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Airdate: Dec 07, 2017
Scientist: Boris Vinatzer

The Dark Side of Cloud Seeding

The Dark Side of Cloud Seeding
There may be more in a rain shower than you think.

The Dark Side of Cloud Seeding

Ambience: Thunderstorm, A few decades ago, scientists discovered that a bacteria present in clouds was enabling the water to freeze at much higher temperatures than normal. The hope was that we could seed clouds with the bacteria, making rain when needed. There was only one problem. I'm Jim Metzner and this is the Pulse of the Planet.

Vinatzer: The hope was that they could use whatever it is for cloud seeding to induce precipitation. But when they found that it was a known plant pathogen, they were disappointed, saying cannot spray a plant pathogen into clouds.

Boris Vinatzer is an Associate Professor in the Department of plant pathology, Physiology & Weed science at Virginia Tech. He says the bacteria in question, called pseudomonas syringae, was pathogenic - known to cause diseases in plants. But Vinatzer and his students and colleagues in France also found non-pathogenic kinds of pseudomonas syringae which had the same ability to make water freeze.

Vinatzer: Nobody so far has systematically looked for bacteria in rainfall. We're doing the first systematic study of trying to find all possible bacteria that come down with rainfall and see which of these bacteria have a similar activity to pseudomonas syringae. Since nobody looked for them yet, the hypothesis is that there are many others.

Vinatzer: We started collecting rain at the beginning of this year, and through research, we know that there are up to 100,000 bacteria of pseudomonas syringae per liter of rain. Some of them are pathogenic; others are not.

Now why do you think bacteria would evolve to have the ability to freeze water? We'll find out in future programs. Pulse of the Planet is made possible in part by the National Science Foundation. I'm Jim Metzner.