Artificial Rain from Clouds: The Science of Cloud Seeding Against Urban Pollution and Its Real-World Limitations

As the winter season begins, the northern plains of India, especially the capital Delhi and its surrounding areas, become enveloped in a blanket of toxic smog. When the Air Quality Index (AQI) crosses 308 and reaches the 'very poor' or severe category, breathing becomes difficult. In such a critical environment, a scientific solution is often discussed vigorously to clear the atmosphere: artificial rain or cloud seeding. In this method, special chemical particles are sprayed into the clouds floating in the sky to induce rainfall, so that the dust and smoke particles suspended in the air are washed away and settle on the ground.

According to an NDTV report, an aircraft equipped with cloud seeding technology was kept ready by the Indian Institute of Technology Kanpur (IIT Kanpur) to reduce pollution levels in Delhi. Under this plan, if clouds with sufficient moisture formed in the sky, the plan was to dispatch the aircraft from Kanpur to reach over Delhi in approximately one hour and begin the operation. A plan to implement this emergency measure was formulated under a Memorandum of Understanding (MoU) signed between the Delhi government and IIT Kanpur. But what is the science behind this technology, how does it work in the sky, and can it truly eradicate the problem of urban pollution from its roots?

History and Scientific Discovery of Cloud Seeding

The idea of converting natural clouds into liquid rain through human intervention is quite old. In 1891, Louis Gathmann proposed the idea of inducing rain by releasing liquid carbon dioxide into rain clouds. Subsequently, in the 1930s, a theory called the Bergeron-Findeisen process emerged, which stated that rainfall begins through the interaction between supercooled water droplets and ice crystals within a cloud. Vincent Schaefer, a researcher at General Electric (GE), accidentally proved this method in a laboratory on July 14, 1946.

Schaefer was trying to create an artificial cloud by breathing into the laboratory's deep freezer, but the temperature was not dropping low enough. To quickly lower the temperature, he placed a piece of dry ice (solid carbon dioxide) inside it. In a moment, millions of microscopic ice crystals began to sparkle, proving that water can be transformed from a supercooled state into ice within the limit of minus 40 degrees Celsius (-40 °C). Just a few weeks later, his fellow scientist Bernard Vonnegut discovered a compound called silver iodide through the study of chemistry, whose crystalline structure is identical to that of natural ice. On November 13, 1946, 6 pounds (2.5 kilograms) of dry ice was released from an airplane into a cloud in the skies of New York, successfully causing snowfall for the first time in western Massachusetts.

Physics: How Chemicals Work in Clouds

The process of artificial rain is not magic, but a pure physical and chemical process. Clouds are generally made of water vapor and ultrafine droplets. Often, even though the temperature inside the cloud has dropped below zero degrees Celsius, the water droplets remain in a liquid state, which in scientific language is called supercooled water. To turn these droplets into ice or large raindrops, a base or seed is needed, which is called ice nuclei or condensation nuclei.

When chemicals like silver iodide (AgI) are sprayed inside the cloud by an airplane, rocket, or ground-based generator, their micro-particles act as a center. The crystal lattice of the silver iodide crystal is hexagonal, just like that of a natural ice crystal. Therefore, the supercooled water particles immediately begin to freeze around this chemical particle. This process is called heterogeneous nucleation. The droplet gradually becomes larger and heavier, and is pulled towards the ground due to gravity. As it passes through the lower warm layers of the atmosphere, it melts and becomes a raindrop.

Scientifically, this method proves most effective when the temperature in a cloud is between minus 7 degrees and minus 20 degrees Celsius (−7 °C to −20 °C). This process is called static seeding. In addition, there is another method called dynamic seeding, in which the latent heat released during the ice-formation process strengthens the cloud's updraft, thereby increasing the cloud's size. In today's modern era, hygroscopic materials such as common salt, as well as modern technology involving the release of electric charges into clouds via drones in the United Arab Emirates (UAE), are also being utilized. In July 2021, rainfall measuring around 6.9 millimeters was recorded with the help of the drone method at Al Ain.

Testing Cloud Seeding Against Urban Pollution

When air pollution spikes significantly, particulate matter such as PM 2.5 (PM 2.5: particles smaller than 2.5 micrometers) and PM 10 remain suspended in the air for extended periods. Natural rainfall pulls these particles down to the ground with it, a process known as 'wet scavenging'. An attempt is made to achieve this exact result by artificially inducing rainfall through cloud seeding.

In late October 2025, the Delhi government conducted two rounds of cloud seeding trials at an altitude of approximately 30,000 meters near the Indira Gandhi International Airport. In the previous year, testing was conducted at an altitude of approximately 10,000 meters. However, neither of these October 2025 tests yielded significant results. According to an evaluation by IIT Kanpur, the moisture content in the clouds was extremely low, preventing the formation of precipitation. If sufficient natural moisture and appropriate clouds are not present in the sky, rain cannot fall no matter how many chemicals are sprayed.

Scientific Efficacy and Divergent Views

Despite decades of experimentation, deep divisions persist within the global scientific community regarding the precise capabilities of cloud seeding. According to a report released in December 2024 by the US Government Accountability Office (GAO), conflicting findings are still observed regarding whether this technology statistically and significantly increases precipitation. A study by the United States National Academy of Sciences (NAS) found no solid statistical evidence of cloud seeding's efficacy. Stanford University environmentalist Jerry Bradley noted that while snowfall or rainfall can be slightly increased under specific conditions, regular rainfall cannot be brought about by it.

In contrast, a study by the Wyoming Weather Modification Pilot Project (WWMPP) found that cloud seeding could increase the snowpack by a maximum of up to 3% over an entire season. The American Meteorological Society noted in 1998 that seasonal precipitation in mountainous clouds could be increased by about 10%. A 2010 study by Tel Aviv University claimed that the use of silver iodide and dry ice has a negligible effect on the amount of rainfall. During the 2008 Beijing Olympics as well, an attempt was made to force clouds to precipitate outside the city to prevent rain during the opening ceremony, regarding which weather expert Roelof Bruintjes commented that humans cannot create or disperse clouds at will.

Environmental Risks and Safety Assessment

Questions are also raised regarding the safety of silver iodide, the primary component used in artificial rain. According to the National Fire Protection Association (NFPA 704), silver iodide is given a health hazard rating of 2, which indicates that excessive exposure can cause temporary incapacitation or bodily injury. Excessive accumulation of silver in the human body can lead to a condition called argyria, in which the color of body tissues changes.

However, most ecological studies show that the quantity of chemicals used in cloud seeding is extremely small. Globally, about 11,000 kilograms of silver iodide is used annually for cloud seeding, with a negligible amount of only 10 to 50 grams used in each experiment. This proportion is about one percent of the silver released from industrial pollution. Assessments conducted by an independent panel in California's Sierra Nevada in 1995 and in Australia in 2004 found no hazardous accumulation of chemicals in soil or vegetation. Nevertheless, environmentalists have expressed concern over its impact on creatures like the pygmy possum in sensitive biosphere reserves such as Australia's Kosciuszko National Park.

Is Artificial Rain a Permanent Solution to Pollution?

Cloud seeding cannot be considered a panacea against air pollution. Sunil Dahiya, founder of the environmental organization EnviroCatalysts, clarified to NDTV that this technology does not strike at the root source of pollution. In the days following Diwali, when air pollution reaches its peak, it can provide temporary relief as an emergency measure, but it is not a permanent remedy.

The biggest limitation is that even for artificial rain, it is essential to have clouds in the sky with a sufficient amount of moisture and the right temperature. In winter, the plains of North India often have dry air and low humidity, which led to the failure of Delhi's experiments in October 2025. If the sky is completely clear or the clouds lack moisture, cloud seeding proves to be entirely ineffective. Therefore, depending solely on artificial rain without controlling root problems such as vehicular emissions, industrial discharge, construction dust, and stubble burning is not practical from a scientific perspective.