FAITH LAPIDUS: In the study, Mr. Dai examined rising temperatures linked to climate change. He says the higher temperatures probably will create increasingly dry conditions. He says these conditions will be seen across much of the world in the next thirty years.

The scientist also considered the possibility that drought could be much worse by the end of the century. At that time, he says, lack of moisture in many places could be as bad as or worse than any in modern time.

He made the predictions after looking at earlier studies and research. His study used modern proposals of possible conditions. It also employed twenty-two computer climate models and a list of drought conditions. The International Panel on Climate Change used twenty-two models in its two-thousand-seven report.

BOB DOUGHTY: Mr. Dai said he based the new predictions on the best current projections of carbon dioxide and other gases linked to climate change. The projections are estimates of future amounts of such greenhouse gases. He says many conditions will decide what actually happens.

The conditions include natural climate cycles and the amount of greenhouse gases that will be released into the air. Two good examples of such cycles are El Nino and La Nina. They are periodic events that change moisture levels in the atmosphere.

FAITH LAPIDUS: The study identified areas threatened with major drying in the future. They include much of Central and South America. Southeast Asia, large parts of southwest Asia, and most of Africa and Australia also will be affected. The research shows that drying in areas along the Mediterranean Sea could also become intense.