Cloud seeding involves releasing silver iodide, a naturally occurring compound, into storm clouds.
Cloud seeding involves releasing silver iodide, a naturally occurring compound, into storm clouds. (Photo: Mike Cavaroc/TandemStock)

Scientists Are Controlling the Weather

Ten or so percent of it, anyway

Cloud seeding involves releasing silver iodide, a naturally occurring compound, into storm clouds.

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Frank McDonough, a life-long snowboarder and atmospheric scientist, has five generators strategically situated along the Sierra crest. Metal and boxy with little chimneys, they look like meat smokers at the top of the world. If they do their job, they’ll help bring snow back to California during its historic drought. 

“We’re being funded to try to put a little extra water in the Truckee River,” says McDonough, a research meteorologist with the Desert Research Institute in Reno. With the flip of a switch down the mountain at DRI headquarters, the generators come to life and start belching white smoke into the air. “We’re trying to make extra snow pack in the Tahoe Basin,” McDonough says, “so that water will end up coming down through this area to be available for recreation and human uses.”

McDonough is just the latest in the long line of humans who have tried to manipulate the weather to improve the environment. But the difference between the work done in the Sierras this winter and, say, rain dancing, is that McDonough and the DRI have seen results: using modern “cloud seeding” technology—which involves releasing silver iodide, a naturally occurring compound, into storm clouds—the team can compel storms to dump anywhere from five to 15 percent more snow. In the Sierras, that translates to more water in the summer and more powder at Alpine Meadows and Squaw Valley in the winter.

This is a big deal. For the last 60 years, onlookers have snickered at weather modification programs in the U.S. while conspiracy theorists have worked themselves into fits over the what weather scientists are really doing. (Try setting up a Google Alert for weather modification news: there are an impressive number of forums dedicated to discussing the belief that the government is spraying chemicals from airplanes, resulting in “chemtrails” in the atmosphere.) But, after years of doubt, studies are showing that cloud seeding does indeed work. A seminal ten-year study in Wyoming, published last year, looked at regions where cloud seeding was deployed versus nearby areas where storms were left au natural. The results: up to 15 percent more snow in the seeded areas. (The results shouldn’t be a surprise to ski resorts—Colorado’s Breckenridge and Winter Park already help fund regional regional cloud seeding efforts, and Vail has been working on seeding since the 1970s.)

The drive to re-engineer our planet—to make it work for us or undo the damage we’ve caused—is a tempting, contentious prospect. Although it’s been worrying scientists for a generation now, modern technology allows us to geo-engineer different aspects of the environment—from dispersing iron into the ocean to boost plankton populations to capturing carbon from the air with huge towers and building an artificial mountain in Dubai to promote rain.

But in many ways, cloud seeding is the original geo-engineering. The technique was discovered by Bernard Vonnegut (brother of author Kurt) at the General Electric Research Lab 70 years ago. In the 1940s, researchers in their lab, in Schenectady, New York, were busy creating clouds inside a sealed atmospheric laboratory, trying induce them to drop rain. The team knew that dry ice dropped into clouds below-freezing temperatures led to the formation of thousands of ice crystals. Vonnegut, an esteemed atmospheric scientist, discovered that the compound silver iodide, normally found in trace amounts in minerals, worked even better and that when added to freezing clouds, the gray dust would lead to increased snowfall. A decade later, Vonnegut’s realization led to a cottage industry that still exists today, populated by cloud-seeding companies that contract with local governments to fly planes loaded with silver iodide into storm clouds and ground-based projects like the DRI's, which burns silver iodide in its generators atop the Sierras.

But, to be fair to the conspiracy theorists of the world, weather modification hasn’t only been used add water to irrigation ditches. In the ‘60s and ‘70s, the U.S. government spent over $20 million on a classified program called Operation Popeye aimed at modifying the weather above Vietnam. The goal, declassified documents show, was increased flooding along the Ho Chi Minh Trail to disrupt North Vietnamese supply lines. To this day, weather modification inspires such dystopian dread that Pacific Gas and Electric, a large utility in northern California that operates ground-based cloud seeding generators in the Sierra foothills to both increase hydroelectric power and benefit a local irrigation district, has a 78-page document dedicated to helping answer community questions on the project. One constant concern: that seeding clouds in the mountains “robs” the foothills and valleys of water—something Joe Busto of the Colorado Water Conservation Board flatly denies. “It's folklore,” Busto says in an email. “Several studies of the impact of cloud seeding downwind of the intended target areas have indicated that the precipitation is typically increased not decreased.”

In spite of the Orwellian overtones, the last five years have been booster seasons for the weather modifiers as widespread drought convinced municipalities to pay for any extra water they could get. California has at least a dozen ongoing cloud seeding programs, from big players the city of Los Angeles to small county water department in places like Santa Barbara County. According to PG&E, cloud seeding is taking place in 11 states across the west and Canada; in Colorado, at least two projects look to dump more snow on ski resorts. According to a 2013 report from the California Department of Water Resources, “precipitation enhancement” technologies added about 400,000 acre feet of water—enough to serve 600,000-1,000,000 houses—to the state’s watery coffers that year. In total, the efforts upped the state’s runoff by about 4 percent. 

For their project above Lake Tahoe, the Desert Research Institute estimates they’ve added between 15,000 and 17,000 acre feet of water to the snowpack—enough water for up to 45,000 houses in the region. The Truckee Meadows Water Authority, the local water district, pays DRI about $200,000 a year for the work and John Enloe, director of Natural Resources Planning and Management for water authority, says the project is definitely worth the money. “In years like 2015, every bit of precipitation we could get was important,” Enloe says. 

An extra five-to-eight percent in the reservoir is handy these days, but what do the Truckee Meadow Water Authority customers think? “I would say most are probably not aware we even do it,” Enloe says.  

Lead Photo: Mike Cavaroc/TandemStock