Dimming the Sky | Council on Foreign Relations

It sounds like something out of a movie. 

Geostorm: 0:20 Thanks to a system of satellites we can control our weather. 


A movie with a really big disaster. 

Geostorm: 1:26 There’s potential for catastrophic weather events on a global scale. A geostorm. 

https://www.youtube.com/watch?time_continue=21&v=EuOlYPSEzSc&feature=emb_logo (1:26 – 1:33)

But the idea of manipulating our climate in order to survive is a real thing. It’s being developed by scientists, right now. And it’s called solar geoengineering. 

The problem is, it’s risky. 

I’m Gabrielle Sierra and this is Why It Matters. Today, should we dim the sky? 

CBC/Radio-Canada: 0:00 A dire warning this morning from climate experts, a UN panel says governments around the world must take rapid action to curb rising temperatures.


ABC News (Australia): 0:46 Earth’s climate is now changing faster than at any point in the history of modern civilization.


CBC/Radio-Canada: 0:19 The very livability of our planet is at stake, not in ten years, twenty years, thirty years, but right now. 


David KEITH: So solar geoengineering is the idea that humans might deliberately alter the climate somehow to change the energy balance of the earth to reduce some of the climate change that comes from accumulated carbon dioxide. It can’t undo all the environmental risks of carbon dioxide. Indeed, maybe it won’t even undo hardly any of them; we really don’t know very well. But at best, it reduces some of them.

That’s David Keith. He’s a professor of both engineering and public policy at Harvard. He’s also one of the world’s leading researchers on geoengineering. 

KEITH: …So I’ve had a big onstage argument with Al Gore, in fact, just a few years ago where he I think his underlying position was that it was dangerous to even talk about solar geoengineering because it would distract away from emissions cuts. To me, the worst way to handle this is to keep the kind of taboo intact, to not bring this out in the open, to keep not talking about. And then to get to a situation where even if we don’t talk about it some country moves forward to deployment, and then we have under crisis to make decisions both about the technology and about its governance.

Today, people are starting to talk about solar geoengineering… a little bit. And if you want to know what it is, you have to start at the beginning. With climate change. So here goes.

KEITH: The most important driver of climate change is energy use—fossil fuels, coal and gas and oil. When they’re burned to provide us all the energy that allows the modern world to work, they put carbon dioxide in the air. And that increase in carbon dioxide in the atmosphere makes the atmosphere trap more heat, and it tends to warm up the climate…

A good way to understand this is to think of carbon in the atmosphere as a huge blanket covering the earth. It traps in the heat. The more carbon in our atmosphere, the hotter it gets under the blanket. 

KEITH: …and that causes all sorts of changes. So the most obvious one is warming. But it will, say, melt the big ice sheets and can raise sea levels. It’ll increase the intensity of extreme storms and rainfall events. All those collectively will produce a series of human and environmental impacts. 

And that’s where solar geoengineering comes in. But…how does it work? 

SIERRA: Give me just like a step-by-step of that process.

Suchi TALATI: Sure. So, in a very basic way we would want to get aerosols of some sort into the upper atmosphere, probably with specially designed planes. 

This is Suchi Talati. Suchi is the research, governance, and public engagement fellow at the Union of Concerned Scientists. 

TALATI: They would emit these aerosols, which would then stay in the atmosphere for on average of a year or two. And then we would need to continue that process again and again to maintain the temperature that we have reduced.

SIERRA: So aerosol, like hairspray?

TALATI: Basically, but a different chemical compound.

SIERRA: OK, so these planes would fly up super high, release a chemical compound that would then make a cloud?

TALATI: Essentially, but more kind of a dispersed layer that would kind of cover the whole globe.

SIERRA: And that would then do what?

TALATI: And so that layer would reflect sunlight.

The idea here is that when we bounce sunlight back into space, we reduce the amount of incoming heat. 

SIERRA: So you’d have to keep doing this over and over.

TALATI: You’d have to keep doing this. 

SIERRA: Has this been tested?

TALATI: No. This has not been tested. The only test we have is a natural analog of a volcano. So the most recent volcano that exploded that got aerosols into the stratosphere was Mount Pinatubo in 1991. And we noticed that there was about a half-degree of cooling that lasted for a few months.

SIERRA: So people just looked at that and they were like, oh, let’s do that. 

TALATI: I think people were like, oh, that’s really interesting. I think we should look into that further. And then that research kind of led into this space as a potential way to help cool the planet.

We can’t just wait for volcanoes to erupt, so scientists are trying to figure out synthetic ways to do the same thing. And aerosols in the stratosphere are just one of the options. 

KEITH: There are other ideas of manipulating cirrus clouds, ways that you could reduce the amount of these thin, high clouds which act as heat trappers. There are proposals to modify marine stratus clouds—the kind of low clouds you see off, say, the coast of Seattle—to make them a little more reflective. And finally, at least in principle you could imagine humanity constructing some kind of reflective shield in space between the Earth and the Sun.

Aside from these methods, there’s another one that involves recreating woolly mammoths. Yup, you heard that right, wooly mammoths. Another plan involves spreading sand over sea ice to keep it from melting. 

But the one method that is getting the most attention, the one we’re talking about today, is atmospheric aerosols.  

And a big part of this conversation is…risk. 

TALATI: So the scientific risks are not well-understood. We’ve done a lot of modeling in this space. And there is general ideas of how it could affect precipitation or extreme weather. But it’s not a robust understanding and especially at, you know, a small enough scale for different countries to know how it might affect them.

SIERRA: So what are the chances that messing with our climate this way will have side effects and unintended consequences?

KEITH: It’s a hundred percent certain that something you do at this scale will have side effects and unintended consequences. Anyone who thinks that this is some magic fix that will perfectly reduce climate risks and work exactly the way we expect—anybody who thinks that is a nut. I think we can do lots of research and we could learn a lot, but in the end there will still be lots of unknowns.

SIERRA: Are there any known risks already?

KEITH: Oh, lots of known risks. So it could deplete the ozone layer. It could change the circulation in the stratosphere. It could cause air pollution, because we’re talking about adding aerosols to the atmosphere and we know those are pollutants. By blocking some sunlight, it could reduce crop productivity. There is a big range of risks. For each of the risks I said, there are now quite a few scientific papers that have begun to really look at those quantitatively. And for each of the risks I said, it looks like, based on early research, that the actual scale of those risks is pretty small compared to the benefits of reduced harms through the reduction of climate change. But I wouldn’t leap to the conclusion that we know that the risks are small compared to the benefits. I think we could say with confidence is, there’s enough reason to believe it could dramatically reduce human and environmental risks this century that it deserves serious research. 

SIERRA: So what are the chances that some regions will suffer more from the consequences of geoengineering than others? Because, if someone just decides that they’re going to do it, it’s not just going to hover over one country. It will affect the entire world.

KEITH: So we know for sure there are ways that geoengineering could be done that would produce hugely unequal and destructive impacts. So for example, if you only did it in the northern hemisphere, and reflected sunlight in the northern hemisphere, put aerosols in there, and none in the southern hemisphere, you would shift the band of rainfall in the tropics, with big, big impacts. We know for sure that would be destructive. The evidence is that if it’s done in a way that is globally uniform, where you aim to have roughly the same, what we call radiative forcing, the same kind of amount of sunlight being reflected almost everywhere—north to south, east to west. If you do that, and if you do it in a way where you’re not doing too much, you’re using it to take the edge off the risk, the pain from the CO2 in the air—in that circumstance the evidence from current models is that actually no major regions are left worse off, and all regions have significantly reduced climate risk. 

SIERRA: So you just do a little bit of geoengineering not, you know, a ton?

KEITH: Well, yes. The dose makes the poison. So if you asked objectively, is geoengineering good or bad, what impacts does it have? There’s no answer to that. So if you do a huge amount of it, it will for certain have big impacts. But the question is if we do a moderate amount, using it not to drive the climate back to preindustrial but using it simply to reduce the total amount of climate change over the century, while we bring emissions to zero and then slowly take CO2 out of the atmosphere—in that circumstance there is really is evidence it could significantly reduce climate risk.

Computer models can’t predict all the risks. But there’s one problem that’s already getting a lot of attention.  

SIERRA: OK. So let’s say we start solar geoengineering and decide we don’t like it, can we just stop anytime we want to?

TALATI: So termination shock, which is abruptly stopping geoengineering, is something that people are also extremely concerned about. So if we were, you know, deploying solar geoengineering at a pretty high level and then abruptly stop, we would see abrupt warming—really fast warming and the impacts that come along with it.

So, why would termination shock be so bad? Let’s imagine a scenario. Let’s say the world comes together on geoengineering, and we decide to do enough to stop global temperatures from rising more than 2 degrees. Fifty years pass, and the world is significantly cooler than it would have been. 

Now, let’s imagine that during these 50 years, we went on burning fossil fuels. All of that carbon still goes into the atmosphere. The only reason things aren’t getting hotter is because we slathered on the sunblock via solar geoengineering. Well, if we stop all of a sudden, fifty years of warming could happen…real fast. 

That means all the melting, flooding and extinction would also happen rapidly. We’d have no time to adapt. And that would be very bad news.

SIERRA: So it would be accelerated?

TALATI: Yes. That said, though, the situation in which termination shock would happen is probably unlikely. So you know, if we were to start solar geoengineering and realize that it’s having some unintended harm, we could slowly turn down that temperature, right. And in the ideal world, solar geoengineering would only be happening in the context of aggressive emissions reductions, right? And so it would have an end date. And so that way it would be tapered off, you know, by default. And so I think that’s the ideal situation of using it.

SIERRA: That we would reach our goal point and then slowly taper off?

TALATI: Right.

SIERRA: As opposed to stopping in the middle because we’ve decided, you know, it’s having more harm than good.

TALATI: Right. And stopping in the middle is not something we would ever want to do. And so hopefully that’s where governance would come into play, right? And so even if it were potentially having some harms or consequences, you know, scientists and researchers, hopefully before we had deployed this, would have strategies of how to slowly reduce solar geoengineering use to where it’s not as harmful, so we can slowly taper off. Outside of scientific risks, I think even more dangerously potentially are the political risks. The geopolitics of geoengineering is incredibly risky. We have no idea how different countries might react to such a process.

No one may know for certain, but there are some people who have a pretty good guess. One of those people is Gernot Wagner. He was the founding co-director of Harvard’s Solar Geoengineering Research Program. And he’s particularly good on the political risks. So, we Skyped him. 

SIERRA: Every country on Earth has a shared interest in keeping global temperatures from rising, right, but every country also has their own interests. So I’m just curious about what type of conflicts you see rising after geoengineering gets started.

WAGNER: Should we start with outright war or should we end up there? So yes, there are—huge huge disagreements of where we ought to go. And yes, this is—right, this is where politics comes in and this is where things get messy.

SIERRA: So I mean, it’s kind of like two roommates who have one thermostat, and one person likes it super hot and the other one likes it chillier, and then they go to war.

WAGNER: Sure, except, right, two roommates can usually at least – at least you know who to talk to, right?

SIERRA: Mmm hmm.

WAGNER: Now, you know, scale that up by seven billion, right?

SIERRA: Right. Just a slight tweak.

WAGNER: So solar geoengineering is an extremely powerful potential technology that has lots of potential benefits. But it also comes with risks; it comes with uncertainties, and as so often, there are winners and there are losers. Well, it doesn’t take much to imagine that those losers some may in fact have, let’s say, nuclear technology at their disposal, speaking of countries now, may want to stop those from trying to solar geoengineer, to do so. So imagine the rapidly developing, large Southeast Asian country that is particularly badly hit by, yet another hundred-year tropical cyclone. And basically say, we have the technology. We can do this. So now you have a country solar geoengineering with the best of intentions—


WAGNER: Now imagine, right, country A blaming country B for devastating floods or droughts or anything in between while everyone knows that country B is, in fact, solar geoengineering the planet?

SIERRA: So you mean that, like, a country could say, OK, we got flooded, and it’s your fault because you started geoengineering without us saying OK?

WAGNER: For example, yes, right? And then in many ways it won’t matter whether it’s true or not. It won’t matter whether there’s a link, scientific or otherwise, right? Wars have been started for much less. Another scenario. Petro-state, right, who has every interest in the book, right, to maintain the status quo—pumping fossil fuels, you know, selling them, burning them, dumping CO2 in our atmospheric sewer, right? Vast economic interest to keep the status quo. Well, imagine that country having the capacity to just pull the trigger to go do it. Whoever controls the dial here has, in fact, a lot of power.  Well, that’s why countries do have militaries, to prevent others from accumulating this kind of power. You know, cue the wars, right? Cue the conflict. Worst-case scenarios may well be along the lines of countries disagreeing where to set the dial. So imagine somebody trying to geoengineer to make it cooler and somebody else saying, no, no, no, we like it just the way it is, right? You could imagine a scenario where someone tries to release powerful greenhouse gases into the atmosphere trying to, in fact, warm it rapidly.

SIERRA: Wow. Yeah, that sounds like a—definitely sounds like a movie. I mean, it sounds like Mr. Freeze trying to make the whole world really cold, and then Poison Ivy trying to make it all real warm because she just really likes that, and then what we get is just some sort of like puddly soup that we’re all just really in trouble about. 

WAGNER: Yeah. I mean, frankly, right, we’ve had two, you know, fairly bad but still Hollywood movies on exactly this topic already, right?

SIERRA: (Laughs.)

WAGNER: On the other hand, yeah, the screenplay writes itself.

Beyond the scientific and political risks, there’s another problem, one that comes down to basic human nature. 

KEITH: To be clear, the reason that lots of really thoughtful scientists and policymakers oppose the kind of work I’m doing, oppose research and debate about this topic, is their fear that no matter what we say the inevitable result will be that people will just decide to keep the fossil fuel party going.

SIERRA: I mean, you know, I can totally see people being like, well, this is a great shortcut, and I don’t have to change my ways, and things are getting better anyway. And it’s really hard, and it’s going to be expensive. So I’ll just keep doing what I’m doing, and you guys just keep geoengineering.

KEITH: I – there’s no question that impulse is out there.

TALATI: This is actually an argument that was used against talking about adaptation in the ’90s. They thought if we talked about, you know, actually building up ways to help address the impacts of climate change, we wouldn’t actually continue trying to limit climate change itself. We’ve obviously moved past that, but it’s still an argument here. And in some ways, you know, it’s a concern. I think there are a lot of politicians and people who might view it as a silver bullet, as a quick fix so that they don’t have to change industry. You know, the fossil fuel industry’s incredibly entrenched. And you know, if they view it as a way to continue business as usual and pick it up, that’s a legitimate concern. Now, they haven’t done that yet. This is not something the fossil fuel industry is involved in yet, but it is a concern. And so that’s kind of the moral hazard argument.

WAGNER: I know nobody studying, looking at, talking about solar geoengineering in any sort of sensible way, shape or form, who doesn’t go to pains to start, like, every sentence, or maybe every paragraph at least, with the demand for we have to cut CO2 emissions. There is no way around this. Whatever your medical analogy, solar geoengineering is not the solution. Solar geoengineering is not addressing the root cause. It’s the Band-Aid. It’s the painkiller. It’s the opioid. It’s the stuff that has some real nasty side effects.

KEITH: There is no way that it perfectly substitutes for emissions cuts. And so if you think that geoengineering is an excuse to just keep the fossil fuel party going, and keep burning fossil fuels forever, and then continuously doing more solar geoengineering, that world walks us closer and closer to doom.

SIERRA: So is it worth it? Should we do it?

WAGNER: You know, frankly, if you ask me today should we pull the trigger on actual geoengineering deployment tomorrow or next year or never, ever do it, frankly I would probably vote for never, ever doing it. Now, of course, we know that’s—that too is an idealized scenario. The cat is out of the – we can’t squash this technology anymore. We can’t pretend it doesn’t exist. So in many ways the conversation of course ought to be, ok, how do we govern this potential technology? How do we govern the kind of conversations that ought to happen around this technology? How do we govern research into this technology? And frankly, how do we guide from a public policy perspective the kind of research that ought to happen to make a better-informed decision, even when that question in fact is on the political table?

TALATI: Are we going to be able to make a decision where everyone’s happy? No. I mean, I don’t even think that’s possible for any decision. But we have to have as many voices at the table as possible. We have to have a more inclusive discussion. We have to have more scientists in the conversation other than scientists in the United States and Europe. We have to have more civil society organizations working on climate change at the table on this issue. You know, and we have to have just a general level of education on this topic.

Most people are able to tell you in some way what climate change is. And so they’re able to make at least somewhat informed decisions when it comes to voting on issues related to it. We’re nowhere near there on geoengineering. And so we need to get to that point to make sure this is a more democratic decision.

SIERRA: So there are just so many unknowns with this. And it’s a decision that will affect later generations. So is it fair for us to make this decision?

TALATI: That’s an incredibly complicated question. And there have been a lot of ethicists looking at this topic as well. Climate change is also going to affect future generations. And so is there a responsibility to try and address this in some way? Or is there a responsibility to address this in one particular way? You know, I don’t know the answers to these questions, but I think whatever decision we make we have to do it with future generations in mind, because they’re the ones who are going to maintain whatever system it is that we build.

As always, you can head on over to CFR.org/Whyitmatters for more information on each episode. The page for this episode includes more about the wooly mammoths, which is pretty cool. 

If you have any questions or just want to say hi, send us an email at [email protected]. Subscribe to the show on Apple Podcasts, Spotify, Stitcher, or wherever you get your audio. And if you like the show, leave us a review! 

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Why It Matters is a production of the Council on Foreign Relations. The show is created and produced by Jeremy Sherlick, Asher Ross, and me, Gabrielle Sierra. Our sound designer is Markus Zakaria. Robert McMahon is our Managing Editor, and Doug Halsey is our Chief Digital Officer. Christian Wolan is our Product Manager. Original music is composed by Ceiri Torjussen. Rafaela Siewert, our fabulous former intern, provided research for this episode. Special thanks to Richard Haass and Jeff Reinke.

For Why It Matters, this is Gabrielle Sierra, signing off. See you next time!