What to Know About Cloud Seeding

Medically Reviewed by Nayana Ambardekar, MD on April 11, 2024
4 min read

Cloud seeding is a scientific process that improves a cloud’s ability to make rain or snow, as well as control other weather events. The technique, which experts also call weather modification, can really help in areas that don’t have a big enough supply of natural water. After cloud seeding, precipitation (rain or snow) will fall from the clouds onto the ground.

This method started in 1946 by scientists at the General Electric Research Laboratory. They discovered that they could use silver iodide -- an inorganic compound -- and dry ice to improve the creation of ice crystals in clouds.

Today, cloud seeding still involves silver iodide and dry ice. But in the last 60 years, experts have learned a lot more about this method. This has since boosted the understanding of rain and snow processes and improved seeding methods.

Not all clouds create rain. Even if they do make rainwater, only a few clouds are able to produce enough moisture that allows for large raindrops.

This may happen because there aren’t enough ice particles within a cloud. Because of this, there aren’t enough cloud droplets to combine and make raindrops. Another reason that certain rainclouds may struggle to make rain is that some don’t last long enough to have cloud droplets gather to create rain.

Cloud seeding gives these clouds a lot more ice crystals (or cloud nuclei). If experts complete seeding at the right time, it leads to more moisture supply, which will eventually create rainwater.

Experts use silver iodide because its structure is very similar to natural ice crystals. When they put silver iodide in the top part of a growing cloud, the silver iodide crystal grows quickly once exposed to the cloud’s moisture. Right after, the ice crystal becomes a heavy, large raindrop. It will then fall through the cloud and onto the ground. Just 1 gram of silver iodide can create up to 10 trillion artificial ice crystals.

Scientists have found two main ways to conduct cloud seeding:

Release silver iodide particles from below the cloud base. Pyrotechnics (or flares) on the wings of planes burn silver iodide from below the clouds. The updraft from the cloud takes the particles high into the center of the cloud.

Drop silver iodide particles from above the cloud. Planes can also let off electrical pyrotechnics over the top of clouds. The flares become ignited once they fall off the plane and onto the cloud.

Sometimes, silver iodide may not be the best option. In droughts, clouds may not be able to create cloud droplets with this approach. But the clouds still have a lot of water in them, it’s just in tiny droplets. If this is the case, a hygroscopic material (like regular salt) might be a better option to cloud seed with.

Experts may also use liquid propane, dry ice (solid carbon dioxide), and other salt compounds to “seed” clouds.

In 2021, the United Arab Emirates began to experiment with the use of aerial drones for cloud seeding. The new twist on the old concept uses drones to cast an electric charge. This “zaps” clouds with a laser beam, which causes water droplets to combine and leads to rainfall.

Cloud seeding can help in many ways. It can:

  • Create more winter snowfall and lead to more mountain snowpack
  • Enhance the natural water supply to communities
  • Lessen hailstorms by reordering water vapor in clouds, which breaks down large hailstones

So far, experts haven’t found any harmful effects of cloud seeding with silver iodide on the environment. The concentration of silver in a storm from cloud seeding is far below the accepted limit of 50 micrograms per liter. There is a lot more iodine in iodized salt (the salt that humans eat) than there is in this form of rainwater.

Even in projects that have lasted 30 to 40 years, researchers haven’t found any major concerns in cloud seeding processes.

Rainwater from seeding clouds doesn’t taste or smell any different than regular rainwater. You wouldn’t be able to tell the difference between the two.

While we don’t know specifically if cloud seeding poses a threat, some experts believe that it could lead to silver toxicity and environmental concerns if the practice becomes common on a much larger scale. Similarly, people worry that cloud seeding could throw off earth’s natural balance of moisture. They fear that this could have effects on evaporation and precipitation.

Cloud seeding has faced some public concern. Many people don’t understand the science behind seeding, which has led to websites that contain false claims or conspiracy theories about the technique.