How Does Cloud Seeding Work? A Controversial Technology
A controversial technology gets another look.
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How does cloud seeding work? Learn about what cloud seeding is, its history, the positive and negative effects of cloud seeding and its potential long-term impact on the environment.
by Mark Hall
Many folks around the globe are distressed about water availability. It’s no wonder, given that a quarter of the world’s population nearly exhausts their water supply on a regular basis. This level of scarcity is especially prevalent in northern Africa and the Middle East, where four out of every five people live with this condition. At the same time, the global demand for water continues to increase, and has now surpassed twice what it totaled in 1960.
As part of an intensified effort to avoid the looming threat of profound water shortages, cloud seeding has once again garnered increased attention from proponents and critics alike. This weather modification technique seeks to increase precipitation from clouds through chemical infusion; but is it the right solution? You decide.
History of Cloud Seeding
So how does cloud seeding work? Cloud seeding has a long history, tracing back to 1946. While looking for possible methods to reduce airplane icing, General Electric Company scientists Irving Langmuir and Vincent J. Schaefer conducted experiments with supercooled water. Free from minerals, dissolved gases, or sediments, these pure droplets found in clouds can remain liquid below 32 degrees Fahrenheit. However, they will, in fact, freeze onto something that strikes them, such as an airplane. To reduce this threat of icing, the two scientists endeavored to solidify these droplets into ice crystals prior to their contact with the aircraft.
Soon, the scientists put their theory to the test, and their laboratory experiments were successful. They were able to create ice crystals instantly with the introduction of dry ice, but that wasn’t all. The dry ice also sped up the natural cloud process of conglomeration, as all the newly formed ice crystals bounced around and fused onto each other. In a cloud, this rapid buildup of ice crystals saturates it, resulting in precipitation — and this is exactly what happened in the experiment.
A short time later, fellow GE scientist Bernard Vonnegut made his own discovery. In his supercooled water experiment, Vonnegut found that the substitution of dry ice with silver iodide — a chemical compound with a molecular structure comparable to ice — brought about similar results. However, instead of instantly forming supercooled water droplets by an abrupt temperature change, the silver iodide itself furnished a core surface for ice to form around.
Attempting the First Weather Modification Techniques
One year later, as part of “Project Cirrus,” a contract between GE, the Army Signal Corps, and the Naval Research Laboratory, more than 180 pounds of dry ice was dumped on a hurricane from the belly of a B-17 bomber. It was the first attempt to moderate the weather by means of seeding clouds. Championed by Schaefer, Project Cirrus had been developed to conduct experiments with aircraft belonging to the U.S. Air Force.
The hurricane had ravaged the state of Florida before spinning its way far offshore. In pursuit, the team of researchers and military air crew flew out over the Atlantic Ocean, hoping to break up the huge storm. After more dry ice was deposited into the hurricane, the upper surface of the cloud started to disintegrate, and the top of a heavily seeded cumulus cloud expanded. The storm clouds were separating, and the team considered the project a success.
However, things were about to take a literal turn for the worse. Immediately following the seeding, the storm pivoted sharply toward the west, started to pick up strength, and ultimately pounded Savannah, Georgia, a few days later. Public opinion was blistering, with the scientists blamed for the sudden change in the storm, which had resulted in a fatality and extensive damage stretching into South Carolina. Because of this tragedy, there wouldn’t be another official cloud-seeding project for many years.
Finally, in the early 1960s, the Department of Defense and the U.S. Weather Bureau decided to take another crack at seeding hurricanes. “Project Stormfury” was created with the bold objective of limiting the destructive power of these storms, and a plan to reduce their top wind speed was put into place. The focus was on the debilitation of the extraordinarily strong winds of the hurricane’s eyewall. This could be accomplished, it was purported, by seeding outside the eyewall with silver iodide, in order to create another wall. It was thought that the artificial eyewall would disrupt and reform the original hurricane into one with a larger radius, resulting in reduced wind speed. Under this plan, a total of eight hurricanes were seeded over the next two decades. Wind speeds in half the storms were reduced by as much as 30 percent.
In the 1980s, scientific doubt was cast upon the initially favorable results because of a likely inability to recognize a difference between the conduct of natural storms and those that were seeded. Also, research found that hurricanes carry too much natural ice and not enough supercooled water for there to be much hope of success. It became clear that the natural fury of hurricanes couldn’t be steered, stopped, or even diminished by human intervention. Consequently, Stormfury was terminated in 1983.
Another cloud-seeding effort made by the U.S. government in the early 1960s did prove to have some benefit. In 1961, Congress passed legislation that hoped to demonstrate a rationale for applying weather modification technology to the growing water shortage problem. Funding was provided for the formation of a program, called “Project Skywater,” which would develop seeding technology, analyze its financial feasibility, and determine its environmental impact.
For many years, Skywater worked to expand winter snowpack in the The Rockies and bring much-needed rain to the Plains, while improving the technology. The expansion of the program was longed for, but by the late 1980s, federal funding for Project Skywater had dried up, and the very capable private sector was left to handle cloud seeding alone.
During several of the years Project Skywater was operating, the U.S. government had also secretly turned cloud-seeding technology into a weapon wielded in the Vietnam War. When “Operation Popeye” was finally declassified in 1974, the public learned that the Air Force had worked to lengthen the monsoon season, in an attempt to hamper the progress of the Viet Cong’s supply chain with muddy roads. The controversial news didn’t sit well with the American public. In 1976, the Environmental Modification Convention, which was passed by the United Nations, completely banned, during the war, hostile weather modification practices that could result in nearly any kind of environmental change.
International cloud-seeding entities are numerous. In all, about 50 countries have seeded clouds, some for a long time. In fact, Australia began seeding as early as 1947. By 1965, a total of 79 private companies worldwide were known to be seeding clouds. The technology is used around the world to increase rainfall, enlarge snowpacks, control wildfires, clear smog near large cities and airports, prevent hail, and even avoid rain during military parades.
Potential Negative Effects of Cloud Seeding
Unfortunately, despite the wide variety of useful abilities, many concerns still exist regarding the potential for harm caused by cloud seeding. China, the most extensive user of cloud-seeding technology on the planet, employs the method to a colossal degree. Before and during the Beijing 2022 Winter Olympics, for instance, 15,000 small rockets filled with silver iodide were launched from anti-aircraft cannons in one six-month period. The chemical was released from aircraft 241 times during that same period, as well. The intent was to dry out distant rain clouds before they neared the Olympic Village.
Regrettably, bombarding the clouds with silver iodide, whether from airplanes, cannons, or ground-based generators, creates an environmental risk. Soil samples show that the toxicity risk of silver iodide (an inorganic compound that can be poisonous to humans, animals, and plants when absorbed) is low, but the potential risk is unclear when the chemical is applied repeatedly, year after year, in a particular area. It’s feared that long-term use of this chemical could also increase atmospheric carbon dioxide and cause a reduction in the ozone layer, further harming the environment.
A host of other materials are used in cloud seeding. Some of these are sulfur dioxide, potassium iodide, propane, and sodium chloride. Research to find alternative seeding materials is ongoing. Calcium chloride and other negatively charged ions are also used and considered less harmful. However, silver iodide is still the most common chemical used for seeding because it’s extremely effective at inducing ice crystal formation.
Skeptics share other concerns, such as the possibility of water wars between neighboring nations. These could occur because the unequal distribution of precipitation that results from seeded clouds. They also warn of the potential for widespread flooding and devastation in arid regions that don’t have the infrastructure needed to handle the extra rainfall. There’s even broad disagreement over the effectiveness of cloud seeding, although the claims of most entities regarding the increase in precipitation over and above the clouds’ natural ability range anywhere from 5 percent to 30 percent.
Water shortages may indeed be coming, and cloud seeding can help mitigate that concern to a degree. However, while we’re taking yet another look at this 80-year-old technology, we must recognize that there’s still a serious question that must be answered: Are the benefits of cloud seeding worth the associated risks, both short-term and long-term? This question has been hanging around for far too long and more research is needed before we can get a definite answer.
Editor’s note: The sources listed in the July/August 2025 printed issue were incorrect, and the correct related sources are listed below.
Sources
- Cummins, Eleanor. “With Operation Popeye, the U.S. Government made weather an instrument of war: As geo-engineering projects soar, the declassified project is newly relevant.” Popular Science, 21 March 2018.
- Griffin-Elliott, Thia. “70th Anniversary of the First Hurricane Seeding Experiment.” NOAA’s Atlantic Oceanographic & Meteorological Laboratory.
- Hunter, William. “Cloud Seeding is Used Around the World — Not Just in Dubai: How Countries Including the US, China, Switzerland and Australia Have Implemented the Weather Modification Technique — and Why It’s Controversial.” Daily Mail, 18 April 2024.
- Huseynli, Orkhan. “Unleashing the Power of Cloud Seeding: Navigating Potentials and Pitfalls.” Earth.org, 18 April 2024.
- Kuzma, Samantha, Liz Saccoccia, and Marlene Chertock. “25 Countries, Housing One-Quarter of the Population, Face Extremely High Water Stress.” World Resources Institute, 16 August 2023.
- Means, Tiffany. “What is Cloud Seeding? Understanding Weather Modification: Clouds Can be Prodded to Make More Rain and Snow. But is It Ethical?” Treehugger, 11 February 2022.
- Rogers, Jedediah. “Project Skywater.” Bureau of Reclamation, 2009 (revised 2013).
Mark M. Hall lives with his wife, their three daughters, and numerous pets on a four-acre slice of paradise in rural Ohio. Mark is a veteran small-scale chicken farmer and an avid observer of nature. As a freelance writer, he endeavors to share his life experiences in a manner that is both informative and entertaining.
Originally published in the July/August 2025 issue of Countryside and Small Stock Journal and regularly vetted for accuracy.
