Cloud Seeding Methods and Criticism
There are three modes of cloud seeding: static, dynamic and hygroscopic. Static cloud seeding involves spreading a chemical like silver iodide into clouds. The silver iodide provides a crystal around which moisture can condense. The moisture is already present in the clouds, but silver iodide essentially makes rain clouds more effective at dispensing their water.
Dynamic cloud seeding aims to boost vertical air currents, which encourages more water to pass through the clouds, translating into more rain [Source: Department of Academic Science, Colorado State University]. Up to 100 times more ice crystals are used in dynamic cloud seeding. The process is considered more complex than static clouding seeding because it depends on a sequence of events working properly. Dr. William R. Cotton, a professor of atmospheric science at Colorado State University, breaks down dynamic cloud seeding into 11 separate stages. An unexpected outcome in one stage could ruin the entire process, making the technique less dependable than static cloud seeding.
Hygroscopic cloud seeding disperses salts through flares or explosives in the lower portions of clouds. The salts grow in size as water joins with them. On his Web site, Dr. Cotton claims that hygroscopic cloud seeding holds much promise, but requires further research.
 Image courtesy Mustafa Quraishi/Associated Press A modified Cessna 340 aircraft demonstrates its flares used to seed clouds. The government of India’s Andhra Pradesh state used these planes to try to stave off a drought in the summer of 2004. |
Cloud-seeding research has been performed in Russia, Israel, Thailand, the Caribbean and South Africa. In addition, Australian scientists conducted numerous experiments, discovering that static seeding was not effective over Australia's plains but appeared to be very effective over Tasmania.
Despite some successful tests, cloud seeding still has many problems. The fundamental concern is: Does it work? It may be a chicken-and-the egg type problem -- would it have rained in a given area without the use of cloud seeding, and would it have rained less? Cloud seeding is also very dependent on environmental conditions like temperature and cloud composition.
In 2003, the United States National Academy of Sciences declared that 30 years of studies had not produced "convincing" evidence that weather modification works [Source: Things Asian]. On the other hand, the American Meteorological Society claims that some studies on cloud seeding show a 10 percent increase in rain volume [Source:The Edwards Aquifer Website].
Cloud seeding is quite expensive, though potentially cheaper than other projects, like diverting rivers, building new canals or improving irrigation systems. Then again, the allure of cloud seeding may redirect attention and funding from other projects that could be more promising. Then there are questions about altering weather. Are some areas taking moisture out of the air that would have fallen as rain in another region?
Despite reassurances from cloud-seeding companies, concerns remain about exposure to silver iodide toxicity and soil contamination. Other safety issues are more transparent. In China, wayward munitions have damaged property, and they even killed one person in May 2006. The Chinese government contends that it has improved training, licensing and safety practices.
In the end, cloud seeding has strong supporters, but it remains controversial. And although the practice has lost momentum in the U.S., China is counting on its legion of farmers-turned-weather-gods to clear the skies for the opening ceremonies of the 2008 Summer Olympics.
For more information about cloud seeding, weather control and other related topics, please check out the links on the next page.
