The polar bear is the world's largest bear and also the world's strongest swimmer. It's considered a marine mammal -- like walruses, seals and whales -- because its main habitat is sea ice.
Male polar bears stand 8 to 11 feet tall and can weigh as much as 1,400 pounds. Part of that poundage is due to a 4-inch layer of fat that helps keep the bears warm.
Polar bears have one of the lowest reproduction rates among mammals. Polar bear cubs are born blind, hairless, and about the size of a squirrel. Females rear cubs for nearly three years.
As sea ice decreases, polar bear females may not gain enough weight to reproduce cubs with enough insulating fat -- jeopardizing their ability to survive.
Since 2002, many polar bear populations in Alaska have shown increasing signs of stress, including drownings, malnutrition and cannibalism. The U.S. Geological Survey (USGS) estimates that all polar bears in Alaska will likely be extinct as early as 2050.
More than 25 percent of the world's polar bear populations are already in decline.
