Polar bears are probably the most iconic species of the Arctic. They’re the largest terrestrial carnivore and are at the summit of the sea ice food chain, but they’re also considered to be a marine mammal. Last week was polar bear week—a time to celebrate this fascinating and important bear species, and a time to support efforts to reduce human conflicts with bears and promote conservation. In a rapidly changing polar environment, polar bears are on the front lines of climate change in the Arctic and an indicator species for the effects of global warming.
The volume of Arctic ice in the winter has decreased by a third over the past 20 years and the rate of ice loss is accelerating. The ice-covered island of Greenland will lose ice at a faster rate this century than over the past 12,000 years, and if we do not make dramatic reductions in greenhouse gas emissions, the rate of ice loss will be even greater.
The Arctic has warmed by 0.75 °C in the last decade. Globally, we are worryingly on track to experience an average warming of 2°C, but it’s predicted that the Arctic will be 4°C warmer over the year, and 7°C hotter in the winter. The changing Arctic climate is not only causing melting, but climate change is leading to more, stronger storms in polar regions, which are also breaking up ice sheets.
Arctic sea ice has melted so significantly that in the future even an unusually cold year will not have the same amount of summer sea ice as observed in the mid-20th century. In addition, the Arctic has become so warm that instead of snow, rain will fall for several months of the year by the middle of this century.
Polar bears are dependent upon Arctic sea ice for survival, traveling hundreds of miles across this critical habitat, hunting for prey and building snow cave dens to raise their cubs. More than 96 percent of the polar bear’s critical habitat is sea ice, and just four percent is onshore.
However, recently published scientific research has described how the declining area and thickness of the polar bear’s ice sheet habitat is causing them to spend more and more time on land. In the 1980s, polar bears would spend most of their summer months on sea ice searching for prey, and would only spend a couple of weeks onshore. Bears are now spending roughly two months on land. In addition, the proportion of bears summering on the land has increased dramatically from just five percent to 50 percent or more.
Scientists are predicting that by 2040, more than half of the polar bear population will be spending three to four months, or more, on land. This shift in distribution is going to lead to more conflict with humans as bears will be spending more time closer to human settlements and activities. In particular, there will be a much greater overlap between the distribution of bears and oil and gas industry facilities. A large proportion of the polar bear’s critical habitat on land already overlaps with oil and gas leases, and climate change will make the potential for conflict between bears and human activities even greater.
One particular project of concern is the massive “Willow” development project, which overlaps with critical denning habitat for Southern Beaufort Sea polar bears. This project will have up to 250 oil wells, hundreds of miles of pipelines, an extensive road system, at least one airstrip, a gravel mine and other construction. The Willow project is the single largest oil drilling project proposed on federal lands. In addition to the disruption the project would have in terms of polar bears and their habitat, it's estimated that the project would add more than 250 million metric tons of carbon to the atmosphere over the next 30 years. This is equivalent to the emission of roughly a third of the annual emissions of all coal plants in America.
In addition to the loss of polar bear habitat, climate change is also leading to other changes in the Arctic environment, such as increasing numbers of toxic algal blooms and increasing levels of toxic heavy metals, released from melting ice into the Arctic Ocean.
Polar bears are currently going through a scientific review process to determine whether the changing science on climate change, and the effects of other human activities on polar bears, such as hunting, will affect its listing on the Endangered Species Act. Polar bears were listed as “threatened” under the U.S. Endangered Species Act in 2008 and the U.S. Fish and Wildlife Service (FWS), which oversees the management of polar bears, is coming close to the end of their five-year review of this species. The purpose of this review is to assess whether the status of the polar bear needs to be updated in light of the latest scientific information.
These reviews are important, especially in the case of polar bears and other species effected by global warming. The science of climate change moves fast. If you don't stop and look at the latest science once in a while, you could miss important data essential to conservation.
In the face of so much new information on the rapid change in the Arctic environment, it’s hard to see any rational scenario where the need to augment conservation efforts for polar bears doesn’t dramatically increase.