Finally, scientists had found a way to control the weather -- at least in the lab. For the next 30 years, researchers and entrepreneurs across the world began applying the principles developed by Langmuir, Schaefer and Vonnegut to real-world cloud seeding. They flew airplanes into the clouds, releasing their own clouds of silver iodide as they went, or fired artillery shells filled with silver iodide into clouds. In some cases, these weather modifiers were trying to produce rain in drought-afflicted areas, mitigate hail damage by preventing hailstones from growing so large, or disperse fog banks around airports. Many proprietors of this new technology made audacious claims about their cloud seeding services. Unfortunately, hard science could never substantiate the claims. If anything, rigorous experimentation seemed to suggest that cloud seeding barely worked or, worse, didn't work at all.
Still, enough tantalizing evidence has accumulated over the years to keep interest in weather modification alive. For example, research conducted in South Africa and Mexico has shown that seeding warm rain clouds with salt particles -- what is known as hygroscopic seeding -- is more effective than seeding cold rain clouds with silver iodide. And Chinese scientists believe they have mastered cloud seeding to such a degree that they can guarantee a certain day will be rainy or sunny, like say the opening ceremony of the 2008 Summer Olympics in Beijing, as this related article describes.
It's one thing to control precipitation from a few clouds over a localized area. But is it possible to prevent hurricanes from forming? Some scientists think so. Computer modeling of recent major hurricanes, such as 1992's Andrew, reveals how even one or two small changes could have turned a major catastrophe into a minor storm. This is the heart of chaos theory, a set of scientific principles describing highly complex systems, such as weather systems, where small changes in initial conditions radically change the final results.
Now meteorologists wonder whether they could put chaos to good use to prevent hurricanes from forming in the first place. If they could change one or two variables just as an Atlantic storm is beginning to coil itself into a monster, maybe they could diminish its strength or divert its path. Changing sea temperatures seems the most likely scenario, and a few scientists have proposed coating the ocean surface with a thin layer of biodegradable oil. This could, in theory, reduce evaporation, the process that drives hurricane formation. Similar ideas could work on tornadoes, as well. One physicist has proposed disrupting funnel-cloud formation by zapping the atmosphere with beams of microwaves shot from solar-powered satellites.
But right now, this sounds like more science fiction, where controlling the weather remains as easy as flipping a switch on the Weather Modification Machine and dialing up just the right amount of rain, snow or sun.