This podcast was originally published on Undark and is republished here with permission. Read the original article.

Welcome to The Undark Podcast, which will deliver — once a month from September to May — a feature-length exploration of a single topic at the intersection of science and society. In this episode, join science and environmental journalist James Dinneen and podcast host Lydia Chain as they take a tour through the history of refrigerants and the not-so-new alternatives that will replace the potent greenhouse gases commonly used in fridges today.

Below is the full transcript of the podcast, lightly edited for clarity. You can also subscribe to The Undark Podcast at Apple Podcasts, TuneIn, or Spotify.

[Grocery store ambience]

James Dinneen: This DeCicco & Sons grocery store just north of New York City looks like your average upscale supermarket. There are shelves stocked with dry goods in the middle of the floor. Refrigerated cases full of fancy cheeses and craft beer line the perimeter. Masked people peruse the fruits.

But in one invisible way, DeCicco & Sons is rare among America’s 38,000 or so supermarkets: It’s one of just a few hundred that no longer use the potent greenhouse gases called hydrofluorocarbons in their refrigeration systems.

Hydrofluorocarbons, or HFCs, have been used since the ’80s, and are hundreds to thousands of times more potent than carbon dioxide at trapping heat in the atmosphere.

And HFCs aren’t only in supermarkets. HFCs are used in air conditioners in buildings and in cars, in refrigerated trucks and warehouses. Unless you live in Europe or Japan, HFCs are most likely in the fridge in your kitchen. If you want to know for sure, check the label on the inside door.

[Fridge door opens. Tinkling bottles.]

James Dinneen: R-134a, yep.

[Fridge door shuts]

But probably by the time your fridge conks out and you get a new one, all that is going to change.

[Undark theme music]

Lydia Chain: This is the Undark Podcast. I’m Lydia Chain.

In December of last year, Congress passed with bipartisan support the American Innovation and Manufacturing Act as part of its government funding bill.

Among other provisions, the AIM Act gives the Environmental Protection Agency authority to phase out most HFCs over the next 15 years.

Environmentalists hailed it as one of the most significant pieces of climate legislation passed by Congress in decades.

The legislation adds the United States to the list of more than 100 countries phasing down HFCs, in what is no less than the third great transition in refrigerant history, expected to prevent up to half a degree Celsius in warming by the end of the century.

But transition to what? What will replace HFCs in every fridge in America?

The legislation doesn’t specify, and the chemistry is not cooperative.

James Dinneen has the story.

[Grocery store ambience]

John DeCicco Jr.: You want some coffee?

James Dinneen: I’m good for now thanks. I’ve had my caffeine.

James Dinneen: John DeCicco Jr. runs DeCicco & Sons. He’s one of the sons.

John DeCicco Jr.: You want to sit upstairs first?

James Dinneen: Yeah, sit there and chat and then maybe go check out the fridge.

In 2015, DeCicco was building this new store in Larchmont, and DeCicco saw an opportunity to make it as environmentally friendly as possible.

John DeCicco Jr.: We have a very educated, higher-end demographic that is very keen to be, you know, what stance every business is making towards the environment. And being environmentally conscious can also save a company money at the same time and creating a win-win situation.

James Dinneen: He put in LED lighting, solar panels, and extra-large fans to improve air circulation. And he decided to do something about HFCs.

Not only were they potent greenhouse gases, but federal and state regulations on which ones could be used kept changing.

John DeCicco Jr.: Every year, we had to make upgrades to our older stores to improve the gas or eliminate a gas. And I was like, there’s got to be a better way to do this.

James Dinneen: After doing a bunch of research, he decided to take the plunge, and abandon HFCs completely. Instead of an HFC system, he would install a refrigeration system that used carbon dioxide, CO2, as a refrigerant.

And it was a bold choice. At the time there was only a few other stores in the country that had CO2-based refrigeration systems. The only other store in New York was a flagship Whole Foods in Brooklyn. DeCicco & Sons was just a small family-run outfit, and installing a CO2 system was expensive. It wasn’t just a matter of using a different gas; it required using different machinery, even different pipes. But DeCicco was committed.

John DeCicco Jr.: You know, my kids, who, I have two young kids and I want to make sure that the world is going to be in a good environmental place for them and want to make sure I’m doing my part in order to keep the environment, you know, improving from the situation it’s in right now.

James Dinneen: Now, carbon dioxide might strike you as an odd choice for a climate-friendly refrigerant. But CO2 is actually a relatively weak greenhouse gas.

It has what’s called a low global warming potential.

Piotr Domanski: There are two parameters that are important for global warming potential.

James Dinneen: This is Piotr Domanski, a chemical engineer who researches alternative refrigerants at the National Institute of Standards and Technology.

Piotr Domanski: One is the ability of the molecule of the compound to trap infrared radiation. And the second is the atmospheric lifetime of the compound.

James Dinneen: In other words, how good is the gas at trapping heat in the atmosphere, and how long does the gas stick around trapping heat before dissipating?

CO2 is used as the yardstick for all other gases, and has a global warming potential of 1, which is low. CO2 plays such an outsized role in climate change because of the huge quantities of it released by burning fossil fuels.

HFCs are released in tiny quantities compared to CO2, but they are far better at trapping heat in the atmosphere and stick around for decades, giving them an extremely high global warming potential.

The HFC refrigerant R-134a is commonly used in home fridges; it has a global warming potential of 1,430 over 100 years. The HFC refrigerant R-404A commonly used in supermarkets has a global warming potential of nearly 4,000.

Avipsa Mahapatra: So imagine I, as an average consumer, I bike to my local store; I take my tote bag so I don’t have to use plastic; I pick up the organic stuff; but I just opened the refrigerator to get a pizza out or something, and I have just, without knowing, you know, sort of undone all of the climate savings.

James Dinneen: This is Avipsa Mahapatra, climate campaign lead at the Environmental Investigation Agency, an environmental advocacy nonprofit. She works on a campaign to raise awareness about HFCs in supermarkets.

Avipsa Mahapatra: People think it’s something that’s inside the equipment … Well, what we know, and we’ve said again and again, is that when you are looking at a central refrigeration system in a supermarket, it is not 100 percent tight system. You are leaking these gasses out.

James Dinneen: According to a 2011 report by the EPA, the average American supermarket loses about 25 percent of its refrigerant each year, with a climate impact equivalent to over 1,500 metric tons of CO2. Added up across every supermarket in the country, that amounts to emissions equivalent to more than 12 million cars driving for a year.

James Dinneen: How frequently did the HFCs have to be recharged?

John DeCicco Jr.: Generally once a year, twice a year, there’d be a leak in a store. Sometimes it can be 50 pounds, but sometimes it can be 1,000 pounds of refrigerant leaking out depending on the severity of the leak. Of course there’s leaks too with CO2, but they’re not as, you know, adverse to the environment as a refrigerant leak is or could be.

James Dinneen: How do you know when there’s a leak? I mean, it’s a, look around, there’s a lot of refrigerators.

John DeCicco Jr.: There’s a leak usually when you lose refrigerant, or you lose the whole system all at once. And that’s how you usually know there’s a leak. When everything stops being cold.

James Dinneen: What’s odd about all this though is that despite the hype about CO2 as a climate-friendly refrigerant, it’s nothing new.

[Archival film music plays]

CO2 was a common refrigerant a century ago, in the early days of mechanical refrigeration.

U.S. Air Force training film: Refrigeration is part of our daily lives.

James Dinneen: That is to say, carbon dioxide, an old-fashioned refrigerant, is now replacing HFCs, which, as I’ll explain, were themselves a replacement for the refrigerant that replaced carbon dioxide.

It’s like a married couple got divorced, married and divorced other people two more times, then got back together.

What happened?

James Dinneen: Well, first you have to know something about how refrigeration works.

Air Force training film: You might say that a refrigerator works by taking heat from the inside of the box and getting rid of it on the outside.

James Dinneen: To move heat from the inside to the outside, a refrigerator uses cycles of pressure to force a substance called a refrigerant to change from liquid to gas and back again.

Air Force training film: Solid, liquid, and gas are called the three states of matter.

James Dinneen: It’s a basic property of matter to absorb or give off heat when it changes state.

Under low pressure, liquid refrigerant becomes a gas and absorbs heat from the inside of the refrigerator. Then, the refrigerant flows outside, where pressure is increased. As the refrigerant transforms back to a liquid, it gives off heat.

Air Force training film: You have seen the basic principles of refrigeration…

James Dinneen: Now, the nature of this process limits which compounds make good refrigerants. You can’t just use any old gas. A refrigerant has to be able to change between a liquid and a gas at the right temperature and do it efficiently. It also has to be stable enough to last.

Mark McLinden: In the early days of mechanical refrigeration, a whole variety of fluids were tried.

James Dinneen: This is Mark McLinden, another chemist at the National Institute of Standards and Technology who has worked on alternative refrigerants for decades.

Mark McLinden: But things sort of settled or sort of converged on just a few, notably ammonia and carbon dioxide.

James Dinneen: Later on, hydrocarbons like propane and isobutane were introduced. But this so called “whatever works” generation of refrigerants had certain drawbacks.

Piotr Domanski: These fluids, other than carbon dioxide, they were either toxic, or they were flammable, or both.

James Dinneen: Here’s Domanski again.

Piotr Domanski: And accidents did happen.

1934 Video: Fire in one of the great ice factories in Brooklyn meant not only danger from fire but from poisonous gas and explosion too!

James Dinneen: Ammonia was toxic and somewhat flammable.

The hydrocarbons were very flammable.

Carbon dioxide was neither, but it wasn’t very efficient.

Piotr Domanski: The need for safe refrigerants was very strong and obvious.

James Dinneen: There was also more demand for refrigeration itself.

Archival Video: Refrigeration is part of our daily lives.

Mark McLinden: So famously, in the late 20s, the director of research for General Motors, which is the parent company for Frigidaire, went to one of his research scientists and said, “We need a better refrigerant.” And that is what led to the CFCs, the chlorofluorocarbons.

James Dinneen: Yes. As though this wasn’t already confusing enough, before there were HFCs, there were CFCs.

And CFCs, chlorofluorocarbons, had all the thermodynamic traits of a good refrigerant. They were also non-toxic, non-flammable, and extremely stable.

To demonstrate this, the chemist who invented CFCs once inhaled them and then blew out a candle. He didn’t die and the building didn’t burn down.

Mark McLinden: They were the perfect refrigerants. And they really came to dominate things.

James Dinneen: For decades, all was well.

Mark McLinden: They just had this one little problem of transporting chlorine to the upper atmosphere where they destroyed ozone.

Narrator from 1986 Nova Video: For the first time, waste from industrial activity may be altering climate on a global scale.

James Dinneen: In 1974, two atmospheric chemists found that CFCs could deplete stratospheric ozone, a thin layer of molecules high in the atmosphere which absorbs much of the sun’s harmful ultraviolet radiation. They realized that because CFCs were so stable and long lived, they could float all the way up to the stratosphere before breaking down, releasing chlorine atoms that eat away ozone.

Narrator from 1986 Nova Video: The groundwork for this understand was laid by chemist Sherwood Rowland.

Sherwood Rowland in 1986 Nova Video: For a long time the view was that if you put something into the atmosphere it goes away. We now know that it doesn’t go away. It accumulates there.

James Dinneen: A decade later, other scientists in Antarctica discovered that a hole had, in fact, formed in the ozone. And after a contentious debate, CFCs were determined to be the cause.

In 1987, the nations of the world signed the Montreal Protocol, agreeing to stop the production and use of CFCs and other ozone-depleting gases over the next few decades. And fortunately, alternatives were already available, namely hydrofluorocarbons, HFCs.

Mark McLinden: So that made the prospect of phasing out the CFCs not quite as scary to the industry.

James Dinneen: HFCs had no chlorine, so did not destroy ozone, and, despite their high global warming potential relative to carbon dioxide, were actually less potent greenhouse gases than the CFCs and other refrigerants in use.

Over the next 20 years, CFCs and other ozone-depleting refrigerants were phased out, and HFCs were phased in. And all was well again.

Mark McLinden: I think for a long time most folks in the industry felt that, you know, HFCs were the long-term solution.

James Dinneen: But as climate change became a more urgent issue, the high global warming potential of HFCs was no longer tenable; in 2016, after years of negotiations, an amendment to phase out most HFCs by 2035 was added to the Montreal Protocol.

Called the Kigali Amendment after the city in Rwanda where it was negotiated, it has since been ratified by 119 countries and the European Union. Recently, the U.S. and China said they would ratify the amendment. India, the other notable holdout, has not yet made a commitment.

But unlike the previous refrigerant transitions, from whatever works to CFCs, then from CFCs to HFCs, this time there’s not really a new one-sized-fits-all alternative waiting in the wings.

Mark McLinden: There’s no easy answer.

James Dinneen: The ideal refrigerant doesn’t exist.

At least, that’s what McLinden and Domanski argue. And they did their best to find it.

Mark McLinden: We went to this very large database of, you know, 60 million chemicals. And we said, OK, let’s try to identify molecules with these particular properties.

James Dinneen: After filtering out all the chemicals with high global warming potential, and all the chemicals that depleted ozone, and all the chemicals that are large molecules which tend to make poor refrigerants, they were left with about 200,000 molecules.

Mark McLinden: Um…OK.

James Dinneen: They then ruled out the chemicals with the wrong thermodynamic properties.

Mark McLinden: You want something that’s volatile.

James Dinneen: Which got them down to…

Mark McLinden: Something like 138.

James Dinneen: Then, they crossed off the chemicals that were unacceptably toxic, or flammable, or unstable, or inefficient, and…

Mark McLinden: With that, we got it down to 29 fluids.

James Dinneen: 29 candidates. Out of 60 million molecules.

Mark McLinden: And sort of the disappointing thing was that we didn’t really find a good replacement…

James Dinneen: None of them could replace HFCs in all their applications without accepting some tradeoff.

Piotr Domanski: Basically, the chemistry didn’t cooperate. We need better options the chemistry didn’t give us. It is what it is.

[Grocery store ambience.]

James Dinneen: But no ideal alternatives, doesn’t mean no alternatives. It just might take a whole lot of reconfiguring.

[Grocery store music.]

John DeCicco Jr.: So one set is a frozen food set, which is low temp, and the two other sets are commercial temps.

James Dinneen: DeCicco leads me down a few corridors to the refrigeration system in the basement. Rows of metal pipes line the ceiling.

John DeCicco Jr.: It’s gonna be loud.

James Dinneen: Loud is good.

John DeCicco Jr.: Not that loud. But loud.

[Walk into compressor room. Loud buzzing of refrigeration system.]

John DeCicco Jr.: So this is essentially the refrigeration system. There’s four medium-temp compressors, which generally keep the temperature between 32 and 40 degrees.

James Dinneen: The system is a minivan-sized version of what happens behinds every home refrigerator. Refrigerant — in this case CO2 — moves heat out of the fridges and freezers in the store. Back in the basement, the refrigerant is compressed and the cycle begins again. For an extra dose of efficiency, the heat the CO2 gives off as it’s compressed is reused.

John DeCicco Jr.: What we do in this case is we run all the water, all of our hot water, through this first heat exchanger. And this basically heats all the hot water we need for the store…

James Dinneen: Your refrigeration system also heats your water?

John DeCicco Jr.: Yes. Heats the water, heats the store. And cools the store.

James Dinneen: Wow. I’m just imagining, 38,000 supermarkets around the country.

John DeCicco Jr: A lot of these to put in. That’s a lot of HFCs to eliminate. 1,000, 2,000 pounds per store times 38,000 is a big number.

James Dinneen: I can’t do it in my head.

James Dinneen: When DeCicco installed his CO2 system it was one of the first in the country. Since then, a few hundred others have followed suit.

There are also stores using low global warming potential refrigerants like ammonia, or a new class of synthetic refrigerant called hydrofluoroolefin, or different refrigerant blends.

Some supermarket chains such as Walmart have made commitments to phase out HFCs, but, according to Mahapatra, have not moved quickly enough.

Avipsa Mahapatra: Often we have heard really, really, you know, at this point, laughable excuses as to why some companies can’t move to other technologies, but it usually comes down to the lack of wanting to spend that money.

James Dinneen: I reached out to Walmart several times for comment on this but received no response.

And that’s just supermarkets.

HFC’s are used for many other things, from air conditioning systems both large and small, to refrigerated trucks and train-cars, to you and your neighbor’s fridge.

So what exactly will replace HFCs in every fridge and AC system in America?

Mark McLinden: OK, that is a complex question. Things are not going to be quite as simple as they were in years past. This time around, there aren’t any silver bullet molecules left. There are tradeoffs.

James Dinneen: For instance, CO2 is great for many large-scale applications but has efficiency problems at smaller scales and in hotter climates. It also can’t just be swapped in for HFCs in an existing system; it requires installing a new one.

Ammonia has long been used for large-scale commercial refrigeration, but it is flammable and toxic and it stinks. That’s an acceptable risk in many commercial settings, but it rules ammonia out for residential use.

Hydrocarbons like propane or isobutene can be used in home refrigerators, and are already frequently used in Europe and Japan. They’re flammable, but it’s not a huge issue since home fridges use such a small amount of refrigerant.

Another option are the synthetic hydrofluoroolefins, or HFOs. They have negligible global warming potential, but it takes energy to make them, and they are, wait for it…flammable.

There’s also some controversy about a substance leftover when HFOs breakdown in the atmosphere called trifluoroacetic acid or TFA, which can be toxic to aquatic organisms

There are refrigerant blends which can mitigate some of these drawbacks for some applications, but they have their own problems. For instance, blending HFOs with HFCs reduces flammability, but spikes global warming potential back into the hundreds.

At the end of April, the EPA issued its first rule under the AIM Act setting HFC production and consumption baselines. The agency estimates the phase down will eliminate emissions equivalent to 4.7 billon metric tons of carbon dioxide by 2050, about as much as a billion cars emit in a year.

And pulling that off, after decades of research in pursuit of the perfect refrigerant, a barely averted ozone disaster, and a still unfolding climate emergency, just might mean going back to where we started: whatever works.

[Grocery store ambience.]

James Dinneen: It seems like phasing out HFCs over the next 15 years is really gonna happen in this country. Do you feel like you are way ahead of the game?

John DeCicco Jr.: Yeah, we’re done already. We’re set. Yes, absolutely. Yeah, everyone has a lot of money to spend and a lot of catch-up to do.

Lydia Chain: James, thanks so much for the story and for joining us to talk about it.

James Dinneen: Thanks for having me. It’s been really fun to work on and it was the first in the field reporting assignment I’ve had during the pandemic so thanks for that.

Lydia Chain: Yeah, it was great to get some real sound. One thing I was wondering was how this transition is expected to unfold — should I be waiting for someone to come take my fridge?

James Dinneen: So as far as somebody who has a refrigerator in their kitchen nothing will change immediately. Where you as an average consumer, where you’re most likely to see the change is when you go buy a new refrigerator in a few years. The refrigerators for sale probably will not have HFCs in them. They’ll use propane or maybe HFOs. You also might see the effects of the phase down at supermarkets, who will be required to make those changes more rapidly.

Lydia Chain: Sometimes when there are new requirements or regulations there’s industry pushback. How has this new rule been received by industry or consumers?

James Dinneen: Well, the AIM act itself was actually bipartisan legislation which is something pretty rare these days. And as far as the response to the act there were a number of petitions recently filed with the EPA from different environmental groups and from cooling industry groups, and while there are differences among them, they largely agree that the HFC phase down is a good thing and that it should happen and they’re ready for it to happen.

Lydia Chain: As we worked on this piece together I was struck by the fact that in so many technological stories, there’s some promised advance, some silver bullet that will fix it, and that’s not really the case here.

James Dinneen: Yeah, that’s originally why I became interested in this story and a little bit of the history of refrigeration. I think it does challenge some ideas we have about the inevitability of technological progress. As I discuss in the episode, there were important reasons CFCs replaced the “whatever works” refrigerants, and there were important reasons HFCs replaced CFCs, and now there are important reasons HFCs have to go. But, sort of, progress is hard to see in this story. It’s not really a straight arrow pointing to the future. It’s more of a circle.

Lydia Chain: James Dinneen is a science and environmental journalist from Colorado and based in New York. Archival tape in this episode comes from Nova’s “The Hole in the Sky,” British Pathé, and the United States Air Force. Our theme music is by the Undark team and additional music in today’s episode comes from Stirling Rutty. I’m your host, Lydia Chain.