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Millions have seen the heart-wrenching video of a polar bear clinging to life, its white hair limply covering its thin, bony frame. Shot by Paul Nicklen and Cristina Mittermeier of the nonprofit group Sea Legacy, and published on National Geographic in early December, the video ignited a firestorm of debate about what scientists know, and don't know, about the impacts of global warming on polar bears. Without examining the bear in the video -- thought to have died -- it's impossible to know for sure what ailed that individual, but now scientists have published new findings that shed more light on the risk to the species overall.

Because of melting sea ice, it is likely that more polar bears will soon starve, warns a new study that discovered the large carnivores need to eat 60 percent more than anyone had realized. It turns out they are high-energy beasts, burning through 12,325 calories a day -- despite sitting around most of the time, according to a unique metabolic analysis of wild bears published reently in Science magazine.

"Our study reveals polar bears' utter dependence on seals," said lead author Anthony Pagano, a wildlife biologist with the U.S. Geological Survey (USGS).

Polar bears rely almost exclusively on a calorie-loaded diet of seals. To minimize their energy consumption the bears still-hunt, waiting for hours by seals' cone-shaped breathing holes in the sea ice. When a seal surfaces to breathe, the bear stands on its hind legs and smacks it on the head with both of its front paws to stun it. Then the bear bites it on the neck and drags it onto the ice.

"They are far more successful doing this than via any other method of hunting," Pagano said. That's why the melting of the Arctic sea ice threatens polar bear survival.