Polar bears: This is how their lives are changing because of the climate crisis

No other animal represents the devastating effects of global warming like the polar bear – indeed, long ice-free phases in the Arctic make it difficult for predators. This is shown by a complex study in the journal “Nature Communications”, for which researchers observed 20 polar bears in Canada very closely for several weeks. The team, led by Anthony Pagano of the Alaska Science Center, found that polar bears also search for food on land, but are unsuccessful and lose weight.

Advancing climate change is leading to a decline in sea ice in the Arctic. This is a problem for polar bears because they hunt seals on the ice from late spring to early summer, when they give birth to their cubs. As the sea ice retreats, polar bears are forced to move onto land. Due to global warming, ice-free periods have lengthened significantly: three weeks from 1979 to 2015, so polar bears now spend 130 days a year on land.

It is not clear whether polar bears can survive longer periods without sea ice by using less energy or exploring new food sources. To find out, Pagano's team studied 20 polar bears in Canada's Hudson Bay during a time when there was no sea ice.

The authors determined the animals' daily energy consumption and their body mass changes. Using camera-equipped GPS trackers, the researchers were able to observe how the animals behaved, what they ate and how much they moved.

“We observed very different behaviors among polar bears,” Pagano said, according to a Washington State University press release. “Some bears expend little energy simply lying down and sleeping. Others actively forage, subsisting on bird and caribou carcasses, seaweed and berries. Three animals even swam several kilometers into the sea in search of food.”

The researchers also found large differences in the animals' daily energy consumption, depending on activity. In total, 19 of the 20 polar bears lost weight: between 0.4 and 1.7 kilograms per day and between eight and 36 kilograms over a three-week observation period. “Some animals were able to find food,” Pagano explains, “but ultimately they spent more energy searching for food than they got back by eating.”

Some experts assumed that polar bears on land behaved like their cousins, grizzly bears: they went into a resting mode or foraged on land. But it's not obvious. “Polar bears are not white-furred grizzlies. They are very different from each other,” said co-author Charles Robbins of the Washington State University Bear Center. “Polar bears are big and heavy. To maintain their weight, they eat the energy-rich fat of seals – and they catch it in the sea ice.

Although polar bears can largely adapt their behavior, the results show how long periods without sea ice increase the animals' risk of starvation. “Because polar bears have to retreat to the mainland earlier, they have less time to build up the energy reserves necessary for survival,” Pagano says. “We assume that more animals will starve to death in the future, especially young polar bears and females with cubs.”

The conservation organization WWF has pointed out that this development will also have an impact on people. “As polar bears spend more time on land, the risk of interactions and conflicts with people in Arctic coastal communities is greater,” the organization said. According to Pagano's experts, polar bears in western Hudson Bay may be more vulnerable to the effects of climate change than those elsewhere in the Arctic.