SNOW GROWER? Can human intervention bring on bouts of precipitation such as this week's snowstorm in China?
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At long last, it snowed in northern China. The first snow of the year came to Hebei, the northern province surrounding Beijing. In the Chinese capital, it was the first real bout of precipitation since last October. The blizzard caused 12 area highways around Beijing to close.

Travel inconveniences aside, the blast of moisture was more than welcome in China, which is suffering through its worst drought in decades. Earlier this week, government officials announced that even the country's massive water projects, like the North-South Water Transfer Project, couldn't hope to deal with future shortages—the country would have to cut back its demand as well.

It should come as no surprise, then, that the Chinese government wanted to claim a little credit for the good weather fortune, and they have. Officials said their cloud-seeding program directly caused the snowstorm. Engineers blasted more than 400 cigarette-size sticks of silver iodide into the sky shortly before the storm, and a senior engineer told Reuters that it was "a procedure that made the snow a lot heavier."

Cloud seeding and other weather-modification schemes have been around for years. But how do they work? And can you really claim that cloud seeding caused a particular storm? We asked cloud-seeding expert Arlen Huggins, associate research scientist in the division of atmospheric sciences at the Desert Research Institute in Reno, Nev., to give us some answers.

[An edited transcript of the interview follows.]

Tell us a little about the basics of cloud seeding.
Clouds, whether in summer or winter, are not perfectly efficient at producing precipitation. There's some part of a storm that's much less than 100 percent efficient in turning clouds into precipitation. In winter, the problem is that there aren't sufficient ice crystals. If droplets fall in liquid form they generally evaporate. The idea is to add ice-forming particles.

Why silver iodide?
One thing people discovered early on is that the structure is very similar to that of ice. The lattice structure at the molecular level is very, very close. We think that's why ice wants to bond to it.

When did scientists get serious about experimenting with cloud seeding?
I think it was the day after they finished the experiments in the lab [chuckles]. The initial discoveries were in the 1940s, with substances like silver iodide. It was a short period before they started trying to affect larger systems, without much success.

Wasn't Kurt Vonnegut's brother one of the lead scientists in the 1940s?
Yeah, Bernard Vonnegut.

[Editor's note: Bernard Vonnegut, the older brother of the late novelist Kurt, uncovered silver iodide's weather-modifying properties as a researcher for General Electric in 1946. He later taught atmospheric science at the State University of New York at Albany before passing away in 1997.]