Lee Kuan Yew, the iron-willed founder of modern Singapore, was once asked what the most important invention of the 20th century was. He didn’t say penicillin, which has saved over 500 million lives, or the nuclear bomb, which has shaped geopolitics like nothing before. He didn’t even say TV!
Instead, Lee had a simple two-word answer: “Air conditioning.” Without air conditioning, Singapore, where temperatures regularly reach into the 90s with tropical humidity levels, would never have developed from a tiny city-state with a per-capita GDP that was a third of Western Europe’s in 1960 to one of the most prosperous countries in the world.
Air conditioning is as essential to the modern world as the internet itself. But like the internet, A/C gets a bad rap. Cooling already eats up 10 percent of global electricity, and demand from air conditioners is expected to triple by 2050 without tougher energy efficiency standards. Many units still use refrigerant gases that produce a planetary warming effect that is thousands of times that of a similar amount of CO2.
Air conditioning is also a physical manifestation of the energy gap between the rich who can afford it, and the poor who must sweat. It has enabled the development of energy-intensive cities in places where humans just shouldn’t live, like Phoenix. Fundamentally, A/C is seen by some as an unnecessary luxury, a prime example of a “harmful habit of consumption,” as Pope Francis once put it.
I get the point. It seems morally wrong for so many of us to use a device that contributes about 3 percent of global greenhouse gas emissions — only so we can escape the effects of that warming.
But “seems” is not the same as “is.” Air conditioning has become far more than a luxury. So on this, the second day of summer, when the East Coast is about to be enveloped by a truly suffocating wave of heat and humidity, I offer five reasons why we should be grateful for air conditioning.
Heat isn’t just uncomfortable. It’s dangerous, killing more Americans in a typical year than any other form of extreme weather. Access to air conditioning can mean the difference between life and death. Seven hundred and thirty-nine people died in the great Chicago heat wave of 1995, but having a working air conditioner reduced the risk of death by 80 percent. Another study looked at cities in multiple countries between 1972 and 2009 and found that more air conditioning helped reduce excess heat deaths.
As a 2021 review in the Lancet explained it, air conditioning “is set to become the most prevalent strategy worldwide for coping with hot weather and heat extremes.” And while only about 8 percent of the 2.8 billion people living in the world’s hottest regions have A/C at home, that’s an argument for closing the A/C gap — not an argument against the very real value of air conditioning.
If you struggle to concentrate when the heat and humidity is high, you’re not alone. One study looked at office work and found that productivity begins to decline around 73 to 75 degrees Fahrenheit, while at 86°F, performance falls by almost 9 percent. Another study found that every 1 degree increase in average classroom temperature over a school year corresponded to a roughly 1 percent loss in students’ expected learning — but installing air conditioning eliminates about three-quarters of that effect.
As temperatures continue to increase, the importance of air conditioning in schools and businesses will only grow. A 2016 working paper finds that widespread adoption of air conditioning — especially by the most productive plants — substantially offsets the heat-induced drop in US manufacturing output, making cooling a critical adaptation tool.
The more we learn about sleep, the more important it appears to be — and keeping cool is a key part of a decent night’s sleep.
Humans fall asleep fastest around 64–68°F, while temperatures above 75°F cause vital deep sleep and REM sleep to crater. A 2024 review of more than 50 lab and field studies found that bedroom cooling increased total sleep time 15 to 20 minutes and cut the total amount of time people spent awake after falling asleep by a third.
It’s given us everything from the movies to microchips
Do you like going to the movie theater to catch a summer blockbuster? Well, you can thank air conditioning — before its invention, movie attendance always dropped during the hot summer months. It’s no coincidence that the first public air conditioner was installed in a cinema, New York’s Rivoli Theater, in 1925.
But maybe you prefer to take in your movies in the comfort of your own home? Well, producing the microchips that go into your streaming TV or smartphone requires total precision in temperature control and humidity. In short: no A/C, no microchips.
It lets millions live and travel where they want
Look, my negative feelings about living in red-hot metros like Phoenix are a matter of public record. But I am clearly in the minority: Americans love to live in hot places. Maricopa County, where Phoenix is located, added 1.2 million people between 2013 and 2023, more than any other county — and 96 percent of the new housing built to absorb those new residents comes with A/C.
What US cities like Phoenix or Houston or Atlanta have in common with Singapore and Hong Kong is that none of them would exist as anything like they are today without the widespread use of air conditioning. Before A/C, the American South was mired in poverty, far behind the rest of the country. After A/C, the South more than caught up, and the otherwise uninhabitable Southwest became a magnet for people. If you think it’s good that people can choose from a wider spectrum of places — and I do — A/C is one of the main reasons why that’s possible.
Air conditioning as it exists today is far from perfect. But it’s also necessary, especially in an ever-warming world. What we need is not less air conditioning — unless you happen to work at an office where they keep the temperature at 60°F — but better air conditioning, with more efficient units powered by cleaner electricity.
If you want to go without A/C, go right ahead (though I probably won’t be visiting your house in the summer anytime soon). But either way, it should be a choice.
A version of this story originally appeared in the Good News newsletter. Sign up here!
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