05:54 PM PDT on Friday, June 23, 2006

By GLENN FARLEY / KING 5 News

Global warming is hot news this week after the National Academy of Sciences said the Earth hasn't been this warm in 400 years.

But University of Washington scientists are working with NASA to study a possible missing link in the global warming debate – the effect of particles floating in the air we breathe.

When we hear the word "aerosol," we usually think of the familiar spray can. But scientists are focusing on something bigger: "aerosols" in the atmosphere – tiny solid and liquid particles coming from many different sources such as industrial pollution, burning of forests and other biological material, and the effects of dust storms.

"They can reflect sunlight or absorb sunlight, and they can change the properties of clouds," said Tad Anderson, U.W. Atmospheric Scientist.

Anderson is one of two U.W. scientists who are advisors to a NASA satellite program called Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO).

CALIPSO uses light as a form of radar to measure the altitude and density of these pollutants in the atmosphere. The project is particularly interested in the interaction between pollutants and clouds. For example, do pollutants make more rain, or less?

"So down here is what I am presuming is a plume of pollution in the Bay of Bengal," said Anderson pointing at a map. "And embedded in that plume of pollution are these white spots, which are actually small cumulus clouds."

But how much stuff is up there even on days when there are few clouds or no clouds at all?

One satellite image shows dust clouds coming from China. But these "aerosols" have different effects on global warming. Volcanic ash reflects sunlight, and scientists say enough of it can lower temperatures.

But soot from fires and industry can absorb the sun's heat, worsening global warming.

"This is an extremely complex issue. Because the particles we're looking at only remain in the atmosphere for a few days," said Anderson.

The real results from CALIPSO may not be known for five to ten years.

CALIPSO actually follows the same orbit as five other satellites that photograph and measure other things in the atmosphere. The data sent so far is preliminary.