Besides housing design, people had other tricks: taking naps during the heat of the day, carrying hand-held fans around, and, of course, swimming. My grandmother told me she used to pay a bus fare and sit on the open, upper deck for hours, riding all around the city.

The first machine resembling a modern air conditioner was built in 1902 by an inventor named Willis Carrier in an attempt to prevent paper from wrinkling in the heat and humidity at the Sackett-Wilhelms Lithographing and Publishing Company in Brooklyn. Soon, industrial buildings and hospitals began adopting the technology. The first person to air condition his private home was Charles Gates, son of industrialist and profligate gambler John Gates, who set up a cumbersome system at his house in Minneapolis in 1914. (Minneapolis seems like an odd place for the first home air conditioner, but, hey, if you've got the cash, who's to stop you?)

In the 1920s, innovations made air conditioning units smaller and safer (older versions had used a toxic coolant). During the Depression, few places could afford to install the systems, but one venue saw returns on such an investment: movie theaters. The air conditioning in theaters became an attraction in itself, and people flocked to them. Not coincidentally, what many consider Hollywood's Golden Age began around the same time.

It was during the postwar period that air conditioning arrived en masse in American homes, with more than one million units sold in 1953. The machines were heavily promoted by two key industries. Air conditioning served the needs of homebuilders eager to build huge numbers of cheap houses and utilities were only too happy to keep ramping up electricity sales to the burgeoning suburbs. AC for cars became a status symbol, too, so much so that some people without it supposedly drove around with their windows up in 100 degree heat to give an impression otherwise. The suburban American dream was built on the sweat of air conditioners.

Many of the central changes in our society since World War II would not have been possible were air conditioning not keeping our homes and workplaces cool. Florida, Southern California, Texas, Arizona, Georgia, and New Mexico all experienced above-average growth during the latter half of the 20th century—hard to imagine without air conditioning. In fact, the Sunbelt's share of the nation's populations exploded from 28 percent in 1950 to 40 percent in 2000. And hubs of business and technology in hot regions of the globe, such as Dubai, may never have taken off.

Computers throw off a lot of heat, too. The development of the entire IT industry might not have happened without cooling technologies first pioneered by air conditioning.

The advent of air conditioning has shaped our homes and family life as well. Houses are designed not for ventilation but for central cooling systems. Porches, where they exist, are relics of another age, and few new homes include them. Families gather inside, in the comfort of 72-degree living rooms, to watch TV. Would television have even gained its central place in American family life, were the rooms from which we watch it not so enjoyably cool?

As Americans think about reducing their energy consumption, many are considering keeping their air conditioners off. But air conditioners haven't merely chilled the air around us—they've reshaped our infrastructure, our entertainment, and our habits.

So, go right ahead and turn off your AC but there's no switch to roll back the systems it's propelled.