Welcome to Entanglements. In this episode, hosts Brooke Borel and Anna Rothschild ask: Should we run outdoor geoengineering experiments? Geoengineering — intentionally altering the planet’s climate to slow the effects of climate change — has been fiercely debated for years. And although some scientists are increasingly open to the idea, there is still disagreement on whether or not to move forward.
As always, to dig in, our hosts invited two experts with differing opinions to share their points of view in an effort to find some common ground. The point isn’t to both-sides an issue or to try to force agreement. Instead, they aim to explore the nuance and subtleties that are often overlooked in heated online forums or in debate-style media.
Their guests this week are Frank Keutsch, an atmospheric chemist at Harvard University, and Raymond Pierrehumbert, a planetary physicist at Oxford University.
Below is the full transcript of the podcast, lightly edited for clarity. New episodes drop on Wednesdays. You can also subscribe to Entanglements on Apple Podcasts and Spotify.
Brooke Borel: OK Anna, I want to read a social media post to you.
Anna Rothschild: OK, I’m kind of nervous, but I’m ready.
Brooke Borel: OK. So this is a post from July 5th on the platform X from Marjorie Taylor Greene, a congresswoman from Georgia.
Anna Rothschild: OK…
Brooke Borel: It reads: “I am introducing a bill that prohibits the injection, release, or dispersion of chemicals or substances into the atmosphere for the express purpose of altering weather, temperature, climate, or sunlight intensity. It will be a felony offense.”
Anna Rothschild: Wow.
Brooke Borel: And then it goes on to say: “We must end the dangerous and deadly practice of weather modification and geoengineering.”
Anna Rothschild: Oh my goodness. Are we finally doing a geoengineering episode?
Brooke Borel: We sure are!
[MUSIC]
Hi listeners, this is Entanglements, the show where we wade into heated scientific debates and search for common ground. I’m Brooke Borel, articles editor at Undark Magazine.
Anna Rothschild: And I’m science journalist Anna Rothschild. OK, Brooke, let’s get back to the geoengineering.
Brooke Borel: Yes! So geoengineering is basically deliberately tweaking the planet’s climate to try and slow climate change. And Greene’s bill — which, who knows what’s going to happen with it, right? But Greene’s bill is covering some other stuff, too, but in general she’s opposed to anyone intentionally injecting stuff into the atmosphere to alter it.
Anna Rothschild: Yeah, this is getting more mainstream now, but I know this has been a debated topic even among scientists for years.
Brooke Borel: Yeah, I mean, the idea of trying to intentionally change the climate on our entire planet is really controversial. Especially when you start thinking about who gets to make a decision like this on behalf of our whole species and everything else on the planet.
Anna Rothschild: Right, exactly. And there are some pretty wild ideas out there, right? Like I heard there’s one about putting giant mirrors up in space to reflect sunlight away from Earth? Things like that.
Brooke Borel: Right. And most scientists are not seriously considering doing anything like that anytime soon. But some are thinking about other ways we might reflect sunlight away from Earth, like altering Earth’s atmosphere to be more reflective. So, one way you could do this would be injecting little reflective particles up into the atmosphere. Another idea is to brighten marine clouds to make them more reflective. And these approaches are commonly called Solar Radiation Modification, or SRM.
Now, this is also controversial. But there are some scientists who are increasingly open to it because they think it just might be necessary in light of where climate change is headed.
Anna Rothschild: Yeah, I can see that.
Brooke Borel: Right. So that is what we’re talking about today. And in particular, we’re asking the question: Should we be doing geoengineering experiments? And let me just say: It was not easy to find two experts willing to tackle this one.
Anna Rothschild: Why?
Brooke Borel: Well, here is a direct quote from someone who is very against geoengineering, when I was trying to entice him onto the show. He said: “There are a few people with scientifically respectable thoughts on this subject, but there are also a lot of geoengineering zealots out there I don’t want to be in a direct public discussion with.”
Anna Rothschild: Oh! OK, gotcha.
Brooke Borel: Guess what though? I got that guy to come on the show and I found someone he was willing to talk to.
Anna Rothschild: Oh! You’re so good.
Brooke Borel: I tried. It took me months but here we are. So we’re going to hear from the pro-geoengineering experiments person first.
Anna Rothschild: Great, I’m so excited.
Brooke Borel: Let’s get into it.
[MUSIC]
Frank Keutsch: I started really getting into this field about 10 years ago, and before that I had heard about this field, but was quite honestly thinking that the idea of working on this topic and people pursuing this kind of research was really a little crazy.
Brooke Borel: This is Frank Keutsch. He’s an atmospheric chemist at Harvard University. And despite his initial reaction, a few years later he was spearheading a potential geoengineering experiment called SCoPEx. That project never happened — and we’ll get into why in a moment. But for now, all you need to know is that when it comes to geoengineering, his stance is: No, it’s not time to deploy it, but it’s time to start exploring it.
Brooke Borel: What changed that made you decide to pursue something like this?
Frank Keutsch: After much internal debate, the reason I actually went in this direction is that if I — I looked at the expertise I have. I’m an atmospheric scientist, an atmospheric chemist, and I really wanted to do work that I felt could address impacts of climate change in a significant way, potentially. And when I looked around, one of the things I noticed is that there was this field of, as people refer to it, solar geoengineering, and there were virtually no atmospheric chemists in this field. And so I thought at least here, there may be a place where my expertise could come in usefully, in particular, to answer a huge array of open questions that correspond to risks in this research that I thought really needed to be addressed.
Brooke Borel: So what kind of things are helpful to include in that from the perspective of an atmospheric chemist? Like what was missing did you think?
Frank Keutsch: The really detailed understanding of what happens when I introduce particles into the stratosphere. And the reason I also was interested in that, in that it sort of fits in the broader research that I’m doing. And that is really trying to understand how human activity is resulting potentially in a new state of the stratosphere.
Brooke Borel: But Anna, to be clear, we are nowhere near this yet. When Frank first got into this field, it was with a super small-scale experiment.
Anna Rothschild: OK.
Brooke Borel: He wanted to release about a kilogram of particles to see how they would spread through the atmosphere, what pattern they would make. And the experiment didn’t even use the same types of chemicals that would be used in an actual geoengineering project.
Anna Rothschild: OK. So what was the point then?
Brooke Borel: Well, before anyone even thinks about putting particles in the atmosphere to reflect sunlight, first they need to understand basic things about how the atmosphere spreads and moves them around, which is called turbulent mixing.
Anna Rothschild: OK. And that way they can figure out how actual reflective particles would move around if they did ever decide to put those in the atmosphere later.
Brooke Borel: Yep. Here’s how Frank describes it:
Frank Keutsch: Imagine you have a giant Olympic-size swimming pool and I’m putting in a drop of ink, right? How does that spread out until it fills the whole swimming pool? And that is a big unknown. And the question is, does it even spread out evenly? That was the main scientific topic that we wanted to explore with SCoPEx.
Brooke Borel: So I’m curious from your perspective, what makes — whether SCoPEx or just other geoengineering projects more broadly — what makes this kind of research controversial?
Frank Keutsch: It really just doesn’t address the problem, right?
Brooke Borel: The problem of climate change, that is.
Frank Keutsch: At best it’ll address symptoms of a problem. What SRM is offering is a painkiller or anesthesia that takes away some of the symptoms, which is the pain, but essentially never addresses the underlying problem.
And that of course comes with a number of risks that are associated with it. And I think one of the main risks is what has been called moral hazard or mitigation deterrence. The idea that if you know there’s a painkiller, rather than going to the dentist right now and having a tooth fixed, you’re like, oh, I have all these important appointments. Let me just take some painkillers and I’ll do that some other day.
Anna Rothschild: OK, that is so relatable.
Brooke Borel: Yeah, who among us has not put something off that we really should do right now?
Anna Rothschild: Yeah, I have a list.
Brooke Borel: Yeah, I have a list too. So to apply that to climate change, the moral hazard issue is that if we have a technology that can help cool the planet, maybe we won’t work so hard to address the actual problem, which is to take carbon out of the atmosphere and also just produce less of it.
Anna Rothschild: Right. But all this said, Frank doesn’t sound like he’s some sort of geoengineering deployment evangelist, right?
Brooke Borel: No, not at all. But given our climate change predicament, he thinks it’s at least worth understanding all the options on the table. So, he says, hey, I’m a scientist and I can help answer some key, basic questions about this sort of project. And then at least people who decide these things can be more informed.
Anna Rothschild: Right. But wait, what happened to SCoPEx? Because you said he didn’t even get to do that, right?
Brooke Borel: Right. Because for some people, even a geoengineering experiment is a step too far.
Ray Pierrehumbert: Of all the kinds of research on solar geoengineering, the most threatening kinds of research are outdoor geoengineering experiments where you actually put something in the actual atmosphere to see what happens.
Brooke Borel: This is Raymond Pierrehumbert. Ray is a planetary physicist at Oxford University and he basically researches the climate of any planet with an atmosphere — including Earth.
Ray Pierrehumbert: All of these experiments are really too small-scale to answer any of the really serious questions of what would happen in a full-scale deployment or even a partially full-scale deployment. But nonetheless, the dangerous thing about most of these experiments, these outdoor experiments that people would like to run, is that to some extent they all develop engineering technologies that would make it possible for somebody to deploy the technology, whether it’s wise or safe to do so or not.
Brooke Borel: Are you more concerned then about the actual materials in a small-scale experiment that are going into the atmosphere, or you’re more concerned with the fact that they would then be developing technologies to make this easier in the long run?
Ray Pierrehumbert: So, in terms of the dangers of outdoor experiments, for the ones that are actually proposed so far, I’m not so concerned about the actual physical effects of these experiments. You know, they are legitimately described as small enough scale that their actual physical hazard, I think, is not the main issue. The hazard is a technological issue. The fact that it makes it easier for somebody to deploy these technologies.
Anna Rothschild: So this is a slippery slope argument.
Brooke Borel: Exactly. The initial experiments may not harm the planet, but they will provide the next step to get geoengineering off the ground. Large scale deployment will likely require technology that doesn’t exist yet: Like airplanes equipped to spray the particles high up into the atmosphere. So, a small scale experiment may help, develop, say, a nozzle to spray those particles out.
Anna Rothschild: Mm-hmm.
Brooke Borel: And like Frank, Ray’s first reaction to geoengineering schemes was more or less: This is crazy. But unlike Frank, he has not budged on that idea, and he just still doesn’t like it.
Anna Rothschild: Right.
Brooke Borel: And he says it’s only getting worse.
Ray Pierrehumbert: I’m a lot more scared now because for decades, it was a tiny fringe of people who were pushing this idea. There was no funding, there was just a trickle of funding from a few philanthropic organizations. But, you know, I thought there was a reasonable chance it was all just gonna go away.
As the climate crisis has become more clear and present, and as the frustration with not making progress on decarbonization of the economy has grown, the frustration of that lack of progress has grown, even some scientists who have been hanging out on the edge, and certainly a lot of political leaders, are starting to think, well, we’re in a panic. We have to do something. And in a panic is not a good way to make good decisions.
Brooke Borel: What potential consequences of geoengineering worry you the most?
Ray Pierrehumbert: The most threatening thing about it if it should ever become deployed is that there’s a fundamental mismatch in the timescales over which carbon dioxide persists in the atmosphere and causes warming and the timescales over which these aerosols, which reflect sunlight persist in the atmosphere.
Brooke Borel: In other words, the aerosols last a far shorter time than carbon, so you have to keep putting them in.
Ray Pierrehumbert: So if you get into a situation where you need solar geoengineering to make the earth habitable, then you’re stuck doing it essentially forever. That’s what I call millennial commitment. Because if you stop injecting stuff into the stratosphere, those particles will fall out in a matter of two years or so.
Then if something ever happens in the next thousand or 10,000 years to force you to stop, like there could be climate wars. If Russia doesn’t like the geoengineering and wants to have warm water ports in the Arctic, there could be world depressions, there could be wars, pandemics. You know, all sorts of things can happen.
Brooke Borel: So, Ray isn’t just worried about these major global events. He’s also worried about what would happen if they disrupted ongoing geoengineering work and triggered what’s called termination shock.
Anna Rothschild: That sounds sort of post-apocalyptic.
Brooke Borel: Yeah, a little bit, yeah. So, the idea is that if geoengineering is the only thing keeping the temperature down, and then you have to suddenly stop the geoengineering scheme, the temperature is going to bounce back up to whatever it would have been without that technological intervention. And this will happen quickly, too, so it’s bad news.
Anna Rothschild: Yeah, I don’t love that.
Brooke Borel: Me either! And here, he and Frank agree: Termination shock is a big concern. And they also agree about the moral hazard issue.
Ray Pierrehumbert: As long as you’re emitting CO2, the world will continue to warm because CO2 will continue to accumulate in the atmosphere. So right now when we haven’t really started the process of getting carbon dioxide emissions down to zero, this is a particularly dangerous time to be developing the technology because it increases the temptation to actually use solar geoengineering instead of decarbonizing.
Brooke Borel: Is there not some value? Can’t we have both things happening at once, where we’re focused on bringing down carbon levels, but also developing this technology? I mean, it seems like if we did get to the point where we would need to deploy such a thing and we don’t have it in place and haven’t done the work to get it in place, that we wouldn’t have it when we might possibly need it. This would be an argument anyway that you would hear from folks that are more gung ho about this technology. What do you say to that?
Ray Pierrehumbert: Yeah. And that’s the desire to have a plan B and the problem with that scenario is just what do you do about termination shock? Either you do it just a little bit, in which case it’s just a minor part, not a critical thing, not the make or break thing, or you do it big.
Brooke Borel: Then you have the risk —
Ray Pierrehumbert: Then you have the risk of this big termination shock.
Brooke Borel: And Ray has other concerns too.
Ray Pierrehumbert: Even in the scientific community, sometimes people who are reasonably well-informed, they still don’t understand this mismatch in timescale issue. You know, you often hear the sentiment that we’ll use it to buy time until we reach net zero. And that sort of implies that you can maybe do some solar geoengineering while we’re waiting to reach zero emission of carbon dioxide and then we can stop. But that’s not the case. Because that CO2 we emitted while we’re buying time is still in the atmosphere and we’ll still be there at significant levels for thousands of years.
[MUSIC]
Brooke Borel: OK, Anna, let’s address the elephant in the room.
Anna Rothschild: You mean what happened to Frank’s experiment?
Brooke Borel: Exactly. So Frank spent almost a decade trying to make SCoPEx happen.
Anna Rothschild: Stop trying to make SCoPEx happen!
Brooke Borel: A lot of people did, OK! So he and his colleague at Harvard, a physicist named David Keith, they first wanted to do the experiments in the American Southwest.
Anna Rothschild: K.
Brooke Borel: But then in 2020 they moved the plans to Sweden. And there was enough pushback there that the whole plan fell apart.
Anna Rothschild: Ooh gosh.
Brooke Borel: It did not happen. And Ray was among the critics who ultimately got the whole thing squashed.
Anna Rothschild: Oh, I wonder how Frank feels about that.
Brooke Borel: Well, take a listen.
Frank Keutsch: Ray may be surprised to hear that I have absolutely no problem at all. That Ray went out and, and sort of tried to, and — not just tried, was effective in arguing against this experiment. That is entirely fine. The much more interesting question is who you actually should talk to about a stratospheric experiment, but in a sense that Ray, who opposes this, goes and talks to people to oppose this is entirely understandable, and sort of what he actually should be doing.
Ray Pierrehumbert: Well, yeah. So actually, I have to say that I sort of helped get it going, but the prominent environmental campaigners like Bill McKibben and Greta Thunberg, in the end, probably did much more than I did. Although I think I provided much of the scientific underpinning about why many of us think this is going down this slippery slope. But part of the reason I thought this experiment was a dangerous direction to go, not physically, but in terms of sort of crossing a boundary that was not justified by the kind of scientific payback you get from this is that it’s an actual release of a material into the stratosphere at a time when there’s no governance to actually say what’s an allowable experiment and what isn’t.
Brooke Borel: Frank, so one of the criticisms is that an experiment like yours could potentially help push the technology and develop the technology that would be needed to then eventually have a geoengineering scheme like maybe making a certain nozzle that you need for the experiment that then eventually would evolve into the type of nozzle you might need, for example, on an airplane to do this on a larger scale. Do you think that that is a valid concern when it comes to experiments like SCoPEx?
Frank Keutsch: I think the technology that we would’ve used for this would not really have been scaled up and it wouldn’t have been useful. I’m not saying that for other experiments. I think it is, to me, important that if people develop some nozzle, say, for example, for marine cloud brightening, where there are experiments going on, you know, the nozzle design and how you do it — that, I think, that should be made publicly available, knowledge of that, so that there’s no, I would say, commercial self-interest in doing this. Now that does leave open that you maybe develop a technology that could advance use or not. And I admit that is true. But I can speak to the kind of science I’m doing. I’m really not trying to develop deployment technology. I’m more interested in fundamental properties. Fundamental science — influence of turbulence, how does this plume evolve. I personally am not that interested in development of technology — at least at the moment. Things can always change.
Brooke Borel: I’m curious, Ray, do you think that there is any potential scientific value in SCoPEx, even though you ultimately opposed it? Could you see any value in it at all?
Ray Pierrehumbert: I mean, I did my thesis on turbulent mixing. I don’t have my turbulent mixing hat. But if I put on my turbulent mixing hat —
Brooke Borel: We all want one of those.
Ray Pierrehumbert: — the places where you get this turbulence are very different from one place to another. And that’s another issue with something like SCoPEx. How much sampling do you need before you actually have a picture of the stratosphere? So scientifically, actually, if I thought of this just as a turbulence experiment and there wasn’t this SRM risk out there in the future, I should be pretty interested in it.
Frank Keutsch: So, I’ll say, Ray, actually what I heard you say just now is that there need to be multiple SCoPEx experiments. I’m very supportive of that, Ray.
Anna Rothschild: OK, but Ray doesn’t really think that there should be more SCoPEx experiments.
Brooke Borel: No, no, no, no, no. They definitely still don’t agree on the point regarding small scale experiments. And they also disagreed on an even broader point, which is: What role should scientists even be taking in this discussion? Should they just do their science to help inform the people who make the ultimate decisions? Or should scientists weigh in on the ethical and societal implications?
Anna Rothschild: Oh.
Brooke Borel: Frank falls squarely into the first category.
Frank Keutsch: I think I have absolutely no say in that. I’m a scientist. I can provide information, I can conduct research, but I have no mandate to make decisions. I have no training in making policy decisions, none of those things.
There are people who are experts on governance, and I feel if I start, as a physical scientist, start talking about governance and what future generations should decide or not, how would I feel if they start telling me something about small-scale stratospheric turbulence, the governance people? So I personally, because I don’t know enough, think if I talk about governance, it’s actually slightly disrespectful to some really highly trained people who really know what they’re talking about.
Ray Pierrehumbert: Yeah. And here is — I completely disagree about how separated the issues of opinions on governance or the sociopolitical setting are from the basic scientific questions. I think people who understand the scientific impact of their technologies and of their research are, in some ways, the best place to actually understand what the implications are.
So, for example, you know, no amount of research is going to make the problem of termination shock go away. You know, unless someone waves a magic, you know, develops a way of sucking massive amounts of CO2 out of the atmosphere rapidly, no amount of research could make that go away. That’s sort of a fundamental thing.
And so that has certain implications for governance. And I know, I’ve looked at some of the professional governance literature. And I’m not that convinced that the people doing this theoretical political science have a better grip on what the world would be like under SRM than I do. A lot of these, these governance regimes that are proposed, they assume a complete science fiction world where the world can make agreements and stick to it.
Brooke Borel: Is there something that each of you wish the other would understand or give more weight to when it comes to geoengineering experiments or even what to do about climate change?
Frank Keutsch: It’s actually — I think it’s the opposite. I think I would enjoy talking more with Ray to sort of really understand his point of view better. You know, sometimes it takes a few conversations to really get that.
Ray Pierrehumbert: I should mention that we’ll have lots more time to talk. I accepted a faculty position at MIT starting January, so I’ll be there —
Frank Keutsch: Fantastic.
Ray Pierrehumbert: — at least one semester a year going forward.
Frank Keutsch: I look forward to it.
Ray Pierrehumbert: Yeah, but I’m glad that we, unlike so much of political discourse out there these days, we do share a reality.
Frank Keutsch: Yes, I would agree. Yeah.
Ray Pierrehumbert: We share a reality, quite a lot of reality.
[MUSIC]
Anna Rothschild: So nice that they agree that they exist in the same reality and —
Brooke Borel: Hey, I mean, especially in today’s world, like —
Anna Rothschild: Exactly. I mean, they can actually have a discourse on this.
Brooke Borel: Which is what we’re trying to do here.
Anna Rothschild: Exactly. Good job, Brooke.
Brooke Borel: Yeah, yeah. I mean, sometimes it works, sometimes it doesn’t, but it feels really good when it works.
Anna Rothschild: It does.
Brooke Borel: But one thing that they both talked about that I did not have you listen to yet, is this other idea that this technology is already getting commercialized.
Anna Rothschild: Oh, OK.
Brooke Borel: There are some groups that aren’t even just like proposing to do small-scale experiments, which is of course what we were listening to the sort of pros and cons on here. But there are companies that are trying to develop proprietary technology to be hired to do this, for example.
Anna Rothschild: Wow. And how would that even work, like from a regulatory standpoint?
Brooke Borel: It’s — well, that’s a good question. There are not very many regulations on this. Usually it’s whatever the municipality that the company or the experiment is existing in, or the country. There aren’t really any global sort of oversight governance things happening yet with geoengineering that are binding.
There are some groups trying to figure that out, right. But it’s really the Wild West, as we like to say, when there’s no regulation on stuff like this. And one of the companies that’s doing this, it’s a company based in Israel called Stardust. Undark has written about this in the past. And they’re quite secretive about what they’re doing, but they’re making what we think are proprietary materials to inject into the atmosphere, developing technologies that are kind of under wraps to do that. And there’s just not a lot of transparency in what they’re working on.
Anna Rothschild: Hmm. OK. Wow. Yeah. The thing that I keep coming back to is, you know, I get the moral hazard argument about like, doing these geoengineering projects would maybe make it less desirable to just cut carbon. But, you know, I don’t know why I don’t see that as huge of an argument, as the termination shock issue.
Brooke Borel: Yeah, I kind of feel the same way. Because it seems like, OK, we could work really, really hard to get this off the ground and have it work. And then even if it worked, even if it was able to help sort of mitigate some of these issues with climate change, even if we had all of the answers as to how those particles are floating through the atmosphere and what they’re gonna do and how much light they’re gonna reflect, if we cut it off, we’re still in really big trouble.
Anna Rothschild: Exactly. I don’t love the idea that we’re doing something that’s almost just like a Band-Aid that needs to keep being reapplied. If it felt more sustainable, I would have a little bit more enthusiasm maybe about this.
Brooke Borel: If the world were a more stable place.
Anna Rothschild: Exactly. Exactly. But yeah, I don’t think we can rely on humanity to, you know, keep something going for the rest of time. Like that just seems really difficult.
Brooke Borel: It’s a really big ask.
Anna Rothschild: Yeah, it’s a huge ask.
Brooke Borel: It’s a really big ask.
Yeah. So, I don’t know. I wonder what our listeners think. Is that a big ask? Do they think that this technology sounds promising? What do they think about all of this?
Anna Rothschild: Yeah, send us an email at [email protected].
Brooke Borel: And that’s it for this episode of Entanglements, brought to you by Undark Magazine, which is published by the Knight Science Journalism Program at MIT. Our wonderful producer and editor is Samia Bouzid. The show is fact-checked by Undark deputy editor, Jane Reza. Our production editor is Amanda Grennell. And Adriana Lacy is our audience engagement editor. Special thanks to our editor-in-chief, Tom Zeller Jr. I’m Brooke Borel.
Anna Rothschild: And I’m Anna Rothschild. Thanks for listening. See you next time.