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The Why, How, and Maybe Not of Geoengineering


Eliza Strickland: Man-made climate change is already reshaping our planet, and carbon emissions aren’t coming down fast enough to stave off real disaster in the decades to come. But rather than giving into despair, some engineers, policymakers, and activists are pursuing a novel strategy. It’s often called geoengineering in the popular press, but the preferred term is climate intervention. I’m Eliza Strickland, guest host for IEEE Spectrum’s Fixing the Future podcast. And I’m here with Kelly Wanser, executive director of the non-profit SilverLining, to hear the latest thinking on climate interventions. Kelly, thanks so much for joining me on Fixing the Future.

Kelly Wanser: Thank you, Eliza. Many in our community are fans of IEEE, and I’m really pleased to be here.

Strickland: Can you tell our audience what SilverLining does and how you define climate interventions?

Wanser: So SilverLining is a four-year-old non-profit organization, and we support both research and policy to advance science-based approaches to responding to near-term climate change. So the problem that you mentioned in the introduction about the escalating climate impacts, what we’re seeing now, what’s forecast for the next 20 to 40 years, that’s our focus. And we think that science and innovation are really key and quite central to society’s ability to navigate what’s happening in the climate system.

Strickland: Why don’t you focus on just cutting carbon emissions?

Wanser: Well, my background is actually from the technology sector myself, and so I asked the same question early on. And what I learned from scientists is that emissions reduction acts on the climate system quite slowly. It does not act on the greenhouse gases that are already in the atmosphere. And so those come out in a natural way over longer periods of time, a century or more. And so reducing emissions is key to not increasing the problem, but the problem that you already have in the system, emissions reduction doesn’t help you too much. There is an exception to that in the category of what they call super pollutants, the very powerful but shorter-lived gases and chemicals that come from things like fertilizer production, methane. So those are really important, and those are a little bit different. But carbon dioxide itself is a slow-acting process to bring out of the atmosphere unless you do more interventional types of things.

Strickland: So let’s talk about some of the strategies. If you think about the basic problem we’ve got here, there’s carbon dioxide trapping heat in the atmosphere. So it seems that there are two basic strategies: taking carbon dioxide out of the atmosphere or reflecting the heat. Can you talk a little bit about those two possibilities and where SilverLining has done the most work?

Wanser: Certainly. Well, taking carbon dioxide out of the atmosphere and potentially other gases like methane is a really sensible concept in principle because that would accelerate the process of moving back to the sort of pre-industrial sustainable climate that we have. But it’s a challenging thing to do, and we haven’t yet figured out ways to do it at scale that are cost-effective and sustaining, meaning you’ve taken the carbon dioxide out and it stays out reliably. So there are a couple of different big categories within that. One is using what they’re now calling nature-based approaches, but basically organic processes, from growing trees to growing algae to seaweed in the ocean. All of those biological processes are sort of self-propagating, and they take up carbon dioxide fairly quickly, but they’re highly uncertain in terms of how long they store it. So that’s one class. The second class is industrial carbon dioxide removal, or what they call direct air capture, where you use an industrial process of filters. One of the biggest challenges of that is the carbon dioxide in the atmosphere is very diffuse. It’s very low concentration. So you end up having to spend a lot of energy filtering a lot of air to bring it out of the atmosphere. And so the cost of that right now is really, really high. It’s only been done on a pilot level.

At some point in the future, we might get good at it, and it might be quite a scaled activity. But right now we’ve got some distance to go with any of these ideas. And if you think about the scale of the problem where you might need 20 gigatons a year to offset just the US, then you’re looking at a multidecadal issue of trying to figure out how to get things operating at the kind of scale that would be meaningful. And so if you’re worried about the problem in the next 30 or 40 years where scientists are telling us in these big global climate assessment reports that under every scenario, the Earth continues to warm, right now, we still don’t have anything that operates in that sub-30-year time scale. And that’s where the other class of approaches comes in, which is, well, are there more rapid ways to take either greenhouse gases or heat out of the atmosphere? And it turns out where scientists landed on that in scientific assessments was that one of the most promising ways to reduce heat in the atmosphere quickly is one of the ways that nature does that, which is the reflection of sunlight from clouds and particles in the atmosphere.

And so if you look at the Earth from space and you see that shiny blue marble, the principle is that if you could make the atmosphere or the Earth about 1% more reflective, that you might be able to offset a doubling of CO2 or two or more degrees of warming. And so one of the reasons that my organization SilverLining has been interested in advancing research in that area is because against the problem of near-term risk over the next 10, 20, 30, 40 years, where we’re seeing escalating disasters, we’ve got pressures on the big natural systems that are starting to look unstable that right now this appears to be the class of approach that might be the most promising method for disaster risk reduction in a way of keeping the system safe and stable for a while. So I’ll stop there, but I’ll say that there’s a lot that we don’t know. And so we would like to know a whole lot more than we do about all of these options.

Strickland: And in terms of reflecting sunlight or heat from the atmosphere, I guess it can operate on several levels. Right? You can either try to put particles in the stratosphere or you can go lower down. Can you talk a little bit about the variety of approaches that people are exploring?

Wanser: I would be happy to. And again, scientists look to what they’ve observed before when arriving at these ideas. And so back in, I believe it was the 80s, it might have been earlier than that, Paul Knutson who famously identified the ozone whole problem, he put forward the idea that putting material in the stratosphere might be an interesting way to reflect sunlight to cool the planet. And that was based on observations of volcanoes. Very large, very energetic volcanoes will emit material that reaches all the way up into the upper atmosphere, the stratosphere, 60,000ft or higher and becomes entrained and stays up there for a year or two. And when that happens, when that’s happened in the past, they’ve observed a global cooling effect. Most famously in 1991, or most recently famously in 1991, Mount Pinatubo erupted. It was an energetic volcano and it was observed to provide over a half a degree Celsius of cooling of the entire planet, which gradually dissipated over the course of about a year and a half. So it’s been observed before. And the stratosphere is relatively uniform environment compared to the lower atmosphere, so scientists have also been able to do what they think is more reliable modeling of what might happen. And so they have a reasonable amount of confidence that if you put similar kind of material, which in this case would be sulfates, into the stratosphere, that you can achieve this kind of cooling.

What they don’t know is what happens over longer periods of time and what kind of side effects might emerge and what kind of problems might you see from that. And those are very important, serious questions. In the stratosphere, in particular, they’re concerned about the health of the ozone layer and also how this might trap heat in the stratosphere in ways that changes the way that the atmosphere works. That’s called stratospheric warming. So those are the kinds of questions that they would like to study before they would say, “Oh yes, we know this is a good idea, or we know this is a bad idea.” So that’s the stratosphere, which has been maybe the most prominent concept for trying to cool the planet in this sort of rapid way. Another concept is based on observation of something that’s happening now. And the thing that’s happening now is the particulates that come from pollution in the lower atmosphere, so this is from ships, factories, cars, certain kinds of particulates stay in the atmosphere as haze like you see you in LA smog. They also mix with clouds. If you’ve ever seen pictures from space with streaks in the clouds where the shipping lanes are, those are these dirty sulfate particles that they’re actually trying to get rid of. They’re bad for breathing, but these dirty sulfate particles provide what some scientists call a masking. They create a reflective effect and slightly increase the reflection of sunlight from the Earth.

So in climate reports, you’ll see where they talk about this and they say, well, we have some cooling offsetting the warming we would otherwise have and it comes from this pollution, what they call cloud aerosol effect. So based on that, science was proposed in the 90s, maybe you could create a sort of cleaner, more intentional form of this kind of low atmospheric cloud cooling. And that idea became what they call now marine cloud brightening. And in marine cloud brightening, the idea is that you use a mist of microfine salt generated from seawater and you’re aiming at– you’re sort of misting the layers of clouds over the ocean in parts of the Earth where certain types of clouds, they’re called marine strata cumulus, occur. And these marine strata cumulus are very thin and they’re very susceptible to adding little particles that make them a little bit thicker. And so by aiming at what is effectively about 3 to 5 percent of the ocean surface but across these banks of clouds in three or four parts of the world and brightening those banks of clouds by just 5 to 10 percent, that you could offset a couple of degrees of warming. That’s the theory. Now in both cases, and especially in marine cloud brightening, there’s a lot that we don’t know. And that effect of particles on clouds is one of the big uncertainties in all of climate science.

So some of the research that they would like to do to determine whether marine cloud brightening would work is actually quite important research potentially for how well we can predict a climate system and this sort of accidental cooling effect. So those are the two sort of most common or most prominent approaches that people have been talking about.

Strickland: And can you talk a little bit about where those studies are in terms of real-world experiments. Like the marine cloud brightening effort, I know that’s going on at the University of Washington and Xerox PARC, and they’ve got some cool on the ground experiments. Right?

Wanser: Yes. So I think one of the things that we’ve worked on in SilverLining is trying to help identify what is the research path, what are the minimum set of things that you need to do to try to evaluate these approaches? And so there’s a lot of desire I think from a lot of people across the spectrum to be able to use computer models to say how would these things play out? Can we model out whether they would be safe, how people in different parts of the world would be impacted, what the magnitude of the effect is? And what we found is that the problem is in order to do that modeling, you need to be able to characterize the primary process. So what are the particles that you’re going to be putting in the atmosphere? How do they behave in a very local way when you release them? What are the first effects that happen in the atmosphere? And then you have a shot at sort of modeling it out at bigger and bigger scales. Even though the kinds of studies you would do in an atmospheric sense are very small like the equivalent of one trail of an aircraft or one plume of a ship, they’re not small in engineering terms. So, for example, in marine cloud brightening, the desire is to generate sea salt particles pretty consistent, tiny size, similar to what comes out of an asthma inhaler. So you’re sort of nebulizing sea salt from seawater, but at a scale that could reach up a few hundred feet so that we get entrained in the cloud layer.

And so as an engineering task, it’s not nuclear fusion, but it’s not trivial either. It’s something that takes some capital and some concerted, pretty serious engineering effort, and it hasn’t been done before. And that hasn’t been done before for these stratospheric ideas either. People who’ve looked at the space have heard people say this is cheap and easy to do, and it is cheap and easy to do relative to transformation of the global economy. Absolutely, but it’s not necessarily cheap and easy to do in an absolute sense. What we found is you’re looking at eight figures of money to do experiments with single plumes in several years of engineering and then studying. So the marine cloud brightening project at the University of Washington is probably the furthest along in the world in terms of going that step to say, okay, we want to generate the kind of plume that’s being proposed for this concept so that we can perturb a cloud and study what happens. And so a group of retired physicists and engineers started eight years ago to look at could we create nozzle-level technology to nebulize sea salt, which turns out to be a tricky problem. Your first mental model, even if you’re an engineer, is something with tiny holes and they burn through titanium and platinum and you have this high pressure and you have salt and everything’s corrosive.

So they came up with some really elegant concepts for how to do that, and the one that they’re using in the research path right now is called electro spray and use electrostatic process. But they were working on a voluntary basis for about five years, these four or five retired engineers, and then started a partnership with Palo Alto Research Center, PARC, where, of course, they have amazing facilities and a younger generation of people to sort of pick up the mantle as well. And so they all collaborate together now and they’re at this stage where they’ve identified and been able to test the nozzles and configure them into an integrated system which is being built right now. And so that system is being built right now and then it will be starting to be tested with the notion that maybe sometime next year, early next year, there would be the ability to go out and look at what happens when it gets introduced into the atmosphere. The idea is that from that point, you could create a plume which would– if you think of like the plume that comes out of a cargo ship, except maybe about a third to a half of the mass and a lot cleaner because it’s really just distilled salt from seawater, that would be the plume that they’re looking to study. And to take that out on the ocean aiming at the low cloud layer.

And in order to study it, you actually need either airplanes or drones or both in the sky as well as a trailing vessel because the plume is over hundreds of meters, even a mile or so. And so that’s the kind of experiment that they would propose to do. And that would give a lot of information to then plug into models of how do these processes between the clouds and the particles work and what does that mean for the cloud system and what does that mean as you extrapolate it out over the planet? That program is integrated all the way up through various scales of modeling, all the way up through global climate models. And as part of that program, they worked with us on putting the Department of Energy’s super-sophisticated Earth System Model onto the Amazon cloud and to start to study modeling the brightening effect on these cloud decks in different parts of the world. So they’re probably the most mature, integrated program in doing that. There’s lots of different and really interesting and talented people studying the possibility of putting material into the stratosphere. That is the most common sort of prospect.

And we worked with teams at the National Center for Atmospheric Research and the UK Met Office and Cornell University to develop module to more realistically represent what it would look like in a controlled way to put material into the stratosphere and then see how that plays out in the Earth System in a way that you could study impacts on agriculture, water, storms, temperature extremes. And so those kinds of studies are going on, but it’s still going to take probably some engineering and experiments in the stratosphere to have the representation be really realistic of what that would do. So that was a long-winded answer to your question.

Strickland: So are governments getting involved in this research or is it still too controversial for them to touch?

Wanser: The quick answer is they’re stepping forward. And from a SilverLining perspective, we think that’s a really, really good thing because like other environmental matters that operate at scale, the ultimate question is environmental protection and public safety. And governments look to their own expert bodies, their science agencies, their expert panels who look at environmental protection questions, public health and public safety questions. So it’s really important actually that, in the public sector, scientific enterprises have capacity to look at what these things do from a pure evaluation perspective. Not saying whether these are a good idea. Can we as policymakers, can our system evaluate them, can we determine what we need to have to observe and monitor them, what kind of decision structures we need for them. So in the US, there’s been some advancement in science agencies to start to step forward on both the direct questions about these interventions and sort of filling gaps in some of the areas of science around them where maybe we’re weaker than we should be. So this whole question of particles in the atmosphere and how they interact with clouds and how they reflect sunlight and how that affects the climate system, we’re under-invested in that question. It’s one of the key questions in climate science.

Wanser: And it’s a really important near-term question outside of interventions because we’re taking this aerosol layer down. We’re cleaning up that aerosol layer and depending on how strong that effect is, it would be a good idea for us to understand it better. In the US, the advances in research are really across both the anthropogenic or the pollution effects, as well as these intentional intervention ideas, because the tools and the science that you need and the observations that you need are essentially the same. So that’s moving forward, I think, in a way that’s positive on both fronts in the United States. The United States is a little bit ahead, I think, of other places in looking at this. Although China has had a really quite sizable modeling program looking at stratospheric intervention for quite some time, and the UK historically has been at the forefront of atmospheric research. And some of the prominent researchers who proposed these ideas came from the UK, and they did the first scientific assessment at the Royal Society back in 2009. And then there’s now emerging some pockets of analysis in developing countries partly funded by non-profits and so forth. But it’s definitely a question that’s come on the radar, that’s starting to move into the government arena, I think, but still has quite a ways to go in terms of scientific research.

Strickland: And I guess maybe on the government level, is it still seen as a very controversial field of endeavor? It seems like in the public imagination, there is concern that there will be unintended consequences, that it’s such a big system, we don’t know what moving one lever would do to the rest. But I don’t know if that kind of controversy exists at the government level or scientific level, or if it’s more just the sort of public misperception.

Wanser: I think there’s an appreciation for the fact that it’s been controversial and that at the same time as the climate situation worsens, that it’s an important thing to understand from a policy perspective. Whether because you’re trying to understand it to ensure that you’ve explored all possible options to keep people safe or whether you’re trying to understand it to make sure you understand it in a global security context where if anyone anywhere in the world steps forward on it, that you’d like to be able to be knowledgeable and understand how to respond. So I think our experience of policymakers is that they’re very pragmatic that way. And then when you’re talking to them about the kind of science that’s needed to help evaluate and answer questions about it, that we’ve actually, in the United States had really good success in a bipartisan way of stepping forward. It’s different than the sort of philosophical or evaluative question of whether you should use these things, and our position is that we don’t have enough information to answer that question. And so the activity of generating more information is something that many policymakers can agree on at this point, but it’s not necessarily the conventional wisdom.

And I think partly it’s because in this space there’s been a conflation of the research with the implementation of the scaled activity. So, for example, SilverLining is an organization that we fund research and we really promote research, but we want to genuinely know the answer as to whether or not these things are useful or not. And in that way, we’re a bit like a medical foundation, and that’s different than a drug company that might be ready to scale up and sell the medicine. And so we really are trying to draw the distinction for people because this is a different set of decision processes to look at the science and say whether or not these are things you would ever use. But I would say we found actually probably more receptiveness to that amongst policymakers than sometimes we have in other communities.

Strickland: I recently read two science fiction books that both deal with the topic of climate interventions. Neal Stephenson wrote one called Termination Shock, in which a rogue Texas billionaire starts firing sulfur missiles into the stratosphere. And Kim Stanley Robinson wrote a huge book called Ministry for the Future, which had a lot of different threads, but one of them was sucking up the ice melts from below the glaciers in Antarctica, pumping it to the surface and refreezing it. So I’m curious to get your take on both those two books on a couple different levels, whether the science was plausible, but also whether you found them useful for the cause or a poor representation of what’s possible.

Wanser: I was raised on sci-fi, so I quite enjoyed both books. I’ll start out by saying that. And with that said, actually a lot of the science of both books is quite good. We actually know some of the experts they drew from their points, and I think Neal Stephenson talked about this. The missiles into the stratosphere is the weakest part. So is some of the delivery mechanisms for this stuff, and a little bit in Kim Stanley Robinson’s book too just sort of aligning that, oh, it was super easy for India to go ahead and do this. So one of the things that we try to explain to people and it actually raises the point I want to re-emphasize again, we do not today have any technology for this, and it’s not entirely trivial to have it. So I would say the part where they make it seem like, wow, any country or billionaire could come in the next couple of years and do this and so the most important thing we need is some kind of global committee to figure out what to do, that’s probably the least helpful part because we’re trying to say to people, actually, we’d be lucky if we had something inside of a decade if you decided that these things were needed. So that part of it, I would say, where it sort of triggers people’s fears about this running away before you can catch it, and maybe has people overly confident that these things are in the bag or in the back pocket.

Strickland: Well, Kelly Wanser, thank you so much for joining me. I really appreciate you taking the time to share your thoughts with our audience.

Wanser: Well, thank you. We’re great fans of IEEE and great fans of your audience and really appreciate your interest.

Strickland: Today on Fixing the Future, we were talking with Kelly Wanser about climate intervention strategies. I’m Eliza Strickland for IEEE Spectrum, and I hope you’ll join us next time.

Podcast transcripts are provided for convenience and accessibility, but in case of discrepancy between the transcript and the podcast’s audio, the audio is considered the authoritative source.

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