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In one of his more meteorological moments, science-fiction author Robert Heinlein cheekily explained the difference between climate and weather: "Climate is what you expect, weather is what you get." Air-conditioning is what humans use to make sure that what we expect and what we get resemble each other.

There were certainly other ways of trying to outsmart the weather before air-conditioning came along, at the dawn of the 20th century. During a third-century summer, the eccentric Roman Emperor Elagabalus sent 1,000 slaves to the mountains to fetch snow for his gardens. And fans — be they electric gadgets or palm leaves wielded by servants — have helped create their share of faux wind. But it was AC that truly signified the onset of man-made weather by both cooling air and controlling humidity.

The first system was designed in 1902 by inventor Willis Carrier (the Edison of air-conditioning) as a solution to keep muggy air in a printing plant from wrinkling magazine pages. He successfully used coils to both cool and remove moisture from the air, and would eventually establish the first mass manufacturing plant for air conditioners. While the first home unit, proportional in size to early computers, was installed in 1914, air conditioners remained too bulky, noisy and full of chemicals to become widespread for several more decades.

Advances in technology eventually yielded the more convenient window air conditioner in the late 1930s, though it remained out of reach for most. The general public — those not privy to the few luxurious hotels and cars that used cooling systems early on — often first encountered air-conditioning in movie theaters, which started to widely use the technology in the 1930s. Before the window unit's heyday, Carrier produced a system for theaters that cost between $10,000 and $50,000. It was one of the few things proprietors sprung for during the Great Depression, and theaters were one of the rare places where the hoi polloi could enjoy chilly, artificial air.

In the beginning, as with all new things, air-conditioning was regarded as a luxury, especially for tightfisted bosses who viewed such worker comfort as contradictory to the sweat they were paying for. So in the 1940s and '50s, the air-conditioning industry gave its product a different spin. Keeping employees cool was simply a matter of productivity, and there were numbers to prove it. According to Gail Cooper's Air-Conditioning America, tests of federal employees showed that typists increased their output by 24% when transferred from a regular office to a cooled one. By 1957, the AC's early reputation for making workers lazy had been successfully inverted; Cooper writes of another study showing that, by then, almost 90% of companies cited air-conditioning as the most important factor in office efficiency.

America remained at the forefront of AC adoption. In 1947, British scholar S.F. Markham wrote, "The greatest contribution to civilization in this century may well be air-conditioning — and America leads the way." By the time 1980 rolled around, the U.S. — which then housed only 5% of the world's population — was consuming more air-conditioning than all other countries combined. Essayists lamented people's reliance on the electricity-devouring invention. "It is thus no exaggeration to say that Americans have taken to mechanical cooling avidly and greedily," remarked former TIME writer Frank Trippett in 1979. "Many have become all but addicted."

Over the years, air-conditioning has been credited with the survival of institutions and industries: the heat-sensitive world of computer networks; the U.S. federal government, which often had to shut down in swampy Washington, D.C., before the embrace of man-made coolness; Las Vegas. But even the cool bliss of AC has raised the temperature of some critics. Environmentalists who are concerned about global warming have long called for cutting back on AC use. "It's just one of those technologies that tends to create the need and desire for even more of it," said Stan Cox, author of Losing Our Cool: Uncomfortable Truths About Our Air-Conditioned World (and Finding New Ways to Get Through the Summer), in a recent interview. Cox, discussing early July's Northeastern heat wave, conceded that the invention still has a clearly proven public-health benefit. Regardless, record-breaking temperatures might not provide the best inspiration for people to embrace the weather au naturel.