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Sunday, Jul 12, 2009
China is spending millions to modify the weather for the Olympics. As the U.S. knows, nature doesn't bend to human will.
By Suzanne Bopp
Read more: Environment, Olympics, China, Science, Environment & Science, Suzanne B. Bopp
Aug. 6, 2008 | This week, days before Friday's opening ceremony of the Beijing Olympics, cannons and rocket launchers by the thousands will be trained on the Chinese skies. In the cross hairs: the clouds.
This is latest of China's many efforts to control the weather. China is probably the world's largest practitioner of cloud seeding, spending about $90 million a year. Last April, it claimed a major weather victory after seeded clouds deposited a centimeter of snow on the Tibetan mountains. Now, eager to ensure rain comes before -- not during -- the Olympics, the Beijing Weather Modification Office plans to seed the clouds that float by beforehand, hoping to wash the pollution from the air and wring out any event-delaying precipitation.
But U.S. scientists are skeptical. "China is promising something they can't deliver," says Bruce Boe, director of meteorology for Weather Modification Inc., a Fargo, N.D.-based company. "To alter a cloud's aerosols in such a dramatic way that it won't rain -- the cost will be extreme, and I don't know how to do it confidently. Nature is so large and powerful it can always overwhelm you." China has no scientific evaluations to support its promises. And, he says, it's just not possible to exercise such precise control over the weather.
Whether or not it's possible to exercise any control at all over the weather remains subject to debate. While countries around the world -- including the United States -- continue to fund cloud seeding in drought-stricken regions desperate to refill reservoirs or water crops, the efforts have been beset with failures and few successes since the very first clouds were treated.
That was in the 1950s, near the New York labs of General Electric, following the discovery that dry-ice shavings could convert super-cooled (colder than freezing) water droplets to ice crystals. That mattered because clouds need ice crystals (or some kind of small particles ) to form precipitation. Cloud seeding tries to fill that need. Today silver iodide -- its structure mimics that of ice crystals -- is most commonly used in a method called glaciogenic cloud seeding.
Another method, hygroscopic cloud seeding (which some scientists say holds the most promise today), uses materials such as salt to provide a droplet-attracting nucleus; it can be used in warmer clouds. Both methods, whether dispersed through planes or rocket launchers, need to start with a cloud; they can't create clouds. Cloud seeding is more like cloud fertilizing: It tries to make a cloud a more efficient producer of rain or snow.
After the discovery at GE, the company hired a plane to release dry ice into clouds during the winter of 1946. On the final day of the experiment, Schenectady, N.Y., had its heaviest snowfall of the season, causing GE to worry about the legal liabilities of changing the weather.
The initial promise of the discovery was quickly swamped by disillusionment. "People had all kinds of immediate aspirations that they could control the weather," Boe says. "But there was a lot of overselling. If your town had a drought, people would show up and try to sell this, then get out of town fast if it didn't work. That did a lot of damage to cloud seeding's reputation. Worldwide, that still happens."
While dozens of foreign countries -- Mali, Burkina Faso, Saudi Arabia, Indonesia and Australia, to name a few -- continue to try to get the weather they want, the U.S. hangs back slightly. "In other countries, you don't have people sitting around saying, 'We're not sure this works,'" Boe says.
In America, that refrain is heard frequently, but cloud seeding continues on the order of 60-some projects in 10 Western states a year, funded mainly by local and county governments, agricultural interests and, occasionally, ski resorts. Although the American Meteorological Society says some studies have shown a 10 percent increase in rain volume, the National Academy of Sciences has said there is no conclusive evidence that cloud seeding works.
It's not the initial cloud-seeding equation that is in doubt: Silver iodide does produce ice crystals in clouds. "You can see on a radar how it grows to larger particles," says Dan Breed, a project scientist with the National Center for Atmospheric Research. "But the chain of events between that and precipitation hitting the ground is much more complicated."
Some clouds, it turns out, are less complicated than others. Winter orographic clouds, which form over mountains in winter, are simpler to work with than convective clouds, which cause thunderstorms. Orographic clouds occur almost every day in the Western mountains, where shortages of winter snowpack (needed to fill lakes, rivers and reservoirs in the spring) mean extra precipitation is most often needed.
Glaciogenic seeding is also used for hail suppression; by providing many ice particles for hail to form around, it prevents very large hail from developing. But hailstorms are extremely complicated, Breed says, and experiments with hailstorms are risky. "You do a project or experiment and you can end up with insurance claims or crop damage," he says.
