A Sizzling Scientific Debate

By Charles P. Alexander

Environmentalists staged Earth Day to dramatize a simple message: The planet is threatened by a host of man-made ills, from toxic landfills to ozone depletion. But at least one part of the message -- the theory that the buildup of carbon dioxide and other greenhouse gases in the atmosphere will cause global warming -- has come under considerable attack. A small but vocal group of scientists contends that the case for warming is sketchy and based on inadequate computer models.

Forces within the White House, led by chief of staff John Sununu, have seized upon the debate and persuaded President Bush to take a cautious approach to the problem. While not dismissing the greenhouse threat, the President has emphasized the need for more scientific research to help determine the proper policy response. This go-slow approach has irritated government officials in several other countries, especially in Western Europe. As the Europeans point out, many scientists still fear that global warming could take place unless strong action is taken to prevent it.

Last week representatives from 18 nations gathered in Washington for a global-warming conference set up by the White House. The Administration had hoped to get a debate going on the uncertainties of the greenhouse effect. Instead, most of the delegates appeared to agree that the global-warming threat is real and potentially serious. In the face of this strong sentiment, President Bush denied that he was taking global warming too lightly. The President reconfirmed a U.S. pledge to cooperate in a United Nations effort to forge an international agreement on dealing with climate change.

The greenhouse dilemma illustrates the difficulty of setting policy based on uncertain projections of the future. Scientists generally agree that an unchecked accumulation of greenhouse gases will eventually lead to warming, but no one knows when it will start, how much will take place or how rapidly it will occur. The most widely accepted estimate is a rise in the earth's average temperature of 1.5 degrees C to 4.5 degrees C (3 degrees F to 8 degrees F) as early as 2050. An increase in the upper part of that range could produce disastrous climatic effects, including rising sea levels and severe droughts in some areas.

But the computer models that make the projections may not accurately reflect such factors as the role of clouds and the heat-absorbing capacity of the oceans. As these phenomena are better understood, warming projections will undoubtedly be revised in one direction or another.

Evidence that greenhouse warming has already started is at best tenuous. Even though some scientists believe the concentration of CO2 in the air has shot up 25% since the early 1800s, the average global temperature has risen by no more than 0.5 degrees C (1.1 degrees F), and even that measurement is suspect. Moreover, the rise has been uneven. From about 1940 to 1970, a cooling period inspired some forecasters to predict a return of the ice ages.

Despite the uncertainties, there is a broad consensus that nations should slow down the rate at which they are changing the atmosphere. Said West German Environment Minister Klaus Topfer at the Washington conference: "Worldwide action against the climatic threat is urgently required, even if the complicated scientific interrelationships of climatic change have not been fully understood."

To his credit, Bush has already taken several steps that will help combat global warming. Among other things, the White House has 1) earmarked $1 billion for global climate research next year; 2) committed the U.S. to phasing out production of chlorofluorocarbons, potent greenhouse gases, by the year 2000; and 3) vowed to plant a billion trees, which would absorb CO2 from the air. But Administration officials admit that Bush advanced most of the measures for reasons other than reducing global warming. And environmentalists argue that the Government should do much more to discourage the burning of fossil fuels. Among the possibilities: raise the gasoline tax or use financial incentives to encourage people to buy smaller, more efficient cars.

The White House, however, worries about the economic consequences of forcing sudden, drastic curbs in fossil-fuel use. From the Administration's point of view, draconian action seems highly debatable so long as the scientific evidence for the greenhouse effect is sketchy. "We are not at the point where we can bet the economy," says a Sununu aide.

That may be so. The Administration is wise to consider the possible economic damage before committing itself to a major reduction in carbon dioxide < emissions. But surely the Government can safely do much more than it has already done to spur energy conservation. It is possible to buy a great deal of insurance against global warming without sabotaging the economy.

CHART: NOT AVAILABLE

CREDIT: TIME Chart by Steve Hart

CAPTION: THE THEORY . . .

. . . SOME UNCERTAINTIES

With reporting by Michael Duffy and Glenn Garelik/Washington