Polar Bear

The polar bear is a brown bear that went to sea. Over a few hundred thousand years it turned white, doubled down on meat, and built its entire way of life around a habitat that is now disappearing under it: Arctic sea ice.

Overview

Polar bears live right around the top of the world, wherever the ocean freezes for part of the year — the coasts and islands of Canada, Alaska, Greenland, Svalbard, and Russia. Scientists divide them into 19 subpopulations. They are classified as marine mammals, the only bear to hold that status, because they depend on the ocean (via its ice) for food.

Built for the cold

A polar bear is superbly insulated. Under up to 10 cm of blubber sits black skin, and over that a double coat: dense underfur for warmth and long, hollow, colourless guard hairs that shed water and scatter light. The combination is so effective that an active polar bear can overheat at temperatures well below freezing, and it loses almost no heat on infrared cameras.

Large, slightly webbed front paws — up to 30 cm across — work as paddles and snowshoes. The soles have small bumps and fur between the pads for grip on ice. A polar bear’s sense of smell is its main hunting tool: it can detect a seal’s breathing hole hidden under snow from more than a kilometre away.

Diet and hunting

Polar bears are the most carnivorous of all bears. Their staple is the ringed seal, with bearded seals and, opportunistically, walrus, beluga, seabird eggs, and whale carcasses. The classic technique is still-hunting: the bear finds a seal’s breathing hole in the ice, lies motionless beside it for minutes to hours, and hauls the seal out with a single explosive strike when it surfaces. It eats the energy-rich blubber first and often leaves the rest.

This only works from the ice. On land in summer, most bears cannot replace those calories and survive on stored fat.

Reproduction and life cycle

Females den in snowdrifts on land or thick ice in late autumn. After a pregnancy with delayed implantation — the fertilised egg pauses its development for months so birth times with the den — one to three tiny cubs are born in December or January, each weighing about 600 grams. They nurse on 30%-fat milk in the dark den and emerge in spring at 10–15 kg.

Cubs stay with their mother for about two and a half years, learning to hunt. Because females only breed every three years or so and cub survival is low, polar bear populations recover very slowly from any decline.

Threats and conservation

The polar bear is listed as Vulnerable and is the animal most often used as a symbol of climate change, for concrete reasons:

• Sea ice loss. Across the Arctic, ice now forms later and breaks up earlier. Longer ice-free periods mean longer fasts, poorer body condition, and fewer cubs surviving — already measurable in the western Hudson Bay and southern Beaufort Sea populations.
• Reduced access to dens and prey as ice patterns shift.
• Pollution and contaminants that concentrate up the Arctic food chain, plus localised pressure from shipping and resource extraction as the Arctic opens up.

Hunting is now regulated by quota across the range, so the long-term outlook depends less on hunting policy than on how much Arctic sea ice the world’s carbon emissions leave behind.