Even the reading experience you’re having right now is contingent upon air-conditioning—this book was printed in an air-conditioned facility.* In fact, air-conditioning was invented for a facility not too dissimilar from the one that printed this book. In 1902, a young engineer named Willis Carrier was tasked with solving a problem in Buffalo, New York: A printing company’s magazine pages were warping due to summertime humidity. Carrier created a device that essentially reversed the process of electric heating, running air through cold coils instead of hot ones. This reduced humidity, but it also had the useful side effect of decreasing indoor temperatures. Carrier went on to make more inquiries into what he called “treating air,” and the company he cofounded, the Carrier Corporation, remains one of the largest air-conditioning manufacturers in the world.

Heat has long been a worry for humans. In ancient Egypt, houses were cooled by hanging reeds from windows and trickling water down them. Then, as now, controlling indoor temperatures wasn’t only about comfort and convenience, because heat can kill humans. In an essay with the catchy title “An Account of the Extraordinary Heat of the Weather in July 1757, and the Effects of It,” the English physician John Huxham wrote that heat caused “sudden and violent pains of the head, and vertigo, profuse sweats, great debility and depression of the spirits.” He also noted that the urine of heat wave victims was “high-colored and in small quantity.”

In many countries today, including the United States, heat waves cause more deaths than lightning, tornadoes, hurricanes, floods, and earthquakes combined. A 2003 European heat wave that was concentrated in France led to the deaths of over seventy thousand people. Deadly heat waves from Australia to Algeria and from Canada to Argentina have been common throughout history, but one of the weirdnesses of the Anthropocene is that in the wealthier parts of the world, heat is now more of a health problem in mild climates than in hot ones. Over the past twenty years, people living in usually cool central France, where home AC is uncommon, have been far more likely to die from heat waves than people living in usually sweltering Phoenix, where over 90 percent of households have at least some form of air-conditioning.

There is another peculiarity of modern air-conditioning: cooling the indoors warms the outdoors. Most of the energy that powers air-conditioning systems comes from fossil fuels, the use of which warms the planet, which over time will necessitate more and more conditioning of air. According to the International Energy Agency, air-conditioning and electric fans combined already account for around 10 percent of all global electricity usage, and they expect AC usage will more than triple over the next thirty years. Like most other energy-intensive innovations, AC primarily benefits people in rich communities, while the consequences of climate change are borne disproportionately by people in impoverished communities.

Climate change is probably the biggest shared challenge facing twenty-first-century humans, and I fear future generations will judge us harshly for our failure to do much about it. They will likely learn in their history classes—correctly—that as a species, we knew carbon emissions were affecting the planet’s climate back in the 1970s. And they will learn—correctly—about the efforts in the 1980s and 1990s to limit carbon emissions, efforts that ultimately failed for complicated and multifaceted reasons that I assume the history classes of the future will have successfully boiled down into a single narrative. And I suspect that our choices will seem unforgivable and even unfathomable to the people reading those history books. “It is fortunate,” Charles Dudley Warner wrote more than a century ago, “that each generation does not comprehend its own ignorance. We are thus enabled to call our ancestors barbarous.”*