Feeling confident after recent successful attempts to control rainfall in the country, China is planning to seed clouds around the 16th Asian Games next year with chemicals that will keep it from raining on its parade, or at least the games' opening and closing ceremonies.
Even though the November 2010 games to be held in Guangzhou's 80,000-seat Guangdong Olympic Stadium will take place during southern China's supposed dry season, the Olympic Council of Asia, the continent's main sports governing body, announced earlier this week that liquid nitrogen, dry ice and silver iodide will be used to all but eliminate any chance of precipitation.
All three cooling agents can be used to either induce or suppress precipitation, depending on the amount that is administered and the condition of the clouds. In the case of China, they are likely planning to use smaller amounts of each agent in an effort to cool any moisture in clouds headed for the stadium, forming smaller ice particles that would evaporate before they hit the ground, says Dan Kottlowski, an expert senior meteorologist with weather forecasting service AccuWeather. Dry ice (which is solid carbon dioxide) is often used to flash freeze food, and silver iodide (a chemical sometimes used in antiseptics) has molecular structure very similar to that of ice, allowing the substance to induce freezing when introduced to clouds. Liquid nitrogen is a cryogenic fluid at around –320 degrees Fahrenheit that can cause rapid freezing on contact with living tissue, which is why it's sometimes used to remove skin lesions such as warts.
This approach could also backfire, however, depending on the amount of the agents used. "What they do is break up the clouds that produce the precipitation," Kottlowski says, adding, "It's all in the way they use the compounds." If they don't put enough into the cloud, they could end up creating a rainstorm rather than preventing one, he says.
And the conditions have to be just right for their rain-suppression plan to work. "They'll have to bombard any clouds before they thicken up," Kottlowski says. If the clouds are already too filled with moisture, the Chinese could end up creating what they set out to stop.
Most cloud seeding around the world aims at increasing precipitation or suppressing hail, says Joe Golden, a retired senior meteorologist for the National Oceanic and Atmospheric Administration (NOAA). While it is well known that you can overseed, possibly diminishing the chance of precipitation, there have been very few scientific studies documenting this process, says Golden, who managed the last federally sponsored weather modification program in the U.S., which ended in 1995.
Still, Chinese officials claim to have performed "successful rain elimination" during the 2009 Olympics held in Beijing, according to the council. Earlier this year, the Chinese said a cloud-seeding program directly caused a snowstorm in Hebei, the northeastern province surrounding Beijing. Engineers had blasted some 300 cigarette-size sticks of silver iodide into the sky shortly before the storm.
Russia has likewise been known to attempt to overseed clouds to prevent rain from spoiling outdoor activities in Moscow. While there is little documentation of success, reports indicate last summer the Russian Air Force dropped a bag of cement through the roof of a residential home while trying to keep weather from interfering with celebration of the country's June 12 holiday. The bag was supposed to pulverize in the sky, letting loose cement particles to seed the cloud.
Cloud seeding, whether to induce or suppress precipitation, is anything but a precise science. "Attributing one storm to seeding is very difficult unless the cloud system is incredibly simple, like fog that has no chance of precipitation," Arlen Huggins, associate research scientist in the division of atmospheric sciences at the Desert Research Institute in Reno, Nev., explained in a February Scientific American "Ask the Experts" article.
Either way, Kottlowski points out, cloud seeding does not alter climate or affect weather systems. "It only works over a few dozen square miles," he says. "You can't keep away a major storm" such as a hurricane.