Tornado Science, Facts and History
Editor's note: Updated at 2:00 pm ET
China's plans to force Mother Nature's hand with "cloud seeding" and keep rains at bay during the start of the Olympic Games this August may be all wet, one scientist said today.
"I'm very skeptical about what they claim they can do," said Roelof Bruintjes, the lead researcher for U.S. National Center for Atmospheric Research in Boulder, Colo., at an international symposium on weather modification held today in Westminster, Colo.
Chinese officials will reportedly try to force the rain out of the clouds before the opening ceremony through a process called cloud seeding to clear the smog-filled skies and keep the rain from drenching the athletes and spectators. China has been investigating ways to control the weather for decades, and has invested $500,000 in cloud seeding technologies in the past five years, according to news reports.
China isn't the only place that has attempted these control strategies; several drought-plagued western U.S. states have explored cloud seeding as a way to boost winter snow pack, an important water source. Wyoming launched an $8.8 million cloud-seeding project in 2005 with this aim.
More than 40 countries are currently conducting over 150 projects, with more than 60 projects being run in United States alone, Bruintjes said.
Cloud seeding is done by artificially enhancing the processes that form water droplets and ice crystals in clouds. Droplets and crystals needs a surface to form on, which is usually provided by tiny aerosol particles (whether naturally-formed or from pollution) in the atmosphere.
"Every droplet, every ice crystal forms on a particle," Bruintjes said.
To seed a cloud, scientists inject particles into an existing cloud for the water to coalesce on or ice crystals to grow on. One of the methods most commonly used is the injection of silver iodide into the cloud — these crystals have the same structure as ice crystals and so can readily grow them on their surfaces.
But a cloud must already exist before scientists can seed the atmosphere.
"We can not make clouds, we cannot chase away clouds," Bruintjes said.
Bruintjes is skeptical of China's claims because they rely on the results of studies done in the 1960s and 70s before the complexity of Earth's weather was fully understood and there is little data to back-up claims of success.
"There is no evaluation, there is no scientific literature available that can substantiate their claims," he said.
The studies that have shown the most success in cloud seeding have been done in winter clouds to increase snow pack in mountain regions, said Arlen Huggins of the Nevada State Weather Modification Program. One such studied showed that seeding can increase ice crystal formation and get an annual increase of approximately 10 percent in snowfall under the right conditions, he said.
Measuring the effect of cloud seeding can prove difficult because seeding not only affects the physical processes within the cloud, but also the cloud's lifetime, specifically, "how long the cloud will be raining," Bruintjes said.
Cloud seeding may also work differently in different regions and under different atmospheric conditions — what may work in an unpolluted region may not in a highly polluted one.
"What we know now is that cloud seeding may not work the same on a day-to-day basis, a season-to-season basis," Bruintjes added.
Another matter complicating cloud seeding is that pollution artificially seeds clouds everyday. If you drove your car to work today, "you have in effect been cloud seeding," Bruintjes said.
In fact, pollution has been blamed for the loss of snow pack in regions that depend on clouds that form over mountains.
"Pollution over the last few decades has caused a systematic decrease in snow pack in those regions over the past few decades," said Joe Golden, with the National Oceanic and Atmospheric Administration
But recent studies have shown that strategic seeding can reverse that trend and increase the snow pack where it's needed, he noted.
Golden also said it is time to re-open federal programs that look into weather modification because new technologies have come along that better enable researchers to look at the effects of cloud seeding in the clouds themselves.
Bruintjes said that while China is beginning to update its technologies, its current programs are unlikely to be able to do much to counteract rainfall for the time being.
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