Arctic climate models playing key role in polar bear decision

Mar 11, 2008

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 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."

A discussion of the uncertainty inherent to climate models sometimes creates the impression that the models cannot provide useful information, he says, which is absolutely not the case.

Instead, he likens climate modeling to other predictive sciences like weather forecasting and economics. While short-term predictions may accurately pinpoint specifics, longer-scale projections are expected to reveal bigger-picture trends but fewer details.

For Arctic sea ice, the trend is clear, DeWeaver says - all models point to widespread reductions in sea ice in coming decades. What's less certain is how much melting to expect and how quickly.

Since each model represents climate in a slightly different way, the exact degree of melting - and timing of the first occurrence of an ice-free Arctic - vary from model to model.

Far from being a drawback, these variations in model output are "enormously helpful in understanding a range of outcomes," DeWeaver says. "Having a multi-modal ensemble gives you a way to boil things down to the essentials," identifying the most robust changes consistent across several models.

Anticipated climate change has been a key element of the polar bear equation throughout the entire listing process, he says. Unlike most species considered for federal protection, polar bears' numbers have not yet shown significant decline.

However, escalating habitat losses anticipated due to global warming and other pressures are expected to severely impact bear populations in the near future, according to the listing petition filed by the advocacy group the Center for Biological Diversity.

In the scientific reports filed with the FWS, the climate models predict a loss of more than 40 percent of prime spring and summer polar bear habitat by 2050, based on current rates of greenhouse gas production. Polar bear biologists believe these losses will lead to the demise of more than 60 percent of the current population within the next 50 years, with near-extinction likely by the end of the century.

The application of climate science to this decision is a win-win situation for both scientists and policymakers, with the need for information driving advances in basic scientific knowledge and improved policy, DeWeaver says. "It sets a precedent that yes, you can use models [that include] uncertainty - and that's good," he says.

Source: University of Wisconsin-Madison

Explore further: Historic climate data provided by Mediterranean seabed sediments

add to favorites email to friend print save as pdf

Related Stories

Extreme science in the Arctic

Feb 25, 2015

A research team from Northwestern University was dropped by helicopter in the desolate wilderness of Greenland with four weeks of provisions and the goal of collecting ancient specimens preserved in Arctic lakebeds.

A song of fire and ice in the ocean

Feb 10, 2015

Cyclic changes in the tilt of the Earth's axis and the eccentricity of its orbit have left their mark on hills deep under the ocean, a study published in Science has found.

Recommended for you

Lightning plus volcanic ash make glass

Mar 03, 2015

In their open-access paper for Geology, Kimberly Genareau and colleagues propose, for the first time, a mechanism for the generation of glass spherules in geologic deposits through the occurrence of volcan ...

A new level of earthquake understanding

Mar 03, 2015

As everyone who lives in the San Francisco Bay Area knows, the Earth moves under our feet. But what about the stresses that cause earthquakes? How much is known about them? Until now, our understanding of ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.