Is Large-Scale CDR Sustainable?
Two recent journal publications point to potential risks associated with large-scale carbon dioxide removal (CDR). Is 10 gigatonnes annually a realistic and sustainable target? Should we aim for 1 gigatonne, or could 28 be feasible? What land use and energy limitations are inherent in large-scale CDR, and what policy measures could ensure a just and scientifically rigorous implementation of this emerging technology?
In this episode, our Policy Panel discusses both the potential pitfalls and the potential necessity of large-scale carbon removal, as humanity continues to emit over 40 gigatonnes of CO2 annually (and counting).
A must-listen for those who question the viability of CDR as well as those who believe in the "gigatonnes or bust" approach.
On This Episode
Resources
Science paperEnvironmental Science & Technology paperHolly's book Ending Fossil Fuels
Subscribe to Climate Workers Anonymous
My other show, Reversing Climate Change
Books referenced in the podcasts, at Bookshop
Full Transcript
Announcer: You’re listening to Carbon Removal Newsroom, a weekly show about current events in the world of carbon removal, from technology and innovation to policymaking and job growth. Brought to you by Nori, the carbon removal marketplace.
Radhika Moolgavkar: Welcome to the February 13th episode of Carbon Removal Newsroom. Today, we dive into the murky waters of what seems like a clear climate solution, large-scale carbon removal. We’ll be unpacking research that sheds light on the potential pitfalls of this technology and asking the crucial question, is large-scale carbon removal sustainable? Amid the promise of sucking carbon out of the air lies a complex web of potential consequences for our planet and its inhabitants. So today joining me, Radhika Moolgavkar, VP of Supply and Methodology at NORI, is our usual policy panel, Holly Jean Buck, Assistant Professor of Environment and Sustainability at the University at Buffalo.
Hello, Holly.
Holly Jean Buck: Hi.
Radhika Moolgavkar: And Wil Burns, Co-Executive Director of the Institute for Carbon Removal Law and Policy at American University. Hello, Will.
Wil Burns: Hey, how are you?
Radhika Moolgavkar: I am well. I hope all is well in Chicago.
Wil Burns: Indeed.
Radhika Moolgavkar: All right, so let’s just jump into it. In the last month, two papers have been published raising concerns about large-scale CDR. I don’t think they raise new issues, but it’s always good to kind of revisit what people are thinking about. So let’s start with you, Will. We throw around the term large-scale or gigatonne-scale carbon removal a lot, but can you give our listeners maybe a sense of just how massive that is?
Wil Burns: Yeah. Yeah. Well, there’s a lot of ways of looking at it. One is in terms of actual mass. A gigatonne is a pretty astounding thing. So if you thought about a gigatonne from a standpoint of mass, it’s equivalent to the mass of all land mammals other than humans in the world. One gigatonne is. It’s also roughly twice the mass of all human beings in the world. And if you think about the amount of emissions that we look at right now, we’re talking about at the end of 2023, about 40. 9 gigatonnes.
And the estimates are if we’re going to reach 350%. You know, the kind of the talisman for a lot of people of rolling us back to a quote unquote safe climate. It’s been estimated that we’ll have to remove about 500 gigatonnes from the atmosphere by the end of the century.
Radhika Moolgavkar: That’s a little mind blowing. I must say I have never heard it thought about in those terms or described in those terms. It’s amazing we’ve released that much, actually, if you think about it.
Wil Burns: Yeah, well done.
Radhika Moolgavkar: Holly, just a few days ago on February 1st, the Journal of Science published a paper titled Sustainability Limits Needed for Carbon Dioxide Removal, in which the authors assert that many governments and industries are relying on future large-scale land-based carbon dioxide removal to avoid making necessary steep greenhouse gas emission cuts today. So as a person who literally wrote a book called Ending Fossil Fuels, what do you think of this statement and do you agree with it?
Holly Jean Buck: It’s kind of complicated because I’m not sure that these governments or industries know that they’re relying on it. So is it fair to say they’re relying on it? I know that sounds weird, but I just think that the awareness that net zero involves carbon removal is Even among people who work on sustainability strategies is still pretty low. And so, yeah, implicitly they might be relying on it, but it’s not like they’re going out and making plans to get it. So I think maybe there’s a different language we could use to describe that problem a little bit.
Radhika Moolgavkar: So how would you describe it? Because... I agree with you. It doesn’t seem like carbon removal is so accepted that you have people who are putting off cuts today because they think they’re going to buy carbon removal tomorrow. But clearly there is a large concern around the lack of action around reductions of emissions.
Holly Jean Buck: Yeah, well, that’s a whole other problem, though. I mean, and what this paper argues is, you know, other papers argue that it’s linked, but There’s lots of other reasons that people are not reducing emissions besides carbon removal. So I guess I would say if I was to revise the statement, governments and industries have signed on to targets that imply they would need carbon removal, but they may not be aware of that and they’re certainly not planning for it. But we might have a different take.
Wil Burns: Yeah, I do have a different take. When I look at the, I think it’s that, I’m trying to remember if it’s that piece or it’s the other piece we’re discussing. I think it’s the other piece we’re discussing. And, you know, it talks about the fact that the NDCs right now use about 12 million square kilometers of land-based CDR by 2060 under their assumptions. And That study estimates that’s about three or four times higher than what’s sustainable. I think that countries are starting to play this game where they’re either playing the game of assuming massive overshoot and then magical re-descent through CDR, or they’re taking the balancing language in Paris and extremists by starting to come up with some very high land-based CDR commitments.
And that worries me a lot.
Radhika Moolgavkar: So first of all, Will, can you define NDCs for our listeners?
Wil Burns: Oh, I’m sorry, Nick. So under the Paris Agreement, the temperature goals are supposed to be effectuated by nationally determined contributions.
Radhika Moolgavkar: And so it’s a bottom-up process whereby countries And just to poke a little further at what you said, Why do you think countries are starting to play this game? Is it because it’s just they’re punting and they’re making a pledge that they know they’re not going to keep? Is there because you think carbon removal is cheaper than emission reduction? What’s driving this behavior?
Wil Burns: Yeah, it’s probably all of the above. It’s probably politically easier to put in large amounts of CDR and hence not have to poke the cage of reducing emissions in the short term, which will be very expensive and also has some extremely powerful political forces on the other side. And, you know, some of these countries are also large Fossil fuel producers themselves, like the United States, right? So it’s easier to rely on CDR. And I think some of them do believe that these approaches will be cheaper than structurally decarbonizing, which both of the pieces suggest to some degree would be true.
Radhika Moolgavkar: So Holly, going back to this paper that sustainability limits needed for carbon dioxide removal, it mentioned socio-ecological thresholds for CDR deployment. So can you elaborate on what these thresholds might be and how they can be used to determine a safe and sustainable level of carbon dioxide removal implementation?
Holly Jean Buck: Well, I think there’s different ways you could define this. I didn’t find it super well-scoped in this policy forum piece, although they point to a whole bunch of different things. So they reviewed the literature, including meta-reviews of other papers, and they talk about constraints like the impacts of large-scale land use change on biodiversity, food security, and the rights of indigenous and local peoples. They also talk about What you might think of more as sustainability issues like freshwater use, you know. So there’s a lot in there. And you could imagine a different group of people defining it a little bit differently.
But the main point is that there’s both social and ecological risks that need to be better taken into account.
Radhika Moolgavkar: I think this is something that we’ve talked about a lot on this show and particularly with you, Holly. And it doesn’t sound like this paper introduced anything new to your thinking. But have you seen progress in the last few months in this area or is it just continue to be something we’re talking about even as the U. N. moves forward on these different contribution limits? Do you see anything happening in the space?
Holly Jean Buck: No, and this frustrated me a little bit because Chris Field and Katie Muck wrote a piece in Science back in 2017 called something like Right Sizing Carbon Dioxide Removal. And this is kind of like, I mean, it’s basically the same sort of argument. They did a little bit more calculations on land use implications, for example. But really, I see the main point of this piece is to point to like a much larger, serious research agenda that would be Involve a lot more different types of models and disciplines and what they say is that here in this piece that research on a sustainable and realistic CDR budget across all CDR methods should be prioritized and they say it should Assess ecological and biophysical risks.
It should access social feasibility. And it has like a list of things of like you would want to do if you were to actually undertake this research, I don’t know, program. But it’s not the program itself. It’s like the argument for why we need that big invest time and energy to really answer these questions.
Radhika Moolgavkar: Yeah. Do we have the time? And do we have the energy? I’m just not sure. But it does seem like a nice bridge to a question for you, Will, which is, is this the place we need policymakers to step in? And how do we balance all these competing interests, political interests, obviously environmental interests, justice issues?
Wil Burns: Yeah. Well, I don’t know about the latter, but in terms of the former, first of all, I really agree with Holly. It’s absolutely kind of a broad scale sort of mapping of what needs to be done without really telling us how to structure it. But in all fairness, I guess that’s what they were seeking to do. But I think it’s time to Probably try to start putting meat on the bones in terms of doing that and figuring out What legal mechanisms we have to facilitate that. I think there’s things under the Paris Agreement that would permit us to start to do that.
I think the fact that the Article VI supervisory body started talking about sustainability considerations in the context of CDR, not very well in my opinion, but at least Started talking about metrics in that context. Should be a useful segue for the regime to start trying to meaningfully figure out how to incorporate this into the standards for both the nationally determined contributions and the long-term emissions standards that they call on the parties to set up. And you have language in the preamble or the introductory section of Paris that says that When you’re not only supposed to take into account the impacts of climate change on people, including vulnerable people, but the impact of response measures.
And so I think that gives you a framing of To authorize the parties to start to look at these issues. And I thought one thing that the science piece did a good job on was it had some broad recommendations of what should be done, right? They said, not only should you have separate emissions reduction and CDR targets, but you should seek to maximize emissions cuts and strive to limit land-based CDR footprints. Holly’s excellent piece that talked about how we define residual emissions is, I think, a good starting point for that.
I don’t think it’s something that we’ve been doing in earnest at this point. I think that piece and the other piece both suggest that countries may be playing games a bit on defining residual emissions in a way That’s so capacious that allows them to avoid meaningfully decarbonizing the economy. And so the parties to Paris probably should start working on some metrics that circumscribe that as much as possible.
Radhika Moolgavkar: So Holly, I’m going to ask this question to you, though maybe Will will want to jump into. We’re aware that a lot of the nature-based solutions, and not many of these solutions, right, require either land use changes or an abundance of land. So how do you think about engaging what is needed, which are these solutions, in a way that doesn’t exasperate other potential biodiversity loss, threaten food security? Because sometimes I wonder if some of these things are Not even for nefarious reasons, but for protective reasons. People are acting this way, right?
Because they don’t know what this means. Or at the worst, a violation of human rights. How do you structure, Holly, something that will be meaningful and will be resonant with policymakers?
Holly Jean Buck: I think it’s a big question because it’s very context dependent. And so you could imagine different recommendations and different Geographic areas. I know that seems like a cop-out answer in some ways, but there’s just been so much riding on this because we had, you know, after the food price spikes circa 2008, again, 2010, 2011, there were these large-scale land acquisitions, many of them just paper deals that never went anywhere, but like for large areas of agricultural land in the global south. With speculative food production, but there are also biofuel deals.
You know, there’s also been these carbon credit deals. I mean, so a lot of people in response to that kind of dynamic have observed it and made plenty of recommendations about what you should do. And I think we’re still trying to link that experience when we think about future carbon removal. And I think that link has been drawn somewhat, but it could be drawn out even further.
Radhika Moolgavkar: All right, we’ll turn to the other paper right now, which, Will, you already sort of alluded to, which is from Environmental Science and Technology and is titled Prioritizing Non-Carbon Dioxide Removal Mitigation Strategies Could Reduce the Negative Impacts Associated with Large-Scale Reliance on Negative Emissions. Quite the catchy title.
Wil Burns: It sounds like- So the academics are known for.
Radhika Moolgavkar: That’s right. Drew me in. It sounds like they’re taking a different approach, which is sort of prioritizing emission reductions over large scale CDR. Can you summarize the argument for this approach and maybe how it’s a little different than what the other paper was trying to, you know, state?
Wil Burns: Yeah. I mean, I think they were good bookends because one of the things that this piece does is it emphasizes, you know, it emphasizes once again, there’s no such thing as a free lunch. And whereas the science piece really focused on the sustainability limitations associated with nature-based solutions, this one said, you know, novel CDR also has some serious sustainability considerations, right? Direct air capture with Large amounts of energy requirements, large amount of energy requirements for enhanced rock weathering and so forth. And so they developed these scenarios for low use of CDR defined as like a gigatonne annually, a medium scenario of eight gigatonnes, and then a high scenario of 22, right?
And then mapped out what that would look like, right? And Ultimately concluded that when you get to those high scenarios, right, it requires massive amounts of energy. Massive amounts of cropland, for example, that would be diverted. Though even at a gig, they conclude that you’re going to reduce food and odd food cropland by about 20%, right? But it’s 50% when you get to the 22 gigatonne pathway. And they suggest that if we do that, if we get to these high scenarios, we’re going to not only have sustainability considerations, but we’re going to lose a lot of the co-benefits And they talk about lung cancer and stroke and things like that.
One other thing that I thought was interesting in it is they talked about to some degree, though it’s interesting why they didn’t conclude that this might be equally interesting, that The trade-off is that we could have very higher costs associated with getting to our temperature goals if we have to spend huge amounts of money for renewables and other options, right? And one of the things that I thought was a striking number in there was when they talked about the fact that They said that if you go with the low CDR uptake scenario, one gig, marginal costs are going to reach about $2,700 per tonne of CO2 to get to 1.
5. CDR scenario, the marginal cost for reducing emissions is about $300 per tonne. So it’s going to cost society a lot more. The question is, will it disproportionately impact certain groups and then tip the balance toward arguing for more CDR? I think as Holly suggested, there’s just a huge number of factors and equities to weigh, and it’s difficult to sort it all out, right, and determine what’s optimal, I think, at least.
Radhika Moolgavkar: Yeah, so as Will was saying, Holly, right, this study suggests limiting global CDR deployment to about one gigatonne by 2050. Is that really feasible when you think about the scale of both the emissions challenge and just the amount of carbon dioxide currently already in the atmosphere? And do you see any alignment with current policy proposals?
Holly Jean Buck: I mean, on the second part, no. And on the first part, I think it’s probably more feasible than 8 or 22 gigatonnes, which is what they compared in the study. So... You know, I don’t know if they were necessarily suggesting limiting global deployment to one gigatonne. It was more like, let’s put that constraint in the model and see what the model turns out. And so they didn’t really necessarily look at all the trade-offs comparing these things, though, because there’s a lot of nuclear and hydrogen in what came out of their model.
So in terms of feasibility, it’s like, will people want to pay for and build more nuclear? If we’re building out hydrogen to a greater degree, is that hydrogen going to leak and cause some methane and other problems? We kind of don’t know. Are people down with all the extra critical minerals to build the renewable to the degree in that scenario? I don’t know. So you’d have to really do this in a much more structured way where you look at a lot of different things. And I don’t know how people are going to read The trade-offs of one option or another in terms of more or less feasible at the end of the day.
Radhika Moolgavkar: Oh, so depressing, Holly. Anyway, both papers highlight the risks of over-reliance on CDR. And so I was wondering if either of you could give me concrete examples of negative impacts that We might see if we go down that path. It all feels very theoretical to me, but I always feel like it’s like this or this, but not as to Holly’s point. There are all these other considerations that you have to put in there. You know, it always seems like there’s two states they’re considering, not the infinite that we live in.
So any concrete examples?
Holly Jean Buck: I mean, in terms of negative impacts, if we overrely, I think there’s a category of negative impacts if we actually went forward and built the 22 gigatonnes that would involve land displacement and extreme costs and those sorts of things. But also there’s the risk of overlying and then not building it, which people talk a lot about mitigation deterrence. But I think A, you have adaptation deterrence where people were saying, we’re going to get to 1. 5 by building this CDR. And then they haven’t adapted for two and a half for wherever we’re really headed.
I also think that people get to a sense of frustration when they see that we’re not going to get to this 10 gigatonnes. And then they’re like, oh, well, let’s go for solar geoengineering because it won’t necessarily be like, oh, we can’t do 10 gigatonnes. Let’s double down on energy storage or whatever. That might not be where this conversation goes. So that’s another risk I see with overlying on CDR. Yeah.
Wil Burns: I guess one more I’d add is, again, I’m not sure which paper will discuss this, but one of them had a lot of discussion about over-reliance to allow large overshoot, right, of temperature targets and then, you know, magically drying back down, right? And that’s one of the things that keeps me up at night because I think That once you overshoot the temperature targets, first of all, it’s going to take a while to get back down with CDR, right? And second of all, you could have all kinds of irreversible impacts internally.
And also when you start overshooting to 2. 5 or 3 or above, you start to get a lot of nonlinear sort of responses in the system that may be irreversible. And so I think we play a dangerous game with allowing overshoot by building in large amounts of CDR in our assumptions.
Radhika Moolgavkar: Yeah, I agree with you. I feel like this is just like a human nature issue, not a CDR issue, right? We’re like internal optimists that technology is going to fix all of our problems rather than- Yeah, right, right.
Wil Burns: We got ourselves in this trouble with technological optimism, but now this new technology is what will save us for sure.
Radhika Moolgavkar: Yeah. Instead of focusing on the like concrete actions you can take today, there’s always something down the road that’ll save us. So next question for you, Will, is the IPCC report clearly acknowledges the need for both emission reductions and CDR. We’ve talked about that a lot on the show. So how do we kind of disengage the humans, you know, natural techno optimism and actually produce strategies that are balanced and complementary and, you know, do what we need?
Wil Burns: Yeah, I don’t know. It’s a difficult question. But again, I think that there probably has to be an acknowledgement that That decarbonizing structurally has to be job one and should be the focus. And we should start to try with realistic sort of metrics to define how much we can realistically reduce emissions in every sector and define residual emissions and then carve out a role for CDR that It’s almost singularly focused in that context, maybe with some room also for developing countries to continue to emit at a higher level for a while to balance the equities, but that’s going to require a huge amount of research and it’s going to have to require actual commitments.
I mean, I hate to bang the same drum, but I think if we continue to rely on this wild west of voluntary carbon markets to create a benign and virtuous pathway to the future. It’s a fool’s errand, right? We’re going to need a regulatory approach that tries to mandate these kind of measures and then allocates emissions and carbon removal reductions accordingly. And we better start sooner rather than later or we’re going to be locked in to these assumptions.
Radhika Moolgavkar: Well, a regulatory approach, I mean, we can’t even decide whether someone can be on our ballot in the United States.
Wil Burns: I know, a boy can dream.
Radhika Moolgavkar: Fuck. So Holly, a question about these papers, you know, both obviously mentioned economic, technological and social challenges associated with large scale CDR. Can you just talk about any potential solutions? Like if you were queen of the world, what would you do to address some of these issues?
Unknown speaker: I mean, I could write a book about that.
Holly Jean Buck: No, I just like. Okay, so in these papers, I wouldn’t necessarily ask the modelers about the social challenges. I will point out like one data point about the economic challenges, which I think these models focus on, which is this environmental science and technology paper said that, okay, if you did one gigatonne by 2050, novel CDR, the optimal marginal cost required globally to reach the modeled 1. 5 pathway Increases to over $2,700 a tonne of CO2 compared to about $300 a tonne when novel CDR scales to 22 gigatonnes by 2050. So I know that was a lot of like numbers to parse if you’re listening and not seeing it on the page.
But the takeaway there is that you can see why these models throw in a bunch of CDR, right? I’m not the best person to comment on how we overcome the economic challenges of CDR or of mitigation, but the one thing that’s clear to me is that we need to build Understanding among voters about these challenges so that they will vote and support policies. And we especially need policy proposals that are going to distribute those costs equitably and not have them fall among the people who can least afford it. So that’s number one for me right now.
Radhika Moolgavkar: You’re both such optimists. So, Will, last question for you today. Do you think there is a future for large-scale CDR in a sustainable climate solution? And under what conditions would it be most effective?
Wil Burns: Yeah. Well, you know, again, an extremely tough question. I think when it comes to the land-based approaches, the ones that were looked at in here, backs and afforestation and reforestation, right? There seem to be some Clear biological limits and whatever innovations we might develop in these sectors in the future probably aren’t going to do a whole lot to change those, right? And so there’s certain things we can do. One of the pieces suggested more of a focus on restoration, for example, than afforestation will make some sense. Emphasis on using You know, crop residues and things like that instead of relying on trees and dedicated energy crops.
But on the technology side there, I think there’s some possibilities. But again, it’s a big caveat, right? I think direct air capture could have a huge potential role to play. But its primary constraint remains the energy question, right? If we’re going to use a quarter of our renewables to drive direct air capture, you know, in the latter part of the century, that’s... Is that going to be the optimal use of the renewables that we have, assuming that there’s a limit to the renewables that we can produce, right? If we can get past that issue, I think that’s a system that could potentially scales without huge land use requirements, water requirements, things of that nature.
I think some of the other approaches even help us address some of the sustainability challenges potentially such as biochar and enhanced rock weathering if it really does contribute to soil health and increasing crop yields, right? So I think there are scenarios under which this can happen, but it’s early days and that’s part of the frustration. How much capital do we expend to determine if we can reach that? How much do we rely? On these approaches and our assumptions of where we’re going, if that diverts us from doing other things that may be a sure bet in terms of reducing emissions.
Radhika Moolgavkar: Yeah, I have two thoughts about what you just said. One is, I mean, I know I was just making fun of techno-optimists, but there are some interesting new technologies that don’t use so much energy, photosynthetic or sunlight-driven. I just had ban you on the podcast last week, and so... Maybe there are pathways to less energy, but of course we shouldn’t rely on it. And the other comment I would just add of is, we’re mismatched in time, right? We’ve done a lot of damage for a long time, but maybe the technologies are so new, we don’t know the trade-offs that we’re making.
It’s It is what it is. Interesting.
Wil Burns: Yeah. I tell my students, you know, if we were trying to start getting our act together and it was 1980 or 1970, right, we’d have the luxury of really looking at these in a granular fashion in terms of assessment. But we waited so long, we’re hitting critical thresholds and we feel like we need to move quickly in conditions of very high uncertainty, right? My parents’ generation shouldn’t have put this generation in there. Those crosshairs, but we did.
Radhika Moolgavkar: Yeah. My kids thank us.
Wil Burns: Yeah.
Radhika Moolgavkar: So Holly, last question for you today. What message would you give to policymakers, individuals regarding the role of large-scale CDR in addressing climate change?
Holly Jean Buck: Well, first, I don’t think people should be taking this 10 gigatonne figure that’s circulating as like The given need, I think that people are a little bit quick to assume that these models are working in the ways we want them to. I mean, they may not have the latest assumptions about how to, you know, mitigate emissions from industry. That’s something that improves quickly. So what would I tell them to do? I would say one thing we should be doing is investing more in R&D in things like Mitigating nitrous oxide emissions, like look at those things that are really comprising the leftover residual emission and put more R&D now into things that are going to be able to eliminate that much more in 2050.
And then, you know, you won’t need 10 gigatonnes, you’ll need less. And there’s a lot of exciting stuff on the horizon. Like, I don’t feel depressed about this. I think that, you know, Aim for one or two or three. And that would probably be more realistic and fruitful than 10, 10, 10 all the time.
Radhika Moolgavkar: Gotcha. Yeah, that makes a lot of sense, Holly, as always. Both of you brought great perspectives today. I really appreciate it. So thank you both for joining me and have a wonderful rest of February. A happy Valentine’s Day and midwinter break if you need to have either or celebrate either of those. And to our listeners, thanks for listening as always.
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