High heat: The wave of the future?

Updated 8/3/2006 9:04 AM ET

By Dan Vergano, USA TODAY

A preview of the future — much hotter decades on a warming planet — has been delivered today by the continent-spanning heat wave, climate experts say.

"Heat wave projections all agree. They are going to intensify in length and frequency" in this century, says climate scientist Claudia Tebaldi of the National Center for Atmospheric Research in Boulder, Colo.

Global warming is projected to raise average temperatures worldwide about 3 to 9 degrees in this century, according to a U.N. climate panel. Warmer temperatures load the dice in favor of extreme weather such as heat waves, says climate modeler Gavin Schmidt of the NASA Goddard Institute for Space Studies in New York.

According to the federal National Oceanic and Atmospheric Administration (NOAA), an unusually strong ridge of high pressure lasting for weeks across most Central and Eastern states caused the heat wave now gripping the country. NOAA scientists have generally been more cautious than climate modelers about linking global warming to extreme weather such as heat waves.

But climate models generally agree that looking ahead to 2100, heat waves will become more frequent, Tebaldi says. The models very closely reproduce the high temperatures and air pressures that spawn heat waves in real-life weather, she says. In the future, global warming may create stronger and larger high-pressure "domes" of air that will block cool air from entering the regions they cover, Tebaldi says.

"We can't just say global warming caused this heat wave, but we can say that what we are seeing is very consistent with what you would expect to see in a warmer world," says climate expert Heidi Cullen of The Weather Channel.

Cullen and Tebaldi give these examples of current climate effects with global warming's fingerprints:

•The heat wave's continental breadth. Warnings have been set off from California to Boston.

•Simultaneous heat waves in Europe. England suffered its warmest July on record.

•Heat earlier this year that made the first six months of 2006 the warmest January-to-June stretch since at least 1895.

"If you don't like the current heat wave event, you're going to like it even less in the future," says climate scientist Bill Chameides of the conservation group Environmental Defense.

A study in Nature magazine suggested that global warming was a contributing factor in Europe's 2003 heat wave, which was blamed for 35,000 deaths. During the past century, global average temperatures have risen about 1 degree, largely because of human contributions to the "greenhouse" gases that capture heat in the atmosphere, according to a 2005 National Academy of Sciences report. Such contributions include the carbon dioxide emitted by burning coal, oil and other fossil fuels, the report said.

"Some people suggest a 1-degree increase isn't such a big deal, but here we can see what sort of heat extremes it can to lead to," Cullen says. "And it is devastating."

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