  summer. Without their frozen hunting platform, how will polar bears  survive?
By Susan McGrath
Photograph by Florian Schulz
In August 1881 the naturalist John Muir was sailing off Alaska aboard the steamer 
Thomas Corwin,  searching for three vessels that had gone missing in the Arctic. Off  Point Barrow he spotted three polar bears, "magnificent fellows, fat and  hearty, rejoicing in their strength out here in the bosom of the icy  wilderness."
Were Muir to sail off Point Barrow in August today, any polar bears  he'd see would not be living in a wilderness of ice but swimming through  open water, burning precious fat reserves. That's because the bears'  sea-ice habitat is disappearing. And it's going fast.
Polar bears ply the Arctic niche where air, ice, and water intersect.  Superbly adapted to this harsh environment, most spend their entire  lives on the sea ice, hunting year-round, visiting land only to build  maternal birthing dens. They prey mainly on ringed and bearded seals  (it's been said that they can smell a seal's breathing hole from more  than a mile away) but sometimes catch walruses and even beluga whales.
Sea ice is the foundation of the Arctic marine environment. Vital  organisms live underneath and within the ice itself, which is not solid  but pierced with channels and tunnels large, small, and smaller.  Trillions of diatoms, zooplankton, and crustaceans pepper the ice  column. In spring, sunlight penetrates the ice, triggering algal blooms.  The algae sink to the bottom, and in shallow continental shelf areas  they sustain a food web that includes clams, sea stars, arctic cod,  seals, walruses—and polar bears.
Experts estimate the world's polar bear numbers at 20,000 to 25,000,  in 19 subpopulations. Bears in Svalbard (the Norwegian archipelago where  Florian Schulz made most of these photographs), the Beaufort Sea, and  Hudson Bay have been studied the longest. It was in western Hudson Bay,  where ice melts in the summer and freezes back to shore in the fall,  that the creatures' predicament first came to light.
Read More: 
http://ngm.nationalgeographic.com/2011/07/polar-bears/mcgrath-text