Nay-sayers play down greenhouse threat.

With the United Nation's big environmental meeting coming up next month, and with most other industrialized nations pushing for a strong treaty to limit global warming, President Bush may feel legt out inthe cold. Unlike the leaders of other wealthy nations, Bush has steadfastly opposed any strict controls on carbon dioxide emissions, prompting environmental groups to charge that he has ignored the climate change threat. But a conservative think tank issued a report last week that supports a wait-and-see approach.

Previous reports on global warming from the George C. Marshall Institute in Washington, D.C., have come under fire from climate researchers, who charge that the documents -- which are not peer reviewed -- contain errors and unsupported claims. Because the instutute's conclusions have reportedly reached the administration's ears in the past, its current science update will likely generate renewed controversy.

The report emphasizes a well-known point among climate experts: The world has not warmed as quickly as computer climate models predicted it would. The report also notes that satellite data going back 13 years show a warming rate of only 0.06[degrees]C per decade -- one-fifth of the rate predicted by most climate models, according to the Marshall Institute. Using the satellite data to extrapolate ahead, the report's authors suggest that warming in the next century will be minimal, only about one-fifth of the "best guess" estimate by the Intergovernmental Panel on Climate Change (IPPC), which produced an influential report in 1990 and an update this year. The Marshall Institute report concludes that "temperature increases in the next century, assuming a greenhouse gas increase equivalent to doubling of carbone dioxide in the atmosphere, will almost certainly be less than 1[degrees]C and may be less than 0.5[degrees]C."

Seeing no evidence as yet that a greenhouse warming presents a problem, the report recommends waiting at least five years before making any major policy decisions regarding carbon dioxide. During that time, new research should improve understanding of the climate and the accuracy of models that forecast climated change, suggest the authors.

John R. Christy of the University of Alabama at Huntsville, an atmospheric scientist who analyzed the satellite data quoted in the report, says he certainly agrees with the conclusion that Earth has no warmed as quickly as models predicted. But he cautions against using the relatively short, 13-year satellite record to extrapolate how the climate might respond in the next century. "The uncertainties are tremendous in this, business, and extrapolation is one of the least capable means of prediction, I would think," Christ says.

Climate researcher Tom Wigley of the University of East Anglia in Norwich, England, criticizes many of the Marshall Institute's conclusions and methods. "They're certainly trying to make an impact an unconventional way, where they are not ensuring scientific credibility first. That's not a good thing to do. It's in stark contrast with what the IPCC is trying to do--that is, to go through a process where a lot of scientists are involved in producing a synthesis and then a lot of other scientists are involved in peer reviewing it," says Wigley, who coauthored one of the chapters in the IPCC update.

The Marshall Institute report was written by Frederick Seitz, past president of the National Academy of Sciences; Robert Jastrow, past director of NASA's Goddard Institute for Space Studies; and William A. Nierenberg, past director of the Scripps Institution of Oceanography. To produce report, the authors consulted some 50 researchers, estimate Nierenberg.

In a interview, Nierenberg said that greenhouse gas emissions could cause regional climate changes even if average world temperatures rise only slughtly. The present report does not mention that possibility, although earlier ones did.