What are your experiences with cloud seeding?
My initial experiences were using cloud seeding to try to reduce hail fall. This was in northeast Colorado, where they don't get the massive hail people get in the Midwest, but they got it at a higher frequency. It turned into more of a research project into how hail and thunderstorms work. There was very little evidence that seeding was reducing hail, but we had some success later in increasing snowfall in the Sierra Nevadas, and more success in the mountains of Utah. We were able, in some instances, to monitor the chain of events, following the storms with aircraft. Now we're studying the actual snow for trace concentrations of the seeding material to see how effective the procedure was.
Plenty of scientists and organizations have tried to write off cloud seeding. Why does it keep coming back?
It keeps coming back because of the demand for water, especially the dire straits of the arid Southwest. It's always been seen as a cheap way to add additional water.
What are the best results you can hope for with cloud seeding?
It depends on where you are, and the reasoning behind it. If you're trying to increase rain or snowfall for the water supply, a 10 percent addition could do a lot. If you had a large basin like I work with, between 300,000 and 500,000 acre-feet*, a 10 percent increase would equal 30,000 to 50,000 more acre-feet of water. If you can do that, it's very economically sound.
Can you attribute any one storm to cloud seeding, as the Chinese government has done with this snowstorm?
Generally, you can't look at one individual storm. Would it have snowed anyway? You don't know. NCAR (the National Center for Atmospheric Research in Boulder, Colo.) is in Wyoming studying several seasons in comparison, where you seed one place and withhold another. Attributing one storm to seeding is very difficult unless the cloud system is incredibly simple, like fog that has no chance of precipitation. If you see snowfall then, that's pretty demonstrative evidence that you succeeded.
Will China's cloud-seeding efforts help to end its drought?
If they are in a drought, they wouldn't be able to draw enough from cloud seeding, just for the lack of clouds. You treat the storms you have, so cloud seeding certainly isn't going to bring you out of a drought. The best time to do cloud seeding is when you have normal levels, or higher-than-normal levels, of precipitation. Then you could save the extra water in a reservoir for when you are in a drought. It certainly won't bring you out of one.
Is cloud seeding unnatural?
Those concerns generally come from places where there's never been a cloud-seeding project before. The problem with saying it's unnatural is that as a human species, since we first set foot on the planet—or at least since we started burning fossil fuels—we've been modifying weather systems on a much larger scale than cloud-seeding projects. We actually get more questions about the potentially harmful effects of chemicals like silver iodide. As a pollutant, silver iodide is almost overshadowed by smokestacks spewing kilotons of pollution, or by auto exhaust.
*Correction (2/25/09): The unit "acre-feet" originally appeared as "acres."