© Kt Miller/Polar Bears International
12/3/2014 11:17:46 AM
When Might Polar Bears Disappear?
If global warming continues on the trajectory it's now following, polar bears' habitat-Arctic sea ice-will almost completely disappear by 2100, according to scientists.
In 2007, Steven Amstrup, PBI's chief scientist, and his team at the USGS projected that two-thirds of the world's polar bears could be gone by mid-century if we remain on our current greenhouse gas emissions path. He also projected the last polar bears would remain through the end of the century in the far northern Canadian Arctic Islands. A just released study now projects when even those Canadian Archipelago bears may reach their limits.
Polar bears depend on sea ice to hunt seals. In the southern portions of their current range, polar bears have always been forced onto land when their sea ice foraging grounds melt entirely in the summer. In those areas, bears are already facing longer ice-free periods of food deprivation, with the sea ice breaking up earlier and forming later. The northern parts of the polar bears' range are currently covered by sea ice year-round. As the climate continues to warm, however, even the ice in the far northern islands of Canada, where a quarter of the world's polar bears live, will be disappearing.
The study, published in the science journal Plos One, looked at just how vulnerable polar bears are to sea ice changes. The scientists predicted a shift from perennial sea ice, which stays frozen through the summer, to annual ice cover, and even ice-free periods that may critically impact polar bears before the end of the 21st century.
Each polar bear population in the northern Canadian Archipelago may undergo two to five months of ice-free conditions, where no such conditions presently exist. Without the ability to hunt and eat, polar bears will not be able to meet nutritional or reproductive demands.
The study's lead author, Stephen Hamilton, stated, "We start to see some starvation in adult males when we have 120 days of ice-free season," and that "under business-as-usual climate projections, polar bears may face starvation and reproductive failure across the entire Archipelago by the year 2100."
The study adds detail to the previously predicted polar bear declines by Amstrup and his team. "By intersecting outcomes from a new climate model with energetic models estimating of how long polar bears can go without food, these authors were able to estimate a possible time frame during which each subpopulation in northern Canada may exceed critical thresholds of ice absence," he said. "In that way, it provides an incremental picture of when each population may disappear if we continue on our current warming path."
Read more: NPR, Shrinking Sea Ice Could Put Polar Bears In Grave Peril By 2100