2/23/00

Mark Shwartz, News Service (650) 725-0224
e-mail mshwartz@stanford.edu

Dawn Levy, News Service (650) 725-1944
e-mail dawnlevy@stanford.edu

Global warming: It's not an exact science, but it's science all the same

Few issues in science are as controversial as global warming.

The debate over climate change has become so contentious that many experts often refuse to make far-ranging predictions, choosing instead to report narrow findings based on a limited set of available data.

But climatologist Stephen H. Schneider says that speculation by scientists can be a good thing ­ especially when the future of the planet is at stake.

"The scientific community that studies the problem of global warming should try to answer the difficult questions," says Schneider, a professor of biological sciences with Stanford's Institute for International Studies.

The struggle, he adds, is "how to reconcile the public's need to have an honest but still subjective assessment, versus the scientist's penchant for not commenting until all of the data are in."

For the past five years, Schneider and Richard H. Moss of the Pacific Northwest National Laboratory have been working with the United Nations Intergovernmental Panel on Climate Change. The IPCC assesses the credibility of scientific research on global warming, and uses that information to advise world leaders and policymakers on options for adapting to climate change ­ such as preventing degradation of forests or reducing the consumption of gasoline and other fossil fuels.

Schneider and Moss recently prepared a series of recommendations for how IPCC members should deal with subjective uncertainties in the climate change debate. They presented their findings at the annual American Association for the Advancement of Science (AAAS) meeting on Feb. 21 in Washington, D.C.

The authors began by asking AAAS delegates the following questions: "How often has someone reporting on a difficult problem exclaimed, 'It's not an exact science, you know'?

"In fact, how many people really know that science is never 'exact' but rather an endless series of refinements?"

Schneider and Moss pointed out that, while scientists strive to be as objective as possible, "nearly all aspects of interesting global change projections (like the amount sea levels will rise and the potential effects this will have on human coastal settlements) involve subjective probabilities."

Many IPCC scientists are "simply uncomfortable with the notion that there was a subjective element to their analyses," but Schneider and Moss argued that, in the real world, there is a difference between traditional, objective science and the more subjective "science for policy."

"'Science for policy,'" they noted, "involves being responsive to policymakers' needs for expert judgment at a particular time, given the information then available.

"Political leaders want such state-of-the-art subjective assessments ­ just as they do for health, economic and military risks ­ even before enough experiments have been performed or data collected to 'objectively' verify possible hypotheses."

Schneider and Moss maintained that "political leaders are not in a position to judge the likelihood of a certain climate scenario any more than a patient is competent to judge which metal should be in the blade of the scalpel used by her or his surgeon."

"It is more rational for scientists debating the specifics of a topic in which they are acknowledged experts to provide their best judgments based on their assessment of the evidence than to have policymakers and other users who are less expert make their own determinations."

It is essential, said Schneider and Moss, that scientists be consistent and clear when advising policymakers on the merits of climate change research. In the past, IPCC experts have issued reports using a variety of vague expressions like "almost certain," "probable," "likely," "possible," "improbable" and "doubtful."

"These terms have not been carefully ­ or quantitatively ­ calibrated" and therefore have been subject to misinterpretation, observed Schneider and Moss.

They recommended that IPCC create a glossary of common terms to be used by all authors so that policymakers, the public and the news media will have a more precise understanding of the meaning of words such as "doubtful" or "unlikely."

The authors also stressed the importance of providing a clearly defined, quantitative scale so that probabilistic terms like "best estimate" would be consistently used in all IPCC reports.

"If we don't offer a carefully hedged but nonetheless expert judgment on global warming, then who's going to do it?" scheider asked. "Politicians? Special interests?"

-30-

By Mark Shwartz