Arctic climate models playing key role in polar bear decision

MADISON - The pending federal decision about whether to protect the polar bear as a threatened species is as much about climate science as it is about climate change.

The U.S. Fish and Wildlife Service (FWS) is currently considering a proposal to list the polar bear as a threatened species under the Endangered Species Act, a proposal largely based on anticipated habitat loss in a warming Arctic.

Climate models - mathematical representations of the natural processes affecting climate - factored heavily in the scientific information requested by the FWS to guide its official recommendation, which was due Jan. 9. While scientists have used such models for decades, their use in this decision demonstrates the growing recognition of the value of modeling to predict future climate conditions and inform policymaking.

Eric DeWeaver, the physical climatologist on the International Polar Bear Science Team and a professor of atmospheric and oceanic sciences in the University of Wisconsin-Madison, evaluated existing climate models to identify those that best represent observed changes in sea ice - a crucial component of polar bear habitat - and which are expected to best predict future conditions in the Arctic.

His findings, detailed in a U.S. Geological Survey report provided to the FWS, were applied in subsequent reports to predict how Arctic sea ice changes over the next 100 years will likely affect polar bear populations.

These reports, available online at http://www.usgs.gov/newsroom/special/polar_bears, formed the basis of the scientific guidance requested by the FWS.

Climate models strive to represent the physical laws that govern climate systems to forecast how climate will respond to changes, such as greenhouse gas increases. Due to the variability of natural systems and the difficulty of mathematically representing such complex systems, all models contain some element of uncertainty, DeWeaver says.

"A climate model is not a crystal ball," he says. "It's impossible to make a perfect representation of climate... There are choices you make in model development that lead to a range of model behaviors. Often it is not possible to say that one [model] is better than another."