Above: Battery of Stiger Vortex rain-making guns at Charleville, Australia, in 1902. Unlike modern cloud seeding techniques that use silver iodide crystals, these guns were loaded with gunpowder (Wikimedia Commons/The Queenslander)

When you got up this morning, you probably wondered what the weather would be today. Any rain in the forecast? Fog? Maybe snow? Any storm warnings? People have always tried to predict the weather in order to prepare for it. After all, you have no control over it. Or do you? Cloud physicists, who study ways to tweak the weather, believe they can. And there is increasing evidence that they may be right.

Cloud seeding

Did you know? Cloud physicists are studying an alternative to traditional cloud seeding that uses negatively charged ions instead of ice-like crystals.In particular, a 70-year-old weather modification technology called cloud seeding seems to be gaining new traction. To put it simply, clouds carry water that doesn’t always get to where it’s needed on the ground. The water molecules are too spread out to feel earth’s gravitational pull. To fall to the ground they must first huddle together and gain some weight.

And that is where cloud seeding helps. It puts ice-like grains in the clouds, and these grains gather up the water molecules into larger ice crystals. The crystals then fall to the ground as rain or snow, depending on the temperature of the air. The ice-like grains are usually made of silver iodide, and they get shot into clouds either from airplanes or from cannon-like devices on the ground.

But why use cloud seeding? How do people benefit from it? The most obvious gain is more rain in areas plagued by drought. In Southwestern Texas for example, the West Texas Weather Modification Association has been seeding clouds since 1997. In Colorado, some ski resorts have used cloud seeding for decades to increase snowfall.

Cloud seeding can also be used to clear away fog by turning it into precipitation, which helps improve visibility around airports. And, when used on hail-producing clouds, cloud seeding increases the number of ice pellets but decreases the size of each pellet, thereby reducing hail damage.

Is it effective?

If cloud seeding has so many uses and has been around for so long, why have so few people heard of it? In fact, weather modification has proven to be a controversial subject over the years.

A persistent argument against cloud seeding has been the absence of convincing evidence showing that it really works. Unless you could seed only one of two identical clouds in the exact same location – which would be impossible to do – how would you know for sure that it wouldn’t have rained anyway? In the absence of proper controls, any positive results have always remained questionable.

But in recent years, the situation has begun to change. Thanks to new radar, satellite, and computing technologies, information about the atmosphere and clouds is not only more accessible and accurate, but it can also be analyzed in much more detail. As a result, cloud physicists can now simulate atmospheric events, and run virtual experiments that provide convincing evidence supporting the effectiveness of cloud seeding.

Potential dangers

Did you know? Cloud seeding is one of many technologies for controlling weather. Together, they form the field of geo-engineering, whose main focus is to fight climate change.However, evidence that cloud seeding works still hasn’t convinced everyone that it’s a good idea. Some argue that the effectiveness of cloud seeding—a 10-15% increase in rainfall, for example—is too low to outweigh the risks it poses to the environment and public safety. Indeed, silver iodide is toxic to aquatic life, and although cloud seeders use amounts that are too small to even detect, it would be best if it could be avoided altogether.

In response to these concerns, testing of nontoxic replacements, such as calcium chloride (salt), is underway. If found effective, the use of salt in such tiny doses is unlikely to harm the environment.

Another problem is the risk of flooding and other undesirable effects of increasing precipitation in a localized area. For example, would rain in one area bring drought to another? Or could cloud seeding cause too much rain to fall? After all, weather systems are very complex and it is impossible to predict exactly how attempts to modify the weather will play out.

While so far no droughts have been blamed on cloud seeding—in fact, adjacent areas tend to get more rather than less rain--many of those affected by a flash flood that devastated Rapid City, South Dakota, in 1972 suspected that nearby cloud seeding operations contributed to the severity of the situation. Even if there is no proof that cloud seeding was to blame, events like this one are bound to raise skepticism about the technology.

There is also the possibility of malicious use and the weaponization of weather modification techniques. Although it was used during the Vietnam War, an international treaty signed in 1977 banned the use of weather modification for military and other hostile purposes.

* * *

Governments in China and Russia are staunch supporters of weather modification technology. However, in North America, cloud seeding is generally seen as too contentious to receive public funding. But that hasn’t kept private companies from using it.

As with many other technologies, the advantages of weather modification must be weighed carefully against its dangers. Do you think cloud seeding should be permitted and, if so, how should it be regulated? In the future, do you think it will be possible to order up sunshine, snow or rain whenever and wherever we want? Do you think that would be a good thing?

Learn more!

How to (Try to) Make It Rain (2014)
Dan Baum, Scientific American

Article listing five ways, including cloud seeding,  that humans have tried to control the weather.

Alberta’s cloud-seeding pilots see 2nd busiest year in 20 years (2014)
CBC News

Planting seeds in Mancos clouds (2014)
Mary Shinn, The Durango Herald (CO)

Fact file: Cloud seeding (2013)
Erika Tucker, Global News

Dry ice helps clear the fog at airport (2012)
Mail Tribune (Medford, OR)

News reports on the use of cloud seeding and other weather modification technologies.

Has the Time Come to Try Geoengineering? (2012)
David Biello, Scientific American

Blog entry arguing for weather modification technology to be given more consideration in the fight against global warming.

Rainmaking in Middle Eastern Desert: Success or Scam? (2011)
Jeremy Hsu & Jeanna Bryner, LiveScience

Article discussing claims by a Swiss company that their weather-modification project successfully produced rain in an Arabian  desert using ion generation.   

Can we control the weather? (2010)

William Harris, HowStuffWorks

General introduction to weather modification technologies with links to additional information.

Cloud Seeding and the Rapid City flood of 1972 (2010)

Arnett Dennis, Journal of Weather Modification

Scientific article on the possible influence of nearby cloud seeding operations on the flood.

Convention on the prohibition of military or any other hostile use of environmental modification technique (1977)
United Nations

International agreement prohibiting the militarization of weather modification technologies.

Magdalena Pop

Magda Popp

I am a biochemist and educator working to increase students’ motivation for learning science. I earned my PhD at the Max Planck Institute for Biophysical Chemistry in Göttingen (Germany), where I did research on human viral infections, primarily HIV/AIDS. In 2001 I started teaching high-school science in Canada, and in 2013 I became a mentor for Alberta's high school teams participating in the international Genetically Engineered Machines (iGEM) competition. Writing articles for CurioCity is one of the ways in which I follow my passion for sparking genuine excitement and curiosity about science. Check out my blog - School Sense - here.


En tant que biochimiste et éducatrice, je travaille afin de susciter l’intérêt des élèves pour les sciences. J’ai obtenu mon doctorat de l’Institut Max Planck de chimie biophysique à Göttingen, en Allemagne. C’est là que j’ai fait des recherches sur les infections virales humaines, principalement le VIH/SIDA. En 2001, j’ai commencé à enseigner les sciences aux élèves du secondaire au Canada. En 2013, j’ai été un mentor pour les équipes albertaines participant à l’iGEM, une compétition internationale de machines génétiquement modifiées. La rédaction d’articles pour CurioCité est une des façons dont j’essaie de susciter un véritable enthousiasme pour les sciences. On peut visiter mon blogue, « School Sense », en cliquant ici.

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