A climatologist with the University of Wisconsin-Madison believes a lack of volcanic activity and not the greenhouse effect may be behind the drought that has scorched the Farm Belt.

Volcanoes send aerosols - fine particles and droplets of sulfuric acid - into the upper atmosphere and they prevent a small but significant amount of sunlight from reaching Earth's surface, said Reid Bryson, an emeritus professor of environmental studies and meteorology.Bryson says the lack of aerosols may be the cause of the drought because the additional sunlight may be altering air circulation patterns. Also, the weather pattern this summer is similar to the one that created the "Dust Bowl" of the 1930s, he said.

"If we want to find a cause of this drought, we should find a cause common to both of them," Bryson said. "About the only common denominator I can see is that both droughts have occurred during periods of very low volcanic activity."

Bryson disagrees with those who say the greenhouse effect is causing the dry conditions. The greenhouse effect is the theory that a buildup of carbon dioxide in the atmosphere will cause a global warming trend.

Many scientists have said the greenhouse effect is already having a measurable impact and that drought and heat conditions may continue for many years.

"I'm a little disturbed when I see well-known scientists making statements like that because generally speaking they're talking about theory," Bryson said. "Up until this year, most of what you heard about the greenhouse effect was that in 50 years the earth will be `x'-degrees warmer.

"That's a 50-year forecast, isn't it? Have their theoretical models ever successfully made 50-year forecasts? Or 10-year forecasts? Or even five-month forecasts? They haven't, so I'm very skeptical that they're ready to use the theory to make claims about what's going to happen in the future."

Meanwhile, Fourth of July weekend festivities were under way across the nation, but the clear skies that favored picnics, barbecues and beach parties put many Midwestern farmers on the brink of catastrophe.

Scattered rain showers were reported in parts of the western Corn Belt and in the Southeast, but drought persisted across the heart of the nation's breadbasket.