Polar bears rely heavily on sea ice for travelling, hunting, resting, mating and, in some areas, maternal dens. Their diet mainly consists of ringed and bearded seals; they need large amounts of fat to survive. Seals are a particularly rich food-source especially for hungry mothers and their growing cubs. The bear puts on most of its yearly fat reserves between late April and mid-July to maintain its weight in the lean seasons. Ringed seals use sea ice exclusively as their breeding, moulting and resting (haul-out) habitat, rarely if ever coming onto land. They create or maintain their holes in the ice using the well-developed claws on their fore-flippers. They survive the Arctic winter by building lairs (small caves) in the snow on top of sea ice during the winter and give birth in the early spring to their single pup inside a snow lair.

Food can be hard to come by for polar bears for much of the year. The food-free season can last 3 to 4 months - or even longer in areas like Canada's Hudson Bay. As their sea ice habitat recedes earlier in the spring and forms later in the fall, polar bears are increasingly spending longer periods on land. This has increased human-polar bear conflict when hungry polar bears go searching for food in the summer. Loss of their sea ice habitat resulting from climate change is the primary threat to polar bears Arctic-wide. The Arctic is warming about twice as fast as the global average, causing the ice that polar bears depend on to melt away. Loss of sea ice also threatens the seals which are the bear's main prey, and which need the ice to raise their young.