How cloud seeding changes the weather

What is it?

Cloud seeding is a form of weather modification where substances are introduced into clouds to encourage precipitation. It is done with the aim of increasing rain or snow, and sometimes to reduce hail or fog.

The science of making rain

The process of cloud seeding involves dispersing tiny particles (like silver iodide or salt) into humid clouds. Water molecules then condense around these particles and become heavy enough to fall as rain or snow.

What’s in a cloud seed?

Silver iodide is the classic cloud-seeding agent due to its ice-like crystal structure. Other materials include potassium iodide, dry ice (frozen carbon dioxide), and salts. These particulates attract moisture the most to create droplets.

Warm clouds vs. cold clouds

Cloud seeding done in warm clouds is known as hygroscopic seeding, and it uses salt particles to encourage raindrop growth. Seeding in cold clouds is called glaciogenic seeding, and uses agents like silver iodide.

A chance discovery

Cloud seeding was accidentally discovered in 1946 by American chemist Vincent Schaefer. While experimenting in a chilled chamber, he breathed into air cooled by dry ice and saw a burst of ice crystals form.

Weaponizing weather in war

In the late 1960s, the US military used cloud seeding as a clandestine weapon. During Operation Popeye in the Vietnam War, aircraft seeded clouds with silver iodide to prolong monsoons and muddy enemy supply routes.

A treaty for the skies

In 1977, nations responded to such weather warfare by adopting the Environmental Modification Treaty (ENMOD), which bans military or hostile use of environmental modification techniques. This international agreement was meant to prevent using weather as a weapon.

Cloud seeding in America

In the United States, cloud seeding is used in about nine western states to boost precipitation or reduce hail damage. However, around 10 states have banned or considered banning weather modification due to public concerns.

Russia and Thailand’s efforts

Russia and Thailand have also turned to cloud seeding. Russia has seeded clouds to reduce damaging hailstorms, while Thailand’s long-running “Royal Rainmaking” program induces rain for farmers and helps quell wildfires.

Proving it works

In 2017, a landmark field experiment called SNOWIE provided the first solid evidence that cloud seeding works. Researchers found that seeding winter clouds in Idaho generated snowfall that otherwise would not have fallen.

Only when clouds exist

Cloud seeding cannot create clouds out of thin air. It only works when suitable clouds are present; in a clear, dry sky with no clouds, seeding can’t conjure rainfall at all.

Modest rainfall gains

In practice, cloud seeding yields only modest rainfall gains even under favorable conditions. Reviews of experiments report changes ranging from no effect up to about 5–15%, with roughly a 5% increase being typical.

Environmental concerns

Nonetheless, experts urge caution regarding potential long-term effects on the environment. It’s not known if much heavier use of silver iodide or other seeding agents could accumulate in ecosystems or affect public health. Monitoring and research continue.

False blame for floods

Experts have debunked claims that cloud seeding caused events like the 2024 Dubai floods. They note those downpours came from natural large storm systems far beyond what cloud seeding could ever generate.

Private sector

Apart from governments, private companies also engage in cloud seeding. In hail-prone areas, insurers fund seeding to reduce damage. Ski resorts attempt to enhance snow, and hydroelectric utilities seed winter storms to boost spring runoff.