4 Things To Know About Cloud Seeding

In the wake of the horrific Texas floods, there is a lot of discussion about cloud seeding. While it certainly did not cause those floods, talk about cloud seeding has flowed out of the fringes into mainstream conversations. As a meteorologist and atmospheric science expert with around thirty years of experience, I thought it would be useful to provide four basic facts about it.

The Concept

I remember sitting in a barber shop one day on a hot summer day as it rained. I told the barbers that rain began as snow in the upper reaches of the clouds. They were baffled. Let me explain. Most U.S. rainstorms are caused by a process called the Bergeron or ice crystal process. In my atmospheric physic class, I get more into the physics of it all, but a summary will suffice here. Precipitating clouds will typically have a mix of ice crystals, supercooled water (water at temperatures below freezing), water droplets, and water vapor. According to the NOAA Glossary, the Bergeron process is, “The process by which ice crystals in a cloud grow at the expense of supercooled liquid water droplets.”

All clouds need “seeds” called condensation nuclei or ice nuclei to properly develop. This could be a speck of dust, clay or pollen in the atmosphere. There are several temperature, moisture, and air motion processes that come into play. However, ice nuclei are very important for the formation of ice crystals in the upper part of clouds. As ice crystals grow larger through clumping with other ice crystals or taking on available water in the clouds, they eventually fall out of the cloud as snow. However, the temperature is often above the freezing mark so they melt, and rainfall is observed at the ground. If temperatures are below freezing all the way down to the ground, it remains as snow. The concept of cloud seeding is to introduce seeds of “ice nuclei” into the upper reaches of clouds to get the ice crystal process started.

It’s Not New

I learned about cloud seeding as a young graduate student at Florida State and even worked with one of the early pioneers at NASA, Dr. Joanne Simpson, who studied it early in here career. Cloud seeding is always a part of my units on cloud formation processes in atmospheric physics or radar meteorology classes that I have taught over the years. I usually end the lesson with, “Studies have been inconclusve (more on that later). According to the Desert Research Institute website, “This rain-inducing technique, called cloud-seeding, has been around for more than 60 years. There were suggestions about doing cloud seeding as early as the 1890s, but work on aircraft icing by General Electric during the 1940s was the ultimate catalyst. Several private and federal studies commenced in the following decades.

The process involves “seeding” existing clouds with a harmless substance called silver-iodide to give water droplets a particle to converge around, allowing them to form an ice crystal.” I strongly urge you to visit the DRI website FAQ, which addresses misinformation and misleading statements on the Internet about cloud seeding related to geoengineering, chemtrails, climate change and the toxicity of silver iodide. I also recommend this NOAA fact check site. What I mostly see is a lot of conflation of thought and concepts related to cloud seeding.

Its Effectiveness Is Limited And Inconclusive

The DRI website points out, “Although not a panacea for drought-stricken regions, cloud-seeding can increase seasonal precipitation by about 10%.” There are certainly private companies, states and governments with varying claims about the efficacy of cloud seeding, most studies have found cloud seeding to be inconclusive. Writing about Dr. Joanne Simpson’s early work in Nature, Bob Houze said, “Although cloud seeding has never proved feasible, Simpson’s studies led to improved cloud modelling….”

Candidly, I can see why there is confusion. Many websites use very definitive language about the efficacy of cloud seeding. It would certainly make sense why some sites would be more aggressive with such claims. However, a 2024 U.S. Government Accountability Office report found:

1. “Reliable information is lacking on the conduct of optimal, effective cloud seeding and its benefits and effects. Without such information, operations will be less effective and the return on funding investments is unclear.
2. Cloud seeding operations can only enhance precipitation when the right kind of clouds are present, which limits opportunities for success.
3. The public may not fully understand cloud seeding…”

Texas Floods

As I wrote this weekend, the Texas Floods had numerous meteorological signals that forecasters warned about even days in advance. On June 30th, NOAA identified Texas Hill Country with a risk for extreme rainfall. The combination of extreme moisture, a decaying tropical system, a mesoscale convective vortex, and tilted trough were clear indicators of an extreme rainfall event. That’s why NOAA and NWS issues advanced warnings and watches in the days to hours leading up to the tragedy. Meteorologist Matthew Cappucci wrote, “Cloud seeding DOES NOT cause floods. If there’s enough moisture to cause a flood, it’s already raining. It’s like wringing the water out of a sponge. That’s not going to flood your apartment. If your apartment is already flooding, that has nothing to do with the sponge in your sink.”

In summary, I promise you that experts like me are aware of cloud seeding. It wasn’t discovered with your Internet search or video.