Global Warming Supercharged by Water Vapor?

Arianne Appel
for National Geographic News
November 10, 2005

Related Photos: A Warming World >>

The latest villain on global warming's most-wanted list is all wet—and a little surprising. Water vapor, experts say, is the culprit behind Europe's rapidly rising temperatures.

Evaporated H2O is a known greenhouse gas—a gas that absorbs and re-emits infrared radiation in Earth's atmosphere, thereby increasing temperatures (see our global warming fast facts).

But only now has a study uncovered evidence that water vapor is a major public enemy in Europe.

According to a team of Swiss scientists, heat from other greenhouse gases is causing more water to evaporate, releasing the vapor into the atmosphere above Europe. That vapor in turn, adds to the greenhouse effect, further warming the region.

Temperatures throughout the Northern Hemisphere have been increasing in recent years. But Europe has been heating up especially quickly, leading to studies, theories, and debate as to why.

In central Europe—Germany, Austria, Poland, Czech Republic, Slovakia, Hungary, Switzerland, and Slovenia—temperatures have risen three times faster than the average for the hemisphere has.

Some scientists have argued that Europe's rising temperatures are due to normal weather-circulation patterns. But the new study's results suggest that large-scale weather patterns are only a minor influence on the temperature increase, said lead researcher Rolf Philipona of the World Radiation Center in Davos Dorf, Switzerland.

"It is an experiment that clearly shows which factors are driving the higher temperatures. It is not the clouds, not the sun, not the aerosols. It is the increased greenhouse gases and the strong water vapor impact," Philipona said.

"We believe strongly that we are observing increased greenhouse effect," said Philipona, whose results were published this week in the journal Geophysical Research Letters.

An increase of greenhouse gases in the atmosphere, from car exhaust, industrial emissions, and other sources, has been observed throughout the planet since about 1960, Philipona said.

Vicious Cycle?

Continued on Next Page >>




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