Such luxuries disappeared during the Dark Ages, and large-scale air conditioning efforts didn't resurface in the West until the 1800s, when well-funded American engineers began to tackle the problem. In the intervening centuries, fans were the coolant of choice. Hand fans were used in China as early as 3,000 years ago, and a second-century Chinese inventor has been credited with building the first room-sized rotary fan (it was powered by hand). Architecture also played a major role in pre-modern temperature control. In traditional Middle Eastern construction, windows faced away from the sun, and larger buildings featured "wind towers" designed to catch and circulate the prevailing breezes.

In late 19^th century America, engineers had the money and the ambition to pick up where the Romans had left off. In 1881, a dying President James Garfield got a respite from Washington, D.C.'s oppressive summer swelter thanks to an awkward device involving air blown through cotton sheets doused in ice water. Like Elagabalus before him, Garfield's comfort required enormous energy consumption; his caretakers reportedly went through half a million pounds of ice in two months.

The big breakthrough, of course, was electricity. Nikola Tesla's development of alternating current motors made possible the invention of oscillating fans  in the early 20^th century. And in 1902, a 25-year-old engineer from New York named Willis Carrier invented the first modern air conditioning system. The mechanical unit, which sent air through water-cooled coils, was not aimed at human comfort, however; it was designed to control humidity in the printing plant where he worked. In 1922, he followed up with the invention of the centrifugal chiller, which added a central compressor to reduce the unit's size. It was introduced to the public on Memorial Day weekend, 1925, when it debuted at the Rivoli Theater in Times Square. For years afterward, people piled into air conditioned movie theaters on hot summer days, giving rise to the summer blockbuster.

It's not an exaggeration to say that Carrier's innovation shaped 20^th Century America. In the 1930s, air conditioning spread to department stores, rail cars, and offices, sending workers' summer productivity soaring. Until then, central courtyards and wide-open windows had offered the only relief. Residential air conditioning was slower to take hold: As late as 1965, just 10 percent of U.S. homes had it, according to the Carrier Corporation. Families in the South made do by sleeping on the porch or even putting their underwear in the icebox. By 2007, however, the number was 86 percent. As cool air spread across the country, Sun Belt cities that had been unbearable in the summer became more attractive places to live and work, facilitating a long-term shift in U.S. population.

Europeans have been slower to embrace air conditioning, but like cold beer and ice water, it's beginning to catch on there, too. Data on air conditioning in the developing world is scarce, but it's safe to say most Africans and South Asians still make do without it. A recent Times of India article on how to stay cool in summer recommended wearing linens and drinking lots of fluids to avoid heat stroke. The modern Indian version of iced tea on the front porch? Nimbu paani (lemonade) from a street cart.

(By Will Oremus, July 13, 2013, www.slate.com.)