Future Forecast: Extreme Weather

By Seth Borenstein
Associated Press
Saturday, October 21, 2006

The world -- especially the Western United States, the Mediterranean region and Brazil -- is likely to suffer more extended droughts, heavy rainfalls and longer heat waves over the next century because of global warming, a new study forecasts.

But the prediction of a future of nasty extreme weather also includes fewer freezes and a longer growing season.

In a preview of a major international multiyear report on climate change that comes out next year, a study from the National Center for Atmospheric Research details what nine of the world's top computer models predict for the lurching of climate at its most extreme.

"It's going to be a wild ride, especially for specific regions," said the study's lead author, Claudia Tebaldi, a scientist at the federally funded academic research center.

Tebaldi pointed to the Western United States, Mediterranean nations and Brazil as "hot spots" that will get extremes at their worst, according to the computer models.

Some places, such as the Pacific Northwest, are predicted to get a strange double whammy of longer dry spells punctuated by heavier rainfall.

As the world warms, there is likely to be more rain in the tropical Pacific Ocean, and that will change the airflow for certain areas, in much the same way that El Niño weather oscillations now do, said the study's co-author, Gerald Meehl, a top computer modeler at the research center. Those changes will affect the Western United States, Australia and Brazil, even though it's on South America's eastern coast.

For the Mediterranean, the issue has more to do with rainfall in the tropical Atlantic Ocean changing air currents, he said.

"Extreme events are the kinds of things that have the biggest impacts, not only on humans but on mammals and ecosystems," Meehl said. The study, to be published in the December issue of the peer-reviewed journal Climatic Change, "gives us stronger and more compelling evidence that these changes in extremes are more likely," he said.

The researchers took 10 international agreed-upon indexes that measure climate extremes -- five that deal with temperature and five with precipitation -- and ran computer models for the world through 2099. What Tebaldi called the scariest results had to do with heat waves and warm nights. Everything about heat waves -- their intensity, length and occurrence -- worsens.

"The changes are very significant there," Tebaldi said. "It's enough to say we're in for a bad future."

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