Aerosols of dust, pollution and bacteria swirling out of deserts in Africa and Asia are traveling thousands of miles in the Jet Stream to the Sierra Nevada Mountains where they affect the snowfall that provides a third of California’s water supply.

A study published last week in the online journal Science found that Saharan dust, which was known to blow across the Atlantic Ocean, also traveled eastward. Scientists at the University of California, San Diego (UCSD) and NOAA's Earth System Research Laboratory (ESRL) were looking to find out what is seeding the clouds that produces the Sierra snowpack, which has been reduced of late.

The study was part of a larger project called CalWater, which began in 2009 as a 3-year, $3 million inquiry. Lauren Morello at Climate Central describes its mission succinctly: “How do aerosols affect cloud formation and precipitation? Where are the aerosols that reach the Sierra Nevada coming from? And how will atmospheric rivers—weather systems that transport huge amounts of water across the Pacific into California—change as the climate warms?”

Part of the impetus for CalWater was a fear that air pollutants could negatively affect precipitation over the mountains. Instead, they found particulates had the opposite effect and are now being fancied as a potential counterweight to the almost certain negative effects of global warming.

Two Sierra storms in 2009 of relatively equal strength were found to have delivered vastly different amounts of snow to the mountains. Analysis of the snowpack found an abundance of dust from Asia. Two years later, samples collected in the atmosphere above the Sierras found more dust and particulate matter from Africa and Asia when more snow fell.

Although scientists sound confident that the dust is affecting the snowfall, their samples are limited in quantity and were taken during very short time periods. The next step is to quantify the scientific effect.

–Ken Broder

To Learn More:

Dusty Springs in Asia, Africa Can Increase Snow in Calif. (by Lauren Morello, Climate Central)

New Study Finds Dust/Biological Particles Traveling from Sahara and Asia Influence Precipitation on West Coast (Earth System Research Laboratory)

Saharan and Asian Dust, Biological Particles End Global Journey in California (University of California, San Diego News Office)

Dust from Africa Affects Snowfall in California (by Alicia Chang, Associated Press)

Sahara Desert Dust Affects California Water Supply, Study Finds (by Bettina Boxall, Los Angeles Times)