by Brian Dunning
January 14, 2025
Humans have been trying to make it rain for millennia. We seem to always need more water, mostly to irrigate our crops, whether we are 21st century people building a highly technological dam or people 5,000 years ago doing a rain dance. Some 75 years ago, a researcher at General Electric discovered that he could use dry ice to seed supercooled water droplets and cause them to precipitate out of the atmosphere as rain. And ever since then, people have debated whether this is science or just another rain dance.
Certainly many have taken it for undisputed science. In preparation for the 2008 Olympics in China, the Beijing Weather Modification Office engaged in large-scale cloud seeding efforts, hoping to divert any possible rain during the Olympic Games opening ceremonies to fall elsewhere. Beginning four hours before the opening ceremony, from 21 locations they fired 1,100 small rockets loaded with silver iodide crystals into the clouds. The opening ceremonies ended up being mostly dry, and many hailed the cloud seeding as a great success.
In early 2024, the United Arab Emirates, which has long practiced cloud seeding to maximize the rain their dry country receives, was deluged with intense rainfall that fell across the entire Persian Gulf region. About 50 people were killed in flooding throughout the Gulf states. Unlike the praise that followed China's effort, it was angry blame that was broadly leveled against the UAE for causing the catastrophic floods.
These examples — plus countless others — would seem to be evidence that cloud seeding is effective at producing rain when and where it's needed; perhaps even too much of it. Yet the practice does not enjoy universal acceptance among atmospheric scientists. Some say it can increase the amount of rain by 30%; some say perhaps 1% at most. Results are virtually impossible to measure since rainfall amounts are never precisely predictable, and whenever we try a specific cloud seeding experiment, it's not possible to have a control for that experiment — once you seed a cloud, you can't compare the results to what you would have gotten if you hadn't seeded it.
