The ecologist Stephanie Penk had spent hours gazing at a young polar bear as it napped on the snowy tundra near Churchill, Manitoba, the remote northern Canadian town on the shores of Hudson’s Bay, also known as “the polar bear capital of the world.” All of a sudden, he woke up, stretched extensively and sauntered over to the team’s specially built polar-bear-viewing truck. There he stood on his hind legs, steadying himself on the vehicle with his paws and looking right up at her through the window. “I felt blown away… these animals are so big, so beautiful,” she said, recalling that moment. She had been monitoring polar bears for years. Around two thirds of the global polar bear population lives in Canadian territory, in the extremely cold north of the country. As the globe warms, the bears’ future looks increasingly bleak.
Penk and her doctoral supervisor Péter Molnár, a mathematical and statistical ecologist, have spent years trying to work out how long the Arctic will retain the ice that polar bears need to hunt seals and survive. Now, for the first time, they’ve got the answer, and it’s dire. If humans continue to warm the planet by pumping greenhouse gases into the atmosphere at high rates, polar bears will be all but extinct by 2100, according to their study published in August in the scientific journal Nature Climate Change. At most a few animals will survive on the Queen Elizabeth Islands in the high Arctic. Even if humans manage to rein in emissions moderately, many of the Earth’s remaining 23,000 or so polar bears will die out by 2100. “This is a depressing story,” said Molnár, the lead author of the study. “This will only get worse the longer we wait.”
Their study is unique, and simple. It asks: How long can a polar bear go without food before it starves to death, or dies out because it can no longer breed or nurse its cubs? The answer hinges on sea ice. Polar bears need sea ice in order to catch their food. If the fasting period, i.e. the time when there is no ice, exceeds 117 days, the young animals die; if it is between 117 and 228 days, the mothers die. Adult males can survive for some 220 days without ice. This results in a scenario of zero or very few polar bears by 2100, if global CO2 emissions continue to rise sharply.
Unlike the brown bears they evolved from, they are not omnivores that can exist on berries and fish. They are steadfast carnivores. In fact, they evolved less than 500,000 years ago specifically in order to hunt fat-laden seals during the Pleistocene epoch, which was often glaciated. As they evolved, their dark fur became white, the better to blend into the snowy landscape. Their claws became shorter, sharper and more curved to allow them to prowl on the ice. Their tails and ears shrank so they wouldn’t freeze off in the bitter cold, while front paws became paddles, the size of dinner plates, to allow them to become expert swimmers. They developed three sets of eyelids to help protect them from the salt water. Polar bears also developed the capacity to store fat on their bodies for the times when sea ice was too fragile to support them, or, in the case of the females, for the long months when they breastfeed their young in dens. During these times they lounge, living off their fat, using as little energy as possible, waiting for the ice to form again.
In the 1970s, when the first routine scientific studies of polar bears in the Western Hudson’s Bay were conducted, the animals fasted on land for an average of 120 days, Penk said. By 2010, the bears were fasting for an additional 20 days a year. She and other scientists can already measure the effects: fewer cubs, thinner bears and a declining population. Meanwhile, hungry bears are coming increasingly closer to human settlements. Canada’s Inuit populations report that the bears are more numerous and northern communities are becoming unsafe because bears are not as afraid of humans as they once were. As well, bears are now more commonly sighted near Inuit hamlets. Two years ago, two residents of Nunavut, a territory in the far north of Canada, died as a result of polar bear attacks, the first such deaths in 18 years. As a result, some Inuit are calling for more bears to be killed. in the Russian Ryrkaypiy, on the other side of the Bering Strait, dozens of hungry polar bears have recently entered the city.
Fifty years ago, when scientists first sounded alarm bells about the fate of the polar bear, the threat was not climate disruption, but too much hunting, Molnár said. In 1973, the five circumpolar nations where polar bears live -- Canada, the United States, Norway, Greenland and Denmark, and the Russian Federation, agreed to help conserve the species by regulating hunting. These days, 700 to 800 polar bears a year are legally hunted in Canada, Greenland and Alaska, mainly by Indigenous people who rely on the meat and skins for food and warmth. But it is global warming which has made the species “vulnerable” to extinction, according to the International Union for the Conservation of Nature.
Already, the Arctic is warming more than twice as fast as the global average. The reach of the ice covering the Arctic Ocean is retreating each year. Each year, the ice gets thinner. A series of recent studies concluded that the Arctic Ocean is becoming more like the Pacific and the Atlantic, with more algal blooms and a dramatic increase in the height of waves. In late July, Canada’s last Arctic ice shelf, the Milne ice shelf on Ellesmere Island, collapsed, another sign of the fragility of the ecosystem. At the beginning of the 20th century, the Canadian ice shelf was a single entity 9,000 square kilometers in breadth. Today, it is reduced to a few small fragments in inlets along Canada’s northern coast, according to the National Snow and Ice Data Center.
It is not only vanishing ice but also pollution that threatens polar bears. Because they are top predators, they ingest accumulated toxins in their food, including plastics, some of which impair their ability to breed. If they are stored in the fat of polar bears, they are released in higher concentrations during longer periods of hunger. In addition, the animals eat garbage more and more often when searching for food in human-populated areas. In a quarter of the stomachs of 51 bears killed in the North Slope region of Alaska between 1996 and 2018, scientists found objects such as plastic, car keys and candy wrappers.
Because the polar bears evolved to live in relative isolation, their immune systems are unsophisticated and are being tested by increasingly frequent encounters with humans and other animals as they scavenge for food. Combined, these phenomena mean that the polar bear could go extinct decades earlier than the Nature Climate Change paper predicts. “From every angle, the paper is sadly optimistic,” said Penk. For his part, Molnár said he feels like he is watching a train wreck in slow motion as humans fail to reduce greenhouse gas emissions and the threats to polar bears become ever greater. “I often wonder,” he said, “when historians look back 100 years from now at our generation, are we going to be known as the generation that should have known better?”