The Hot And Cold Past Of The Air Conditioner

39:09 minutes

On the facade of the office building there are white air conditioners at the Windows. Concept of indoor climate and air circulation
Credit: Shutterstock

state of science iconThis article is part of The State of Science, a series featuring science stories from public radio stations across the United States. This was a collaboration between Science Friday and St. Louis Public Radio’s Shahla Farzan. This story was originally published in October 2021.

In the Northeast, the leaves have started changing colors, heralding the season of pumpkins, sweaters, and the smell of woodsmoke. But in some parts of the country, the heat hasn’t let up. In cities like Dallas, Phoenix, and Miami, temperatures were up in the high 80s and low 90s this week—and with climate change, the U.S. is only getting hotter. 

But humans have come up with an ingenious way to keep the heat at bay: air conditioning. Widely considered one of the greatest engineering achievements of the 20th century, the technology has transformed how and where people live—and it’s prevented countless deaths. But it comes at a cost, and if we’re going to keep up with a warming climate, we’re going to need some other tricks to stay cool.

a black and white photo of an opulent building with a large rotunda and pillars
The Missouri State Building at the 1904 World’s Fair in St. Louis. The St. Louis Republic reported at the time: “Entrance into the Missouri building from the glaring heat outside will be instantly followed by the most delightful relief from the oppressive weather encountered in promenading the grounds.” Credit: Missouri History Museum/Public Domain


This story was produced by Elah Feder, in collaboration with St. Louis Public Radio’s Shahla Farzan. We had production help from Johanna Mayer. All of our music and sound design is by D Peterschmidt. We had research and fact-checking help from Lauren Young. Charles Bergquist was the voice of refrigeration engineers from 1904.

Special thanks to Andrew Alleyne, professor at the University of Illinois and director of POETS, for explaining to us how air conditioners work; Salmaan Craig, assistant professor of architecture at McGill; Komali Yenneti, lecturer in geography, urban planning and environment at the University of Wolverhampton; Wendy Novicoff, professor at the University of Virginia School of Medicine; and Adam Kloppe, a public historian with the Missouri Historical Society.

Like what you hear? Dive deeper with some of the sources we turned to while reporting this show below.

Further Reading

You can listen to the shorter version that aired on the radio show below.

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Segment Guests

Salvatore Basile

Salvatore Basile is a writer in New York, New York.

Gary Ludwig

Gary Ludwig is fire chief in Champaign, Illinois.

Tom Hucker

Tom Hucker is president of the Montgomery County Council in Montgomery County, Maryland.

Myisha Johnson

Myisha Johnson is an environmental justice advocate in St. Louis, Missouri.

Aaswath Raman

Aaswath Raman is a professor of material science and engineering at UCLA in Los Angeles, California.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow.

Later in the hour, remembering the life and work of SETI pioneer Frank Drake. But first, Labor Day marks the unofficial end of summer, right? But even as we look forward to pumpkin pie and cozy sweaters, parts of the country are still gripped by stifling heat. For example, California. High temperature records have been set this past week, reaching as high as 116 in Livermore, just outside of San Francisco. And we’ve seen the deadly impact of hot weather in Europe and Asia all summer long.

A new poll by Gallup shows that this extreme heat has a negative impact on people’s sense of well-being around the world. And since global warming means it’s still going to keep getting hotter, the only tool many people have to survive is air conditioning. Named one of the greatest engineering achievements of the 20th century by the National Academy of Sciences, air conditioning has completely transformed how and where we live.

Last year, in collaboration with St. Louis Public Radio, we took a look back at more than a century of AC and what it means to live without it. Here’s that story, reported by Elah Feder and Shahla Farzan.

ELAH FEDER: In the summer of 1904, visitors to the World’s Fair in St. Louis were in for a rare treat. And it wasn’t the giant Ferris wheel or the elephant made of almonds, though those were both fantastic. It wasn’t the obvious kind of fun really, or anything you could see or touch. It was something that you felt.

So imagine this. It’s August, and you’ve come all the way to St. Louis to see the absolute cutting edge in human achievement. Maybe you checked out the Aeronautics Competition or the X-ray machine that could look right inside you. But by late afternoon, you’ve been wandering for hours. You’re milling through these crowds, and it’s hot and it’s humid. You’re just melting, when you step into this one building, the Missouri State Building.

And inside, it feels so good. Because tucked in the basement is a 30-ton refrigeration plant, allegedly capable of dropping the temperature to just 70 degrees on a 90-degree day. Engineers gushed about it in that year’s Journal of Ice and Refrigeration, its 60-horsepower motor, its horizontal, double-acting ammonia compressor, and the delight of those who experienced it.

SPEAKER: Visitors, not aware that the building was artificially cooled, were struck with wonder, and were unable to account for the very perceptible change felt in the temperature.

ELAH FEDER: Now, artificial cooling, it wasn’t totally unheard of at this point. The Trading Room at the New York Stock Exchange, the Cornell Medical School’s Dissection Room, both of them got their own cooling systems in just the last few years. But in 1904, for most people, artificial cooling would still have been a novelty, something they might have heard about but wouldn’t have experienced for themselves.

Local newspapers loved the installation, in some cases, devoting multiple paragraphs to it. The St. Louis Republic wrote, “Entrance into the Missouri Building from the glaring heat outside will be instantly followed by the most delightful relief from the oppressive weather encountered in promenading the grounds.”

The relief did not last long. Just two weeks before the end of the Fair, the Missouri State Building burned to the ground. It actually happened while the fair was still going. Thousands ran over to watch the building burn. And though the fire brigades did their best, they couldn’t save it.

But the story of air conditioning, though, that was just beginning.

SHAHLA FARZAN: In many ways, St. Louis was the perfect place to introduce people to artificial cooling.

ELAH FEDER: Shahla Farzan is a reporter at St. Louis Public Radio.

SHAHLA FARZAN: It sits right at the spot where the Mississippi and Missouri Rivers come together. And in the summertime, the combination of heat and humidity can feel almost tropical, like breathing through a warm, wet towel. And for a long time, people just had to find workarounds– turn on a fan, sit on the porch, sleep outside in city parks.

And then came air conditioning. Many people credit Willis Carrier as the inventor. But his systems were really building on what others had done before.

SALVATORE BASILE: Willis Carrier was an interesting guy because he was somebody who had the right– call it– nose, and he was in the right place at exactly the right time.

SHAHLA FARZAN: Salvatore Basile is the author of Cool– How Air Conditioning Changed Everything. Carrier was a young engineer, working for a company in Buffalo that made heating and ventilation systems. And in 1902, he got an assignment.

SALVATORE BASILE: A printing firm came to the company with a problem– that summer humidity was causing paper to swell. And that would mean that it would print incorrectly. And rather than a crisp image, they were getting a blur.

SHAHLA FARZAN: They needed something to control the humidity. So Carrier got to work. At first, he tried chemical drying, using a bunch of desiccant. But that contaminated the air with salt droplets, and resulted only in “ruining two perfectly good pairs of expensive shoes.” So he changed tactics. He knew that if you lower the air temperature, it’ll bring down the humidity, too.

It took a few more years of experimenting with cool air, but finally he cracked it. In 1906, he landed on the basic model he’d use for decades to come.

SALVATORE BASILE: Carrier realized that he was onto something. And he borrowed a phrase that was being used in cotton mills– air conditioning.

SHAHLA FARZAN: Not air cooling– air conditioning. Because for Carrier, this wasn’t just about making it cold. It was a top-to-bottom makeover of the air, with four essential components.

CHARLES BERGQUIST: Cleanliness, control of humidity, control of temperature, and circulation.

SHAHLA FARZAN: This was from a promotional video from the ’40s.

CHARLES BERGQUIST: These would never have been commercially possible but for the discoveries and air conditioning developments of Dr. Carrier and his associates.

SHAHLA FARZAN: In the early decades, air conditioning was mostly used in factories– not for the comfort of workers, of course, but for the quality of the product. Like macaroni has to be dried at just the right humidity.

SALVATORE BASILE: Otherwise it would sour or sometimes crack.

SHAHLA FARZAN: Or if you’re spinning cotton, it can’t be too dry.

SALVATORE BASILE: Otherwise the thread will break. On the other hand, something like chocolate cannot be manufactured in a hot environment at all. Many chocolate manufacturers would actually close down for the whole summer. The same with chewing gum. It was, in those days, too sticky to work with during the summer.

SHAHLA FARZAN: But with systems like Carrier’s, manufacturing could chug along. Carrier tried to promote air conditioning just for comfort, too.

SALVATORE BASILE: For years, Carrier would say, why not have a house that is available for you all the seasons of the year, so that you could really live there in the summer, rather than going away to the seashore? No one was interested, because hot weather was something that you put up with. God gave it to you, and you had to deal with it.

There was a very Victorian sensibility that hot weather was simply a given. You would have a fire against cold. But as far as heat, you lived through it.

SHAHLA FARZAN: It was also just very expensive. The first modern home air conditioner was another company’s– Frigidaire’s– and it weighed 600 pounds, cost as much as a car, and didn’t work all that well. But then Carrier found the perfect customer– movie theaters.

SALVATORE BASILE: Movie theaters were in a very bad way by the 1920s. They were famous for being places where the air was unbreathable.

SHAHLA FARZAN: In 1925, Carrier installed a system in New York’s Rivoli Theater. Now, theaters in those days could get very hot, so audiences had all come prepared with fans.

SALVATORE BASILE: And even though the system was starting to run, it hadn’t quite kicked in, and people were fanning away. Carrier was standing at the back of the auditorium very nervous. But then they began to feel the cool, and he noticed all the sounds gradually beginning to stop.

SHAHLA FARZAN: Also there that day was Adolph Zukor, the President of Paramount Pictures. And after seeing this incredible display, he walks up to Carrier and tells him– Yes, the people are going to like it.

SALVATORE BASILE: And this was actually a very unheralded moment. Because this was the first time in human history that the average person, for the price of a movie ticket, could go somewhere and become cool during the hottest summer heat. That was a revolution. Bang. All of a sudden, every other movie theater in the United States had to catch up.


CHARLES BERGQUIST: Yes, you lucky people, just sit back for a moment. Relax, and notice the delightfully clean, cool, and refreshing atmosphere of this scientifically air conditioned theater.

SHAHLA FARZAN: This is from the ’40s. It would run before the show started. I love that this is the selling point. It’s not the great movies you’re going to see. The key is it’s going to be cold.


So at first, air conditioning was just about good times and macaroni. But pretty soon it went from luxury to necessity.

The real shift happened after World War II. Air conditioners were becoming more affordable. And in the ’50s, there were a lot of new houses being built cheaply. So think poorly insulated, with these big modern windows. Basically, what one writer at the time called TV-equipped hot boxes. Air conditioning them was essential.

And over time, mortgage lenders and insurers went from treating air conditioning as an unnecessary amenity to covering it– or even requiring homebuilders to plan for it. And by the late ’70s, about half of US households have systems installed.

And air conditioning changed how and where people lived. Skyscrapers would be deeply uncomfortable without air conditioning, especially on those upper floors. The Sun Belt states, like Florida, Texas, and New Mexico, they started growing much faster than many other parts of the country. And a lot of people think air conditioning allowed that to happen.

And for those who had air conditioning, it wasn’t just keeping them comfortable. It wasn’t just letting them sleep soundly on summer nights. It was actually saving their lives. Which brings us to St. Louis, in 1980.

GARY LUDWIG: I started working for St. Louis two months out of high school. That was 1977.

SHAHLA FARZAN: Gary Ludwig is the Fire Chief in Champaign, Illinois. We met up at his house one weekend in August. And Gary told me he originally enrolled at St. Louis University to become a doctor, but his scholarship money wasn’t enough to cover tuition. So at 18, he joined a federal program that trained people to be first responders.

GARY LUDWIG: Sometimes you’d be on a fire truck and sometimes you would be on an ambulance. And a lot of times I wound up finding myself on an ambulance, because they were short staffed.

SHAHLA FARZAN: A year later, Gary was hired as a paramedic captain. And he was just a kid, really, learning on the job. One of the first times he went out, he says he helped carry a woman who was in labor down six flights of stairs.

GARY LUDWIG: And she’s having this baby in the back of the ambulance, and I have no idea how to deliver a baby. And I think I was more nervous than the mother was.

SHAHLA FARZAN: By 1980, Gary had a few years of experience under his belt. He used to drive a station wagon packed with medical equipment around St. Louis. And when there was an emergency, he was usually the first person there, even before the ambulance arrived.

But on July 1 that year, the temperature started rising. On a typical July day in St. Louis, you get a high of about 80 degrees. That day in 1980, it reached 105. And that was just the beginning. For the next 19 days, temperatures were in the upper 90s and low 100s almost every day.

NEWS ANNOUNCER: Yesterday set a record for power use.

NEWS ANNOUNCER: 108 degrees today. That beat the record all to smithereens.

NEWS ANNOUNCER: This is what summer should be, starting off in May, about 80, and peaking off, in August, about 98 degrees. But we have been nowhere near normal this year.

SHAHLA FARZAN: It would become one of the worst heat waves in recent history, with extreme heat stretching all the way from Texas to Washington, DC. And in St. Louis, as the temperatures rise, the calls start coming in faster and faster.

GARY LUDWIG: So the emergency rooms are starting to fill up. There is one day I know that we hit 350 calls for EMS in a 24-hour period. Which was probably 200% or more above our normal limit. So when you have something like that, you don’t have enough resources. You have calls stacked up, sitting there, waiting for someone to dispatch an ambulance.

SHAHLA FARZAN: So Gary was working these long shifts, sometimes 16 hours at a time, running from one call to another. And he still can’t forget some of the things he saw. This one time in particular has really stayed with him. And a warning to listeners– some of what you’re about to hear is disturbing.

GARY LUDWIG: We break the door down. We go inside. And, sure enough, we find the person on a bed. And as I said, I have seen many dead bodies in my career, but I have never seen a dead body like this before. Because there was no human form there at all.

SHAHLA FARZAN: The body had basically turned to jelly.

GARY LUDWIG: And to our shock– and I say shock– there’s a lady laying next to him. And she’s delusional. She’s suffering either from heat or whatever– we don’t know what she’s suffering from. So we’re able to load her up on a stretcher and get her out the door. And as we’re taking her out the door, she turns and says, are you going to take him also?

SHAHLA FARZAN: And in going to call after call, Gary quickly notices a pattern. The victims of this heat wave tend to be older, lower income, and they don’t have air conditioners.

GARY LUDWIG: I don’t know how many times I would walk in and I would find some elderly person– again, their home was shut up– and they’re sitting in a chair in front of a fan. That’s all they had to cool themselves. And they’re dead. The fan, all it’s doing is blowing hot air on them. Their body temperature still rose to 105, 106, 107, 108, 110 degrees. We found some with 115-116 degree heat indexes on their body.

SHAHLA FARZAN: At least 153 people died in St. Louis during the 1983 heat wave. So many that the local newspaper, The St. Louis Post-Dispatch, began printing the names and ages of the dead. The city medical examiner told the paper they were running out of places to put the bodies.

IRA FLATOW: Unnecessary deaths from the lack of air conditioning would continue, unfortunately, up until this day. Elah Feder continues with the story of AC after this short break. This is Science Friday, from WNYC Studios.

This is Science Friday. I’m Ira Flatow. We’re talking this hour about how air conditioning has transformed America.

Back to Science Friday’s Elah Feder, with that story.

ELAH FEDER: An air conditioner works by taking heat from inside your home or your office or your car and dumping it outside. Usually, it does that with a refrigerant, a kind of liquid that easily evaporates. The liquid runs through the air conditioner’s pipes. And as it evaporates, turning from liquid to gas, it draws the heat out of the air, cooling the air down.

But then that heat needs to go somewhere. So the air conditioner squeezes the refrigerant back down into a liquid, forcing it to release all that heat again, and throws that heat outside. And that’s the cycle– suck the heat from the inside, dump it outside, over and over again.

I like to imagine a very industrious hamster running back and forth with buckets of heat. Our fact checker Lauren Young suggests that you imagine the Hulk, hulking out with heat, and compressing back into a human, and letting that heat out again. Whatever works for you.

Your body works in kind of a similar way, except for, instead of a refrigerant, it’s sweat. When you heat up, the sweat evaporates off your skin, taking the heat with it. And your body, as it circulates your blood, keeps sending heat to the surface– hot blood to the skin, cooled blood back down into your body– on and on, with sweat the cooling engine at the heart of it all.

But sometimes your body gets so hot and dehydrated, you actually stop sweating. And that’s when you’re in real trouble– heat stroke.

GARY LUDWIG: Your internal temperature gets to be 105, 106 107, 108 degrees– and since you stopped sweating, what happens is that your body has no more ability to calm itself down. And that’s why the body temperature rises. So it cooks your brain is what it does. It virtually just cooks your brain. And it also impacts all your organ systems. In fact, you just die.

ELAH FEDER: If you look at deaths in the US over the decades, you see a consistent pattern. Most people die in the winter when it’s cold. Flus and other respiratory diseases spike, and heart attacks. But they also die when it’s extremely hot. And so researchers at the University of Virginia decided to look at data going back to the ’60s. And they saw that, at first, predictably, whenever there was very hot and humid weather, people died. They saw a spike in excess deaths.

That was true in the ’60s. That was during the ’70s. But by the ’90s, the pattern fades. More and more people are surviving the heat. And the researchers’ best explanation was air conditioning. It’s not to say there aren’t other factors, like maybe better medical care, but air conditioning, not surprisingly, is a big one. And the researchers found that the more homes with air conditioning in a region, the fewer people die.

But while the law generally requires landlords to provide heating, for the most part, air conditioning has been considered optional. Nice if you can get it. Except, maybe that’s starting to change.

TOM HUCKER: I’m really glad we’re here today to finish this up. We all know what this bill does and why we’re here.

ELAH FEDER: Last year, Montgomery County, in Maryland, passed a bill requiring landlords to provide air conditioning from June to September. This is Tom Hucker, President of the County Council, at the final vote. He sponsored the bill.

TOM HUCKER: We’ve had a requirement for heat for a very, very long time, because it really is a life or death issue if people don’t have heat. And air conditioning has become a life or death issue as well, not just a comfort issue.

ELAH FEDER: I recently spoke with Tom. And he says, before this bill, they’d received a lot of tenant complaints about lack of air conditioning or failing air conditioning. And this bill just made sense.

TOM HUCKER: For decades, governments have required landlords to provide heat during winter months. When tenants don’t have working heat, unfortunately, tenants perish in the cold. So in a world with climate change and rapidly increasing temperatures year after year, we believe we need to require air conditioning as well.

ELAH FEDER: Montgomery County isn’t the only one doing this. Arizona law considers air conditioning an essential service. So your landlord has to fix it if it breaks. And Dallas mandates refrigerated air from April to October. But in most places, it’s not required, St. Louis included. And someone has to fill in the gaps.


TECHNICIAN: Good morning.

ELAH FEDER: It’s morning, late in August. Here’s Shahla Farzan again, from St. Louis Public Radio.

SHAHLA FARZAN: I’ve been driving around St. Louis with a team of air conditioning installers from a nonprofit called Energy Care. It’s just past 10:00 AM when we pull up in Jennings, a suburb of North St. Louis. The sun beats down on a little brick house with a peaked roof. Inside, 70-year-old Gloria Van has two fans running on full blast. She’s glad to see the techs, and we talk while they work.

GLORIA VAN: This heat has really made it hard.

SHAHLA FARZAN: It’s been a really, really hot summer. Oh, my gosh.

GLORIA VAN: Yes. And at our age, by the time we walk from our door to the car, it’s time to pass out.

SHAHLA FARZAN: Keeping the house cool is a full-time job for Gloria and her husband David. She tells me about all the ways they’ve changed their lives and schedules just to work around the heat– cooking only in the morning or very late at night, baking almost never, and constantly moving fans all day from room to room.

She says they did have two window air conditioners, one for the bedroom, the other for the living room. But this summer, one broke. The other one started leaking all over the floor. That’s when Gloria heard about Energy Care. It’s one of a handful of nonprofits that helps low-income and elderly people in St. Louis pay for their utility bills. She asked them if they did repairs. They said no– we’ll give you a brand new air conditioner, or two, if you want.

GLORIA VAN: So I said, well, I don’t really want to overdo it, but–

SHAHLA FARZAN: You didn’t want to ask for too much?

GLORIA VAN: Yeah, right. Right. And she said, no, we’ll come, and we’ll put two in. I said, thank you, Jesus, because it was a blessing.

SHAHLA FARZAN: It takes about 20 minutes to install two air conditioners in Gloria and David Van’s home. As the nonprofit workers pack up their tools and paperwork, Gloria pauses in front of the humming little air conditioner and holds out her palm.

Oh, wow, you can feel that cool coming off of there.

GLORIA VAN: Yeah, I feel it.

SHAHLA FARZAN: For now, the Vans can relax just a little, knowing they won’t have to wake up in the middle of the night drenched in sweat, or work so hard to keep the house cool.

TECHNICIAN: All right. Everybody, take care now.

DAVID VAN: You, too.

SHAHLA FARZAN: By the end of the season, Energy Care will have installed more than 200 air conditioners in St. Louis. But cooling this city is an uphill battle. Most St. Louis homes are like pizza ovens. They’re made of brick. And that means once they get hot, they stay hot. And they’re old. Most were built before 1939. Sometimes the only way to survive the heat is to get outside.

So why did you guys decide to come to the pool today?

SWIMMING POOL ATTENDEE: Because it was hot.


SWIMMING POOL ATTENDEE: In the summer here, it’s very hot.


SHAHLA FARZAN: On a boiling hot August afternoon, I headed to the Fairground Park swimming pool. JC and Talia [INAUDIBLE] and their cousin Skyler Wilson were there that day, cooling off. The main advantages of the pool, they say, it’s spacious and clean.


SWIMMING POOL ATTENDEE: You don’t really see a lot of bugs, which we like that there’s no bugs.


SHAHLA FARZAN: Talia, who’s 15 and enjoying this remarkably bug-free pool, says they have to keep their air conditioner running all day, but the house is still warm.

TALIA: Our aunt that just turned 85, that house was newly built when she moved into it. So that was like I think maybe the 1930s or something. So it’s like what she said– there’s cracks everywhere, so the heat comes in, no matter what.

SWIMMING POOL ATTENDEE: Yeah. I’m on the third story, and I have my own air conditioner there that I keep on all day.

SHAHLA FARZAN: This pool is actually in the Zip Code where Energy Care installs the most air conditioners, at the far northern tip of the city. Like other US cities, there’s a stark racial and economic divide in St. Louis. It’s cut in half by a street known as Delmar Boulevard. North of Delmar, neighborhoods are predominantly Black and lower income. The South Side is mostly white, more affluent.

People in some of these South Side neighborhoods live up to 14 years longer, on average, than North City residents.

Myisha Johnson is an environmental justice advocate in St. Louis, and she says some neighborhoods even feel hotter than others.

MYISHA JOHNSON: I noticed that the closer we are to the river, it seems to be a little hotter. I never understood that. I thought it would be the other way around. And that’s where most of the Black and Brown communities are.

SHAHLA FARZAN: There’s some research backing this up. In 2018, a master’s student in geography used satellite data to calculate land surface temperatures in St. Louis, and found a distinct band of heat along the Mississippi River and the downtown corridor.

And it’s not just St. Louis. This is a pattern. Across the US, lower-income neighborhoods and places with more people of color are often hotter than wealthier, whiter ones. A lot of that has to do with lack of trees and green spaces– also, large roads and building complexes that retain a lot of heat. One study found that historically red-lined neighborhoods are on average five degrees warmer.

Myisha is worried the heat’s only getting worse.

MYISHA JOHNSON: It’s never been that hot that we can think of. Each year, it gets hotter and hotter and the season last longer.

SHAHLA FARZAN: Climate change will affect regions of the US in different ways. In Florida, sea levels will rise. California will get drier. And Missouri will get a lot hotter. When you look at the cities that will heat up the most in the next few decades, St. Louis and its suburbs are right at the top.

Getting people a few more window air conditioners helps right now. It could even save their lives. But in the long run, Myisha says, it won’t be enough.

MYISHA JOHNSON: As organizations, we can’t keep saying, oh, this is what you need. This Band-Aid will help.

ELAH FEDER: Air conditioning, for all its life-saving technological wonder, might not be the answer. So remember, air conditioning works by taking the heat from inside and dumping it outside. Which means that, as you’re cooling down, your neighbors, your block, your city, it’s actually getting hotter.

There was one study looking at Phoenix that estimated all the heat dumped out by air conditioners was adding up to an extra two degrees in some areas. And then there’s the fact that air conditioning in America uses so much energy. Even though the newer individual air conditioners can be pretty efficient, in the US, all that electricity costs about $29 billion a year. And that’s just for home air conditioning.

The good news is, at least the refrigerants being used are less harmful. Remember, in the ’80s, when everyone was worried about CFCs, chlorofluorocarbons, like Freon, which was used as an aerosol propellant and as a refrigerant. Not only did CFCs help carve a hole in the ozone layer, they’re also very potent greenhouse gases. So they got phased out and replaced with less harmful alternatives.

The bad news is, most of the electricity used to power air conditioners comes from fossil fuels, so they’re still contributing to climate change. And then there are all the other air conditioners– like in cars– running on gasoline, using somewhere from 7 to 10 billion gallons of it each year.

Fortunately, air conditioners are not the only way to stay cool. After all, humans existed a long time before AC. And we came up with some very clever ways to keep buildings cold– things we might take for granted now. Like just courtyards. They provide both lots of cross ventilation and shading. Or kind of a similar concept, the dog trot house. It used to be pretty common in Appalachia. Basically, a house with a big hole right down the middle that let air pass through. Or in truly extreme heat, there’s just living underground.

NARRATOR: The world had been through a trial by fire.

SHAHLA FARZAN: You might recognize Coober Pedy from post-apocalyptic movies, like Mad Max: Beyond Thunderdome, if you caught that. It’s a mining town in the Australian Outback. It’s famous for its underground motels, churches, and homes. And yeah, it kind of looks like the end of civilization. But living underground, it does keep you cool.

So we’ve got living underground, courtyards, dog trot houses, but best of all is the centuries-old technique of beaming your heat into space.

AASWATH RAMAN: It was mostly in Iran, as far as we can tell, about 300 to 500 years ago.

ELAH FEDER: Aaswath Raman is a professor of Materials Science and Engineering at UCLA, and a confounder of SkyCool Systems. And he says, in Iran’s ice houses– these places where they made and stored ice– they took advantage of a strange phenomenon.

AASWATH RAMAN: So basically, they had a thin flat pool of water– and they would be doing this in the winter, so it’s not super warm to begin with– but even though the air temperature almost never got to freezing, that thin sheet of water, if it was exposed to the sky sufficiently, it would freeze overnight.

ELAH FEDER: That’s because of radiative cooling.

AASWATH RAMAN: It’s actually something that all materials do naturally. It’s a basic property of nature that if you’re at a particular temperature, you, as a material, will emit, or radiate, heat away. And the wavelengths at which you radiate that heat away will depend on your temperature.

ELAH FEDER: So that’s what you see on night-vision cameras, all the infrared radiating off of things. The hotter they are, the brighter they glow. And what happens when you put something out on a very clear night is it can radiate out so much heat that it actually cools down– maybe even freezes.

So nine years ago, Aaswath was a PhD student when he learned about this.

AASWATH RAMAN: I was very curious about this, because it sounded pretty amazing. It’s passive cooling that you don’t need to do anything. All you need to do is have something outside, exposed to the sky, and it cools down. It’s almost too good to be true. So it was very perplexing– why hadn’t this been developed further? Why weren’t we using this everywhere?

ELAH FEDER: One of the problems was that this effect was only happening at night. Because during the day, yes, you are still emitting heat as infrared, but it’s totally canceled out by all the heat you’re getting from the sun and your surroundings.

AASWATH RAMAN: So when we began working on it, we asked, well, can we enable this effect during the daytime as well? And if we could enable it during the day, that would be potentially extremely exciting. Because then you could achieve the same kind of passive cooling effect but during the hottest hours of the day, when we need air conditioners and refrigerators the most.

ELAH FEDER: What Aaswath and his team ended up developing was a little more sophisticated than a pool of water, something that was really good at cooling down, and basically counteracting the whole greenhouse gas effect.

So greenhouse gases– think of them as a big invisible blanket over our planet. We send out heat as infrared radiation, our blanket catches it, sends it back down, keeps us nice and snug– sometimes a little too snug. But the blanket doesn’t catch everything.

So if you emit heat at just the right frequencies of infrared, it can blow right past the blanket and into space. So Aaswath and his team designed these films down to their nanostructure, so that they were very good at two things. First, they were really good mirrors. They were really good at reflecting away sunlight. And second, they radiated their heat away at very particular frequencies of infrared radiation, frequencies that could slip right past the greenhouse gases.

And it worked. Like, usually, if you put something out in the sun, it gets hotter, right? But Aaswath’s material, it got colder.

AASWATH RAMAN: So it’s really counterintuitive. And the first few times, I would just touch it just to check that it was actually working. Which of course ruins the experiment, because you have to start it all over.

ELAH FEDER: So if you think about this, it solves a major problem that air conditioners have. Instead of dumping the heat outside and making your surroundings hotter, you send it to space, technically, cooling down the Earth ever so slightly.

And Aaswath is not the only one working on this kind of thing. You might have seen recent news about super white paint. So instead of a film, it’s actually a paint, and you could paint it on, say, rooftops to cool them down. All of this gives me these nightmarish sci-fi visions, where we install these materials everywhere and accidentally freeze the planet.

AASWATH RAMAN: I mean, people have very seriously talked about putting mirrors out in space. If you put it far enough away and it’s substantially large, it can actually create a bit of a shadow. It’s like The Simpsons episode, where Mr. Burns does that.

ELAH FEDER: But we’re obviously nowhere near that. And right now, Aaswath’s company, SkyCool, they’re not even trying to replace air conditioning. They’re actually using these materials to cool down air conditioners so they don’t have to work quite so hard.

Everyone I spoke to was emphatic that we will absolutely need air conditioning, no matter what, especially as the climate warms. But if we’re strategic about it, if we combine reflective materials with the basics– like more tree cover, designing buildings that shade themselves and naturally ventilate– then maybe, even though we’ll still use air conditioning, we’ll need a whole lot less.

CHARLES BERGQUIST: The old saying, everybody talks about the weather, but nobody does anything about it, is not quite true. Heating and air conditioning engineers have done plenty about the weather.

ELAH FEDER: The National Academy of Sciences lists air conditioning as one of the 10 greatest engineering achievements of the 20th century. And it’s true. Our world would be unrecognizable without it. It’s the big things– the skyscrapers, the movie theaters, the data centers– think about computers without air conditioning.

But it’s also that little drip on your head out of nowhere on a clear, sunny day, or that ongoing battle with your officemates about whether it’s too cold or too hot, and whether anything under 70 Fahrenheit is a sexist temperature. And it’s also the hum and the rattle of your ancient window unit that’s lulling you to sleep on a hot summer night.

SHAHLA FARZAN: In August, a period of intense heat gripped the city of St. Louis. Temperatures shot way up, all the way to the mid to upper 90s. We were all ants under a magnifying glass, running from our air conditioned cars to our homes.

But then, one Wednesday– so I just came outside, and I’m standing on my porch in South St. Louis. And it is an absolute downpour out here. I actually have to move because I’m starting to get a little wet. Just constant lightning and thunder and cicadas screaming. This is kind of our summertime soundtrack here. We’ll get these–


There you go.

We’ll just get these kind of incredible downpours in the city, when the heat breaks. We’ll have really, really hot days, and then suddenly the sky just opens up. And that’s what’s happening right now.

We had a couple of days of relief after that storm. We could come out of hiding, walk around outside again. And then, less than two weeks later, the heat was back, worse than before. Because for all of our tricks and technologies, our refrigerants and pumps and compressors, all we’re really doing is buffering ourselves from the outside world, giving ourselves a little bit of relief until nature decides to give us a break.

Air conditioning, it provides comfort. It saved countless people. But at the end of the day, it’s weather that rules our lives.



ELAH FEDER: This story was a collaboration of Science Friday and St. Louis Public Radio. It was produced by me, Elah Feder–

SHAHLA FARZAN: And me, Shahla Farzan.

ELAH FEDER: With production help from–

JOHANNA MAYER: Me, Johanna Mayer.

ELAH FEDER: All of our music and sound design is by–

D PETERSCHMIDT: Me, D Peterschmidt.

ELAH FEDER: We had research and fact checking help from–

LAUREN YOUNG: Me, Lauren Young.

ELAH FEDER: And Charles Bergquist was the voice of refrigeration engineers, from 1904.

Special thanks to Andrew Alleyne, for explaining to us how air conditioners work, and to Salmaan Craig and Komali Yenneti, for talking to us about cool building and city design. And to historian Adam Kloppe, who taught us all about the 1904 World’s Fair.

If you want to learn more about air conditioners, we had a great time reading Salvatore Basile’s book, Cool: How Air Conditioning Changed Everything. We also found Gail Cooper’s Air Conditioning America very illuminating.

We’ve got more information and links up at sciencefriday.com/ac.


IRA FLATOW: After the break, remembering the life and work of SETI pioneer Frank Drake. Stay with us.

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Meet the Producers and Host

About Elah Feder

Elah Feder is the former senior producer for podcasts at Science Friday. She produced the Science Diction podcast, and co-hosted and produced the Undiscovered podcast.

About Johanna Mayer

Johanna Mayer is a podcast producer and hosted Science Diction from Science Friday. When she’s not working, she’s probably baking a fruit pie. Cherry’s her specialty, but she whips up a mean rhubarb streusel as well.

About D. Peterschmidt

D. Peterschmidt is a producer, host of the podcast Universe of Art, and composes music for Science Friday’s podcasts. Their D&D character is a clumsy bard named Chip Chap Chopman.

About John Dankosky

John Dankosky works with the radio team to create our weekly show, and is helping to build our State of Science Reporting Network. He’s also been a long-time guest host on Science Friday. He and his wife have three cats, thousands of bees, and a yoga studio in the sleepy Northwest hills of Connecticut. 

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