Scientists: Climate change will cause population of polar bears to plummet

A polar bear jumps from one ice flow to another in the thinning Arctic ice pack off Alaska. Shrinking of sea ice will mean drastic reductions in bear populations.

A polar bear jumps from one ice flow to another in the thinning Arctic ice pack off Alaska. Shrinking of sea ice will mean drastic reductions in bear populations. Photo: Florian Schulz, Visionsofthewild.com Photo: Florian Schulz, Visionsofthewild.com Image 1 of / 6 Caption Close Scientists: Climate change will cause population of polar bears to plummet 1 / 6 Back to Gallery

The melting of sea ice, vital habitat to polar bears, will cause at least one third of the world's 25,000 polar bears to disappear by the mid-21st Century, according to a new study done by research scientists from Canada, Norway and the United States.

"Loss of Arctic sea ice owing to climate change is the primary threat to polar bears throughout their range," said the study, published this month in the Royal Society science journal Biology Letters.

The scientists looked at four polar bear eco-regions and 19 subpopulations, in the Arctic as well as Canada's Hudson Bay. They analyzed sea ice data and the shrinking Arctic ice pack over a 35 year period from 1979 to 2014.

"Our findings support the potential for large declines in polar bear numbers owing to sea-ice loss, and highlight near-term uncertainty in statistical projections as well as the sensitivity of populations to different plausible assumptions," said the study.

The United States has listed the giant bruins under the Endangered Species Act due to loss of habitat.

The new findings are in line with a recent study by University of Washington scientists, published in the science journal The Cryosphere.

In their report, the UW researchers said: "Their dependence on sea ice means climate warming poses the single most important threat to (polar bear) persistence."

The new study, reported in Biology Letters, finds that sea-ice is retreating 3 to 9 days earlier and forming later by 3 to 9 days over every decade, and for all of the bear populations. The loss of sea ice amounted to nearly two months over the years of study.

By the middle of the century, bears will have to endure an additional seven ice-free weeks.

The bears live much of the year on ice flows, from which they hunt seals. They are already being forced ashore in the Arctic at such locations as Cooper Island north of Barrow in Alaska.

The steady rate of decline could cut the polar population to 9,000 later in the century, and eventually reduce habitat to the area of Baffin Island and western Greenland. Polar bear populations are already in decline in such areas as Alaska's Beaufort Sea.

The Arctic has been warning at approximately twice the rate for the rest of the Earth, the result of carbon dioxide buildup in the atmosphere caused largely by emission of greenhouse gases.

Pollution has consequences. As the study notes:

"Anthropogenic climate change is the primary threat to the species because, over the long term, global temperatures will increase and Arctic sea ice will decrease as long as atmospheric greenhouse gas concentrations continue to rise."