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Weather Will Get More Extreme, Study Predicts

by: MSNBC    14 November 2006

WASHINGTON - The world — especially the Western United States, the Mediterranean region and Brazil — will likely 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.

Titled "Going to the Extremes," the study 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 lead author Claudia Tebaldi, a scientist at the National Center for Atmospheric Research, a federally funded academic group.

"It's the extremes, not the averages, that cause the most damage to society and to many ecosystems," she noted. "We now have the first model-based consensus on how the risk of dangerous heat waves, intense rains, and other kinds of extreme weather will change in the next century."

Hot spots and rain drops
Tebaldi pointed to the U.S. West, Mediterranean nations and Brazil as "hot spots" that will get extremes at their worst, according to the computer models. The modeling assumed a continued increase in greenhouse gases, which many scientists tie to global warming.

And 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 will be more rain likely in the tropical Pacific Ocean, and that will change the air flow for certain areas, much like El Nino weather oscillations now do, said co-author Gerald Meehl, a top computer modeler at the research center. Those changes will affect the U.S. West, Australia and Brazil, even though El Nino is 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."

Models agree on four areas
The researchers took 10 international agreed-upon indices that measure climate extremes — five that deal with temperature and five with precipitation — and ran computer models for the world through the year 2099.

The models agreed that by 2080-2099:
# The number of extremely warm nights and the length of heat waves will increase significantly over nearly all land areas across the globe.
# Most areas above 40 degrees north will see a "significant" jump in the number of days with heavy rain, defined as 0.40 inches or more. This includes the northern tier of U.S. states, Canada, and most of Europe.
# Dry spells could lengthen significantly across the U.S. West, southern Europe, eastern Brazil, and several other areas.
# The average growing season could increase significantly across most of North America and Eurasia.

Longer heat waves, warm nights
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."

The measurement of warm nights saw the biggest forecast changes in the study, which was described as a preview of a major international multiyear report on climate change that comes out early next year.

Every part of the globe is predicted to experience a tremendous increase in the number of nights during which the low temperature is extremely high. Those warm night temperatures that now should happen only once every decade by 2099 will likely occur at least every other year if not more frequently, Tebaldi said.

Warm nights are crucial because Chicago's 1995 heat wave demonstrated that after three straight hot nights, people start dying, Meehl said.

Adaptation strategy: air conditioning
However, heat wave deaths are decreasing in the United States because society has learned to adapt better by using air conditioning, noted University of Alabama at Huntsville atmospheric sciences professor John Christy. He is one of a minority of climate scientists who downplay the seriousness of global warming.

Similarly, the days when the temperature drops below freezing will plummet worldwide. That is not necessarily a good thing, because fewer frost days will likely bring dramatic change in wildlife, especially bug infestation, Tebaldi said.

"It's a disruption of the equilibrium that's been going for many centuries," Tebaldi said.

Christy, for his part, noted that a lengthier growing season in general is good.

"This notion of the greening of the planet ... generally is a positive benefit," Christy said.

Christy, who did not participate in the study but acknowledges that global warming is real and man-made, said an increase in nighttime low temperatures makes much more sense than the rain-and-drought forecasts of the paper.

One of the larger changes in precipitation predicted is in the intensity of rain and snowfall. That means, Tebaldi said, that "when it rains, it rains more" even if it doesn't rain as often.

The new study jibes with the National Climatic Data Center's tracking of extreme events in the United States, said David Easterling, chief of the center's scientific services.

Easterling's group has created a massive climate extreme index that measures the weather in America. Last year, the United States experienced the second most extreme year in 95 years; the worst year was in 1998.

Texas Tech University and Australia's Bureau of Meteorology Research Center also contributed to the new study.