Utne Blogs > Science and Technology

Seven Things You Didn’t Know About Cloud Seeding

by Will Wlizlo

Tags: cloud seeding, geoengineering, China, silver iodide, weather, climate change, global warming, science and technology, Asia Times Online, Orion, Green, Will Wlizlo,

cloudseeding.jpgIn the face of drought, humans have tried many methods to make storm clouds release their life-giving payload. Ancient Israelites tried fasting, others tried rain dancing. There’s a long history of precipitation-based prayer, including the fairly recent public exhortation by Texas Governor Rick Perry. But if a higher power isn’t answering, modern science may be the last resort. That’s why China, according to an article in Orion, has turned to cloud seeding to help alleviate its impending water management crisis.

There is some—albeit contentious—evidence that by launching chemicals into pregnant clouds, we can trick the sky into releasing its moisture early. As the theory goes, if you load a cloud with silver iodide—“either by aircraft flying overhead, or on-ground generators that send up plumes of vapor, or, in the case of the Chinese, by decades-old artillery,” explains Orion—the chemical binds to other water molecules in the cloud as ice. The particulate becomes heavy enough to turn into rainfall.

The entire venture is fascinating. Here are seven factoids to store for your next cocktail party. All un-attributed quotes are pulled from the article in Orion (not yet available online).

1. China employs a veritable army to control its weather. According to a dispatch from Asia Times Online, “each of China’s more than 30 provinces and province-level municipalities today boast a weather-modification base, employing more than 32,000 people, 7,100 anti-aircraft guns, 4,991 special rocket launchers and 30-odd aircraft across the country.”

2. “China faces serious water shortages caused primarily by overuse and population density. Shortages are particularly problematic in the north, where half the Chinese population lives with just 15 percent of the country’s water. The water available for each person is one-fourth the global average, and that portion is expected to shrink as China’s population continues to grow.”

3. “From 1967 to 1972, the U.S. even put weather modification to work during wartime, deploying the 54th Weather Reconnaissance Squadron to seed clouds over Laos. With plans to ‘make mud, not war,’ as one officer put it, they hoped that landslides and heavy rain along the Ho Chi Minh Trail would slow the movements of North Vietnamese troops.”

4. Indeed, the gods of weather are fickle. That’s why “the state of Wyoming has pumped more than $10 million over the last five years into trying to figure out whether cloud seeding actually increases precipitation.” Yao Zhanyu, a researcher at the Chinese Academy of Meteorological Sciences, has found through statistical analysis that China’s precipitation has shown “an average 10 to 15 percent increase in rainfall over each of the last seven years.”

5. In Colorado, a different type of rain gun is used: a hail cannon. Hail cannons, allegedly, “use shock waves to hamper the formation of hailstones.” Like cloud seeding, the evidence of their efficacy is dubious.

6. Cloud seeding is one manifestation of a techno-scientific array of solutions to climate change called geoengineering. Simply, geoengineering is the human manipulation of natural macro-processes—tides, ocean salinization levels, precipitation—to address trends in climate change. According to the New York Times’ Green blog, everyday people and policy makers are starting to consider geoengineering a viable option.

7. “Silver iodide is considered a hazardous substance and toxic pollutant under the Clean Water Act, but scientists engaged in cloud seeding operations in the U.S. say the substance is used in concentrations low enough to be negligible.” Relieving?

Sources: Asia Times Online, Green, Orion (article not yet available online)