Water vapor's effects on atmosphere are debated | McClatchy Washington Bureau

WASHINGTON — Ron Ace's idea to cool the planet by evaporating water could provoke controversy because it collides head-on with a concern of environmental scientists: that water vapor is a potent greenhouse gas.

A recent Texas A&M University study, based on satellite data from the National Aeronautics and Space Administration, warned that if water vapor levels in the atmosphere continue to rise, it "could guarantee" an increase of several degrees Celsius in the Earth's temperatures over the next century.

These scientists warned of potential "positive feedback," in which water vapor traps heat near the surface, the warmer temperatures cause increasing ocean surface water to evaporate, producing even more water vapor, further heightening the trapping effect and beginning the cycle anew.

Kenneth Caldeira, a climate scientist for the Carnegie Institution's Department of Global Ecology at Stanford University whose computer simulation of Ace's invention suggests it would significantly cool the planet, said that scientists are still trying to sort out the complicated role of water vapor.

Among its mixed effects:

It absorbs latent heat near the earth's surface and transports it to higher altitudes, for a cooling effect.

When it condenses at higher altitudes, it releases the latent heat, which then can radiate into space, producing more cooling.

It's a greenhouse gas, trapping heat and causing warming.

It can form low clouds that reflect solar energy, a cooling effect.

It can form more high clouds, which block some sunlight but mostly prevent the release of infrared radiation from below, another warming effect.

Robert Park, a retired University of Maryland physics professor, said scientists are right to worry that water vapor and other greenhouse gases could lead to thermal runaway — a cycle where two or more factors feed off another to propel temperatures higher — but that no one has proved that it's occurring because the atmosphere is so complex.

"This is what makes climate such a horrendously difficult thing to calculate ... by far the most difficult calculation that man has ever attempted," Park said.

Ace hopes that his global cooling invention will help settle the matter.

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The Carnegie Institution's Department of Global Ecology

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