Photo: BJ KIRSCHHOFFER / POLAR BEARS INTERNATIONAL / AFP
A male of the sub-population of the Hudson Bay a weight 20% below normal at the beginning of the fasting summer would be 125 days, compared to 200 today.
Without sea ice, polar bears are dying of hunger. So if greenhouse gas emissions continue to rise, global warming could sign the virtual extinction of these bears housed emblematic of the Arctic by the end of the century.
In a study published Monday in Nature Climate Change, researchers have focused on the biggest threat today on the polar bear : the progressive disappearance of their habitat, the sea ice where they catch seals that are essential to their diet.
The carnivore, who lives in the arctic regions where the temperature may drop to -40 °C in winter, one can fast for months, including during the summer period where the sea ice is melting each year.
But with the warming of the planet, two times faster in the Arctic, no ice lasts longer and longer. Unable to find in their environment in a different power supply as rich as the seals, more and more hungry bears venture already sometimes far from their territory, close to populated areas.
The melting of the ice is a challenge in particular for females, which come to fall into their lair to put down in the middle of the winter and emerge in the spring with their cubs.
“They must catch enough seals to store enough fat and produce enough milk to nourish their pups during the fasting of the summer “, explains to the AFP Steven Amstrup, one of the authors of the study and chief scientist of the NGO Polar Bears International.
“In estimating the weight maximum and minimum of the bear, and modeling the energy expenditure, we calculated the limit on the number of days of fasting that can withstand a polar bear before that the survival rate of adults and small begins to decline,” says Peter Molnar, of the university of Toronto.
For example, a male of the sub-population of the Hudson Bay a weight 20% below normal at the beginning of the fasting would only survive 125 days, compared to 200 today.
Tear down the last ?
The approximately 25 000 polar bears are divided into 19 distinct sub-populations in Canada, Alaska, Siberia, Svalbard and Greenland, some of which are poorly known.
According to the study published Monday, these groups will not be all affected at the same rate.
But if greenhouse gas emissions continue at the same rate as today, ” the fall of the reproduction and survival will endanger the persistence of almost all the sub-populations by 2100 “, conclude the researchers. With the exception, perhaps, of the island of the Queen Elizabeth, notes Steven Amstrup.
And even if warming was limited to 2.4 °C compared to the preindustrial era — nearly half a degree above the objective of the Paris Agreement, it “would not save the polar bears in the long term,” insisted the scientist.
“If by magic, even with rising temperatures, the ice is maintained, it would probably go for the polar bears. But their habitat is literally melting with the rising temperatures.”
The planet has earned more than 1 °C since pre-industrial times, leading already to a multiplication of heat waves, droughts or floods. And while the current commitments of the States will lead to a world at + 3 °C, these events of extreme weather are known to worsen with each half-degree, extra.
Classify the polar bear “critically endangered” on the famous red list of the international Union for the protection of nature (IUCN), which considers them only as ” vulnerable “, would probably be nothing to the fate of the plantigrade arctic.
Many of the species endangered is due to poaching or to the direct destruction of their habitat by Man. But ” you can’t build a fence to protect polar bears of the temperature that goes up “, stresses the scientist of Polar Bears International.
To save the species, some point to a reintroduction of captive-bred animals, or even their move to Antarctica. Infeasible, according to Steven Amstrup. “It may need to consider to tear down the last polar bears, instead of letting them die of hunger.”