Polar bears range across the frozen top of the Northern Hemisphere. They are found in the northernmost reaches of Alaska, Canada, Russia, on Norway's far-flung Svalbard Islands, and along the coasts of Greenland. They reach their southern limit in Canada's Hudson Bay. An estimated 21,000 to 28,000 polar bears roam across large distances of the Arctic. While not considered endangered, some isolated populations are vulnerable to pollution, and possibly to the effects of global warming.
Most polar bears live on ice where it meets open water.
Some polar bears live at least part of the year on actual land, after winter ice and snow melt. Unlike other bears, they inhabit habitats virtually free of vegetation. Small animals and vegetation, if available, supplement their diets during food shortages. The polar bear is a slow breeder. Most females reach breeding age at four or five years, and usually do not breed more than once every two or three years.