The polar bear is both the world’s largest bear and largest land carnivore. Although born on land, polar bears are excellent swimmers, spending so much of their time at sea and on sea ice that their scientific name—“Ursus maritimus”—translates to “maritime bear.” While closely enough related to the brown bears more common in temperate zones that rare interbreeding has been documented, polar bears have evolved unique adaptations to their arctic and largely aquatic environment: a longer nose helps warm cold air; smaller ears reduce radiated heat loss; large, scooped feet distribute weight when walking on ice and provide better propulsion when swimming; and a thick layer of blubber provides insulation, buoyancy, and sustenance when food is scarce.

Polar bears posses an extremely keen sense of smell, and are able to detect their primary food source—ringed and bearded seals—up to a mile distant. They primarily hunt at and around the edge of pack ice—the ice shelf that extends in winter months from land—often sneaking up and catching their prey as they surface in ice holes to breathe. When the pack ice recedes in summer and early fall and polar bears are unable to hunt seals, they live primarily off their fat reserves. Polar bears have been known to supplement their diet with a wide variety of plants and other animals, but their digestive systems are specially adapted to seal meat and blubber, and cannot derive sufficient caloric intake from other sources.

Because of their reliance on seals, polar bears are especially vulnerable to the polar warming associated with global climate change. The relatively thin pack ice shelf from which polar bears hunt seals is climatically fragile; rising temperatures melt this ice earlier and further with each passing spring, forcing polar bears to land before they have amassed sufficient fat reserves to survive the lean summer and early fall. Reductions in the thickness and area of pack ice also force bears to swim more frequently and for longer distances in search of food, further depleting their energy and occasionally leading to drowning.

While some may insist on debating the causes of climate change, its consequences on the worldwide polar bear population are undeniable. For example, polar bears’ feeding season in the western Hudson Bay is three weeks shorter than in was 30 years ago; in the same period, the polar bear population has declined over 22%, with the average weight of pregnant females dropping 20%. This insufficient nourishment also leads to lower reproductive rates among adults and lower survival rates among cubs.

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