Out on the wind-swept sea ice well north of Svalbard, a male polar bear walks with a rolling gait. Far away, he seems to disappear against the white background of the snow, which is the whole idea. He is by no means white. Each of his guard hairs is transparent and hollow, scattering light, while his skin is black in order to absorb the small amount of sun that reaches the high Arctic. To science he is Ursus maritimus, the sea bear, the largest terrestrial carnivore alive. On average, adult males weigh from 300 to 800 kg and range from 200 to 250 cm nose to tail, while females are about half that size, weighing from 150 to 300 kg. Polar bears have a marked sexual dimorphism; males have wider heads and heavier upper bodies, as well as a more streamlined shape. They are slimmer than brown bears and have a longer neck and a flatter skull, both suited to paddling in water and shoving their heads into seal breathing holes. All of this indicates a marine lifestyle. A layer of blubber up to 11 centimeters thick is present beneath their fur and an extensive undercoat is in place. Their enormous paws, usually 30 cm across, feature rough and hairy soles that can grip the ice and distribute their weight on it like a snowshoe, and their claws are kept relatively short and curved, which is more useful for catching seal skin than for digging. Polar bears are categorized as marine mammals because they spend much of the year on the ice of the sea rather than the land. These animals inhabit the polar region within the jurisdiction of five nations: Canada, the United States of America (Alaska), Greenland (Denmark), Norway, and Russia. There are 19 recognized populations of polar bears in the Arctic. These vary in terms of how close they stay to the shorefast ice throughout the year, with some moving great distances on the pack ice, from the Beaufort Sea to Siberia. During the summer, when the sea ice has melted and the polar bear is forced onto land, it must fast on stored body fat. Seals allow the polar bear to maintain this fasting. Ringed seals and bearded seals are most often hunted for this purpose, and the most common method of hunting is still-hunting. The polar bear waits until it has located a breathing hole in the ice, moves into position downwind from the hole, and then remains motionless for up to an hour or more until a seal swims to the surface of the water. The seal is then killed, pulled onto the ice, and most of the seal’s blubber consumed, sometimes leaving the rest for arctic foxes and gulls. But the diet must be dominated by seal blubber to enable the female to produce sufficient milk in order to nurse the cubs while she is unable to eat anything while denning. Polar bear breeding and denning occur in conjunction with the seasons. Copulation occurs in April and May, but the fertilized egg does not implant until autumn. In October or November, a pregnant female burrows herself into a large mound of snow, either on land or on sea ice, to give birth. One or typically two blind and tiny (less than 1 kg) cubs are born in the den during December or January. The mother will not drink or eat anything for months, and the cubs feed on her fat during this time. The mother and her offspring usually emerge from their den in March or April, after the cubs have been with her for some 2 to 2 ½ years, at which time they are ready to learn to follow her, to learn which breathing holes are likely to be used by which seal, and to read the sea ice. Accurate numbers of polar bears are difficult to assess because of the animals’ large and remote geographic distribution. The International Union for Conservation of Nature lists polar bears as Vulnerable with estimates for their population at 22,000 to 31,000. Population trends vary throughout the range and the IUCN estimates that the Southern Beaufort Sea population (off the north coast of Alaska and Canada) is declining. The major impact facing the polar bear is the reduction of sea ice during the warmer months which restricts the length of the period when hunting occurs. Other issues include pollution, industrial activity and increased contact with humans, as the ice-free periods force bears to land where they may have fewer food resources and poorer cub survival rates. In the wild, most polar bears live 15 to 18 years, with some females reaching their late twenties. Some captive polar bears have survived into their 30s. These animals can swim continuously for hours, have been tracked covering more than 100 kilometers without rest, and can smell a seal nearly a kilometer away. For Inuit peoples of the Arctic, polar bears are nanook, and have been for centuries, representing not just the physical animal but also a part of a spiritual and hunting connection to the land, sea, and all that dwell on and in it. And so, you watch the polar bear. You see a bear on the ice. It pauses beside a pressure ridge, smells the air, and then lies down next to the hole. The ice, the seal, the bear, these things have happened here, together, for at least 120,000 years. What is different now is how long the ice holds.