A groundbreaking study from researchers at the University of Toronto Scarborough (U of T Scarborough) has established a direct connection between polar bear population decline in Western Hudson Bay and the rapid loss of Arctic sea ice due to climate change.
Polar Bears Losing Critical Hunting Time Due to Melting Sea Ice
The study, published in the journal Science, highlights how shorter hunting seasons and reduced access to food are driving the population decline.
Using an advanced bio-energetic model, the researchers determined that polar bears are not getting enough energy to survive and reproduce. The disappearance of sea ice means the bears spend less time hunting seals—their primary food source—and more time fasting on land, leading to severe energy deficits.
"A loss of sea ice means bears have fewer opportunities to hunt seals and are forced to go without food for extended periods," says Dr. Louise Archer, a postdoctoral researcher at U of T Scarborough and the study's lead author. "This negatively impacts their energy balance, resulting in fewer cubs, lower survival rates, and ultimately, population decline."
Nearly 50% Population Decline Over Four Decades
The study examined over 40 years of polar bear monitoring data (1979–2021) from the Western Hudson Bay region, revealing alarming trends:
Polar bear numbers in the region have nearly halved over the study period.
The average size of polar bears is shrinking—adult females have lost 86 lbs (39 kg), while one-year-old cubs have dropped 47 lbs (26 kg) in body weight.
The model closely aligns with real-world observations, confirming that continued sea ice loss will lead to further population declines.
"Our model does more than show a correlation between shrinking sea ice and polar bear decline," says Dr. Péter Molnár, an associate professor at U of T Scarborough and co-author of the study. "It provides a clear mechanism: less ice leads to less hunting time, less energy intake, and ultimately, population loss. The data matches real-world outcomes almost perfectly."
Polar Bear Cubs and Mothers Are at Greatest Risk
The research also highlights that polar bear mothers and their cubs are especially vulnerable to these climate-induced changes:
Shorter hunting periods mean less milk production, which directly affects cub survival.
Cubs that fail to gain enough weight before their first fasting period face higher mortality rates.
Smaller litters—monitoring data shows an 11% drop in cub litter sizes compared to nearly 40 years ago.
Mother bears are keeping their cubs longer because they are too weak to survive on their own.
"Cubs are the future of the polar bear population," Archer explains. "If they don’t survive, neither does the species."
A Warning for Global Polar Bear Populations
The Western Hudson Bay polar bears serve as an early warning sign for global polar bear populations. With the Arctic warming nearly four times faster than the global average, the researchers warn that similar population declines are likely in other regions as sea ice continues to disappear.
"This population has been closely monitored for decades, providing some of the best long-term data available," says Dr. Molnár. "If these trends continue, we can expect similar declines across other polar bear populations as sea ice loss accelerates."
Urgent Action Needed to Protect Polar Bears from Climate Change
The study, funded by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Canada Foundation for Innovation, underscores the critical need for climate action. Organizations like Polar Bears International are urging global policymakers to reduce greenhouse gas emissions and protect Arctic habitats before it’s too late.
As sea ice continues to shrink at an alarming rate, the fate of polar bears in the Arctic depends on immediate and sustained efforts to combat climate change and preserve their hunting grounds.