According to a study published this week online by the National Academies of Science, extreme weather events such as floods and droughts are likely to increase in frequency and severity over the next century in the United States. The forecast suggests these events could be large enough to disrupt the country's economy and infrastructure.

The climate model run on computers at Purdue University analyzed weather patterns for different regions across the country. The projections are not about specific events. But the study's author -- Purdue assistant professor of earth and atmospheric science Noah Diffenbaugh, says the projections do create a remarkably detailed picture of the kind of weather Americans can expect in the years ahead. "The desert southwest shows the largest increases by the end of the 21st century," he says. "In those areas we are looking at what is now the hottest 2-2 ½ weeks of the year to last for up to 3 months."

The model also forecasts warmer winter days, says Purdue's Noah Diffenbaugh. "If you imagine the coldest 2-2 ½ weeks of the year in the northeast -- the temperatures that are reached at present during the coldest weeks of the year are reached very rarely by the end of the 21st century," he says. "In fact the coldest temperatures that are reached at the end of the 21st century will be up to 10 C warmer than they are now."

The climate model analyzed hundreds of dynamic environmental factors from ocean currents, cloud formations, and vegetation cover to atmospheric heat-trapping greenhouse gases.

Researchers first did a test run of the climate model, looking back in time to 1961-1985. The results fairly accurately matched what actually happened during those years.

Then the model worked non-stop for five months to chart the future trends. Noah Diffenbaugh says improvements over prior climate models allowed the team to look at smaller plots of land at higher resolution than ever before. "The state of the science was 50 kilometer resolution, and what we have done is that same special extent - the full contiguous United States - but we've don't it at 25 kilometer resolution," he says. "So, we have greater spatial detail and we have more reliable statistics."

The model assumes that heat trapping carbon dioxide will double over the century if current trends continue, a scenario also described by the Intergovernmental Panel on Climate Change, a group charged by the United Nations to assess the impacts of global warming.

Noah Diffenbaugh says that could mean major disruptions in everything from water and energy supply to public health threats like West Nile virus. "West Nile virus is limited in the winter by extreme cold temperatures. So (warming temperatures) could be a release of that cold limitation," he says. "But at the same time the vectors that spread West Nile are also sensitive to extreme precipitation and to extreme heat. So we don't know how those three factors will interact."

Mr. Diffenbaugh says while the climate model is not perfect, it is a vehicle to begin discussion about the future consequences of climate change. He says the research tool is being used to study many regions of the world and for the first time researchers include a growing number of scientists from developing countries.