Can we control the weather?

Let's start with a brief history. Numerous Native American tribes, especially those living in semiarid desert country, such as the Pueblo, Hopi and Zuni, engaged in elaborate dances to coax moisture from the rain-stingy skies. In the late 1800s and early 1900s, rainmakers roamed across the western United States, promising to end droughts for a fee.

These itinerant salesmen used a combination of pseudo-science and grand showmanship to convince communities that their technique, often a device or structure used to deliver chemicals or gases into the air, would bring rain in short order.

Even the U.S. government got in on the act. In 1891, Congress appropriated $19,000 to conduct rainmaking tests in Texas under the guidance of Robert Dryenforth. Dryenforth's results were inconclusive, and as the century turned, politicians and citizens began to regard rainmakers with increasing skepticism.

It would take another four decades before the scientists involved with weather control began to overshadow the charlatans. The real turning point came in 1946, when Irving Langmuir and Vincent Schaefer, chemists working at General Electric Research Laboratory in Schenectady, N.Y., discovered that they could introduce ice crystals into a supercooled cloud and create snow. They called the process glaciogenic cloud seeding and soon enlisted the help of physical chemist (and brother to novelist Kurt Vonnegut) Bernard Vonnegut.

Vonnegut searched for another crystalline substance that would have a similar effect, and he found it in silver iodide. Over time, the team worked out the basic science of cloud seeding, which goes like this: Often, the drops of moisture in clouds can't freeze without some extra help. If these drops encounter crystals of silver iodide, they glom onto the crystals and freeze. Once the ice grows big enough, it falls from the cloud, either as snow or, if it passes through warmer air, as rain.

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 manipulation 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.

Meanwhile, 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 reduced a major catastrophe of damaging weather 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 water 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.

Today's scientists remain committed to reshaping our ecosystem so that humanity is not constantly threatened -- whether it's carbon dioxide removal to fight global warming or dense asteroid dust to create a solar barrier. One physicist has even 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. We may not be able to turn a dial up to increase rainfall or down to remove carbon dioxide, but progress is being made. As research into space geoengineering and solar engineering intensifies, the entire planet stands to benefit.