A weather-modification technique that aims to coax more water from clouds than they would yield on their own. Aeroplanes deposit silver iodide within clouds to stimulate precipitation.
Cloud-seeding was invented in the 1940s by scientists at General Electric Research Laboratories in New York. Commercial and government operations spread quickly; by the 1950s about 300m acres (1.2m square kilometres) of American land were targeted. The main use is to cause snow in winter, thickening the snowpack and thus increasing the flow of rivers in spring and summer, rather than to cause rain during a drought. A study in the Journal of Applied Meteorology and Climatology in 2014 found it can increase rainfall by up to 15%.
The federal government does not carry out cloud-seeding, but nine American states have active programmes. The South Texas Weather Modification Association, an organisation of local water agencies, contracts private firms to seed clouds over south-central Texas.
In 2025, 22 American states introduced bills to ban or restrict weather modification. Florida enacted its ban in June 2025, with a prison sentence of up to five years. Much of the opposition is entwined with conspiracy theories about government control of the weather. After Hurricane Helene hit North Carolina in September 2024, Marjorie Taylor Greene, a Republican congresswoman from Georgia, wrote on X: "Yes they control the weather." On July 15th 2025 she proposed the Clear Skies Act, a federal ban on weather modification that would also outlaw research on solar geoengineering. The bill would make it a felony to release chemicals into the atmosphere with intent to modify the weather.
Scientists have faced doxxing and lawsuits from weather conspiracy theorists. The Climate Science Legal Defence Fund has provided legal aid to researchers targeted in such campaigns.
Rainmaker is a startup backed by Peter Thiel that aims to make cloud-seeding cheaper by using drones rather than aeroplanes. In early July 2025 it deposited 70 grams of silver iodide within two clouds over south-central Texas. When deadly flooding hit nearby Kerr County two days later, social-media users blamed Rainmaker's technology—though meteorologists attributed the downpour to atmospheric water vapour from the remnants of Tropical Storm Barry. Augustus Doricko, the founder and chief executive, was physically threatened and hired a security detail.
Honesty is the best policy, but insanity is a better defense.