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And it’s getting lower on polar bears.

There are now about 600 polar bears in the Western Hudson Bay, one of the most threatened of the 20 populations of the white beasts. That’s about half the number of 40 years ago, says York, senior director of research and policy at Polar Bears International. His latest study, with a team of scientists from various fields, shows that if the world doesn’t cut back more on emissions of heat-trapping gases “we could lose this population entirely by the end of the century,” he says.

To read more about the work Dr. Julienne Stroeve is doing in the Arctic, please visit the Associated Press.

The report, “Ice-free period too long for Southern and Western Hudson Bay polar bear populations if global warming exceeds 1.6 to 2.6C”  published June 13, 2024, in Communications Earth and Environment was developed in collaboration with researchers from the University of Toronto Scarborough, National Snow and Ice Data Center, The Arctic University of Norway, Fisheries and Oceans Canada, Environment and Climate Change Canada, and Polar Bears International.

As it is increasingly unlikely that the world will meet the most ambitious Paris Agreement target of limiting global warming to 1.5°C, the team of biologists and climate scientists came together, using the latest science, to reevaluate the future of Hudson Bay’s sea ice, polar bears, and seals. The report analyzes various climate warming scenarios if greenhouse gas emissions continue and we surpass 2°C warming above pre-industrial levels, the upper limit set in the Paris Agreement.

“If we fail to limit global warming to less than two degrees Celsius, we will lose Hudson Bay’s populations of polar bears,” says lead author Professor Julienne Stroeve, University of Manitoba, adding, “The disappearance of the Southern Hudson Bay polar bears is imminent, with Western Hudson Bay not far behind. Our research underscores the rapid changes human activity imparts to our climate. It’s incumbent upon us to understand the impending impact on our natural world, so that we can make policy decisions informed by science.”  

A Comprehensive Approach for an Interconnected Ecosystem

This report offers the first holistic look at the future of Hudson Bay’s ecosystem—encompassing polar bears and seals alike—and predicts a polar bear extirpation, which means a localized extinction, between the 2030s and 2060s. Unlike previous reports analyzing partial regions, often looking retrospectively at historical data, this report provides a comprehensive examination of the future of the Hudson Bay area. This shift addresses changes in sea ice thickness and snow thickness, which are critical for polar bear hunting, polar bear denning, and seal pup denning. 

This study analyzes sea ice thickness to determine polar bear survival, which has never been done before. Previous approaches assessed sea ice coverage, which authors found could overestimate polar bear survival by 50 days. Sea ice is not always thick enough for a polar bear to use for successful hunting, as seen in this video clip, therefore this report analyzes ice thickness of at least 10 cm – minimum for supporting a male polar bear hunting.

Key Results: Polar Bear Survival Depends on Melting Ice

Polar bear survival is directly related to Arctic sea ice, as they need the ice platform to hunt their main prey, seals. When polar bears are forced onto land by melting ice, terrestrial food is an insufficient replacement, with prior research finding that survival and reproduction are constrained by bears’ capacity to fast. This new report finds that under 2°C of warming, southern Hudson Bay will be ice-free for 174 to 182 days, which would impair reproduction and strain survival. Western Hudson Bay will maintain sea ice for longer, with 163 to 168 ice-free days. Analyzing the projections from 20 climate models, the Western Hudson Bay region becomes an unsuitable habitat at 2.2°C or 2.6°C. The southern Hudson Bay sub-population faces a more dire projection, with ice-free periods becoming excessively long for most bears at 1.6°C to 2.1°C. Therefore, if the Paris Agreement is breached, and the world surpasses 2°C of warming, this report finds that the southern population will disappear, and the whole of Hudson Bay’s polar bears will be at or near their survival limit. If we do surpass 2°C global warming, the timing of that breach and localized extinction depends on the rate of greenhouse emissions by human activities over the coming decades. 

“Unregulated emissions could mean we see the disappearance of the Southern Hudson Bay subpopulation as early as the 2030s,” says assistant professor and co-author, Alex Crawford.
“Changing policies to achieve more aggressive emissions reductions could delay the breach of the 2°C threshold to the 2060s, maintaining the survival of Hudson Bay’s polar bears.”

This map illustrates the boundaries of the Western Hudson Bay and Southern Hudson Bay polar bear populations (Credit: Alex Crawford)

Significance of Hudson Bay’s Polar Bears

Hudson Bay is home to two of the world’s 19 polar bear subpopulations, representing the world’s southernmost polar bear populations, which have long been considered an indicator of how the rest of the world’s polar bear subpopulations will fare in the future. Hudson Bay’s polar bears are the best-studied polar bears in the world, and this report includes models using over 50 years of data since monitoring of Hudson Bay’s polar bears began in the 1970s. Beyond serving as a “canary in the coal mine” for other Arctic regions, these polar bears hold significant cultural value for communities around Hudson Bay.

“This report is more detailed and alarming than previous studies, reinforcing that Hudson Bay’s polar bears are not on a good trajectory unless significant emissions mitigation measures are implemented,” says co-author Geoff York, senior director of research and policy at Polar Bears International, adding, “This cross-disciplinary, forward-looking and comprehensive analysis of all of Hudson Bay provides more actionable insights for policymakers and wildlife managers.” 

Implications for Seals and Other Species: 

As rainfall, rather than snowfall, increases in the Subarctic and Arctic, it will be more difficult for both seals and polar bears to make dens to give birth to offspring, with rain potentially washing away their dens. There are three seal species in Hudson Bay, of which the ring seals are polar bears’ preferred prey. This report highlights how less snow can impact seal pup survival, as ring seals need at least 32 cm of snow depth to dig lairs for their pups. Future studies could look at the sea ice thickness needed for other species, like caribou and walrus that travel across the ice. Future research may analyze future sea ice roughness, which determines where snow sticks and accumulates, and therefore where seals can den. 

This research underscores the importance of swift greenhouse gas emissions reduction, and multi-disciplinary, holistic approaches to research, management, and policy. 

Rivkin and researchers from Environment and Climate Change Canada, Polar Bears International, MacEwan University, Government of Northwest Territories, and San Diego Zoo Wildlife Alliance developed an innovative SNP genetic sequencing chip, a new tool, to analyze samples from polar and grizzly bears. Their report analyzed 371 historic polar bear and 440 historic grizzly bear samples from across Canada, Alaska, and Greenland and confirmed that only the eight already-known are hybrids, thus underscoring the rarity of hybridization. 

Range expansion, facilitates hybridization of two large carnivores

“Polar bears evolved from grizzly bears several hundred thousand years ago and although gene flow has occurred between the two species in the past, it appears that recent hybridization is restricted to a small group of polar bears and brown bears in the western Arctic,” says co-author Evan Richardson, Research Scientist at Environment and Climate Change Canada, adding, “This study develops a new genomic toolset to rapidly detect hybrids and indicates that contemporary hybridization is not a conservation concern.” 

Hybridization, increasing but rare

This report answers the question of, “How many polar-grizzly bear hybrids are there?” which responds to an expectation that the numbers of polar-grizzly hybrids were increasing. Out of 819 wild grizzly and polar bears across Canada, Alaska, and Greenland, encompassing four subpopulations, this report found that only eight hybrids exist, or 1 per cent of the samples, collected between 1975 and 2015. The first hybrid did not appear until 2006. While it is a rare occurrence, it is a recent one, suggesting hybridization is a result of warming temperatures causing their habitats to increasingly overlap. 

“We were surprised to find no new cases of polar-grizzly hybrids despite speculation of increasing numbers,” says Rivkin, who also co-authored the study. “We’re proud that this new chip allows rapid identification of polar-grizzly bear hybrids, which will be an important tool as the climate warms and polar and grizzly bears come increasingly into contact.”

About hybrids (also known as pizzly bears or grolar bears)

Hybrids of grizzly and polar bears are often referred to as grolar or pizzly bears depending on the paternal lineage, i.e., a grolar bear when the father is a grizzly bear, and a pizzly bear when the father is a polar bear. This study confirms the existence of eight known grolar bears in the wild as the descendants of one female polar bear. Hybridization is only possible in areas where grizzly and polar bear distributions overlap (thus excluding regions like the high Arctic). Hybridization is uncommon but expected to increase as climate change pushes grizzly bears northward, increasingly into polar bear territories, but hybrids are still ill-suited to adapt to the changing Arctic. 

“This report underscores that hybridization is remarkably rare, and that hybridization is not an adaptive capability of polar bears,” says Geoff York, senior director of research and policy at Polar Bears International, who was not involved in the report. “The report introduces a new tool for wildlife managers to use as they evolve their strategies due to a warming climate and changing ecosystems.” 

Technological breakthrough

This research developed the new 8K genotyping chip, called the Ursus maritimus V2 SNP chip, which is a genetic tool used to analyze polar bear samples in a lab. It reads the genetic samples, allowing rapid and reliable genome analysis and spots polar bear-grizzly hybrids with 100 per cent accuracy. The Ursus maritimus V2 SNP chip is a result of years of development through the Genomics Research and Development Initiative STAGE funding by Environment and Climate Change Canada. The authors had access to long-term, robust polar bear data from Canadian government and territorial monitoring programs, which have been collecting data since 1966, and which were critical to the research and Ursus maritimus V2 SNP chip development. This chip is an important tool for wildlife managers, scientists, policymakers, and conservationists to identify hybrid bears and further enable their protection and more effective wildlife management. 

“Our newly developed technology allows rapid and accurate consideration of over 8,000 genetic markers in polar bears,” notes lead author Dr. Joshua Miller, Assistant Professor, Biological Sciences, MacEwan University, adding “This will allow for the assessment and monitoring of genetic diversity, which is a key part of a species’ ability to survive changing environmental conditions.”

As sea ice formation continues to vary, the bears could experience “dramatic impacts,” he said.

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