How Does Global Warming Effect Polar Bears – New science sheds more light on recent debates about how much large carnivores are affected by melting sea ice.
Millions have watched the heartbreaking video of a Polar Bear clinging to life, his white hair loosely covering his thin, bony frame. The video, shot by Paul Nicklen and Cristina Mittermeier of the nonprofit group Sea Legacy and published on National Geographic in early December, sparked a firestorm of debate about what scientists do and don’t know about the effects of global warming on Polar Bears. . It’s impossible to know for sure what disturbed this individual without examining the presumed dead bear in the video, but scientists have now published new findings that shed more light on the risk to the species as a whole.
How Does Global Warming Effect Polar Bears
More polar bears will soon starve to death as sea ice melts, a new study finds that large carnivores need to eat 60 per cent more than expected. They are high-energy animals, burning up to 12,325 calories a day despite sitting around most of the time, according to a unique metabolic analysis of wild bears published Thursday in the journal Science.
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“Our study reveals polar bears’ complete dependence on seals,” said lead author Anthony Pagano, a wildlife biologist with the U.S. Geological Survey (USGS).
Polar bears rely almost entirely on the calorie-laden seal diet. To minimize energy consumption, bears still hunt and wait for hours in seals’ cone-shaped breathing holes in the sea ice. When a seal surfaces to breathe, the bear stands on its hind legs and hits its head with both front paws to stun it. The bear then bites him on the neck and drags him onto the ice.
“They are much more successful doing this than other hunting methods,” Pagano said. Melting Arctic sea ice therefore threatens the survival of polar bears.
A polar bear watches over her cubs in Hudson Bay, Manitoba, Canada. The Gulf is famous for its polar bears, but their population is decreasing.
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A polar bear watches over her cubs in Hudson Bay, Manitoba, Canada. The Gulf is famous for its polar bears, but their population is declining.
Climate change is warming the Arctic faster than anywhere else, and sea ice is shrinking by 14 percent per decade. Even today, in the midst of a bitterly cold Arctic winter, satellites show there is about 770,000 square miles less sea ice than the average between 1981 and 2010 (an area larger than Alaska and California combined). In late spring, ice breaks up more quickly and forms later in the fall, forcing bears to expend large amounts of energy by walking or swimming long distances to reach the remaining ice. Or they stay on land longer, fasting during the summer and increasingly the autumn, subsisting on the fat they obtain from the seals they catch in the spring.
Pagano’s work involved the capture of nine female bears in the Beaufort Sea off Alaska, where there are normally plenty of seals around. The bears were fitted with GPS collars with cameras that would record point-of-view video of each bear. Blood and urine samples were also taken. Eight to 11 days later they were all recaptured. By then one bear had moved 155 miles away. Blood and urine samples were taken again and video and other data were downloaded.
The data showed that the bears were active about 35 percent of the time and rested the rest, but they burned 12,325 calories per day, mostly from body reserves. That’s about 60 percent more than previous studies had estimated. The videos revealed that four of the females failed to catch a single seal. Measurements showed that the animals lost 10 percent or more of their body mass.
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One bear lost nearly 44 pounds, including lean muscle, in 10 days. This bear even jumped into the sea in an unsuccessful attempt to catch a swimming seal. “He might have been desperate,” Pagano speculated.
“This is a really powerful study,” said Steven Amstrup, chief scientist at Polar Bears International, a conservation-focused organization who was not involved in the study. “This suggests that polar bears are more like big cats like lions and tigers, which are predatory carnivores with high energy metabolisms,” Amstrup said.
As solitary hunters, bears are more similar to tigers, except that they are twice as large and some tip the scales at around 1,100 pounds. And yet they are uniquely vulnerable due to their almost exclusive reliance on a single type of prey.
If these results hold, they indicate that sea ice loss may have a larger impact on bears than previously thought, said Amstrup, a former USGS polar bear expert. Amstrup’s 2010 study predicted that continued decline in sea ice would reduce the global bear population by two-thirds to fewer than 10,000 by 2050.
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Best estimates say there are 20,000 to 30,000 polar bears in 19 different groups, or populations, scattered across the hills of the United States, Canada, Greenland, Norway and Russia. Four of these populations are thought to be declining. Bears in the Beaufort Sea region are among the best studied, and their numbers have declined by 40 percent in the past decade. Five populations are thought to be stable, and there is not enough information about the others to make judgments. (See how scientists are trying to track polar bears across vast regions of Russia.)
Polar bears are considered endangered in the United States and are listed as “vulnerable” by the IUCN as their sea ice habitats are threatened by climate change.
Andrew Derocher, Canada’s leading polar bear expert and a professor at the University of Alberta, said that although this study was only a 10-day snapshot, it confirms that polar bears were not built to walk. They are not efficient walkers, but they can roam an area as large as 95,000 square miles thanks to their high-energy diet of seals, Derocher said in an interview.
Bears can lose weight quickly, but if they can catch seals they can gain it back quickly. “I’ve seen a 500-kilogram (1,100-pound) male consume 100 kilograms (200 pounds) of seal in one meal,” he said.
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The further bears have to travel to reach the ice to hunt, the more weight they lose. They eventually begin to lose muscle, which hurts their chances of hunting success, which can lead to a downward spiral. As sea ice decreases, bears also swim more, Derocher said.
Although polar bears can swim long distances, they expend much more energy doing so than walking, according to a recent study published in Polar Biology.
“As sea ice melts earlier and earlier, polar bears are forced to swim increasingly further to reach seal populations,” author Blaine Griffen, a biologist at BYU, said in a statement. One female bear Griffen studied swam 426 miles over nine days. She lost 22 percent of her body weight and, worse still, lost the cub that had started the journey with her.
More swimming could lead to bears becoming smaller, reducing their reproductive rates and even increasing their risk of mortality, which has already been seen in western Hudson Bay and around the southern Beaufort Sea, Griffen said.
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Amstrup said there is no doubt that more and more bears will starve to death as sea ice shrinks. “I don’t know if the poor bear in that video died of starvation. “I know that the only solution for the long-term survival of the polar bear is to combat climate change.”
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These powerful carnivores are spending more time near humans foraging for food. A portable radar unit can prevent the types of encounters that rarely end well.
A year later, Cristina Mittermeier explains what she and her team were trying to achieve with this heartbreaking image. If global warming continues unabated, polar bears could become nearly extinct by the end of the century as a result of shrinking sea ice in the Arctic. scientists said Monday.
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Researchers believe nearly all of 19 subpopulations of polar bears, from the Beaufort Sea off Alaska to the Siberian Arctic, will face extinction as loss of sea ice will force the animals to move ashore and stay away from food sources for longer periods of time. aforementioned. Prolonged starvation and reduced breastfeeding by mothers will lead to rapid declines in reproduction and survival rates.
“If greenhouse gas emissions continue at so-called business-as-usual levels, the likelihood that polar bears will persist anywhere in the world is very low, except perhaps for a very high small subpopulation in the Arctic,” Peter K. Molnar said. said. is a researcher at the University of Toronto Scarborough and lead author of the study published Monday in the journal Nature Climate Change.
Even if emissions are reduced to more moderate levels, “unfortunately we will still lose some, particularly some of the southernmost populations, to sea ice loss,” Dr. Molnar.
The fate of polar bears has long been a flashpoint in anthropogenic debates.
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