In certain regions of the high Arctic, polar bears are experiencing ice accumulation and resulting injuries to their feet, likely as a consequence of altered sea ice conditions due to climate change. During a health assessment of two polar bear populations, researchers noticed cuts, hair loss, ice buildup, and skin ulcers mainly affecting the feet of adult bears, along with other body areas. Some bears had ice blocks measuring up to 1 foot (30 centimeters) in diameter stuck to their paw pads, which caused severe cuts and made walking challenging.
This research, led by the University of Washington and published on October 22 in the journal Ecology, marks the first documentation of such injuries in polar bears.
Researchers propose several reasons why the transition from consistently sub-zero temperatures to fluctuating freeze-thaw cycles could result in ice accumulation and injuries.
“Besides the expected effects of climate change on polar bears, there will also be additional, unforeseen effects,” explained Kristin Laidre, the lead author and a senior principal scientist at the UW Applied Physics Laboratory, as well as a professor in the UW School of Aquatic and Fishery Sciences. “Strangely enough, as temperatures rise, more frequent freeze-thaw cycles, along with increased wet snow, contribute to ice forming on polar bears’ paws.”
From 2012 to 2022, Laidre and co-author Stephen Atkinson, a wildlife veterinarian, investigated two polar bear populations located above 70 degrees north latitude and observed these injuries.
In the Kane Basin group, situated between Canada and Greenland, 31 out of 61 polar bears displayed signs of ice-related injuries, such as bald spots, cuts, or scarring.
Similarly, in the second group from East Greenland, 15 out of 124 polar bears exhibited comparable injuries. In 2022, two bears in Greenland were found with large ice balls attached to their feet.
“I had never witnessed this before,” Laidre said. “The two bears most severely impacted were unable to run — they struggled to walk as well. While we were immobilizing them for research, we took great care in removing the ice balls. They were not just tangled in their fur but were actually attached to the skin, indicating the bears were in pain when we examined their feet.”
Despite studying these two polar bear populations since the 1990s, researchers have not previously reported such injuries. Consultations with lifelong Indigenous subsistence hunters and a review of scientific literature imply that this phenomenon is a new occurrence.
Polar bears have small protrusions on their foot pads that enhance grip on slippery surfaces. These bumps are larger than those on the foot pads of other bear species, such as brown and black bears, making it easier for wet snow to adhere and freeze on their paws. This issue is also seen in sled dogs in northern areas.
The authors speculate three potential factors contributing to the rising ice accumulation on polar bears’ feet, all connected to climate change. One factor is an increase in rain-on-snow events that create slushy snow, which clumps onto the bears’ paws and solidifies as temperatures drop.
Another possibility is that more frequent warm spells cause the surface layer of snow to melt and subsequently refreeze into a hard crust. Heavier polar bears might break through this crust, cutting their paws on the sharp edges.
Lastly, both populations inhabit “fast ice” that connects to land, near the confluence of freshwater glaciers and the ocean. Warming in these habitats results in thinner sea ice, allowing seawater to infiltrate the snow. This moist snow can adhere to bears’ feet and later freeze into ice. Furthermore, unlike in other regions, polar bears living near glacier edges rarely swim long distances in spring, preventing them from thawing and dislodging accumulated ice chunks, as the water temperature is warmer than the air.
Although it is evident that the bears are affected by ice buildup, the researchers advise caution when drawing broader conclusions about the health of these populations.
“We have identified icing-related injuries on individual polar bears,” Laidre remarked. “However, I would hesitate to make blanket statements about what this might mean for the population as a whole. There is still much we do not understand.”
Melinda Webster, a research scientist at UW’s Applied Physics Laboratory, recently published a separate study examining snow cover on Arctic sea ice over recent decades.
“The Arctic sea ice’s surface is changing due to climate change,” Webster mentioned. “There is less snow in late spring and summer, and the existing snow experiences earlier, sporadic melting along with increased rainfall. These conditions create challenging surfaces for polar bears as they travel.”
When asked what actions could be taken to support the polar bears, Laidre responded straightforwardly: “We can lower greenhouse gas emissions and aim to curb climate warming.”
The field studies of polar bears were funded by the governments of Canada, Denmark, Nunavut, and Greenland, and Laidre is also associated with the Greenland Institute of Natural Resources.
