As the end-of-the-year holidays approach, images of cute polar bears in sweaters seem to be everywhere. But for real polar bears, navigating a warming world is not so benign.
As the end-of-the-year holidays approach, themes of ice-skating rinks, snowflakes and cute polar bears in sweaters decorate many homes and shops. But if you’ve ever dreamed of visiting or have traveled to Churchill, Manitoba, Canada, in fall, you’re probably thinking about the real polar bears you’ve longed to see or been privileged to observe, who are waiting on the shores of Hudson Bay so that they can make their livings on the ice floes that will, hopefully, soon form.
Unfortunately, though, climate change and global warming are affecting polar bears in serious ways. More time stranded on land means a greater risk of starvation for polar bears, and the strategies of their grizzly bear relatives won’t work for them. And as the Arctic warms, today’s polar bears face increased chances of contracting several pathogens that the bears of three decades ago didn’t. Their feet, too, are suffering injuries—an unexpected consequence of climate change.
There’s no doubt that concerted action is required to mitigate the impact of warming on polar ecosystems and to better sustainably manage these unique habitats. We may have recently identified a good first step: mapping polar biodiversity.
Larger than grizzly bears, adult male polar bears can reach 10 feet in length and weigh 1,500 pounds, compared to grizzly bears’ typical eight feet and 800 pounds.
Polar bears are unlikely to adapt to longer summers
Some biologists and bear experts have speculated that polar bears might adapt to the longer, ice-free seasons due to climate warming in the Arctic by acting like their grizzly bear relatives and either eating terrestrial food or resting.
Usually larger than grizzly bears, adult male polar bears can reach 10 feet in length and weigh 1,500 pounds compared to grizzly bears’ eight feet and 800 pounds. To maintain that great mass, polar bears rely on the energy-rich fat of seals, which they can catch best on the ice.
Since little is known about polar bear energy expenditure and behavior when confined to land, researchers from Environment and Climate Change Canada, the U.S. Fish and Wildlife Service, the U.S. Geological Survey, the U.S. National Science Foundation and Washington State University used collars with video cameras and GPS to track polar bears summering in the western Hudson Bay region of Manitoba, Canada. They wanted to see what these specialized ice-hunters ate and did during the extended time on land when their preferred seal prey was out of reach.
Many of the adult male polar bears in a recent study simply lay down to conserve energy, burning the same number of calories as they do when hibernating.
For three summer weeks, scientists closely observed 20 polar bears that tried different strategies to maintain their energy reserves, including foraging, resting and scavenging. The researchers also weighed the bears before and after the observation period and measured their energy expenditures.
The scientists found a great diversity in the bears’ behaviors; and, as a result, a wide range of energy expenditures. Many of the adult male polar bears simply lay down to conserve energy, burning calories at rates similar to those used in hibernation. Others actively searched for food, consuming bird and caribou carcasses, as well as berries, grasses and kelp.
In all, the researchers found a five-fold range in energy expenditures, from an adult male that rested 98% of the time to the most active, who clocked 205 miles. Three polar bears went for long swims: one swam about 110 miles across the bay. Two found carcasses in the water, a beluga and a seal, but neither bear could feed on their finds while swimming nor bring them back to land. Some adult females spent as much as 40% of their time foraging.
Some polar bears looking for food in a warming Arctic went for long swims: one swam about 110 miles across Hudson Bay.
Yet all that activity didn’t pay off. The terrestrial foods did give them some energetic benefit; but ultimately, the bears had to spend more energy to access those resources. Even the bears that were foraging lost body weight at the same rate as those that lay down. Nearly all lost weight rapidly: on average, around 2.2 pounds per day. Only one bear out of the 20 gained weight after stumbling across a dead, marine mammal on land.
None of the tried strategies will allow polar bears to exist on land beyond a certain amount of time, conclude the scientists, who published their results in the journal Nature Communications in February 2024. While they focused on the southernmost extent of polar bear range in the western Hudson Bay region—where climate warming is likely impacting the bears at a faster rate than in other Arctic areas—the researchers say their study indicates that polar bears across the Arctic are at risk of starvation as the ice-free period continues to grow. The polar bear population in western Hudson Bay has already declined by an estimated 30% since 1987.
As polar bears are forced on land earlier, it cuts into the time when they normally acquire most of the energy they need to survive. Sadly, the expectation is that, with increased land use, polar bears will suffer higher rates of starvation, particularly adolescents and females with cubs.
Female polar bears with cubs are especially susceptible to a warming Arctic. The environmental shifts associated with global warming are creating new opportunities for bacteria, parasites and viruses to infect Arctic wildlife.
In their published paper, the scientists add that polar bears are not grizzly bears wearing white coats. They’re very, very different.
Polar bears are increasingly exposed to pathogens
There’s another problem for polar bears as the Arctic heats up. They now face a greater risk of contracting several pathogens than the polar bears of three decades ago did, according to U.S. Geological Survey scientists in a new study published on October 23, 2024, in the open-access journal PLOS ONE.
In this new study, researchers examined blood samples from polar bears in the Chukchi Sea in 1987 to 1994 and then again three decades later, in 2008 to 2017, looking for antibodies to six pathogens. Five of these pathogens had become more common in the later samples: the parasites that cause neosporosis and toxoplasmosis, the bacteria that cause brucellosis and rabbit fever, and the canine distemper virus. The increases in the prevalence of these pathogens represent some of the most rapid changes in exposure ever reported among polar bears. For some pathogens, the number of polar bears testing positive for serum antibodies, an indicator of pathogen exposure, more than doubled and were among the highest levels ever identified in a population. These results suggest that pathogen transmission pathways have changed in the Arctic ecosystem.
Indigenous peoples living in the Arctic sometimes hunt polar bears for food, and many of the pathogens detected in polar bears can be transmitted to humans. That’s why some researchers say native populations should be screened for signs of disease.
Researchers also looked at factors that increased the bears’ risks of exposure to these pathogens and found that they varied with diet and were higher in females than males, potentially because pregnant females den on land to raise cubs.
In the Arctic, where warming is occurring at nearly four times the global rate and polar bears are experiencing a rapid loss of their sea-ice habitat, infectious diseases present a growing concern to both wildlife managers and human communities. People living in the Arctic sometimes hunt polar bears for food, and many of the pathogens detected in this study can be transmitted to humans.
Polar bears are experiencing more paw injuries
In addition to pathogens, polar bears in some parts of the High Arctic are developing ice buildup and related injuries to their feet, due to changing sea-ice conditions in a warming Arctic.
Due to anthropomorphic climate change, sea ice has less snow in late spring and summer; and the snow that does exist is experiencing earlier, episodic melt and more frequent rain. All these things can create challenging surface conditions for traveling polar bears.
Between 2012 and 2022, researchers from the University of Washington studied two populations of polar bears living above 70 degrees north latitude and found hair loss, ice buildup, lacerations and skin ulcerations primarily affecting the feet of adult bears, as well as other parts of their bodies. In the Kane Basin population, located between Canada and Greenland, 31 of 61 polar bears showed evidence of icing-related injuries, such as cuts, hairless patches or scarring. In the second population in East Greenland, 15 of 124 polar bears had similar injuries. Two Greenland bears at separate locations in 2022 had ice blocks up to one foot in diameter stuck to their foot pads, which caused deep, bleeding cuts and made it difficult for them to walk. When immobilizing the bears for research, the scientists carefully removed the ice balls. The chunks of ice weren’t just caught up in the hair; they were sealed to the skin, and it was apparent that the bears were in pain.
Polar bears have small bumps on their foot pads that help provide traction on slippery surfaces. These bumps, which are larger than those on the pads of other bear species like black and brown bears, make it easier for wet snow to freeze to the paws and accumulate. This problem also affects sled dogs in the North.
The researchers published their new study in the journal Ecology in October 2024. While these two polar bear populations have been studied since the 1990s, these types of injuries have never been reported before. Consultations with lifelong Indigenous subsistence hunters and a survey of the scientific literature suggests this is a recent phenomenon.
In addition to the anticipated responses to climate change for polar bears, there are going to be other, unexpected ones, such as ice buildup in paws.
The study’s authors suggest three possible reasons for how the shift from a climate that used to remain well below freezing to one with freeze-thaw cycles (with more wet snow) could be causing ice buildup and injuries. One is more rain-on-snow events, which creates moist, slushy snow that clumps onto paws and then freezes to form a solid once temperatures drop. A second possibility is that more warm spells are causing the surface snow to melt and then refreeze into a hard crust. The heavy polar bears break through this ice crust, cutting their paws on its sharp edges. The final possible reason is that both these populations live on “fast ice” connected to the land, near where freshwater glaciers meet the ocean. Warming in these environments leads to thinner sea ice, allowing seawater to seep up into the snow. This wet snow can clump onto bears’ feet and then refreeze to form ice. Also, unlike other areas, polar bears living at the edges of glaciers rarely swim long distances in spring, which would help thaw and dislodge accumulated ice chunks because the water is warmer than the air.
While the bears are clearly affected by the ice buildup, the researchers are cautious about making broader conclusions about the health of the two populations. While they’ve seen icing-related injuries on individual polar bears, they don’t know how this is affecting them at a population level.
Asked what can be done to help these apex predators, the researchers had a simple response: we can reduce greenhouse gas emissions and try to limit climate warming.
Wet snow accumulating and then freezing on the paws is a problem that also affects sled dogs.
Polar bears could benefit from biodiversity mapping
Polar regions contain vast and as yet undiscovered biodiversity, but they are both the most threatened and least understood areas of the world. Now, scientists from the British Antarctic Survey and England’s University of East Anglia are calling for a road map of polar ecosystems to fill that knowledge gap, preserve polar life, and even protect everyday human life and our planet’s health. The scientists hope to map all the biodiversity in the polar regions, from the atmosphere to the deep sea, and from land to the oceans. Their plan was published in Nature Communications in November 2023.
Remote, polar regions play substantial, but often underappreciated, roles in the carbon cycle and drive global nutrient and dissolved organic matter fluxes. In the Arctic, temperatures are rising at least four times faster than elsewhere, destabilizing the Arctic jet stream and increasing the likelihood of extreme weather events, including drought, flooding and heat waves in temperate regions. Consequently, polar environmental and ecological processes are intimately connected with our routine lives and our planet’s well-being, much of which is underpinned by the endemic biota, from viruses to large animals.
Unfortunately, though, polar ecosystems are being lost at a rapid pace and with them all the biology that provides ecosystem services and biology-driven regulation of the climate, including the carbon cycle. Biodiversity projections for the polar regions can only be reliably constructed if scientists have a sufficiently profound understanding of the diversity, ecological functions and interrelations of polar organisms, as well as their resilience to climate change.
Polar life—from microbes to whales and from polar bears to seals—largely depends on low temperatures and a substantial ice-and-snow cover. Global warming, however, is making those conditions more and more rare.
There is strong evidence, say the scientists, that climate-induced changes in the polar regions are already altering species distributions on land and in the sea, with major impacts on the environment. Some species have shifted poleward, which has secondary effects on the food chain. Polar life, from microbes to seals, whales and polar bears, largely depends on overall low temperatures and a substantial snow-and-ice cover.
On land, collapsing Arctic coastlines and permafrost burning and melting are dramatically altering biogeochemistry and ecological interactions due to the release of millennia-old carbon stores, nutrients, trace elements and potentially even deep-frozen, ancient viruses and pathogenic bacteria. In the oceans, the increased seasonal melting of sea ice is stabilizing surface waters too much, which reduces the amount of nutrients required for primary production to take place.
Similarly, the situation in the Southern Ocean and on the Antarctic continent is equally bleak, particularly for the Antarctic Peninsula, which has already experienced substantial levels of warming that have increased the loss of sea ice and glaciers.
Thawing permafrost due to rising global temperatures is not only releasing millennia-old carbon stores, deep-frozen viruses and pathogenic bacteria, it can cause buildings, pipes and roads to collapse. Some communities in Alaska have already been forced to relocate due to permafrost-related damage.
The Southern Ocean around the Antarctic continent is a reservoir for heat and carbon—it takes up about 25% of the global ocean surface but has absorbed about 50% of the excess heat since 2005. The Southern Ocean also absorbs more anthropogenic carbon dioxide from the atmosphere (40%) than its surface area would suggest. Furthermore, sequestering carbon by the organisms living in polar seas is probably the largest natural negative feedback against climate change.
Sequencing technologies have massively changed our abilities to decipher how organisms work. However, their use in polar biology, say the scientists, has been relatively minimal, especially when considering the tens of thousands of species that reside at the poles and are now at threat in our warming world. Genomic screening not only offers the possibility of identifying populations under stress, but it could also be used for the monitoring of invasive species, thereby facilitating early interventions. In addition, understanding how lots of very strange organisms live in extreme cold could help provide benefits for society. Failure to act now, conclude the scientists, will result in a substantial loss of knowledge regarding evolutionary adaptation to a warming world.
Polar bears are symbols of caring for the polar regions
You may or may not travel to the Arctic. But either way, you need to care about it. And not just because it’s home to the iconic polar bear and 4 million people, but also because it helps keep our world’s climate in balance. Arctic sea ice acts as a huge, white reflector at the top of the planet, bouncing some of the sun’s rays back into space, helping to keep the Earth at an even temperature. And the climate impacts on biodiversity and ecosystem functioning in both the Arctic and Antarctic serve as a bellwether for the consequences of global warming, including the very persistence of biodiversity on Earth.
According to World Wildlife Fund, the ice pack is forming later in the season due to anthropogenic climate change, and polar bears must wait longer to hunt seals. We need to care about the Arctic—not just because it’s home to polar bears, but also because it helps keep the world’s climate in balance.
And besides, you need to care because we would all miss those cute images of polar bears in Christmas sweaters.
Here’s to finding your true places and natural habitats,
Candy
