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Matt Ridley is the author of provocative books on evolution, genetics and society. His books have sold over a million copies, been translated into thirty languages, and have won several awards.

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Seeds of an idea

Bacteria that live in the clouds and the prospect of controlling the weather

My good friend Dave Sands is not only a brilliant biologist -- I cite him in The Rational Optimist arguing for genetic modification to improve the quality rather than the quantity of food -- but a very fine poet. He's profiled in yesterday's New York Times discussing his latest theory that ice-forming pseudomonas bactera in the air play a central role in precipitation:

In the last few years, Dr. Sands and other researchers have accumulated evidence that the well-known group of bacteria, long known to live on agricultural crops, are far more widespread and may be part of a little-studied weather ecosystem. The principle is well accepted, but how widespread the phenomenon is remains a matter of debate.

If true, this could have all sorts of implications.

The accepted precipitation model is that soot, dust and other inert things form the nuclei for raindrops and snowflakes. Scientists have found these bacteria in abundance on the leaves of a wide range of wild and domestic plants, including trees and grasses, everywhere they have looked, including Montana, Morocco, France, the Yukon and in the long buried ice of Antarctica. The bacteria have been found in clouds and in streams and irrigation ditches. In one study of several mountaintops here, 70 percent of the snow crystals examined had formed around a bacterial nucleus.

This ability to promote freezing of water at higher-than-normal freezing temperatures has led Dr. Sands and other scientists to believe the bacteria are part of an unstudied system. After the bacteria infect plants and multiply, he says, they may be swept as aerosols into the sky, where it seems they prompt the formation of ice crystals (which melt as they fall to earth, causing rain) at higher temperatures than do dust or mineral particles that also function as the nuclei of ice crystals.

Sands is telling us that the air is a habitat too.

By chance today my son and I were walking in the rain and we started imagining a future in whcih weather is controllable, but some countries decide when it should rain by political means -- referendums, committees, bureaucracies, protests -- while others leave it to the market.

We plan to write a Swiftian satire along these lines. One wet day.