EXPLAINER: The double-edged sword of weather control

As Delhi grapples with worsening air pollution and recurring winter smog, scientists have turned to an unconventional experiment — cloud seeding, a process that attempts to induce artificial rainfall by modifying clouds. The national capital recently witnessed its first-ever cloud-seeding trial, aiming to clear airborne pollutants and improve air quality. While the concept sounds futuristic, it is rooted in decades of meteorological research. The technique involves dispersing specific chemical particles into clouds to stimulate precipitation — a method that has sparked global interest and debate over its scientific validity, environmental impact and potential role in weather management.

What is cloud seeding?

Cloud seeding is a weather modification technique designed to enhance rainfall or snowfall by introducing artificial particles into clouds. These particles act as nuclei around which water vapour condenses, eventually forming droplets heavy enough to fall as rain. The process is typically carried out using aircraft or drones that disperse these particles into targeted cloud formations.

The science behind it

Clouds form when moist air rises, cools and condenses around microscopic particles to create droplets or ice crystals. When these droplets grow large enough, they fall as precipitation. Cloud seeding attempts to accelerate or amplify this natural process by adding specific chemical agents that encourage droplet formation.

Cold clouds (below 0°C): Particles such as silver iodide are used because they mimic the crystalline structure of ice. These particles promote the freezing of supercooled water droplets, leading to snow or rain as they melt while falling.

Warm clouds (above 0°C): In these, sodium chloride (NaCl) or potassium chloride (KCl) is employed to encourage condensation and coalescence of water droplets, thereby increasing rainfall efficiency.

A brief history of artificial rain

The concept dates back to 1946, when American scientist Vincent Schaefer demonstrated cloud formation by adding dry ice to a chilled chamber. A year later, Bernard Vonnegut improved upon this experiment using silver iodide, which became the most common seeding agent used globally.

Since then, countries such as the United States, China and the UAE have experimented with cloud-seeding programmes, especially in drought-prone or mountainous regions. Studies suggest some success in increasing precipitation, particularly in orographic clouds (those formed over mountains).

Effectiveness & challenges

While cloud seeding has been studied for decades, scientific consensus remains inconclusive.

• A 2024 US Government Accountability Office report noted that global evidence on its effectiveness is still limited and inconsistent.
• India’s own trials, conducted by the Indian Institute of Tropical Meteorology (IITM) since the 1970s, reported around 17 per cent rainfall enhancement, but without definitive proof of causation.

Environmental & safety concerns

The technique is not without drawbacks:

• Silver iodide residues have been detected near seeding zones and are considered toxic to ecosystems.
• Dry ice (solid CO₂) used in some experiments contributes to greenhouse gas emissions.
• Strict aviation clearances and weather assessments are required to avoid interference with natural weather systems and ensure flight safety.

Cloud seeding in India

India has experimented with cloud modification since the 1970s, with projects in Maharashtra, Karnataka, Tamil Nadu, and now Delhi. The Delhi trial in 2025 marks the city’s first attempt to use artificial rain as a tool to combat severe air pollution during winter months.

Before each operation, scientists assess:

• The type and stage of cloud formation
• Meteorological data before and after seeding
• Flight safety and regulatory approvals

The road ahead

While cloud seeding holds promise as a short-term measure to mitigate drought or pollution, experts caution that it is not a permanent solution. Continued scientific evaluation, environmental monitoring, and policy regulation are vital to determine whether this technology can play a sustainable role in India’s climate and pollution management strategies.

In essence: Cloud seeding blends atmospheric science and human innovation, but its true effectiveness and environmental safety continue to be matters of debate — making it an important topic for both policymakers and UPSC aspirants to understand.