1 When moist, warm air rises to a cooler elevation, water
condenses onto microscopic “seeds” like dust, ash, or bacteria.
Water + seeds + updraft = clouds. 2 If there’s more water vapor
than places for it to condense, already-formed ice crystals can
also serve as seeds. As the crystals take on moisture, they may
become too heavy for updrafts to support. Time for the umbrella.
3 It makes sense, then, that adding seeds to thin clouds should
make them rain out. Believing the theory, 37,000 Chinese
peasants shot rockets filled with silver iodide (a widely used
seeding agent) into clouds. 4 So much for People Power. After
reviewing 40 years of cloud-seeding efforts in an area north of
Israel, researchers at Tel Aviv University have concluded that
seeding doesn’t actually produce additional precipitation (pdf).
5 Super-seeding: A team led by Stephen Salter of the University
of Edinburgh has proposed using 1,500 oceangoing ships to spray
saltwater into stratocumulus clouds in order to increase our
planet’s cloud cov