Arctic Sea Ice Changes
While polar bears are strong swimmers and divers, the loss of sea ice in both area and thickness, driven by climate change, is testing the limits of that ability.
The loss is forcing them to either head ashore, where they can't hunt their main seal prey, or to embark on long swims in search of sea ice.
The remaining ice is increasingly farther offshore and floats over deep, largely unproductive waters.
- In one study, a collared female polar bear embarked on a marathon, 426-mile swim over nine days without finding a resting place. Somewhere along the way, she lost her cub and 22% of her body weight.
- Long swims are especially hard on younger bears and adults in poor body condition. Reduced body fat gives these bears lower energy reserves and less insulation in the icy waters of the Arctic sea.
- A study of 68 satellite-collared female polar bears with cubs found those bears that undertook long swims had a higher cub mortality rate. Five of the 11 mothers who set off on long swims lost their cubs before, during, or shortly after the swim events.
Scientists predict that as the Arctic continues to warm, two-thirds of the world's polar bears could disappear within this century.
The Ripple Effect
How sea ice changes affect the Arctic ecosystem.
Polar bears have evolved for a life on sea ice, which they rely on for hunting their seal prey. But as the Arctic sea ice rapidly diminishes, the entire Arctic ecosystem—from copepods to seals to walruses—is at risk.
This is because sea ice is as important to the Arctic ecosystem as soil is to a forest. The food chain begins with algae and other tiny organisms that live on and within the sea ice. Arctic cod feed on them. Seals eat Arctic cod. And polar bears prey on seals. It's critical to protect this ecosystem that many animals depend on.