It was not entirely clear how much credit they could take. They had arrived in Texas just at the beginning of the rainy season, and the precipitation that fell before the experiment had been predicted by the U.S. Weather Bureau. As for Powers’s idea that rain came after battles, well, battles tended to start in dry weather, so it was just the natural cycle of things that wet weather often followed.
Despite scepticism from serious scientists and ridicule from some sections of the press, the Midland experiments lit the fuse on half a century of pseudoscience about rainmaking. The Met Office soon found itself embroiled in a media battle to discredit the efforts of self-styled rainmakers who began operating across the country.
The most famous of these was Charles Hatfield, nicknamed the Humidity Accelerator or the Ponzi of the Skies, depending on who you asked. Originally a sewing-machine salesman from California, he reinvented himself as a weather guru and struck dozens of deals with desperate towns. When he arrived in a new place, he would build a series of wooden towers, mix up a secret blend of 23 chemicals aged in barrels, and pour it into vats at the top of the towers to evaporate into the sky. Hatfield’s methods had an air of witchcraft, but he had a knack for playing the odds. In Los Angeles, he promised 18 inches of rain between mid-December and the end of April, when historical rainfall records suggested a 50 percent chance of that happening anyway.
While these showmen and charlatans were filling their wallets, scientists were slowly discovering what it was all about. in fact It made rain — something called cloud condensation nuclei. Even on a clear day, the skies are filled with particles, some no bigger than a pollen grain or a viral strand. “Every cloud droplet in Earth’s atmosphere was formed from a preexisting aerosol particle,” one cloud physicist told me. The types of particles vary by location. In the United Arab Emirates, they include a complex mix of sulfate-rich sands from the Empty Quarter desert, salt spray from the Persian Gulf, chemicals from the oil refineries that dot the region, and organic materials from as far away as India. Without them, there would be no clouds at all: no rain, no snow, no hail.
Many raindrops start out as ice crystals suspended in the air, which melt as they fall to Earth. But without condensation nuclei in clouds, even ice crystals won’t form until the temperature drops below -40 degrees Fahrenheit. As a result, the atmosphere is filled with pockets of supercooled liquid water that is below the freezing point but hasn’t actually turned into ice.
In 1938, a German meteorologist suggested that seeding these areas of frozen water with artificial cloud condensation nuclei might encourage the formation of ice crystals, which would quickly grow large enough to fall, first as snowflakes and then as rain. After World War II, American scientists at General Electric seized on the idea. One group, led by chemists Vincent Schaefer and Irving Langmuir, discovered that solid carbon dioxide, also known as dry ice, would work. When Schaefer dropped grains of dry ice into the home freezer he had been using as a makeshift cloud chamber, he found that water easily freezes around the crystalline structure of the particles. When he witnessed the effect a week later, Langmuir jotted down three words in his notebook: “Weather control.” Within months, they were dropping dry ice pellets from airplanes onto Mount Greylock in western Massachusetts, creating a 3-mile-long swath of ice and snow.