Dramatic changes in next 100 years.

• Position: Climate - Brief Article

The most comprehensive climate model to date of the continental U.S. predicts more extreme temperatures throughout the country and greater precipitation along the Gulf Coast, in the Pacific Northwest, and east of the Mississippi River.

The climate model, run on supercomputers at Purdue University, West Lafayette, Ind., takes into account a large number of factors that have been incorporated incompletely in past studies, such as the effects of snow reflecting solar energy back into space and of high mountain ranges blocking weather fronts from traveling across them, indicates Noah S. Diffenbaugh, the team's lead scientist.

A better understanding of these factors--coupled with a more powerful computer system on which to run the analysis--has allowed researchers to generate a far more coherent image of what weather can be expected for the next century. Those predictions paint a very different climate picture for most parts of the country.

"This is the most detailed projection of climate change that we have for the U.S.," says Diffenbaugh, an assistant professor of earth and atmospheric sciences and a member of the Purdue Climate Change Research Center. "And the changes our model predicts are large enough to substantially disrupt our economy and infrastructure."

Climate models are sophisticated computer codes that attempt to incorporate as many details about the complex workings of our environment as possible. Hundreds of dynamic processes, such as ocean currents, cloud formations, vegetation cover and, of particular import, the increase in atmospheric greenhouse gases, are programmed into the computers, which then attempt to discern the net effects on square-shaped plots of land that represent small pieces of the Earth's surface. The smaller these squares are, the better the resolution the model can provide.

"Just as a digital camera that creates images with more pixels can result in a better photograph, we want to make those squares as small as possible," Diffenbaugh explains. "We'd...