Arctic Warming Reduces Sea Ice and Energy for Polar Bears

Polar bears struggle to have enough energy to survive because melting sea ice makes it harder to find food.

By Amélie Caldon

Human-caused global warming is putting wildlife at risk, and few animals are feeling the effects as much as polar bears (Ursus maritimus). The Arctic is warming faster than anywhere else on Earth, and as sea ice disappears, polar bears are losing their hunting grounds. 

Sea ice isn’t just frozen water—it’s a lifeline for polar bears. It gives them a sturdy platform to hunt their favorite prey: ringed and bearded seals. But without ice, hunting becomes nearly impossible. With fewer opportunities to catch food, many polar bears are starving, and their populations are shrinking. This doesn’t just impact the bears—it ripples through the entire Arctic ecosystem. If polar bears hunt less, seal populations could boom, which might throw the balance of Arctic marine life off course. Scavengers like Arctic foxes also rely on leftovers from polar bear kills, so as the bears struggle, these smaller creatures may suffer too. 

The impact of less sea ice

The effects of less sea ice don’t stop at the Arctic. Melting ice speeds up climate change worldwide. Normally, bright ice reflects sunlight, helping to keep the planet cool. But when it melts, the dark ocean absorbs more heat, making the planet warm even faster. The fate of polar bears isn’t just their story—it’s a warning sign for all of us. The Arctic is changing, and what happens there affects the entire planet.

To understand why polar bears are struggling, Louise Archer of the University of Toronto led a team of scientists to create a special energy model, like a polar bear calculator. This model measures how much energy they need for essential survival tasks like hunting, moving, growing, and reproducing. By analyzing over 40 years of data collected on polar bears in Western Hudson Bay, Canada, the researchers discovered a clear problem: as sea ice melts, polar bears are using more energy than they can replace with food. This energy shortage leads to starvation and a declining population. In fact, since the 1980s, the number of polar bears in Western Hudson Bay has dropped by nearly 50 percent!

The energy struggle: why polar bears are losing the battle

Imagine being asked to run a marathon—but with no food or water to keep you going. This is the harsh reality for polar bears in the Arctic. As sea ice melts earlier each year, they are forced to travel longer distances and endure longer periods without food, pushing them into a dangerous energy deficit. 

Polar bears depend on a high-fat diet, primarily from ringed and bearded seals, to sustain them in the harsh Arctic environment. Their fat reserves act as a vital energy source, allowing them to survive between hunts in a place where food is scarce. These reserves are especially crucial for essential survival activities like hunting, moving, and even reproduction. However, with sea ice disappearing, the balance is shifting—forcing polar bears to burn more energy than they can replace. This is essentially causing population decline in the polar bears, an already vulnerable classified species.

A polar bear’s yearly survival cycle begins when the ocean refreezes during the coldest months, allowing them to return to the ice and hunt. This is their most critical feeding period, as they need to build up fat reserves to sustain them through the warmer months when food is limited. However, global warming is disrupting this cycle—the sea ice is taking longer to form and is becoming less stable, making it harder for polar bears to hunt and store enough energy. For some bears, the challenge is even greater. Mothers with cubs must produce milk and care for their young, burning even more energy. 

When the ice melts, polar bears are forced onto land, where they fast for months, relying entirely on the fat they stored while hunting. If they haven’t built up enough reserves, they face a higher risk of starvation and death during this critical period of time.

Calculating polar bear energy use as sea ice declines

To understand just how much energy polar bears are losing, Louise Archer’s team developed an energy calculator. This measured how many calories polar bears need to survive versus how much they are actually getting from prey. By analyzing over 40 years of monitoring and capturing data, the researchers discovered that polar bears are burning many more calories than they can consume. This has caused a reduction in body size, with cubs struggling to survive and adult bears becoming weaker. This energy shortage is so severe that some polar bears have resorted to scavenging garbage dumps or hunting alternative prey such as seabirds. Sadly, these foods lack the fat content that the bears need to ultimately survive long-term.

Despite these grim findings, there is a rare exception—a unique subpopulation of polar bears in Southeast Greenland that has found a way to survive longer despite climate change. While most polar bears rely solely on sea ice for hunting, this group of bears has learned to adapt to their changing environment by hunting in a completely different way. These Greenland polar bears have managed to survive for up to 250 days each year without sea ice. This far exceeds the usual 180-day fasting limit for the species. But how? Instead of relying on vanishing sea ice, this subpopulation has discovered an alternative hunting ground—freshwater glaciers. This glacial habitat, a mix of icebergs and floating ice chunks from marine-terminating glaciers, provides a year-round hunting platform. Even during the warmer months, when other polar bears are forced to fast on land, these bears continue hunting, reducing their risk of starvation.

Beyond the polar bears

While the decline of polar bears serves as a stark warning about climate change, its impact extends far beyond a single species. The Arctic plays a crucial role in regulating the Earth’s temperature since its bright white sea ice reflects sunlight. However, as this ice melts, that sunlight instead hits the darker ocean and its heat gets absorbed, accelerating climate change on a much larger scale. The loss of polar bears is just one part of a broader environmental crisis—one that influences weather patterns, rising sea levels, and the delicate balance of global biodiversity.

RELATED: Ebbs and Floes: Watching the Arctic Ice Melt

Although tackling climate change may seem overwhelming, small everyday actions can make a difference when adopted collectively. If you want to help polar bears and other Arctic wildlife, reducing your carbon footprint is a great place to start. Simple changes like walking, biking, or using public transportation instead of driving can significantly cut emissions. When driving is necessary, try combining errands into one trip to save fuel. At home, you can conserve energy by turning off lights and unplugging devices when they’re not in use, as many electronics continue to drain power even when switched off. Additionally, reducing meat and dairy consumption—even slightly—can help lower methane emissions from livestock farming, which is a major contributor to global warming.

By making small but meaningful changes, we can all contribute to slowing Arctic ice loss and protecting species like the polar bear—before it’s too late.

This study was published in the peer-reviewed journal Science.

References

Archer, L. C., Atkinson, S. N., Lunn, N. J., Penk, S. R., & Molnár, P. K. (2025). Energetic constraints drive the decline of a sentinel polar bear population. Science, 387(6733), 516–521. https://doi.org/10.1126/science.adp3752

Laidre, K. L., Supple, M. A., Born, E. W., Regehr, E. V., Wiig, Ø., Ugarte, F., Aars, J., Dietz, R., Sonne, C., Hegelund, P., Isaksen, C., Akse, G. B., Cohen, B., Stern, H. L., Moon, T., Vollmers, C., Corbett-Detig, R., Paetkau, D., & Shapiro, B. (2022). Glacial ice supports a distinct and undocumented polar bear subpopulation persisting in late 21st-century sea-ice conditions. Science, 376(6599), 1333–1338. https://doi.org/10.1126/science.abk2793

Featured image from album Wild Polar Bears in Churchill (along the Hudson Bay), by Alex Berger. Licensed under CC BY-NC 2.0. Additional photos courtesy of Polar Bears International.