Weather Modification Comes of Age

Larry O'Hanlon, Discovery News

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.

It's also getting easier to see how air pollution particles, called aerosols, and urban heat are modifying the weather, said Joe Golden, senior researcher for the National Oceanic and Atmospheric Administration's Earth System Science Laboratory.

"This pollution in regions that depend on uplift of air (over mountains) for precipitation...has caused a systematic decrease in snow packs," said Golden. This applies to Colorado, but even more critically to California, where tens of millions of people depend on the slow melting of the Sierra Nevada snow pack for their summer water supply, he said.

Urban heat has also been linked to an increase in cloud-to-ground lightning strikes in Houston, Golden said.

"These are two examples of human-caused effects on weather that concern us," said Golden. So much so that he and other scientists are beginning to collaborate with the U.S. Department of Homeland Security to see if there may be ways to modify weather -- especially hurricanes -- that decrease hazards, he said.

A similar effort, called Project StormFury, was started in the 1960s, but suffered from a lack of data.

"Now we have much better observing tools for looking at hurricanes," said Joe Golden.

That said, the primary reason for cloud seeding worldwide hasn't changed much since the 1950s: to make water fall on thirsty ground, explained Arlen Huggins of Nevada's Desert Research Institute. And there's only so much you can do.

"Cloud seeding is not a drought-busting tool," agreed Bruintjes. "We cannot make clouds; we cannot chase away clouds."

Related Links:

Larry O'Hanlon's blog: Earth Impacts

Planet Green

Discovery Earth Live

How Stuff Works: Lightning

Desert Research Institute