White Snow

     The whiter the snow the longer it stays around.  Just one more reason to be concerned with air pollution.

Fast-melting sooty snow may have impact on state’s water supply.  At YosemiteNational Park, researchers are sprinkling charcoal on the snow to see if they can speed up the opening of park roads in the springtime.  And several recent studies suggest so-called dirty snow also has implications for the state’s water supply.

The concern is this: Pollution from the Central Valley, Bay Area or Los Angeles blows up into the mountains, where tiny particles of soot come to rest on all that beautiful, white snow.

Did you know?  The average snow crystal contains thousands of particles, including soot and dust. The more soot and dust, the darker the crystal. And the darker the crystal, the faster it will melt when exposed to sunlight.

It might not be visible to the naked eye, but those particles decrease the snow’s albedo, or its ability to reflect sunlight. Darker snow absorbs more heat and melts faster, exposing bare ground, which also accelerates melting.  "It’s like placing tiny toaster ovens into the snowpack," Charlie Zender, a University of California, Irvine, associate professor of earth sciences, said in 2007 after concluding that one-third or more of Arctic warming can be attributed to sooty snow.

The most recent of the studies, released earlier this year by the U.S. Department of Energy’s Pacific Northwest National Laboratory, suggests changes in the brightness of the snow results in its melting two or three weeks earlier than pristine, white snow.

And that’s a problem for water managers, who depend on a slow and steady snow melt throughout the spring to store as much water as possible in California‘s reservoirs. Snow melt also is needed for hydroelectric energy and fish.  "I think this is a pretty significant issue over the Sierra Nevada range," Northwest lab atmospheric scientist Yun Qian said.

Other studies already have raised concerns about the Sierra snow melt diminishing earlier in the year because of climate change.

Invisible greenhouse gases may be a more significant factor than the dirty snow, Qian said. But another study, co-authored by the California Institute of Technology’s Jet Propulsion Laboratory, concluded that a decrease in local pollution could help alleviate the impact of climate change on snow melt patterns.

Almost everyone contributes to the problem. Soot comes from tailpipes, from factories or from power plants.  Scientists say the new research gives the public ways to fight climate change now by decreasing the amount of pollution they generate directly or indirectly, such as how much they drive or how much energy they use.

On Wednesday, snow surveyors will trek into the Sierra Nevada for the first time this winter to check on the snow pack. They will do so monthly until April to help water managers predict how much will be available for cities and farms.  Frank Gehrke, head of the snow survey team for the California Department of Water Resources, said his agency is also involved in the charcoal experiments at Yosemite.  "What we’re looking at is trying to quantify just how much does it take to have an appreciable effect," he said.

The good news, he said, is that soot is less likely to darken snow in portions of the Sierra that are heavily timbered.  Researchers say they still need to learn more about how much soot is actually deposited in the mountains, as well as whether other particles, such as dust or ash, can cause earlier snow melt.