Cloud Seeding

Issues & Controversies CLOUD SEEDING

Is cloud seeding a smart means of drought relief? Issue Date: March 8, 2010

SUPPORTERS ARGUE

While cloud seeding does not always produce the intended results, it succeeds often enough to justify its continued use. Among other things, weather manipulation can provide important economic benefits, such as supplying farmers with sufficient water to grow healthy crops. Furthermore, the chemicals used to induce rainfall or snowfall are sprayed in such small quantities that they do not pose an environmental threat.

OPPONENTS ARGUE

Despite decades of experimentation, the science and the ecological impact of weather modification remain poorly understood. Attempts to manage the weather could inadvertently cause both short- and long-term environmental problems. Governments should cease seeding clouds until further research proves its safety and effectiveness.

AP Photo/Charlie Riedel

A pilot for the Western Kansas Weather Modification program flies a cloud seeding mission, emitting particles of silver iodide over a field of crops near Lakin, Kansas.

In October 2009, the mayor of Moscow, Russia's capital, made international headlines with a bold guarantee of a "snow -free" winter for his citizens. Considering that Moscow's winters are notoriously harsh—and particularly snowy—it seemed like a tough promise to keep. But intent on reducing the money his city spends on snow removal, the mayor turned to a controversial technology called "cloud seeding" to make good on his pledge. First developed in the 1940s, cloud seeding involves placing chemicals inside clouds to generate or prevent precipitation. The chemical most often used—silver iodide—can be either shot into the clouds from a ground-based cannon or dropped into the clouds from an aircraft. The chemical cools the air temperature, ideally causing water droplets and ice crystals suspended inside the cloud to bunch together or freeze. Soon, those droplets and crystals grow heavy and fall to the earth as rainfall or snowfall. In Moscow, the mayor enlisted the help of the Russian Air Force to saturate the clouds outside the city with the chemical. His hope was that approaching storm clouds, once "seeded" with silver iodide, would dump their snow in the city's suburbs, and then drift harmlessly over the city. Such plans may seem outlandish, but they are commonplace throughout the world. Indeed, while city governments may be relative newcomers to so-called weather-modification technology, farmers and weather agencies have long experimented with cloud seeding to induce rainfall in drought-prone areas. In the U.S., for example, the practice is particularly popular in water-scarce regions of the Southwest, where the natural ebb and flow of seasonal rains can mean the difference between a healthy harvest and crop failure. Yet cloud seeding has sparked enormous debate over the years. One of the principal issues is whether it is wise for human beings to alter naturally occurring weather patterns. While farmers in arid regions tend to be staunch supporters of cloud seeding, many meteorologists concede that the long-term environmental effects of weather modification remain largely unknown. Additionally, in the Environmental Protection Agency's Clean Water Act (1972), silver iodide is classified as a hazardous material. If the chemical enters the ground or a body of water in sufficient quantity, it can be highly damaging to both fish and vegetation and toxic to human beings. So far, however, cloud-seeding proponents have been able to navigate around such concerns, pointing out that the relatively small quantity of silver iodide used during cloud seeding is insufficient to constitute a public health threat. Yet another source of contention is the more basic question of whether cloud seeding even works. During recent decades, academic studies and field observations have yielded wildly different results. While some studies seem to show that cloud seeding increases precipitation in target areas, others show only marginal improvements in rainfall rates. In still other studies, cloud seeding appears to fail completely in inducing additional precipitation. This inconsistency has led some critics to label cloud seeding a pseudoscientific procedure. Some of the most recent analyses on the subject indicate that climate and weather conditions tend to determine whether cloud seeding yields the desired results. Beyond those general findings, however, the practice is poorly understood. That means despite more than 50 years of spraying chemicals into the clouds, researchers seem to agree on one thing only: Cloud seeding requires a great deal more study before any definitive conclusions on its usefulness or harmfulness can be drawn. Given the lingering uncertainty about the impact of cloud seeding, should governments and farmers continue to endorse its use? Can weather manipulation potentially benefit the world overall, or are humans causing lasting damage to the planet's natural water cycle, of which periodic droughts and floods are key aspects? Critics insist that since cloud seeding has yielded inconsistent results over the years, its use should remain limited until its environmental impact is better understood. Meanwhile, other opponents contend that regardless of whether cloud

seeding permits better control of precipitation, it is irresponsible for humans to try to micromanage the planet's weather. Such intervention, they warn, may have unanticipated environmental consequences for future generations. Although supporters acknowledge that cloud seeding remains an inexact science, they say it works often enough to validate its use. Proponents say inducing rainfall in water-scarce areas benefits society by both reducing drought frequency and boosting agricultural yield. Thus, farmers and governments are justified in manipulating rainfall patterns, they say, if it is done cautiously and under favorable weather conditions. Furthermore, supporters insist that concerns about environmental contamination are overblown, since only small quantities of silver iodide are used to seed clouds.

A Controversial Practice Becomes Increasingly Popular In 1946, an American chemist named Vincent Schaefer became the first scientist to do cloud-seeding research. While working for General Electric, he conducted a series of experiments using solid carbon dioxide ("dry ice") to create small ice crystals in a laboratory setting. He then experimented with cloud seeding in a natural environment, using an airplane to drop several pounds of dry ice into cloud cover above Mount Greylock in western Massachusetts. The trial run appeared to be a huge success, as observers on the ground noticed a visible increase in snowfall. "It seemed as though the cloud almost exploded," Schaefer later observed in a journal entry.

Soon thereafter, the U.S. government expressed an interest in Schaefer's work, and funding for cloud-seeding research

and experimentation increased significantly. Gradually, silver iodide supplanted dry ice as the cloud-seeding chemical of choice. One of the reasons for the change was that silver iodide was structurally similar to ice, meaning the chemical could more easily interact with water droplets and ice crystals inside clouds. Since the field of weather manipulation was comparatively new during the 1950s and 1960s, scientists considered the technology's potential to be limitless. Much of the research concentrated on how to withhold or induce rain, snow or hail over small geographic areas in order to improve crop growth or fight forest fires. Still other, more ambitious plans called for cloud seeding on a massive scale, in order to weaken or change the course of huge weather systems, such as hurricanes. U.S. Defense Department policy-makers even used weather modification as a military tool during the Vietnam War (1959–75). They speculated that inducing massive rainfall over certain parts of Southeast Asia could disrupt the enemy side's ability to move supplies from one part of Vietnam to another. "Operation Popeye," as the project was called, resulted in the introduction of large amounts of silver iodide over the region between the late 1960s and early 1970s to extend the monsoon season. (The program produced mixed results, but was generally considered a success.) By the end of the 1970s, federal funding for weather modification programs had reached $20 million per year. But as cloud seeding grew in popularity, so did concerns about its potentially adverse environmental impact. Indeed, after silver iodide was listed as a harmful pollutant in the 1972 Clean Water Act, enthusiasm for cloud seeding within the U.S. began to wane. The fact that some scientific studies found that cloud seeding could not be depended upon to consistently generate precipitation cast further doubt on the practice's usefulness for agriculture. As a result, from the 1980s onward, funding for cloud seeding projects decreased. There is no federal ban on cloud seeding as of 2010, yet the government no longer funds it. However, a handful of states—including Utah, Nevada and California—have backed weather modification programs in an effort to benefit their agricultural sectors. Other states, meanwhile, have partially or completely banned the practice. During the late 20th century, a huge boom in the popularity of cloud seeding abroad offset the relative decline in the practice in the U.S. In countries like Australia and Saudi Arabia—sprawling nations with generally arid climates—cloud seeding seemed like a sensible means of replenishing limited fresh water supplies, and supporting crop growth. But even wetter nations like France, India, Turkey and Venezuela decided to allocate substantial government funding to cloud seeding research as well. Perhaps more than any other country, China has embraced cloud seeding enthusiastically in recent years. With a population exceeding 1.2 billion, a large agricultural sector and irregular rainfall patterns in large swaths of the country, China has a vested economic interest in staving off drought. For that reason, the country has the world's most extensive cloud-seeding program. In 2009, China earmarked roughly $100 million for weather modification efforts, and employed tens of thousands of people in the programs. Although the practice remains controversial in the U.S., leading weather authorities and researchers have refused to rule out the possibility of endorsing cloud seeding in the future. The American Meteorological Association, for example, released a statement in 1998 declaring that while the effectiveness of weather modification technology is unproven, it was in society's best interests to continue pursuing it. More recently, in 2003, the prestigious National Research Council (NRC) also voiced tentative support. It issued a report urging greater cloud-seeding research, acknowledging that if found to be scientifically sound, the practice may prove beneficial to future generations. Such reports are one of the reasons that U.S. state governments and agricultural operations collectively continue to spend more than $10 million annually on weather modification projects, despite uncertainties about the technology. [See Cloud Generation and Climate Change (sidebar)]

Weather Modification Dangerous, Critics Warn One of the principal objections to cloud seeding is that the short- and long-term environmental implications of inducing precipitation are unknown. Therefore, critics warn, governments and farmers engaging in the practice cannot be sure of what changes they may inadvertently cause to local weather patterns. For instance, critics note that droughts and floods are naturally occurring aspects of the planet's hydrologic cycle, in which excess precipitation in one area tends to be balanced out by scant precipitation in another area. That means cloud seeding in one region could disrupt precipitation in neighboring regions as well, opponents warn. "Small changes in cloud and precipitation properties may result in a spatial and temporal redistribution of rainfall…[and] could mean drought in some regions, or flooding in others," states a 2010 report released by the National Center for Atmospheric Research in Boulder, Colorado. "Such changes in rainfall distribution...can have a dramatic effect on climate and society." Other critics of cloud seeding point out that the Environmental Protection Agency has long considered silver iodide, the principal chemical used to induce precipitation, to be toxic. Despite backers' assurances that the small amounts of the chemical used do not constitute an environmental threat, critics argue there is no way that spraying any amount of a toxic chemical into the sky can be beneficial. Despite the relatively low level of silver iodide used in seeding, some experts, such as Charles Doswell with the Oklahoma-based National Severe Storms Laboratory, cannot help asking, "[H]ow much of a toxic substance is acceptable?" Still other detractors are quick to indicate that cloud seeding's effectiveness remains unknown after more than half a century. They note that the same 2003 NRC report that featured a tentative endorsement of cloud seeding also included an admission that "there is still no convincing scientific proof of the efficacy of intentional weather modification efforts." Why then, critics wonder, should state and national governments continue spending taxpayer money on an unproven technology? "The community of meteorologists as a whole have basically said we don't know if this stuff works or not," says Doswell. "It seems to me if you are making people pay for a process that may or may not be working…there is a potential problem there." Indeed, even some backers of the practice admit that cloud seeding has failed to ease regional water shortages. One of the most acute examples of this ineffectiveness has been in northern China. Since April 2009, says Hu Zhijin, a weather expert at the China Academy of Meteorological Sciences, "it has rained more times in Beijing than in previous years. But as far as the volume is concerned, we haven't had that much more."

Cloud Seeding Defended While many supporters concede there is a lack of hard evidence showing that cloud seeding is consistently effective, they assert that experiments with the technology have yielded promising results. Colorado State University meteorologist William Cotton claims that "the evidence that it works in certain situations is very compelling." Proponents say the fact that weather modification has proven successful in some instances is why, as of 2010, more than 20 nations worldwide are engaged in cloud-seeding research or active cloud-seeding programs. Fine-tuning the technology and understanding more about the weather conditions in which it is most effective will likely bolster agricultural growth throughout the world, supporters add, strengthening national economies and improving the quality of life in communities large and small. "Large-scale operational programs have produced and continue to produce positive effects for society," Cotton asserts.

However, other proponents argue that cloud seeding has already proven itself effective on a regular basis; it is just a matter of recognizing the technology's limits, and understanding when and when not to use it. "Cloud seeding works—it is science fact, not science fiction," contends Peter Beattie, a former premier of the Australian state of Queensland who, while in office from 1998 to 2007, substantially increased weather-modification funding to help offset drought conditions. Other prominent defenders of the practice contend that the chemicals involved in cloud seeding do not, in fact, damage the local environment. They say that is because the total quantity of chemicals needed to seed a cloud is very small, meaning silver iodide is not likely to contaminate the rainfall or snowfall it helps generate. "The published scientific literature clearly shows no environmentally harmful effects arising from cloud seeding with silver iodide aerosols have been observed, nor would be expected to occur," declared a July 2009 report from the Fresno, California–based Weather Modification Association (WMA). "Based on this work, the WMA finds that silver iodide is environmentally safe as it is currently being used in the conduct of cloud seeding programs." Finally, some supporters reject concerns that cloud seeding is an unnatural process that may damage the planet's longterm weather patterns. After all, they say, humans have already impacted Earth's climate in far more dramatic ways, making cloud seeding's contribution quite negligible. "The problem with saying [cloud seeding] is unnatural is that as a human species, since we first set foot on the planet—or at least since we started burning fossil fuels—we've been modifying weather systems on a much larger scale than cloud-seeding projects," asserts Arlen Huggins, an atmospheric science researcher at the Desert Research Institute in Reno, Nevada.

An Uncertain Future for Weather Modification In January 2010—mere months after Moscow's mayor famously promised a "snow-free" winter—plenty of snow did fall on the city, despite the government's attempts to keep the city dry. The episode served as a reminder that despite the widespread use of cloud seeding around the globe, its ability to produce the intended results remains uncertain. "I think there's more science necessary to understand what conditions it will work in and what won't work," admits Roelof Bruintjes, a weather modification expert at Boulder's National Center for Atmospheric Research. Yet even though there is no scientific consensus on the utility of cloud seeding more than 60 years after the technology's invention, its international appeal is unlikely to diminish anytime soon. The perceived rewards of successful cloud seeding remain too great—and the perceived drawbacks of failed cloud seeding too small—for many farmers and governments to abandon it. That is why, despite skeptics' warnings about the pitfalls of meddling with Mother Nature, placing chemicals in the clouds may soon become even more common than it is today—including in the skies above the U.S.

Discussion Questions 1) Do you think it is wise or dangerous for human beings to alter naturally occurring weather patterns? What are some of the potential advantages and drawbacks of a practice like cloud seeding? 2) Throughout history, droughts have been an integral part of the planet's hydrologic cycle. By reducing the frequency and duration of droughts in arid regions like the American Southwest, how might cloud seeding impact the region's climate? 3) Read the sidebar on cloud seeding and climate change. [See Cloud Generation and Climate Change (sidebar)] Is it a good idea to employ cloud seeding to mitigate the effects of climate change? Why or why not?

4) With your class working in groups, research a country experiencing either drought or excessive rainfall. Based on your understanding of cloud seeding, prepare a presentation recommending or opposing the use of cloud seeding to alleviate that country's climate problems.

Bibliography "California Water Plan Update 2009: Chapter 10 Precipitation Enhancement." California Department of Water Resources, October 15, 2009, www.waterplan.water.ca.gov. "Change in the Weather." Nature, June 19, 2008, www.nature.com. "China to Force Rain Ahead of Olympics." Boston Globe, April 25, 2007, www.boston.com. Engber, Daniel. "How Does Cloud Seeding Work?" Slate, May 11, 2005, www.slate.com. Galbraith, Kate. "In the Pursuit of 'Weather Modification.'" New York Times, August 27, 2009, www.nytimes.com. Hegeman, Roxana. "Vote May Scuttle Cloud-Seeding Efforts." Fort Scott (Kansas) Tribune, November 10, 2000, www.fstribune.com. Lambert, Bruce. "Vincent Schaefer, 87, Is Dead; Chemist Who First Seeded Clouds." New York Times, July 28, 1993, www.nytimes.com. Michaels, Jay. "Moscow Testing Cloud Seeding; Promises Winter Without Snow." Meteorology News, October 19, 2009, www.meteorologynews.com. Moseman, Andrew. "Does Cloud Seeding Work?" Scientific American, February 19, 2009, www.scientificamerican.com. "Planned and Inadvertent Weather Modification." American Meteorological Society, October 2, 1998, www.ametsoc.org/policy/wxmod98.html. "Rainmaking in China." Agence France-Presse, June 21, 2004, www.afp.com. Wade, Stephen. "5,000 Years in 50 Minutes at Olympics." Boston Globe, March 12, 2008, www.boston.com. "Weather Modification Association Position Statement on the Environmental Impact of Using Silver Iodide as a Cloud Seeding Agent." Weather Modification Association, July 2009, www.weathermodification.org. Young, Samantha. "Governments Turn to Cloud Seeding to Fight Drought." Associated Press, December 11, 2009, www.ap.org.

Additional Sources Additional information about cloud seeding can be found in the following source: Fleming, James Rodger. Fixing the Sky: The Checkered History of Weather and Climate Control. New York: Columbia University Press, 2010.

Contact Information

Information on how to contact organizations that are either mentioned in the discussion of cloud seeding or can provide additional information on the subject is listed below: American Meteorological Society 45 Beacon Street Boston, Mass. 02108 Telephone: (617) 227-2425 Internet: www.ametsoc.org Weather Modification Association P.O. Box 26926 Fresno, Calif. 93729 Telephone: (559) 434-3486 Internet: www.weathermodification.org

Keywords For further information about the ongoing debate over cloud seeding, search for the following words and terms in electronic databases and other publications: Silver iodide Hydrologic cycle Weather modification Vincent Schaefer

Citation Information “Cloud Seeding.” Issues & Controversies. Infobase Learning, 8 Mar. 2010. Web. 16 July 2015. .

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