The report, "U.S. Market Consequences of Global Climate Change," released last week, found global warming "has the potential to impose considerable costs or produce temporary benefits for the U.S. economy over the 21st century, depending on the extent to which pessimistic or optimistic outcomes prevail."

The decidedly equivocal report was written by Dale Jorgenson, a Harvard University economist, and three other authors. Its climate change projections incorporated the conclusions of the Bush administration's Intergovernmental Panel on Climate Change, which in 2001 predicted that average global temperatures could rise from 2.5 degrees Fahrenheit to 10.4 degrees F (1.4 degrees Celsius to 5.8 degrees C) during the 21st century, with average U.S. temperatures rising by as much as 30 percent.

The Pew team looked at three climate-change scenarios -- low, central, high -- and combined them with two sets of economic projections -- pessimistic and optimistic. The result was a set of outcomes to satisfy most every expectation.

Take the combo of low climate change and pessimistic economic outlook. The report's authors predicted the U.S. gross domestic product would be 0.6 percent lower in 2100 than the baseline case involving no climate change. Under the high climate change-pessimistic economy scenario, however, GDP would be 1.9 percent lower.

Whatever the scenario, however, the researchers found climate change would affect U.S. agriculture the most. Consequently, rainfall levels associated with changing climate become critical. When the researchers examined a "higher and drier" climate scenario, real GDP was reduced by 3 percent in 2100 relative to the 2000 baseline.

The news is not all bad, however. Under some conditions, a warming climate actually could be good for the U.S. economy.

"Under optimistic conditions, real U.S. GDP by 2100 is 0.7 to 1.0 percent higher than baseline conditions across the low, central and high climate scenarios," the report said, although it added "these benefits eventually diminish over time."

Margo Thorning, chief economist for the American Council for Capital Formation in Washington, D.C., remained skeptical.

"I did not find a whole lot useful in this report," Thorning told United Press International. "It is based on erroneous assumptions anyway. I think it's kind of a tempest in a teapot. It doesn't contribute much new to the debate."

Thorning's problem? "First, there is a lot of doubt about the accuracy of the IPCC scenarios themselves (and) to base the report on that is a little shaky," she said.

Thorning cited the work of British economist David Henderson, who has done a series of papers critiquing the IPCC assertions. Those papers "charge that the IPCC has used an unrealistically high growth rate, which means more energy use, which means more (carbon dioxide) in the atmosphere," she said.

"I fault the Pew report for not taking that into consideration," Thorning commented. "The data have been out for two years (and) should have been cited as a reason not to place a whole lot of faith in the IPCC projections. I question the foundation the study is based on -- the accuracy of the simulation."

One apparent constant in the Pew findings is that "for the economy, wetter is better. All else being equal, more precipitation is better for agriculture -- and hence better for the economy -- than less precipitation."

In addition, the report found only small changes in human mortality and illness -- although both are important in assessing the economic impacts. If people die earlier, or get sick more often, it can affect productivity and the consumption of goods.

"In this analysis, mortality and morbidity effects alone account for 13 to 16 percent of the aggregate predicted effect of climate change on the economic welfare of U.S. households," the report said.

The Pew researchers also acknowledged some large holes in the assessment.

"In terms of drawing policy conclusions from these results," they wrote, "the underlying analysis does not address a host of potential non-market impacts associated with climate change. These include species distribution, reductions in biodiversity, losses of ecosystems goods and services and changes in human and natural impacts."

Thorning added some others: "There is no technology out there now to allow us to quickly move away from using fossil fuels without just shutting the economy down. Even if climate change is real and serious, we don't have the technology now to change without enormous economic cost. We need a long-term solution. I didn't see much of that in this paper."

Michael Glantz, a senior scientist at the National Center for Atmospheric Research in Boulder said among climate scientists there seems to be "a big search for 'dread factors'" -- things that can focus the issue of climate change down to the personal level.

For example, Glantz said, people began to take notice of the polar ozone holes when they began relating them to the likelihood of increased cancers.

"With global warming," Glantz told UPI, "they haven't figured out how to bring it to the individual, how to make it personal. You have believers and nonbelievers. The believers recycle, the nonbelievers buy SUVs. The people in the middle are confused."

Economics, Glantz said, is not going to produce that "dread factor."

"It is not the money that is going to do this thing in," he said. "That's a smokescreen."

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