Polar bear, a charismatic symbol of the North

The Arctic Circle is home to the largest bear in the world: the polar bear (Ursus maritimus). They are a vital part of this vulnerable ecosystem. You may be surprised to learn that the polar bear is actually considered a marine mammal. While they are born on land, they spend most of their life on sea ice. This is where they hunt and mate. Polar bears are superbly adapted, well equipped for Arctic life and dependent on sea ice for their survival. They have a streamlined body with large, oar-like feet, sharp claws, which help them, walk on the slippery ice. They also have two layers of fur, a thick layer of body fat, and a water-repellent coat that insulates them from the freezing air and water, and small ears. Males measure from eight to 11 feet from nose to tail and generally weigh about 1,300 pounds but can reach more than 1,700. Females measure about six to eight feet and are usually about half the weight of males. With around 30 cm wide paws, they are considered talented swimmers, polar bears can sustain a pace of six miles per hour by paddling with their front paws and holding their hind legs flat like a rudder. Spending over 50% of their time hunting for food, polar bears live throughout the circumpolar Arctic, with distribution dependent on food availability and sea-ice conditions; they are most often found at the convergence of sea ice and open water, and where seals congregate. These bears are totally reliant on the sea ice as their primary habitat, using it for a number of essential activities including hunting and feeding on seals, seeking mates and breeding, making long-distance movements, accessing terrestrial maternity denning areas, and sometimes even maternity denning itself. Polynyas — areas of open water surrounded by ice and caused by fluctuations in wind, tide or current — are sites of increased marine mammal and bird concentrations and are extremely important to polar bears.

Some polar bears make extensive north-south migrations in response to ice packs receding northward in the spring and advancing southward in the fall. In addition, individuals may travel vast distances to find mates or food and have been seen 100 miles from the nearest land- or icefall. In October and November, males head out onto the pack ice where they spend the winter, while pregnant females seek sites on land or near shore sea ice to dig dens in the snow, where they spend the winter and give birth. Polar bears can live up to 25 or 30 years in the wild. Like other members of the bear family, female polar bears have small litters, reach breeding age late in life, and produce few young in their lifetime. They mate on the sea ice in either April or May, after which a female must accumulate sufficient fat reserves to live and to support her cubs from the time she enters the maternity den between late October and mid-November until the time the family emerges in the spring and she again begins to feed. Cubs are born in snow dens between late November and early January, with timing varying by region and population. Because of their vulnerability at birth, cubs must remain in the maternity den, where the temperature warms to near freezing. They nurse inside the den until sometime between late February and the middle of April, depending on the latitude. The age at which mothers wean their cubs also varies by region, though in most areas cubs are weaned at approximately 2.5 years of age, resulting in a three-year reproductive cycle. After a period of several weeks’ acclimatization, the mother and cubs begin their trek to the sea ice to feed on seals.

Polar bears are at the top of the food chain and have a significant role in the overall health of the marine environment. Over thousands of years, polar bears have also been an important part of the cultures and economies of Arctic peoples. But, because of ongoing and potential loss of their sea ice habitat resulting from climate change–the primary threat to polar bears Arctic-wide–polar bears, were listed as a threatened species in the US under the Endangered Species Act in May 2008. Due to climate change the Arctic is heating up twice as fast as anywhere else on the planet, shrinking the Arctic sea ice cover by 14% per decade. Compared to the median sea ice cover recorded between 1981-2010, we have lost about 770,000 square miles, an area larger than Alaska and California combined. 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, where they are often attracted to areas where humans live. This becomes a concern because it triggered lethal response to human-polar bear conflict. Other grave threats include oil and gas development, toxic pollution in the environment, and direct impacts from industrial development, such as disturbance of maternal dens or contact with an oil spill, and potential overhunting of some subpopulations.

In its July 20, 2020 issue, the science journal Nature Climate Change, a team of researchers at the University of Toronto, Canada, reports its future forecasts on polar bear populations. The report warns the average temperature on planet Earth could rise around 4 degrees centigrade in the coming 100 years due to ballooning CO2 emissions, declaring “polar bears will be nearly extinct by the year 2100,” according to the journal. The report’s projections are based on the assumption that the fasting duration of polar bears will be prolonged due to the loss of sea ice. Using such yardsticks as calculation of the bears’ fat consumption in hibernation, the research team estimates the longest possible fasting period, beyond which survival rates of adult polar bears and their cubs would decline. As a result, some polar bear populations have already reached their limits, according to the researchers. Their report aims to raise the alarm over possible extinction of the king of Arctic animals. Every day, research tells us there is still time to conserve polar bear habitat and manage the worst effects of a warming world if we act now to greatly reduce greenhouse gas emissions. The polar bear’s fate, and the fate of the planet, is in our hands—and we can write a more hopeful future together. Leading with small actions and building towards community, regional, and national responses, we can turn our collective fate around.