When you're lying on your back in a meadow gazing at the sky, the clouds above you might look utterly pristine. But don't let appearances fool you. In recent years, scientists have discovered that clouds are full of hundreds of varieties of bacteria. Moreover, those microbes may actually play a role in creating precipitation.
That's led some researchers to wonder if we might actually be able to deliberately seed clouds with bacteria and make it rain in places where we need it, according to a recent article in the British publication New Scientist.
NEWS: Moon's Gravity Alters Rainfall on Earth
The link between cloud-borne microbes and precipitation began to emerge in the late 1970s, when Montana State University scientist David C. Sands, who was trying to find the source of a mysterious blight afflicting local wheat crops, got a hunch and flew into the clouds in an aircraft, carrying a Petri dish. Sure enough, Sands found the microbe in question. He also developed the concept of bio-precipitation - that is, that bacteria was involved in making rain - but other scientists were skeptical.
In recent years, though, Sands and other researchers have found evidence to support bio-precipitation. In a 2008 study, Sands and fellow MSU scientist Christine Foreman, Brent Christner from Louisiana State University and Cindy Morris, from the French National Institute for Agricultural Research in Avignon, published a study of precipitation in locations ranging from Montana to Russia. They found that most ice nuclei in clouds - an early stage in the precipitation process - were formed around microbes, rather than dust and soot, as scientists previously had believed.
Bacteria apparently use precipitation to spread themselves. What happens, apparently, is that bacteria clinging to the outside of plants is swept by wind up into the atmosphere.
NEWS: Cyclone Drops 10 Years' Worth of Rain on Yemen
When the microbes get into the clouds, ice crystals form around them, and water clumps onto the crystals, making them bigger. Eventually, the crystals turn into rain and fall to back to Earth, where the microbes land on more plants, and then multiply. Then the cycle repeats itself. (Here's an MSU press release with more detail.)
According to New Scientist, Sands and Morris now are looking at the possibility of controlling that process to cause rainfall. One scenario would be to breed plants that host the greatest abundance of ice-nucleating bacteria, and then put them in the right places to seed rain.