September 13, 2004
Los Angeles Times

STEAMBOAT SPRINGS, Colo. -- Every snowflake tells a story to the scientists who sift for clues among the ice crystals.

And the one being told by the flakes that fall each winter near the summit of Mt. Werner here sounds ominous for the future of water in the drought-parched West.

Along the western slope of the Rockies, in a laboratory 10,500 feet above sea level, a team of atmospheric researchers has spent the past decade deciphering a deeper meaning from the blizzards that blanket the Steamboat ski resort in its famously pillowy "champagne powder."

They have skimmed snow clouds with screens to size up their icy content. They have zapped falling flakes with lasers to record digital images of the hexagonal shapes. They have captured crystals in a contraption that melts them with a heat gun and measures the mass of the water droplets.

And they have come to a provocative conclusion: Air pollution is reducing mountain snowfall, the wellspring of drinking water for Los Angeles, Las Vegas and much of the urban West.

Storm clouds packed with microscopic particles from diesel trucks, coal-burning power plants and cow manure produce far less snow than clouds comparatively free of pollution, the scientists from the University of Nevada's Desert Research Institute have determined.

In a study of two otherwise identical storms published earlier this year--one dirty and one clean--they found that the system sullied by specks of air pollution snowed 50 percent less. And the snow that did fall contained 25 percent less water.

"The difference can be as much as 50 percent in the mass of a snowflake," said Douglas Lowenthal, who conducted the study with colleague Randy Borys. "When you aggregate all those snowflakes, you can have a pretty significant effect."

All clouds are full of aerosols, or tiny particles suspended in the air. Most of the little bits are tossed into the air naturally, kicked up by sea spray, dust storms, wildfires and volcanoes.

But human activities are thickening the particle stew, particularly in the air above industrialized nations.

Ten percent of the particles now in the air came from man-made causes such as the burning of fossil fuels, scientists estimate. The majority of the particles are so small that they are not restricted by any environmental regulations.

Numerous scientific researchers are showing that pollution particles in clouds can reduce precipitation. But the Colorado snowflake studies provide some of the most detailed evidence yet that it is happening.

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