In October, as a dense smog enveloped India’s capital city, New Delhi, and the air quality reached hazardous levels, the Delhi government, in collaboration with the Indian Institute of Technology, Kanpur (IIT-K), turned to cloud seeding, a disputed weather-modification technique to induce artificial rain.
Using IIT-K’s aircraft, flares containing seeding agents were released into the atmosphere. But the experiment didn’t lead to precipitation because of a lack of moisture in the air. Cloud seeding doesn’t create clouds but works on existing clouds and moisture.
Manindra Agrawal, Director of IIT-K, told Mongabay-India that the team knew the chances of precipitation were low because the moisture content was below 15 per cent, significantly less than the much-needed 50 per cent. However, they went ahead with the experiment as a way to collect data on cloud seeding’s impact on air pollution levels.
“We aimed to study the relationship between moisture content, the amount of seeding material used, and its impact on local conditions. Even if no rain occurred, we wanted to know whether humidity levels increased and, if so, whether that helped reduce pollution and to what extent,” he explained. In a statement, IIT-K said that there was a reduction of 6-10 per cent in particulate matter. The claim and the experiment itself has been disputed by other experts.
Over the years, cloud seeding has been constantly proposed as a way to curb Delhi’s pollution. Although this cloud seeding experiment in Delhi was conducted after about 52 years, previous governments have also discussed it as an option to mitigate pollution. Last year, the previous Environment Minister, Gopal Rao, sought the Centre’s permission for cloud seeding.
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Human-driven emissions are the primary cause of air pollution. Therefore, what has been observed across various parts of the world is that meaningful progress in reducing air pollution depends on prioritising the control of emission sources.
Chandra Venkataraman, professor, Indian Institute of Technology Bombay
In September, after signing the memorandum of understanding (MoU) with the Indian Institute of Technology (IIT) Kanpur, Chief Minister Rekha Gupta even called the cloud seeding trial “a historic milestone for the city”. But experts have questioned whether the ₹3.21 crore project can be seen as a possible solution to the air pollution crisis.
Researchers such as Shahzad Gani and Krishna Achuta Rao, professors at the Centre for Atmospheric Sciences, Indian Institute of Technology Delhi (IIT-Delhi), have called it “another gimmick in a series of similar unscientific ideas, like smog towers.”
Multiple scientists have also emphasised that there is not enough scientific evidence of cloud seeding having any impact on pollution and any improvement in air quality is minor and temporary.
Complexity of Delhi’s pollution
Delhi’s pollution stems from an array of reasons, including geographical factors, human-driven emissions, and temperature-linked restraints, which add to its complexity.
Climate scientist Roxy Mathew Koll at the Indian Institute of Tropical Meteorology (IITM) explains how the city’s geography makes the problem harder.
“It sits in a low-lying basin bordered by the Himalayas and Aravallis, where winter winds are weak and pollution gets trapped under temperature inversions. But these natural constraints make control of local pollution even more urgent, not optional,” he says. Simply put, temperature inversion is a phenomenon where warmer air traps cooler air near the Earth’s surface.
Further, slower winds during the winter months do not allow pollution to spread out or move away from the city. Instead, it stays suspended over Delhi.
Agrawal also points out the well-known sources, such as “stubble burning, biomass burning within the NCR area, increased coal use during the cold season, vehicular emissions, and construction activities,” contributing to Delhi’s pollution.
No evidence that cloud seeding is a solution for pollution
Cloud seeding, first attempted almost eight decades ago, is intended to modify suitable clouds with particles to increase rainfall. These seed particles are cloud condensation nuclei (CCN) on which water vapour condenses and the blend of seeding agents differs based on the temperature of the cloud base.
In the recent experiment in Delhi, a mixture of silver iodide, common salt, and rock salt was used. While cloud seeding has been widely researched, there is no conclusive data and a lack of studies on whether it can be beneficial in addressing air pollution. Agrawal, who led the recent experiment in Delhi, calls it an “SOS measure.”
Whether artificial rain induced by cloud seeding can help during a severe air pollution crisis is not well studied, says cloud seeding expert Thara Prabhakaran, scientist at the Indian Institute of Tropical Meteorology (IITM). “There is no documented scientific evidence yet that cloud seeding can reduce pollution,” she notes.
Koll emphasises that while cloud seeding is a serious scientific experiment, it is not a solution for air pollution. “It works only when clouds with enough moisture are already present, and even then, its effect is small and short-lived. At best, it may bring a brief drizzle that washes out some dust and particles for a few hours,” he explains.
Sachin Ghude, an IITM scientist whose expertise lies in atmospheric chemistry, urban air quality modelling, and urban fog process, also says that the artificial rain is “sometimes very light, and there is only a momentary improvement in air quality because of the pollution.”
He further points out that to bring down the air quality level from ‘very poor’ to ‘moderate,’ the city would need rain almost every alternate day. “But since cloud cover is only about 20 per cent throughout the winter period, it’s practically impossible to actually go for cloud seeding. Moreover, when air quality is severe, cloud cover is largely absent, and only certain types of clouds can be seeded,” he adds.
Risks involved in cloud seeding
While much has been talked about cloud seeding as an option for reducing air pollution in Delhi, there hasn’t been ample discussion about the risks involved. To trigger rain and initiate condensation, compounds such as silver iodide are used. While these are not so harmful in small quantities, larger amounts and prolonged exposure can harm the environment. “It can be toxic to aquatic systems in large quantities,” says Prabhakaran.
She further points out that since the atmosphere in polluted areas such as New Delhi is already loaded with polluted aerosols and gases, dispersing additional particles at high altitudes could have unknown impacts. “There should be abundant research on the interactions between cloud seeding elements, such as silver iodide, and the aerosols present in the atmosphere,” she adds.
There is also uncertainty involved in this process. Artificial rain could coincide with natural rain, causing excessive precipitation, which could result in flooding.
But Agrawal says this uncertainty is “one of the reasons we need more data to understand how we can better deal with consequences such as natural rain and artificial rain coinciding.”
However, the lack of clarity is not just regarding the amount of rain but also the region. Prabhakaran says there have been cases where downwind areas, far from the seeding site, have experienced increased rainfall. “This shows that weather modification in one location can affect another, adding to the complexity of evaluating such interventions,” she says.
Distraction from real solutions
Experts also worry that focusing funds on experiments such as cloud seeding takes attention away from actual solutions. The hype about cloud seeding’s effectiveness could lead to misinformation.
Koll emphasises that cloud seeding cannot offset long-term climate change patterns. “When such experiments are portrayed as climate solutions, they feed a dangerous illusion that technology alone can undo the damage of unchecked emissions. The danger of misinformation is that it delays real climate action while giving the impression that science provides a quick escape pathway,” he explains.
He adds that treating cloud seeding as a fix for pollution or water stress risks shifts attention from the real, lasting solutions.
Ghude brings up the smog tower, the first in India, which was installed in Connaught Place, Delhi, in 2021 to combat air pollution. It was built at a cost of over ₹22.9 crore; the tower currently lies defunct. “It didn’t even clean the air within the area where it was installed. So, the focus should be on practical solutions and controlling the source,” he says.
What should the focus be?
On November 9, hundreds of people held a public demonstration in New Delhi calling for the government to address the city’s worsening pollution. Holding placards such as “Breathing is killing us,” the capital’s residents demanded action, with some protesters asking the government to declare this a public health emergency. During this time, the AQI was between 300 and 400.
Three days later, on November 12, Delhi recorded an AQI of 414, with seven air quality monitoring stations out of 39 reporting AQI levels ranging between very poor and poor.
Furthermore, the World Health Organisation’s (WHO) Ambient Air Quality Database (updated in January 2024) reported an annual average fine particulate matter mass concentration of 121 µg/m³ in New Delhi. This is about 24 times higher than the healthy level of 5 µg/m3 recommended by the WHO air quality guideline.
Severe air quality conditions can lead to a long list of acute and chronic health conditions, V. Faye McNeill, Professor of Climate at Columbia University, tells Mongabay-India.
“PM2.5, the smaller fraction of particulate matter, can penetrate to the deepest part of the lungs, be taken up into the bloodstream, and transported to other parts of the body. Therefore, it is connected with negative impacts not just related to the lungs but almost every body system, including the brain and reproductive systems,” she explains.
In this light, the focus should be on the primary cause of air pollution: emissions.
“The genesis of air pollution lies in emission sources. Human-driven emissions are the primary cause of air pollution. Therefore, what has been observed across various parts of the world is that meaningful progress in reducing air pollution depends on prioritising the control of emission sources,” says Chandra Venkataraman, professor of Chemical Engineering and Climate Studies, Indian Institute of Technology Bombay and part of the steering committee of CAPHER-India.
Ghude says the expansion of the city needs to stop. “New construction and development will only increase the pollution problem,” he says.
The area of solutions also needs to go beyond cities. Venkataraman says an important intervention is ensuring access to clean household cooking and heating energy, which means transitioning away from biomass fuels commonly used in chulhas. “For example, in China between 2005 and 2015, 90 per cent of the reduction in human exposure to ambient and household pollution came from reducing reliance on household solid and biomass fuels,” she elaborates.
She adds that there is a long way to go in implementing and prioritising effective air pollution control measures. “Pollution levels do not always depend solely on local emissions; emissions from neighbouring regions can also influence them through secondary formation processes. Given the inherent complexity of air pollution, there is a need to develop multi-scale, multi-sector approaches to emission control.”
This story was published with permission from Mongabay.com.
