The top carnivores will disappear during the span of human life, according to the study released on July 20. Climate change is starving polar bears to extinction.
Scientists have confirmed in Nature Climate Change that they are already trapped in a dangerous downward spiral in some areas, with diminishing sea ice cutting short the time bears have for hunting seals.
Their dwindling bodyweight undermines their chances of surviving food-less Arctic winters, the scientists added.
“Bears are facing an increasingly long period of fasting before the ice is refreezing and they can return to feed,” said Steven Amstrup, who designed the study and is the chief scientist of Polar Bears International.
According to current patterns, the study concluded, in 12 of the 13 subpopulations studied, polar bears would have been decimated within 80 years by the galloping pace of change in the Arctic, which heats up three times as quickly as the entire earth.
“By 2100, recruitment” — new births — “will be seriously compromised or unlikely anywhere except maybe in the subpopulation of the Queen Elizabeth Island,” said Amstrup in the Arctic Archipelago of Canada.
The scenario foresees the Earth’s average surface temperature rising above the preindustrial level by 3.3 degrees Celsius. Till now, one degree of warming has triggered a crescendo of heatwaves, superstorms and droughts that have made the rising seas more destructive.
“According to human-caused climate change, the Arctic warms up at 3 times the level of the globe … and as a result, the Arctic ecosystem is changing at an alarming pace,”,” said Jeff Berardelli, meteorologist and climate expert at CBS News. “We ‘re running out of time to minimize the harm done by climate change. There’s no denying that we’re going to lose valuable species forever. The question is, how ready are we to sacrifice? How effectively and confidently are we going to take steps to reduce climate change and habitat destruction?”
The challenge is not rising temperatures, but the failure of top-of-the-food-chain predators to adapt to a fast-changing climate.
“If by chance, even as temperatures increase, the sea ice could be preserved, polar bears would be safe,” Amstrup said by email.
“The problem is, their world is literally melting”, Half of the land-dependent megafauna on Earth is listed as endangered but only polar bears are still threatened by climate change.
But, the authors cautioned, this position might not be special for long and should be seen as a harbinger of how climate could impact other species in the coming decades.
The threat to their survival has been long known, but the new research — building on Amstrup’s groundbreaking work a decade ago — is the first to set a timeline for their imminent demise.
The new method is superimposed on two data sets. And the other is the increasing duration of fasting that varies across continents and can last for half a year or more.
The other is a pair of climate change forecasts that chart the loss of sea ice until the end of the century, based on predictions from the IPCC advisory panel on climate science at the UN.
“By measuring how lean and fat polar bears can be and by modeling their energy usage, we have been able to calculate the threshold number of days that Polar bears will run until rates of cubic and adult survival start to decline, “said lead author Peter Molnar, University of Toronto professor. For example, a male bear in the West Hudson Bay population 20 percent below its usual body weight when fasting begins would have only enough stored energy to live for around 125 days instead of 200 days.
The “vulnerable” status of the polar bear on the IUCN Red List of endangered species — less severe that they are “endangered” or “critically endangered”—does not accurately reflect their plight, the authors argue.
Categories identified by the International Union for Nature Conservation are focused primarily on threats such as deforestation and encroachment of ecosystems that can be resolved through local action on the ground.
“But we can’t build a fence to protect the sea ice against rising temperatures,” Amstrup said.