Catalyst with Shayle Kann - Making sense of solar engineering

Episode Date: June 16, 2022

In some climate circles, solar geoengineering is akin to a swear word. Also known as solar radiation modification (SRM), it means deliberately modifying the earth’s atmosphere to reflect solar radiation. It provokes forceful pushback, because it’s unclear how it would affect the earth’s agriculture, ozone layer and ecosystems. But it’s been attracting interest because it’s clear it would do one thing well: cool the planet. If we’re not moving fast enough on emissions reductions and carbon removal to avoid 1.5 degrees Celsius of warming, could solar geoengineering, despite its risks, be less dangerous than a hotter world? In this episode, Shayle talks to Dan Visioni, a climate modeler who studies solar geoengineering at Cornell University’s Sibley School of Mechanical and Aerospace Engineering. They discuss what solar geoengineering might look like in the real world.  Stratospheric sulfate injections would mimic the effects of volcanic eruptions like Mount Pinatubo in 1991, which cooled the planet by 0.5 degrees Celsius in the following year.  Marine cloud brightening would use salt aerosols to brighten a type of cloud that reflects solar radiation, a phenomenon already created by ocean-going ships. They also cover cirrus cloud thinning and—straight out of a sci-fi movie—space mirrors. They explore key questions, such as: What do we know about the potential effects on ozone, precipitation and ecosystems? What do we need to research and what could we learn by testing? Which could scale faster—Carbon dioxide removal or solar geoengineering?  Solar geoengineering could cost a tiny fraction of the amount required to scale up CDR. Does that mean it could buy us time to draw down emissions more cheaply? Or does the relative affordability enable a rogue actor to deploy it without international collaboration? And who gets to decide whether the world deploys solar geoengineering? Whose hand is on the thermostat, so to speak? Links: Nobel prize winner Paul Crutzen’s influential 2006 paper on stratospheric sulfur injection A provocative New York Times Op-Ed promoting geoengineering from David Keith, professor of applied physics and public policy at Harvard who studies geoengineering Catalyst is brought to you by Arcadia. Arcadia allows innovators, businesses and communities to break the fossil fuel monopoly through its technology platform, Arc. Join Arcadia’s mission and find out how you or your business can help turn a fully decarbonized grid into a reality at arca​dia​.com/​c​a​t​alyst. Catalyst is supported by Advanced Energy Economy. AEE is on the front lines of transforming policy that accelerates the move to 100 percent clean energy and electrified transportation in America. To learn how your business can play a key role in transforming policy and expanding markets, visit aee​.net/join.

from the studios of PostScript Media and Canary Media. I'm Shale Khan, and this is Catalyst. It would take, honestly, less than just a couple of billion dollars per year to do solar geoengineering. We choose a fraction of a fraction of what it would take to scale up CDR solutions. This week, planetary-scale natural systems hacking. That's right. We're talking about geoengineering. When utilities need flexible capacity they can count on, they turn to Energy Hub. Energy Hub works with more than 170 utilities, coordinating over 2.5 million devices to manage

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They're shaped by markets, by policy, by capital, and by the institutions that connect them. I'm Alfred Johnson, CEO of Crux, and host of a brand new podcast, Critical Capital. Each episode, I talk with people deploying capital, shaping policy and building the clean economy. tune in as we unpack how progress is actually made. Listen to Critical Capital on Spotify, Apple, or wherever you get your podcasts.

I'm Shale Khan. I'm a partner at the venture capital firm Energy Impact Partners. Welcome. Okay, so for a long time, the term geoengineering has basically been a swear word in certain circles of the climate community. Anytime somebody prominent would mention the idea of a large-scale intervention to counteract climate change, they would get enormous pushback. Here's an example from last year. This is a headline in response to a New York Times op-ed that was making the case for geoengineering.

The headline is geoengineering, we should not play dice with the planet. But I suspect the tide is starting to turn just a bit on this topic for two reasons. First, with each passing year and each new IPCC report, it becomes clearer that some of the worst effects of climate change are coming for us, even if we move as fast as we can to cut our new annual emissions to zero. From that same New York Times op-ed by David Keith from Harvard, he said, and I quote, eliminating emissions by about 2050 is a difficult but achievable goal. Suppose it is met. Average temperatures will stop increasing when emissions stop, but cooling will take thousands of years as greenhouse gases slowly dissipate from the atmosphere because the world will be a lot

hotter by the time emissions reach zero, heat waves and storms will be worse than they are today. And while the heat will stop getting worse, sea level will continue to rise for centuries as polar ice melts in a warmer world. He says stopping emissions stops making the climate worse, but repairing the damage insofar as repair as possible will require more than emissions cuts. So reason one is just the increasing recognition of the need. Reason two is the recent rise to prominence of the idea of carbon removal or CDR, which we've talked about a bunch on this show already, and I think is a subset of geoengineering, albeit not the one that most folks think of. We're already talking about hacking the biosphere when we talk about adding alkalinity

the ocean or building engineered machines to suck CO2 out of the air. To think about adding sulfuric, is it really so much of a further step to think about adding sulfur to the stratosphere or whitening clouds over the ocean? I'm not sure that it is. Moreover, this conversation that you're about to hear illuminated a couple of points for me that I think are worth highlighting at the front, which is that the cost of solar geoengineering, in theory, is a tiny fraction of the cost of having the same impact on temperature that you would get out of carbon removal. specifically, you might be able to get about a half a degree Celsius of global cooling out of stratospheric sulfur injection for a couple of billion dollars, which is nothing, basically,

comparatively. On the other hand, it raises these enormous questions around ethics and governance. For example, if you can do it for one or two billion dollars, then almost anyone can do it. and what happens when that becomes a reality? So these are really big questions, but I think we need to be talking about them as we talk about deep decarbonization and increasingly just facing them head on rather than trying to avoid the conversation in the first place.

So I wanted to have a good conversation about what is the technology theoretically behind solar geoengineering? What do we know and what don't we know? And so that's what you're about to hear. To help illuminate some of these questions, we had Dr. Dan Vizioni, who is a climate modeler

and a research associate at Cornell's Sibley School of Mechanical and Aerospace Engineering. And as you will hear, spends all his time thinking about these questions. Here's Dan. Dan, welcome. Hello, thank you for having me. I'm excited to talk to you about geoengineering, and I want to start with definitions. When you talk about geoengineering, what is it that you mean? So what I mean, I tend to go by what the IPCC definition is,

which is geengineering is any kind of deliberate large-scale intervention into the climate system. People that do actual engineering might think of geoengineering as engineering of the Earth, but that's another thing. But what we mean is what the IPCC means, which is, yes, exactly that. Is it not then a form of geoengineering, like what we are doing as we, so is like a coal power plant not a form of geoengineering, right, just in the wrong direction? Some people like to argue that, but the key word is deliberate, right? So, yes, we know cold plants and in general, all of our activities affect the climate,

but they affect the climate as a byproduct of other things that's happening. Geoengineering would be the deliberate attempt to control, to change the climate in some ways. Got it. Okay, and then we should talk briefly about a subset of geoengineering by that, definition that we are not going to spend a lot of time on today, which is sort of the world of carbon removal that has gotten a lot more attention recently. This could be direct air capture or some of the nature-based solutions, Bex, all these different things. That qualifies as geoengineering by your definition, right? Yes. Again, it depends on who you're asking, but by my definition, it does. As all of these that you've mentioned, whether it's Kelp, director capture, Bex,

ocean, CDR, even the ones that are called nature-based solutions, they all have a direct effect on the climate. That is not just, in most cases, it's not just the removal of CO2. Right. Okay. So that is, we'll call it part of geoengineering, but not the part that most people probably think of when, at least if they've heard about geoengineering

and they want to talk about it. What they mostly are thinking of, I think, is what we call solar geoengineering. right? Yes, exactly. It's the idea that we can intervene on the solar radiation that is incoming on the planet. Okay, so I want to mostly talk about what the actual, what solar geoengineering is, the various ways we could potentially do it, and what we do and don't know about those options that may be in front of us. But maybe at first start with the, what is the high-level premise here?

What would we be doing with solar geoengineering and what would be the purpose of it? Right. So the observation, the data that we have now, what we see is that the solar radiation comes in, it warms the planet. The planet then tries to be in equilibrium with the rest of the universe. And so it radiates back part of the energy that it absorbs from the sun. But the high amount of CO2 means that too much of the radiation is supposed to escape, stays in the system. And so the planet warms more. So the idea is that while the only way we can fix the, is by reducing the amount of CO2 that is in the atmosphere. There's no doubt about that. But we know, and all the people that do carbon dioxide removal,

we happily admit that that takes time and effort and scaling things up so that they make a significant dent in the amount of CO2 that they're removed. That is going to take time. So the idea is there something we can do at a much faster scale? So can we intervene in the solar radiation that is incoming? Can we reduce that by a little bit? we don't need incredible amount.

It's not a perceivable amount. We're talking less than a fraction of a percent. But can we do that so that the planet warms up a bit less to begin with? And so we don't experience the effect of the global warming too much. Where would you say we are in the trajectory of scientific discovery around solar geoengineering? Are we at the – this makes sense theoretically on paper stage, have small-scale experiments, been tested? Have we actually done it anywhere? Like, where are we in that path? So there are absolutely no small scale or large scale experiments going on anywhere on the planet. There are a few

proposed. Harvard has a very tiny amount of material. They proposed they would inject just to observe what would happen to the initial plume. There are some experiments proposed in Australia. We're going to talk about that maybe a bit more later. But in general, there are no human-made experiments. What we have, and a lot of our understanding, comes from what we can observe from the natural world and what we call natural experiments. So of the main method that is actually the first one that people thought about already in the 80s, because, again, they observed it, is that we know what happens to the planet after big volcanic eruptions.

aside from the ashes, the ashes are a bit tricky, and in case there's very, very big eruptions, they're actually the problem. But from other eruptions, like the one that we've seen in the last 2,000 years, the key thing is that they emit sulfate, and they emit sulfate directly into the stratosphere because they have this massive power, so they push a lot of material up into the stratosphere.

And this sulfate, this SO2 gas, tends to oxidize and produce sulfate aerosols. And the sulfate irasols in the stratosphere, they can stay a lot longer than they would in the troposphere. In the troposphere, there are clouds, there are turbulent processes. So whenever we emit SO2 from the surface, the sulfate irasols tend to fall down pretty quickly. On the other hand, when these sulfate aerosol in the stratosphere,

they stay for one year or longer. And so we have observed in past volcanic eruptions, Pinautubo in 1990, other three or four there have been in the 20th century, that they have cooled the planet for one or two years after the eruption in a measurable way. And so the idea that some people, some scientists have had already again in the 80s, and then Paul Crudson, a Nobel Prize for Chemistry for discovering the ozone oil together with other people.

And he wrote a paper in 2006 where he kind of took the idea out of the, shadow and out of the weird proposed ideas that nobody ever took seriously in a way, and kind of said, well, if we don't get our act together and if we don't manage to reduce CO2 emission, these might actually be the only way in which we can cool down the planet for a certain amount of time in a very quick way. So that's when I say, when we talk about experiments, that's the kind of experiments we think about. Volcanoes for other kind of solar geoengineering, there are other natural experiments that we can think of as well. Okay, so we'll talk about some of the other methods of solar geoengineering, but let's stay on

this one for a minute. So this is stratospheric aerosol injection. It's mimicking the, it's mimicking volcanoes, basically. Would we, if we say we were to do this, you know, is there a sense of how much we would need to do to have an impact on a global scale? Yeah, so we do know, again, we know because we've seen volcanic eruptions, And so roughly, for instance, the biggest one of the 20th century, Mount Pinatubo that derupted in 1991, it injected in the stratosphere roughly around 10 pterograms, that's 10,000 megatons. And it cooled the planet in the year or so after by a bit less than alpha degree. So we kind of have that idea to start, and then of course we have climate model to tell us.

So now that number is not a number that's going to say that much to many people, but just to give you an idea for comparison, so anthropogenic emissions, so man-made emissions of sulfate from the surface, from lots of activities, a lot of activities, I mean, sulfate, they stand at around now maybe 70 pterograms of SO2 per year. At the peak before the US and Europe had cleaner acts, it used to be even over 100. So with a fraction of that, we could cool the planet considerably,

again, because of the difference in the lifetime of the aerosols, compared between the moment in which we inject them from the surface or when we go all the way to the stratosphere to inject them. So, right. So what you're saying is basically like one large volcanoes worth could potentially cool the planet by half a degree. Per year, yes. Per year.

Right. So this is the next question. And so then do we, if we do that, do we then have to keep injecting the same amount into the stratosphere annually? Because otherwise it achieves nothing? Well, I mean, first of all, also the big difference that we would need to imagine is that we wouldn't just dump the same amount of Pinatubo did all in the same day, all in actually is Pinatubo did it in less than six hours. We would do it spread out day by day in different locations, so it would be different. And so the moment we, again, there are for now no proposals to start these anytime soon. But if we were to start it, one could imagine that there would be some time where we start injecting the first days at a amount that is really, really tiny compared to the background sulfate concentration.

And we could learn a lot. So if there were things that we for some reason have missed in our research, we would still have time to learn them at the beginning before it has any climatic effect. But then once we were to do it for long, once we were to keep it up for a couple of years or more, and so we actually have that cooling, then yes, of course, interrupting the injection immediately would just bring us back to whatever temperatures we would have without it. So if we think that we want to stay below 1.5 and so do this, then we would have to keep it up until the concentration of CO2 would allow us to phase it out because just we don't have that need anymore. Virtual power plants are becoming a reliable way for utilities to manage capacity,

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Okay, and then so that I think the question everybody would ask and will ask if we ever consider doing this seriously at the global scale is what are the side effects that this might have on ecosystems on the planet, right? A large volcanic eruption, even ash aside, obviously has a big impact on surrounding communities and ecosystems. What do we know and what don't we know about what would happen if we injected sulfates into the stratosphere? Right. So the first thing to keep in mind that is absolutely central is that by cooling with these methods or with any methods, we would not be just turning back the dial of time to a time where there was less CO2 because the sulfates do cool differently than the CO2 warps. And even if maybe we can try and get it as close as possible, there will still be differences. So we wouldn't have the same climate that we would have if we had emitted all that CO2.

So the first kind of, not even side effect, but the first kind of things that we would see is, of course, a climate that does not look exactly like the one that we deem safe. it might still, and it probably is still going to be better than not doing, that letting the warming just keep unchecked. But it wouldn't be the same. So, of course, we would have to. And there's a lot more that we need to understand when it comes to regional changes. So what would happen to regional precipitation, especially in regions where the

regional, where the cycle, the seasonal cycle of precipitation is very important for agriculture. So, for instance, over India, the monsoon, monsoons over. Africa. So one of the big thing is, again, is to really understand much, much better exactly what kind of a different climate we would have. We would have a climate that globally is cooler. We have no doubt that the sulfate would cool the planet. But we wouldn't be, we are not yet, our models are not there yet. We wouldn't be, we're not sure yet about what the regional, this precise regional outcomes would be. And then there's, this is, but precipitation or local temperature changes is just a tiny bit.

Of course, there's so much more. The sulfur in the stratosphere would react chemically, and so it would interact with the ozone layer. This is the thing that we're studying a lot. We have models with fully coupled stratospheric chemistry where we're trying to understand what would happen. And based on what we've seen with previous volcanic corruptions, we know that the depletion of ozone wouldn't be catastrophic. and it will probably be around plus or minus 5% of what it is now, but still is a thing to keep in mind. And then there are many, many other things that we still need to study.

So, as you said, ecosystems, what would happen? So we have an idea of what would happen, what happens when the sulfate gets deposited down because, again, there's plenty of sulfate going around on our planet, but there are areas where right now there isn't that much deposition of sulfate. So, for instance, it's very high latitudes. There are no sources. So there isn't that much deposition.

And so if we have these thin layers in the stratosphere that eventually would come down, it would deposit in different areas from the place it is deposited in now. Having these aerosols, it would also change what we call the ratio of direct-to-diffuse radiation. So normally, not all the sunlight that reaches the surface comes exactly directly from the sun as a straight ray. that are particles in the atmosphere already. And so a part of this radiation gets, or clouds, and a part of this radiation gets diffused. So it arrives to us in a bit more diffused way,

which means that it's actually more penetrating. So plants react differently to diffuse to direct radiation. By having this constant layer of aerosols in the stratosphere, we would shift a bit that ratio. And so we still need to understand what would happen to ecosystems, what would happen to net primary productivity in forests, for instance. So there's plenty of things and impacts.

What would that do to agriculture and cascade impacts to all of that? So obviously a lot of big open questions around that. I think we'll come back to a little bit later, sort of how you think about this at the higher level from an ethics perspective and how we should think about solar geoengineering, you know, when we need to start really doing it and so on. But I do want to run through the other possibilities, right, because stratospheric aerosol injection is one among a number of different options.

So let's talk about some of the others. Explain cloud brightening or marine cloud brightening. Right. So these other idea came from another, well, not really natural experiment, but looking at just ship tracts. So whenever you have very big ships going through the ocean, you can see the tract that they leave again because they meet particles as well. And so what these particles do over the ocean in the very low levels of the atmosphere

is that they sometimes, not always, but they sometimes make it more likely for clouds to form. So these marine clouds, those are very thick, white, fluffy clouds that tend to reflect a lot of the solar radiation. And so there have been observations and studies looking at these very very, tiny scale effect of ship tracks. And so the idea for this has been, can we kind of make it more likely for this cloud to happen, in particular by seeding low-level clouds with sea salt. So you don't even need other particles. You wouldn't need sulphate in this case. You would just take the seawater that you have and kind of spray it up. The water vapor would, the water would disappear, and then you would have these tiny salt aerosols that are the nuclei of clouds.

Clouds don't just form, most of the times they don't just form by themselves just out of water, but they do need a cloud nuclei, so a solid particle over which the water can kind of co-aculate. So the idea is whether we could do something like that and spray these salt particles and have more clouds and try to cool the oceans a little bit. Now the issue with this is that we don't have the same large. scale experiments. So there's a lot less we understand about cloud formations in the lower atmosphere. We are not sure what the correct size of these aerosols would be. We are not sure whether we could actually scale this up again. You see, the fact is that with sulfate in the

stratosphere, the circulation itself helps us by spreading the aerosols everywhere. And we know it it does. When you are dead low down, you would really need to do it locally. And so there's plenty of doubts in that case over whether it could perceivably change global temperature. Maybe it could be used to mitigate heat waves, for instance, protect coastal environments. That could be a solution. But there's a lot more that we need to understand in that case. Okay, so that's category two, marine cloud brightening. Let's talk about some more wacky wild ideas.

Putting mirrors in space, what might that look like? Well, that would look like, in a way, very close to what the sulfate would do. It would be a very global intervention. Again, you wouldn't need that much. These Pays mirrors, there would not be something that we can see. It wouldn't be like another moon. But they would be there, and they would prevent part of the, again, a fraction of the solar radiation from coming in. In that case, aside from having the same issues that stratosphericic carousal injection have about the difference of a climate with high sea,

but less sort of radiation, there's also the technological problem of we have no idea in the short term, which is the thing that we're kind of concerned about with right now. And in the short term, I mean the next 50 years. It is very unlikely that in the next 20, 30, 50 years, we could scale up space industry in a way that would allow us to have large, gigantic, controllable space mirrors at L2. So at the point, at the Lagrangian point where the gravity of the sun, equals the one of the planet, so we wouldn't really need that much effort to keep the space mirrors there,

but we still need to carry them there. And for now, we have no clue how to do that. This is one that feels to me like it's directly out of a movie, right? Like, there's some apocalyptic climate change movie where it's almost like deep impact or Armageddon only instead of a meteor coming to hit the planet, it's climate change,

and the solution is to build the world's largest mirror and then place it in space. Right. But actually, you know, I mean, to your point, like I guess what it carries, it sounds like it carries the benefit relative to stratospheric aerosol injection that like the sort of ecosystem impact stuff, not as much of an issue. We're not injecting new particles into the stratosphere. We're just reflecting solar radiation from the sun, right? So it's just if we just need to know how to build the mirror and put the mirror up there. Yes, indeed. I mean, in an ideal world where we have such a technology is probably also, in my mind, at least, a world where we have also managed to scale up carbon dioxide removal enough that we don't need it in many ways. But sure, for the sake of comparison, it is true that you would have less ecosystem impacts than putting other particles in the atmosphere. Okay, and then I think there's at least one more category to talk about, which is Cirrus cloud thinning. Tell us about that one. Circe ductal thinning is even more complicated and is, again, about clouds, more than it is about aerosols. So there are, not all clouds help cool the planet. The clouds that we see when we see satellites' photos, the ones that are mostly over the oceans, those are white, fluffy, and they reflect solar radiation.

But there are also clouds much higher hop in the troposphere where the temperatures are much, much, much lower. That are actually made of ice crystals. And these ice crystals are so they are invisible. transparent to solar radiation, but they are not transparent to infrared radiation, so the radiation that comes out of the planet. And so they do trap, they do contribute to the greenhouse effect. They do trap part of the radiation. But the main issue is that we're really not sure how much. We know that from our models and from observation that they do, but we really still have had a hard time figuring out really the magnitude of the warming that is produced by these cirrus clouds. But assuming that we knew that, the idea is that could we reduce somehow the concentration of these cirrus clouds, these ice clouds in the upper troposphere, by seeding them in a way that it makes them, it's quicker for them to fall out and disappear.

And in this case, really, we are still at a point we're trying to understand whether we get the physics right, whether we understand the physics right, whether all the processes that we assume are there, are there. And so there's really, it's much more in the realm of interesting, but almost impossible to test in a way. So stepping back then, what is your sense of where we are in the state of research on solar geoengineering on all these approaches? Is there active progress being made to better understand each of them individually and the challenges and the risks that they carry? is it such a backwater that the state of our understanding is fairly stagnant? What's needed for us to get to the point where we could at least say, with some measure of certainty, here's what it would take for us as a global community to make the decision to do one of these things,

and here's the ramifications of doing so. So I would say that my personal perspective on this subject, I started my PhD in 2015, so now seven years ago. I suddenly immediately got interested about this. And at the beginning he felt, I really feel like I've seen the shift in the last seven years from the very beginning when people were like, are you sure you want to study this? This is really not going anywhere. And also people don't really like to talk about it.

And now in the last two years, a lot more people, a lot more scientists as well, they kind of got on board. If not with the idea itself, with the knowledge that we need to. study the idea. And I've also seen incredible progress. There's really feels like it's a field where there's so much to research and there's so much being done, even though it's a tiny fraction of all the climate change research going on. But still, like, I do think that there have been incredible advances in the last few years in our understanding, and we are definitely getting more people on board that are interested

in looking into this. So people that are interested about ecosystems, so ecologists, biologists, health experts that are interested in understanding how would the temperature change regionally and what would the impact be on the transmission of disease? So there's a lot of people that are now figuring out that this is not just a thing being proposed for the sake of it, but actually may be something that needs to be considered seriously. It doesn't mean that all of these people are endorsing it.

It could be that most of these people are figuring out, oh, let's find the thing that is going to make us say this is impossible to do because it's going to destroy X. But for now I would say that actually we have an enormous amount of information right now about the effects. It doesn't mean that we know everything, but we do know a lot about what the effects would be, what the impacts would be on stratophobic dynamics, on the circulation of the atmosphere, on various aspects of chemistry,

and we're starting also to work a lot more on the ecosystem response. So I would say that there's a lot going on. And you mentioned a lot of people just haven't wanted to talk about it. I think just to confront that head on, there's definitely a perception out there. There has been historically at least that this is a, it's a bad idea to really even seriously put time and effort and money into solar geoengineering because in some ways it's like, well, because one of these like unknown risks to ecosystems and so on. but two, because it's a distraction from the work we really need to be doing in the near term, which is mitigating emissions and potentially removing emissions. How do you think about that?

How do you think about the sort of the governance and ethics questions around solar geoengineering? Right. That's an excellent question. Up to now, I've only talked about the technical part. And that's interesting is the thing I'm most focused about. But yes, it would be it's impossible to talk about sort of, or geoengineering without really tackling head-on all of the ethical and governance issues that are connected to it. And so, yes, there are people that think that even talking about it is a bad thing

because it's going to make us less likely to mitigate. Personally, I respect the people that think that this is the case. I disagree. Otherwise, I wouldn't be studying geoengineering. And mainly because in a way we do have to, and even the people that are opposed to it, we all recognize that over the very short term, there isn't that much we can do.

In the sense, there is a lot that we can do in terms of mitigation, and that's where most of our efforts should be. More than 99% of all of our efforts should be over-mitigating, emitting as little as possible. But now we do know, and the IPCC and all of the countries in the world have signed up to the Paris Agreement saying that we should really try to avoid hitting 2 degrees above industrial, possibly even 1.5, which is incredibly close.

And so starting from there, to me it sounds very wrong in a way, and I would say at least weird, to think to acknowledge the fact that we are basically, as many people say in an emergency, and we have maybe 20 years or even less before we reach 1.5, and the only thing that we want to do is mitigate, which is going to be, again, the only thing that we will need to do in the long term. But what about now? What about if the unknowns that there are are in the climate that we're heading towards? We do know that there are tipping points,

that are points in the climate system in some location that might be much more sensible to this 1.5 increase. The Arctic in particular, permafrost thawing, Amazon. There's plenty of stuff that we know are dangerous, that we know the danger is looming there. And we don't know whether the real danger is going to come at two degrees or 2.1, but we shouldn't even find out in this sense. We should have, for sure, what I think is that for sure, while we put most of our efforts into Mitigate,

we should have this option ready in case we realize there is no other way to avoid warming. And what is you, I mean, obviously, back to our original point about this sort of of carbon removal falling under the category of geoengineering, that world has gained a ton of steam over the past few years. And I think more and more people have sort of gotten comfortable with the idea that maybe over the next 10 or 20 years, we're going to need to start doing some big engineered solutions like direct air capture. We might be doing some big semi-nature based interventions like Bex or converting biomass to biochar or bio-oil. We might be doing. We might. grow big kelp farms and sink them to the bottom of the ocean.

All of that stuff has sort of, I don't know, maybe it's not there yet, but it seems to have sort of jumped over the chasm from the, we shouldn't be thinking about this at all to, okay, we're going to need this as part of a portfolio. Do you think that the solar geoengineering just sort of follows behind that? It's like the next logical step in that progression? From a temporal point of view, I would say that it comes before. When we talk about scaling up CDR and when we really go and, look at the numbers that we would need, not the numbers that we assume, but the numbers that we

would actually need to scale up to, those are really huge. And so all of them and all the things you mentioned, I have confidence that most of them will be scaled up in one way or another, but whether they will be scaled up in a way to make an actual dent into the CO2 concentrations and emissions, because on top of all of this, this is also assuming large cuts in emissions. Right. So I am confident that I'm 100% sure that CDR, it is going to be long-term part of the solution to help us really be at zero emissions. I'm just pretty unsure whether that's going to happen, as I said, in 20 years. I would say that I would be very careful into assuming 20 years, and it would be more comfortable imagining a scale of maybe 50 years. And now, you know, if we had started, if we were having this discussion 50 years ago, but with the technology of now, we could say, well, we have the time,

we should just work really hard and try to scale those up. But now we're not there. We are less than 0.3 degrees away from 1.5. And, you know, the carbon budget is running out. You can put it however you want. But there's really something that I think will need to be done in the next 20 years. And I do not think personally that in the 20 years are going to be enough to scale CDR solutions in a way that would really make an impact. So solar engineering comes at that point.

It comes at the point where we realize that we can scale CDR but slowly and it's going to take a lot of effort. And that we need to do something in the in between. We need to do something to do what we call in a way peak shaving. So we are in the best of words. we only have this risk of maybe overshooting this 1.5 target that the Paris Agreement decided on, and maybe for a short amount of time, there could be decades. It could be multiple decades, honestly, even depending on how things go. What do we do then? What do we do when we hit 1.5? And it could be that solar geoengineering could be the solution that allows us to stay below 1.5

while we do all of the other stuff that is absolutely necessary. Yeah, there's also a cost-to-society question that would be, interest. I can't do this math off the top of my head, but like, you know, to get, so as you said, sort of the theory with stratospheric aerosol injection is to get half a degree Celsius of warming mitigation takes the scale of roughly one big volcano injected annually. I wonder how the cost, who knows what the exact cost is, but how the theoretical cost of that would compare to the cost of doing enough CDR to to impact half a degree Celsius. I presume that would be far more expensive.

It's so the scale from an economic point of view, it's so stagnantly different that is the reason, one of the reasons why it's almost impossible to include solar geo engineering in economic model is that it's so cheap. From a purely economic perspective is incredibly cheap. There are some people that have worked on this a bit. we actually have a paper that we submitted just last week about this as well.

But when you look at the estimate, it would take honestly less than just a couple of billion dollars per year to do solar geo engineering, which is a fraction of a fraction of what it would take to scale up CDR solutions. So it's really not about the cost. At least it's not about the direct cost. Okay, this is just talking about the direct cost of bringing the sulfate up with planes and dumping it there. So the other related question, I think, to the sort of broad ethical question around when should we be thinking about doing it is governance of it. Who would be in charge of deciding about solar geoengineering? Who should be in charge?

And how do we even conceptualize something like that? Yes, absolutely. There's a lot of agreement over the fact that the governance part, is actually the hardest part when it comes to solar geo engineering. In general, the way in which this question is framed is whose hand would be on the thermostat? If we have this option of cooling, who gets to decide how much to do? And it could be that different parts of the world would benefit from different amount of cooling.

We have some studies looking at that. And so how would it work? How would an international agreement work? What kind of international framework would allow this to work? and if you think that there's no possibility for an international framework, does that open the road to single actors doing it? So there is definitely, and whenever we say we should consider doing it, or when we use we, it's really, we should put a lot of care into defining who is this we, right? So who gets to speak their mind, who gets to have an opinion?

Is it just countries? Is it populations? We know that countries usually tend to overlook some parts of their own, Citizens, so how do we make sure that whenever we do something, again, deliberate, that we've never done before, that it is done in a way that takes as much feedback as possible and leaves everyone better off than they would be without it? Yeah, that seems like a key question. Again, back to the economic point, if it only costs a couple billion dollars to do this, that's not very much for lots of different actors.

And you could easily imagine some rogue actor just deciding, oh, well, I'm going to solve this problem myself and inject a bunch of aerosols into the atmosphere. And so without global international cooperation on the solution set, this feels like that's where there's real risk of things going awry. Right. Absolutely. There's a lot of interesting work being done from sort of the game theory point of view into really understanding. We are an interconnected world. We're kind of seeing how hard it is for just a country to do something that every other country finds despicable. And so this could be another one of the things where it is maybe unlikely that a single actor could do it, because as one reviewer once pointed out to me, you can shoot the planes out of the sky.

Okay, well, more questions than answers at this point, but it sounds like increasingly some answers coming, so we'll talk about it again, but thanks so much for doing this, Dan. This was great. Absolutely. Thank you so much for having me. Dan Vizioni is a climate modeler and research associate at Cornell University's Sibley School of Mechanical and Aerospace Engineering. What did you think of today's show? I suspect this one will probably get a lot of reactions. So if you didn't like it, keep your views to yourself. I'm just kidding.

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a venture capital firm that partners with entrepreneurs to address climate change across a range of sectors, including advanced energy, food and ag, transportation, and logistics, advanced materials in manufacturing, and advanced computing, and I will note that solar geoengineering is not on that list currently what's up with that prelude. Get at me. This episode is produced by Daniel Waldorf. Our executive producer is Stephen Lacey, mixing by Greg Vilfrank and Sean Markwand, theme song by Sean Markwand.

Our managing producer is Cecily Mazin Martinez. I'm Shail Khan, and this is Catalyst.