One thing worth considering when you tamper with nature is what sort of nature you’re tampering with. Nature is not kind to the city of Beijing. China’s capital is arid, nearly a desert, and its natural weather patterns are fickle and harsh. Winter is marked by howling Siberian winds; summer, by sweltering monsoon heat. In lieu of showers, springtime is best known for seasonal dust storms that sweep down from Central Asia. Fall is parched and gusty too, but the dust settles down. This basic brutality is overlaid with levels of pollution like those of England’s Industrial Revolution. Many things blot out the sunshine, and most have nothing to do with rain: factory and power plant emissions, construction dust, smoke from stoves burning scrap wood or pressed coal. There are more than 3 million cars on the streets—and the count is said to be growing by 400,000 vehicles annually. It is not unusual to check the AccuWeather international forecast on the New York Times website and find that while other cities’ weather is “mostly sunny” or “overcast,” Beijing’s is “smoky.” In February 2007, authorities finally abandoned a longstanding policy in which haze was referred to as wu, Mandarin for fog, and just called it what it is—mai, or haze.

So the government aims to manipulate the city’s weather. This is a matter of plain bureaucracy, not science fiction. Ren ding sheng tian, went an old aphorism embraced by Mao Zedong: Man must defeat the heavens. The People’s Republic has a colorful history of battling nature with colossal, often ill-starred public-works projects. Imperial flood-control schemes, for instance, begat today’s Three Gorges Dam, designed to be the world’s largest hydroelectric station—and denounced by critics as an environmental disaster. The Weather Modification Office (WMO) is an arm of the Beijing Meteorological Bureau, which is the local branch of the Chinese Meteorological Administration. There are 31 provincial or municipal weather-modification offices in China. The administration employs 52,998 people by its own count. Beijing’s WMO has sixteen full-time employees who direct the activities of several dozen part-time weather modifiers, mostly local farmers. The farmers maintain 21 emplacements of antiaircraft guns and 26 rocket launchers, which fire munitions loaded with silver iodide into the clouds. In the winter, when clouds are lower, the modifiers burn chemical charges in special stoves. A small squadron of planes, flown from a military airfield, delivers silver iodide or dry ice into the clouds from above. In the clouds, the silver iodide mingles with tiny droplets of water—leading, in theory, to the formation of ice particles, which melt into heavier drops and then fall as rain.

The operations of the weather modifiers lend themselves to a kind of science folklore. Beijingers and foreigners in the city harbor pet theories about signs that the government may be tampering with a particular day’s weather—they include unusually fat raindrops, rain from clear skies, or remarkably well-timed breaks of sunshine. Such divination both over- and underestimates the Beijing Meteorological Bureau’s activity. “Normally, if conditions permit, yes, we would modify,” says Zhang Qiang, the deputy director of theWMO. But miraculous transformations have not been the goal—at least until now.