Arctic climate models playing key role in polar bear decision

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.

-- Jill Sakai, (608) 262-9772,