The author of today’s post, Lisa Moore, Ph.D., is a scientist in the Climate and Air program.
"Most Polar Bears Gone by 2050". You may have seen that headline in the news this week. The study behind this depressing conclusion could land polar bears on the list of threatened species under the Endangered Species Act.
Polar bears depend on the sea – and sea ice – for food. Most often they dine on ringed seals, which they catch by hanging out on sea ice next to seals' breathing holes. Without sea ice, they can't get enough food to survive. Unfortunately, summer sea ice has been declining rapidly, raising fears for polar bear survival.
In response to a lawsuit from a number of environmental groups, the U.S. Fish and Wildlife Service recently proposed protecting polar bears under the Endangered Species Act. As part of the decision-making process, the Department of the Interior commissioned a study of polar bears, and how global warming is affecting them. The resulting nine-part report evaluates the distribution and abundance of polar bears in each of four different eco-regions.
Biologists have been studying polar bear populations for years, so they have a good understanding of how sea ice dynamics – particularly the length of the ice-free season – affect polar bear survival. The authors combined this information with climate model simulations of sea ice extent under a business-as-usual scenario of greenhouse gas emissions. The results were sobering.
Polar bear populations in the Western Hudson Bay and Southern Beaufort Sea are declining, and this trend is linked to disappearing sea ice. Polar bears in the Hudson Bay and northern Russia could disappear by mid-century. Polar bears of northern and eastern Greenland may hang on for 75 years. In the archipelagos between northeastern Canada and northwestern Greenland, polar bears are likely to survive through the end of the century, though in smaller numbers.
And these conclusions are conservative. Sea ice models have generally underestimated sea ice loss.
This coming January, the Fish and Wildlife Service is expected to make a recommendation to the Secretary of the Interior on whether or not to add polar bears to the list of threatened species. The legal outcome is a few months away, but in the meantime this comprehensive scientific report hammers home the message that global warming jeopardizes Earth's stunning biodiversity, including some of its most loved, iconic species.
This is deeply alarming, but not a reason to give up. Remember, these results are for a business-as-usual scenario, and scientists have shown that bold action today can minimize global warming. This report is yet more motivation to get going in the fight against global warming.