If only we could control the weather—at the push of a button make it warmer or cooler, wetter or drier. We’d have no more droughts or floods, no heat waves or icy roads. Deserts would become verdant. Crops would never fail. And we could stop worrying about climate change. As it happens, the threat of climate change has sparked some crazy-sounding ideas for hacking the climate, such as spraying sulfuric acid into the upper atmosphere to cool it down or dumping quicklime in the oceans to absorb carbon dioxide and slow down the greenhouse effect.1 Other scientists, meanwhile, are working on realizing the shaman’s dream of making rain; their techniques include seeding clouds with silver iodide and sending electrically charged particles into the sky.2
Clever as humans are, however, we’re nowhere near precision control of the weather. At least if we’re talking about outside. Since the invention of air-conditioning, we can control the weather inside. That is not quite as big a deal, but it has still had some far-reaching and unexpected effects.
Ever since our ancestors mastered fire, humans have been able to get warmer when it’s cold. Cooling down when it’s hot has been more of a challenge. The eccentric, teenaged Roman emperor Elagabalus made an early attempt at air-conditioning by sending slaves into the mountains to bring down snow and pile it in his garden, where breezes would carry the cooler air inside.3
Needless to say, this was not a scalable solution. At least, not until the nineteenth century, when a Boston entrepreneur named Frederic Tudor amassed an unlikely fortune in a similar way. In 1806, he began carving blocks of ice from New England’s frozen lakes in winter, insulating them in sawdust, and shipping them to warmer climes for summer. The idea was to be profitable for the rest of the century, and the warmer parts of the country became addicted to New England ice. Mild New England winters would cause panic about an “ice famine.”4
Air-conditioning as we know it began in 1902, and it had nothing to do with human comfort. The workers at Sackett & Wilhelms Lithographing & Printing Company in New York were frustrated with varying humidity levels when trying to print in color. The process required the same paper to be printed four times—in cyan ink, then magenta, yellow, and black. If the humidity changed between print runs, the paper would slightly expand or contract. Even a millimeter’s misalignment looked—and still looks—awful.
The printers asked Buffalo Forge, a heating company, if it could devise a system to control humidity. Buffalo Forge assigned the problem to a young engineer, just a year out of Cornell University. Willis Carrier was earning $10 a week—below minimum wage in today’s money. But he figured out a solution: circulating air over coils that were chilled by compressed ammonia maintained the humidity at a constant 55 percent. Modern air conditioners use different chemicals as coolants, but the basic idea remains much the same.
The printers were delighted, and Buffalo Forge was soon selling Willis Carrier’s invention wherever humidity posed problems: from textiles to flour mills to the Gillette Company, where excessive moisture rusted its razor blades. These early industrial clients didn’t much care about making temperatures more comfortable for their workers; that was an incidental benefit to controlling the humidity. But Carrier saw an opportunity. By 1906 he was already talking up the potential for “comfort” applications in theaters and other public buildings.5
It was an astute choice of target market. Historically, theaters often shut down for summer—on a stifling-hot day, nobody wanted to see a play. It’s not hard to imagine why: no windows; human bodies tightly packed; and, before electricity, lighting provided by flares that gave off heat. New England ice was briefly popular: in the summer of 1880, New York’s Madison Square Theatre used four tons of ice a day; an eight-foot fan blew air over the ice and through ducts toward the audience. Unfortunately, this wasn’t an ideal solution. The air, though cool, was also damp, and pollution was increasing in New England’s lakes. Sometimes, as the ice melted, unpleasant smells wafted into the auditorium.6
Willis Carrier called his system of cooling the “weathermaker,” and it was much more practical. The burgeoning movie theaters of the 1920s were where the general public first experienced air-conditioning, and it quickly became as much of a selling point as the new talkies. The enduring and profitable Hollywood tradition of the summer blockbuster traces directly back to Carrier. So does the rise of the shopping mall.
But air-conditioning has become more than a mere convenience. Computers fail if they get too hot or damp, so air-conditioning enables the server farms that power the Internet. Indeed, if factories couldn’t control their air quality, we’d struggle to manufacture silicon chips at all. Air-conditioning is a revolutionary technology; it has had a profound influence on where and how we live.
Air-conditioning has transformed architecture. Historically, a cool building in a hot climate implied thick walls, high ceilings, balconies, courtyards, and windows facing away from the sun. The so-called dogtrot house, once popular in America’s South, was two sets of rooms bisected by a covered, open-ended corridor that allowed breezes through. Without air-conditioning, glass-fronted skyscrapers are not a sensible option: you’d bake on the upper floors. With air-conditioning, old workarounds become irrelevant and new building designs become possible.
Air-conditioning has changed demographics, too. Without it, it’s hard to imagine the rise of cities such as Houston, Phoenix, or Atlanta, as well as Dubai or Singapore. As new housing spread rapidly across America in the second half of the twentieth century, population boomed in the Sun Belt—the warmer south of the country, from Florida to California—from 28 percent of Americans to 40 percent.7 As retirees in particular moved from north to south, they also changed the nation’s political balance: the author Steven Johnson has plausibly argued that air-conditioning elected Ronald Reagan.8
Reagan became president in 1980. Back then, America alone, with just five percent of the world’s population, used more than half the world’s air-conditioning.9 Emerging economies have since caught up quickly: China will soon become the global leader.10 The proportion of air-conditioned homes in Chinese cities jumped from under one-tenth to more than two-thirds in just ten years.11 In countries such as India, Brazil, and Indonesia, the market for air conditioners is expanding at double-digit rates.12 And there’s plenty more room for growth: from Manila to Kinshasa, eleven of the world’s thirty largest cities are in the tropics.13
The boom in air-conditioning is good news for many reasons, beyond the obvious that life in a hot, humid summer is simply more pleasant with it than without it. Air-conditioning lowers the death rate during heat waves.14 In prisons, heat makes inmates fractious; air-conditioning pays for itself by reducing fights.15 In exam halls, when the temperature exceeds the low seventies, students start to score lower on math tests.16 In offices, air-conditioning makes us more productive: according to one early study, air-conditioned offices enabled U.S. government typists to do 24 percent more work.17
Economists have since confirmed that there’s a relationship between productivity and keeping cool. Yale University’s William Nordhaus divided the world into cells, by lines of latitude and longitude, and plotted each one’s climate, output, and population. He concluded that the hotter the average temperature, the less productive people could be.18 According to Geoffrey Heal of Columbia University and Jisung Park of Harvard, a hotter-than-average year is bad for productivity in hot countries, but good in cold ones: crunching the numbers, they conclude that human productivity peaks when the temperature is between 65 and 72 degrees Fahrenheit.19
But there’s an inconvenient truth: You can make it cooler inside only by making it warmer outside. Air-conditioning units pump hot air out of buildings. A study in Phoenix, Arizona, found that this effect increased the city’s night-time temperature by two degrees.20 Of course, that only makes air-conditioning units work harder, making the outside hotter still. On underground metro systems, cooling the trains can lead to swelteringly hot platforms. Then there’s the electricity that powers air-conditioning, often made by burning gas or coal; and the coolants air conditioners use, many of which are powerful greenhouse gases when they leak.21
You’d expect air-conditioning technology to be getting cleaner and greener, and you’d be right. But global demand for air-conditioning is growing so quickly, even if the optimists are right about possible efficiency gains, there will still be an eightfold increase in energy consumption by 2050.22 That’s worrying news for climate change.
Will we get inventions to control the outdoor weather, too? Perhaps. But even air-conditioning—a brilliant but simple and straightforward invention—has had some powerful and unexpected side effects. Controlling the climate itself will be neither simple nor straightforward. And the side effects? We can barely imagine.