Weather Modification Comes of Age

April 22, 2008 -- The practice of cloud seeding to create rain, mitigate hail or even quell hurricanes is now on the road from science fiction to fact, said scientists at the meeting of the American Meteorological Society (AMS) and the Weather Modification Association (WMA) in Westminster, Colo. on Tuesday.

On the other hand, there is little hope that China's efforts to keep rain from falling on the Olympics will succeed, they said.

China has spent $100 million and employed 30,000 people in weather modification projects, but they are using old techniques from the 1960s and 1970s and have no way of evaluating whether their efforts are working, said Roelof Bruintjes of the National Center for Atmospheric Research, who recently visited China.

"Personally, I am very skeptical about what they claim they can do," said Bruintjes. But that's not the case worldwide, where more than 40 countries have projects underway to modify weather.

Doppler radar, advanced weather satellites and sophisticated weather models, combined with a lot of accidental, human-caused weather modification, make it finally possible to do the one thing that was virtually impossible in the past -- assess whether humans are having any effect on clouds. That's a big advance for a field that has seen a lot of hope, hype and often a desperate need for progress.

"There was a lot of excitement in the 1950s," said Bruintjes. But without any information about what was happening inside the clouds, it was impossible to tell if a shot of silver iodide into a cloud was really forming rain, or not.

What's more, said Bruintjes, a cloud-seeding technique that might appear to work one day might not work on another day, from season to season, or from place to place. This made it very hard to move ahead with any genuine science of weather modification.

Now, however, it's possible to see changes on the order of 10 to 15 percent in rain or snowfall when silver iodide is used to stimulate rain formation or when special salts are used to increase the size of existing raindrops.

These are the only two cloud-seeding techniques with any scientific backing, Bruintjes said.