The Exchanges

Q the impact of volcanoes, which are another sort of, like, major sudden effect we've seen multiple times in history, where a large volcano spews a bunch of Sulfur into the atmosphere as well, and we've seen cooling effects from that. Are those the same aerosols getting released, more or less, or the same effective molecules coming from a volcano as we saw from shipping emissions, or is it something different?

A They are sort of the same, except that their impact is completely different. Um, so for, for volcanoes, just to remind people, the main thing is that Volcanoes often emit sulfate also in near, near to the surface. There are effusive volcanoes. But once in a while there's these explosive volcanic eruptions that bring A lot of sulfate all the way to the stratosphere, where there's normally neither clouds nor sulfate, just a little bit, and there aren't any removal mechanisms for these aerosols. So these aerosols are free to float around for sort of one year, one year and a half. Um, they grow more because they have more time to condensate stuff around themselves just because there's no removal mechanisms. Uh, and so they tend to have a pretty strong forcing effect just because of the direct Reflection of sunlight from the aerosols, way before the sunlight can get closer to the surface, what we call the troposphere. The, sure, the sulfate is the same that gets produced by the, by products of fuel combustion, uh, when it comes to shipping trucks, except in this case, the aerosols themselves, their lifetime is pretty tiny, because they get emitted very close to the surface, and so they immediately fall down. So the direct, in this case, is not as much a direct effect, that is, that is much, much smaller, but is the indirect effect. So the What we call the aerosol cloud interaction e…

AI assessment note: “They are sort of the same, except that their impact is completely different.”

Q 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 This is stratospheric aerosol injection. Um, it's mimicking the, it's mimicking volcanoes, basically. Would we, if we say we were to do this, um, you know, is there a sense of how much we would need to do to have an impact on a global scale?

A Yeah, so we do know, again, we know because we've seen volcanic eruptions, um, and so roughly, for instance, uh, the biggest one of the Roughly around 10 teragrams. Uh, that's 10,000 megatons. And, and it cooled the planet in the year or so after by, uh, A bit less than half of a 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 amid sulfate, they stand at around now maybe 70% Tereograms of SO two per year, uh, at the peak before the U S and Europe had cleaner acts, it used to be even over a hundred. 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.

AI assessment note: “Roughly around 10 teragrams... cooled the planet in the year or so after”

Q the higher levels. From an ethics perspective and how we should think about solar geoengineering, you know, when, when we need to start really doing it and so on. But I do want to run through the other, the other possibilities, right? Because stratospheric aerosol ejection is one among a number of different options. So let's talk about some of the others. Um, Explain cloud brightening, or marine cloud brightening.

A Right, so this other idea came from another, well, not really natural experiment, but looking at just, uh, ship tracks. So, uh, whenever you have very big ships going through the ocean, you can see the track that they leave, again, because they emit particles as well. Uh, 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, uh, those are very thick, white, fluffy clouds that tend to reflect a lot of the solar radiation. Uh, and so there have been observations and studies saying, uh, looking at this very tiny scale effect of ship tracks. And so the idea for this has been, um, Can we kind of make it more likely for this cloud to happen, in particular by seeding low-level clouds with, um, with sea salt? So you don't even need other particles. You wouldn't need sulfate 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, the water can kind of coagulate. So the idea is whether we could do something like that a…

AI assessment note: “seeding low-level clouds with, um, with sea salt”

Q Where would you say we are in the trajectory of, 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?

A So there are absolutely no, uh, small scale or large scale experiments going on anywhere on the planet. There are a few proposed, uh, Harvard as a very tiny, uh, amount of Material that 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, the main method of Uh, that is actually the first one that people thought about already in the eighties, 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 they, in case there's like very, very big eruptions, they're actually the problem. But from other eruptions, like the one that we've seen in the last 2000 years, what we're, the, 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, um, tends to oxidize and produce sulfate aerosols. And the sulfate aerosols in the stratosphere, they can stay a lot longer than they would in the tr…

AI assessment note: “there are absolutely no, uh, small scale or large scale experiments going on anywhere”

Q Okay, so that's category two, marine cloud brightening. Uh, Let's talk about some more wacky wild ideas. Uh, building, putting mirrors in space. What might that look like?

A 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 space mirrors, they 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 stratospheric carousel injection have about The difference of a climate with high CO two, 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 with the short term, I mean the next 50 years. It is very unlikely that in the next 2030, 50 years, we could scale up space industry in a way that would allow us to have large, gigantic, controllable space mirrors at L Two. Uh, so at the point, 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.

AI assessment note: “These space mirrors, they would not be something that we can see.”

Q of that stuff has sort of, I don't know, maybe it's not there yet, but it seems to have, uh, 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.

A From a temporal point of view, I would say that it comes before. When we talk about scaling up CDR, and when we, we really go and look at the numbers that we would need, uh, not the numbers that we assume, but the numbers that we would actually need to scale up to, um, those are really huge. And so all of them, and all the things you, you mentioned, I, 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 a hundred percent 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 I 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, um, and try to scale those up. But now we're not there. We are less than .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 th…

AI assessment note: “From a temporal point of view, I would say that it comes before.”

Q 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 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?

A 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 that's 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 that is by reducing the amount of CO₂ that is in the atmosphere. There's no doubt about that. But in the, but we've, we know, and you know, 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 remove. That is going to take time. So the idea is, is there something that 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? Uh, 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, uh, to begin with? And so we don't experience the effect of the global warming too much.

AI assessment note: “can we intervene in the solar radiation that is incoming? Can we reduce that”

Q consider doing this seriously at the, at the global scale is, um, what are the side effects that this might have on ecosystems on the planet, right? Well, you know, uh, 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, into the stratosphere?

A 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 hadn't 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. Uh, it might still, and it probably is still going to be better than not doing, uh, than letting the warming just keep unchecked. Uh, but it wouldn't be the same. So, of course, we would have to, and there are, 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 Um, The regional the, the,, 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 the, of the big thing is, again, is to really understand much, much better, um, exactly what kind of a different climate we would have. We would have a climate that globally is cooler. We have no doubt that …

AI assessment note: “We have no doubt that the sulfate would cool the planet. But we wouldn't be”

Q were geoengineering, and then sort of stopped. Um, let's run through that in a little bit more detail, starting with, just walk me through, prior to these new regulations, which we'll talk about, that the International Maritime Organization created, um, what was the type of emissions that we were producing in shipping that was relevant to, you know, impacting climate change, uh, and how much of it were we producing?

A Mm-hmm. Yeah, so we've, We emit, normally, humanity emits a lot of sulfate, mostly through the burning of fossil fuels. And one of the, for a long time, one of the main culprit of this burning was shipping fuels, so emissions from, from ships. And for a long time, they had a, well, the fuel that was used was not particularly clean. And up until the seventies, there were plenty of, there was a very robust theory suggesting that Pollution would actually make clouds brighter, especially in some regions. And one of the main regions where this could happen, it was always suggested to be the North Atlantic corridor. So where most of the shipping happened for a long time, but also one of the areas that was more susceptible to actually being affected by this effect. Um, essentially the, the theory suggests, and actually it's a pretty robust, uh, result, that Whenever you have, so normally you would have cloud just from cloud droplet condensing, water vapor condensing. If you have more cloud nuclei, so particles that allow this, um, coagulation, this condensation to happen, the more nuclei you have, the more this water vapor that condenses is distributed across more nuclei, and so you have smaller water droplets. And the optical depth, so basically how much clouds can reflect solar radiation, depends inversely on the, uh, the surface available, so on the, on the size of these particles.…

AI assessment note: “humanity emits a lot of sulfate, mostly through the burning of fossil fuels.”

Q Okay, so now let's go back to shipping then. So, what are the regulations that the IMO put in place in 2020? And then we can talk about what impact, uh, we've been able to measure since then.

A Yeah, so as I, as I said before, the main, our main worry with sulfate, when it gets emitted so close to the surface, is that we end up breathing it. Uh, normally it also happens very close, those emissions also happen very close to where people live. Um, so it's sort of a big problem. So it's only natural that, um, as long, as soon as there are things that allow us to clean up our air, people want to do that in regulations. End up being in place, right? The Clean Air Act from Reagan was just about that, and it had a massive impact. So the IMO did sort of the same thing. There have been plenty of reports saying how big of an impact on air quality over the north, northern hemisphere this could have if there was this cleanup of shipping emissions. And so they finally put this regulation in place that prescribed that either the content of sulfate in fuels had to go down as a mass fraction from 3.5 to 0.5, So really a seven times less, um, sulfate in fuels from one ear to the other, or that, uh, ships had to have scrubbers capable of cleaning up this SO to this sulfate before it reached the atmosphere. Um, it happened, um, from the first day of 20 20, there was indeed this new regulation. Everybody seems to be, it's also very hard to determine whether, um, actually everybody, um, Respected it, but we, the funny thing is that we can see it indirectly by the fact that we have observe…

AI assessment note: “prescribed that either the content of sulfate in fuels had to go down”

Q And can we go a step further then at this point and say how much that has increased global mean temperature?

A Um, yes and no, in the sense that, so, so what scientists normally do is they don't immediately go into global mean, into talking about global mean temperature for a lot of reasons, but the first thing that we can see is what we call radiative forcing, right? So basically, um, now we can measure it from satellites, so there's plenty, there's a few satellites, there's a very famous NASA one series, um, that has been on for a while, that can basically measure the Energy fluxes in and out of the, of the world, in and out of our planet. So our energy fluxes coming in is just the sun, but the energy fluxes coming out are a bit of solar, of shortwave radiation, so a bit of solar radiation that gets reflected, but also the planetary radiation, the infrared radiation that gets emitted by the planet. Um, so, and normally if the planet was in perfect equilibrium, um, year by year or over longer timescale over a decade, um, There would be a perfect balance. Exactly as much energy comes in, exactly as much energy comes out. Otherwise the planet would just warm. What's happening right now is that the planet is warming, mostly because this budget is not perfectly balanced, because the greenhouse gases trap a bit more solar radiation. And Ceres has been indeed capable of measuring how much of this, this equilibrium of this, what we call Earth energy imbalance has happened over at least the la…

AI assessment note: “what scientists normally do is they don't immediately go into global mean”

Q it would brighten clouds, those clouds would reflect more sunlight, that would have a cooling effect on the Atmosphere. And that was particularly true. It would be particularly susceptible over the North Atlantic, which just coincidentally happens to be a major shipping corridor. Is that right? And can you maybe explain a little bit more like why, why the North Atlantic corridor is, uh, is particularly good for this effect?

A Right, ok. So, in general, the assumption that pollution would brighten clouds sort of applies everywhere in the world. The main problem, though, is over land, um, it's very hard, it's, um, there are so many things changing all at once that sometimes it's very hard to determine why is a cloud forming or not. You know, there's orography, so there are mountains, there are hills, there's many byproducts of pollution, um, so it's very hard to actually figure out is that cloud brighter or not. Um, this effect is sort of more evident over the oceans, just because there's no orography, there's just waves. Uh, and so, and there's the water vapor coming up from the oceans. And of course, the main corridor in which a lot of the shipping happened, especially in the last, in the last 5060 years, was the North Atlantic one. So a combination of the oceans are flat, and so there are many less ways in which clouds can form. There's a lot of ships in the North Atlantic, plus some sort of more complicated reason why the North Atlantic produces more clouds. Produces less clouds normally, and so these clouds can be more affected, right? So this effect, ah, this is very, very complicated, I understand, but, um, so this effect of cloud brightening from aerosol can only happen up to a point. You cannot make these tiny droplets Incredibly small. Um, so if there's already a lot of clouds, and those clo…

AI assessment note: “clouds in the North Atlantic, tended to be the perfect target where these aerosols would reduce”

Q Yes. Per year. Right. So this is the next question. So then do we, if we do that, do we then have to keep injecting the same amount into the, into the stratosphere annually because otherwise it achieves nothing?

A Well, I mean, first of all, also the, the, 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, only actually Pinatubo did 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 this 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, Add 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, any climatic effect. But then once Once we were to do it for long, once we were to keep it up for, um, 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.

AI assessment note: “then yes, of course, interrupting the injection immediately would just bring us back”

Q you also said that this seems to be the one with where the sulfate emissions were most likely to create the biggest impact because it's over the Atlantic corridor. So do we have any sense of, you know, what the overall trajectory of sulfate emission of anthropogenic sulfate emissions might look like and, and the degree to which that might have an even larger version of this effect over time?

A Yeah, I mean, um, absolutely. So if you, you know, another thing that I feel there's a lot of confusion on sometimes when people talk about net zero, or what would happen if suddenly we completely stop all emissions? And the main answer to that is that we know that if today, if tomorrow morning there were no more anthropogenic emission of anything at all in the world, The main impact that we would see in the first decade, it would be a warming, because this aerosol effect that is masking part of the warming would be the first one to go away. Um, Of course, over the long time, we would see other effects, the methane lifetime being smaller, and then overall, CO₂ would trump over everything over, uh, over a century. But that would be the first effect. We know this is exactly what will happen. Um, and for what you said about the trade-off, I say, I would, I would say that this clearly feels like a point where there was a large part of the scientific community that was, uh, a non-zero part of the scientific community that was interested about this issue with shipping. But if you read the literature, I've been reading a lot of that in the last, ah, few months. It was taken for granted that it was obviously going to have a forcing effect, but the step, the consequent step of asking, well, how does this square with Paris Agreement commitments, or in general with our current concerns ab…

AI assessment note: “this aerosol effect that is masking part of the warming would be the first one”

Q it, um, is it such a backwater that there's, you know, that the, the state of our understanding is fairly stagnant? Like 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.

A So I would say that my, my personal perspective on this subject, um, I started my PhD in 2015, so now seven years ago, and I suddenly, immediately got interested about this, and at the beginning it felt, I've really, 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's, 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 …

AI assessment note: “I do think that there's, there have been incredible advances in the last Few years”

Q already doing a version of it. We stopped doing that, and then we can measure the impacts. Is there anything that we can learn from the IMO regulations and the sort of, you know, before and after effects that might tell us about efficacy or cost or anything like that, um, or side effects to do with the opposite, purposefully putting sulfur aerosols in the atmosphere or in the stratosphere?

A Um, Yes and no. So, I think that there's, there's a lot of things that we can learn. They're not necessarily about These, these exact effect playing out, but I think there's a lot that we can learn, and I'll explain a bit better. So there's the main thing that you would assume that if we were already thinking a bit more seriously about this sort of climate intervention, so these actual on purpose interventions in the climate, that we, as scientific community, the whole world would have said, okay, this is happening. Let's make sure that we can detect it. What do we need? Let's actually put a lot more focus into it than what there's been, right? So, um, because the issue is always going to be whatever we do, um, both in a way in terms of Global warming, climate intervention, regulations, anything, is that we only have one planet. Uh, finding the counterfactual, so figuring out what would have happened if we hadn't done this, or if we do this, it's always gonna be hard, and it's gonna, always gonna require us to, in a way, trust in the climate models that we need to use to build this counterfactual. Now, for climate change, it's, in a way, gotten so much easier Um, you know, we've known about climate change even before we could detect the signal, or before we had the climate models to tell us, but now it's so obvious that, in a way, it is pretty easy to say, to attribute the warm…

AI assessment note: “there's a lot of things that we can learn. They're not necessarily about These”