Out on the wind-polished sea ice north of Svalbard, a male polar bear lumbers along with a slow, rolling gait. He looks white on white from a distance, which is the point. The bear is not actually white at all. Each guard hair is transparent and hollow, scattering light, and the skin beneath is jet black to soak up any sun that reaches the high Arctic.

He is Ursus maritimus, the sea bear, and is the largest living land carnivore. Adult males typically weigh from 300 to 800 kg and are 200 to 250 cm from nose to tail. Females are about half the size of the males, 150 to 300 kg. The species displays a marked sexual dimorphism, with males having much broader heads and much heavier shoulders. The body is leaner, the neck longer, the skull flatter, all shapes that help it slip through water and thrust its head into seal breathing holes, compared to a brown bear.


Marine life shows in every detail. Underneath the fur is a layer of blubber up to 11 centimeters thick, overlaid by a dense undercoat. Their paws are enormous, frequently 30 centimetres wide, and have hairy soles that grip ice and spread weight like snowshoes. Even the claws are short and curved, more suitable for hooking seal skin than for digging roots. Polar bears are classified as marine mammals because they spend most of the year on the frozen ocean, not on land.

Their world revolves around the pole in five different countries: Canada, the United States in Alaska, Greenland, Norway and Russia. There are 19 recognized subpopulations that track the seasonal pulse of sea ice. Some bears hang out on shorefast ice all winter long. Others travel the pack for thousands of kilometres, riding with floes from the Beaufort Sea to Siberia. Many come ashore to wait when summer melts the platform they depend on, living largely off fat reserves.

Seals make waiting possible. Most calories come from ringed and bearded seals, most often taken by still-hunting. A seal will come up for air. A bear will find a breathing hole, lie downwind and stay still for an hour or more. Then it strikes, drags the animal out onto the ice and eats the blubber first, sometimes leaving the rest for arctic foxes and gulls. Walrus carcasses, beluga carcasses, and the occasional bird or egg fill the gaps but fat-rich seal blubber is the fuel that allows females to nurse cubs through long fasts.

Reproduction is in accordance with the ice calendar. Mating takes place in April and May but the fertilised egg does not implant until the autumn. In October or November a female will dig a maternity den in the snowdrift, typically on land, but occasionally within stable pack ice. Cubs are born blind, in December or January, usually one or two at a time, weighing less than a kilogram. The mother does not eat or drink in the den for months, changing her own fat to milk. Families are created in March or April, and the cubs remain with her for approximately two and a half years, learning where to locate holes and how to interpret the ice.

Getting numbers in such a huge habitat is hard, but the IUCN classifies polar bears as vulnerable, with an estimate of around 22,000 to 31,000 animals worldwide. Not all sub-populations are doing so well. The Southern Beaufort Sea group off Alaska and western Canada declined as ice-free seasons lengthened. The biggest long-term threat is climate-driven loss of sea ice, which shortens the time available for hunting and pushes bears on to shore, where they meet more human contact, worse nutrition and lower cub survival. Pollution and industrial activity put the species under stress, which is listed as threatened under the Endangered Species Act in the United States.

In the wild most bears live 15 to 18 years, while some females may live into their twenties. They can live to 30 in zoos. They can swim steadily for hours, have been tracked running 100 kilometers without stopping, and can smell a seal nearly a kilometer away. The bear is nanook to Inuit communities that have lived on the land with them for millennia, a figure of respect and caution woven into stories, hunting practice and place names.

Watch that same male again as the light goes down. He pauses at a pressure ridge, sniffs the air, flattens beside a dark hole. He'll wait. The ice, the seal and the bear have been doing this together for at least 120,000 years. What is now different is how long each spring is held by the platform.