Andy Stone: Negative emissions technologies are a key part of the strategy to keep global warming to the two degree target set out in the Paris Climate Agreement. In fact, it’s projected that we’ll need to remove dramatic quantities of carbon dioxide from the atmosphere each year to keep within the Paris goal. Yet today, negative emissions hardly exists in any practical sense, and major barriers lie ahead in the form of high costs, environmental impacts, and uncertain political support.
On today’s podcast, I’ll be talking with the author of the very first textbook on carbon capture, about the challenge of scaling negative emissions technology to the point at which they can meaningfully limit carbon dioxide concentrations in Earth’s atmosphere. Along the way, we’ll look at how the challenge of scaling negative emissions recalls early barriers to growing the wind and solar industries. And we’ll look at recent efforts to ramp up the deployment of negative emissions technologies.
My guest is Jennifer Wilcox, professor of chemical engineering at Worcester Polytechnic Institute, and a member of committees at the National Academy of Sciences and the American Physical Society, charged with assessing carbon capture methods, their costs, and their climate impacts. Jennifer, welcome to the podcast.
Jennifer Wilcox: Thank you.
Stone: Tell us about your work on negative emissions at Worcester Polytechnic Institute.
Wilcox: Sure. A lot of what we’re working on in my group is carbon capture broadly speaking. So not just capture from the atmosphere which would constitute as negative emissions, but also looking at avoiding carbon emissions to begin with. So carbon capture retrofits to existing technologies, maybe it’s a natural gas-fired power plant, or a fluid catalytic cracker at a refinery. So we cover really broadly carbon capture in general.
And we focus in our group on adsorption and membrane-based separation processes for C02. More recently focusing also on C02 mineralization. And then finally some of the work that we do in the group is really about the techno-economic analysis coupled to life cycle assessment. Capturing C02 from the atmosphere is actually something that is very difficult to do. And so part of the systems-based thinking is what energy source are you using in order to remove C02 from air. And then in the end, again thinking about it as a system, what’s the net removal of C02 from air.
Stone: After you’re burning those fossil fuels for example?
Wilcox: Well, so if — no, it depends on if you’re using fossil fuels to provide you with the energy to actually do the direct air capture. And so yes, if you’re using natural gas-fired power plant to provide you with electricity to meet the electricity goals or needs of your separation process, then you have to think about the emissions from that power plant.
And so if you design something that, for instance captures a million tons of C02 per year, depending on what the energy is that you’re coupling to that direct air capture plant, your net removed is going to be lower if you’re using fossil-based energy to fuel it. And so part of our group is very careful carbon accounting of the system. Because in the end, the perspective that matters most is climate’s perspective.
Stone: So let’s talk about this for a moment. What are the negative emissions technologies? You just kind of introduced them briefly, but what are they, and what are the types that are getting the most attention right now?
Wilcox: Sure. So just broadly going through them, there are biological uptake of C02, those include planting trees, it might also include enhancing carbon storage in soils. And also planting biomass such that the biomass can be used for electricity production or energy production in place of fossil, like coal or natural gas. And so those are biological processes for removing C02 from air. There’s also mineral approaches. So using alkaline rich rocks, rocks that are rich in calcium and magnesium which will react readily with C02. Finally, direct air capture is another method that uses chemicals that selectively react with C02 in the atmosphere.
Stone: So looking ahead at negative emissions and its potential, how much carbon dioxide do we actually need to remove from the atmosphere each year, say to meet the Paris goal’s two degree maximum warming limit?
Wilcox: So last January 2019, there was a report that was released by the National Academy of Sciences, and in that it was estimated that ten gigatons of C02 in the form of negative emissions has to take place each year from now until mid-century. And then after, from 2050-2100, that would have to increase from ten gigatons to twenty gigatons each year. And that’s to meet our climate goals.
And in the early stages we — I was a co-author of that study, and what we showed is that to achieve ten gigatons of C02 removal, we actually have the technologies today. And those technologies are at a cost of under $100 per ton of C02. They are mostly in the form of land-based options. So including afforestation, reforestation, or planting trees. Low tillage practices or agricultural practices to help keep carbon and soil and increase the uptake of carbon in soils. And also land management approaches that could include using waste biomass for instance to turn it into a feed stock for biomass fueled facilities that produce electricity for instance.
Stone: What is biomass? In this context can you explain it?
Wilcox: Sure. So for instance, biomass could be if you have waste materials in a forest, that maybe also a cobenefit could be cleaning up forests to prevent forest fires, for instance. And then collecting that biomass. It’s just essentially dead trees and leaves, and biomass that you would find within forests. And the idea is that can we take that biomass on site, convert it into a form that could be used for instance to replace coal, and a unit that burns coal. And this is a field in engineering called torrefaction, and that is — and you might be familiar with pellets and pellet stoves and things like that.
So that’s one way to think about it, is turning biomass into these particles that look like the size of pulverized coal, so that the burner technology that’s used in coal-fired power plants today could be retrofit or updated to burn biomass instead. And in the Academy of Science’s report, globally we saw an opportunity, or we presented an opportunity that there may be up to three to five gigatons of that kind of carbon removal potential in just biomass to electricity.
And again, adding up to ten gigatons we saw other sectors as well. Afforestation, reforestation, or planting trees is really just one of several options that are going to be required to add up to that scale. I’ll add that what happens after mid-century? How do we get from ten gigatons to twenty gigatons per year? How do we increase? It’s our view — it was our view as a committee in that report to look at also technologies like direct air capture and C02 mineralization.
Today, direct air capture is still pretty expensive. Mineralization still requires a lot of advanced research as well. So if we could get those kinds of technologies deployed, investigated further, the idea would be that maybe by mid-century we could get the cost down around $100 a ton, and they would play a larger and more significant role in the second half of the century.
Stone: That’s a really interesting point that you bring up. So it sounds like there’s going to be a variety of different technologies and methods that we’re going to be using. So negative emissions technologies are still quite new, right? Where do we stand today in terms of capacity, actual install capacity for negative emissions?
Wilcox: Sure. So there are projects that are getting started with biomass, and coupled to carbon capture and storage. Also known as BECCS, and a little bit of what I talked about before. And of course there’s practices in terms of low tillage and agricultural practices and reforestation, afforestation, but all of this is taking place on too small of a scale. In addition, when you think of technologies like bio-energy coupled to carbon capture and storage, that second piece is extremely important. How are you going to actually permanently remove the C02 that you’re generating?
And same with direct air capture. Direct air capture in itself is a carbon removal method, but unless it’s coupled to the permanent removal of the C02, it’s not negative. And so some of these technologies, you have to not just capture the C02, but you have to permanently remove it. And then comes the question of what do you do with that C02, how do you remove it from the atmosphere on a timescale that impacts climate.
And today we are doing geologic storage of C02, so putting C02 back in the earth where it came from to begin with. But we’re mostly doing that through a process called enhanced oil recovery. And so today the amount of C02 that’s actually stored in the earth is on the order of about 40 million tons. And so if we’re thinking back —
Stone: That’s what we’re storing every year, 40 million tons?
Wilcox: Every year, roughly 40 million tons of C02.
Stone: We’re talking total emissions in the year is 40 gigatons.
Wilcox: Yes, that’s right. Yeah, we’re 100-1,000 times off our target. Yeah, which — yeah, we have a lot of work to do.
Stone: It gives us a perspective.
Stone: Let me ask you a bit more about direct air capture. As you said earlier, a lot of your resources were actually really focused on that. And that’s actually removing carbon directly from the air. So you have to obviously do something with that carbon dioxide as you just mentioned. It’s a complex solution. It is at this point a very expensive solution, yet it holds a lot of promise. Can you tell me a little bit more what that promise is?
Wilcox: Sure. You know, there are some benefits to direct air capture. The one — I’ll mention a few of them. One is that it’s not tied to arable land, which means that if you have a direct air capture plant, it’s not necessarily needs — it doesn’t need to compete for food. And so that’s one of the drawbacks of biofuels, is how much arable land is there to grow all of the biomass. Direct air capture doesn’t suffer from that.
Another aspect is the process is very efficient. When you use chemicals to remove C02 from air, it can be up to 100 times more efficient than a forest that takes up the same type of land area. So it’s just an efficient process. The other aspect is there’s two technologies really that are driving this today. One is based on a liquid solvent approach, and another one is based on solid sorbents. And in particular, with the solvent sorbents based approach, which isn’t that different from how your catalytic converter looks in your automobile.
And so you have this honeycomb type structure, and within that structure you have the chemistry, the chemistry that selectively reacts with C02. So the air goes through the channels and C02 is captured in the walls of that unit. And so to regenerate that material, which you need to do because it’s, you know, we’re talking gigatons. And so it means that anything you use, any chemistry you use, you need to be able to make it over and over and over again. And so it requires heat. But the heat required to regenerate those materials can be roughly 100 degrees C, you know? And there’s a lot of opportunities —
Stone: That’s not that hot.
Wilcox: It’s actually not that bad, you know? It’s like even warm water, not quite boiling, could work. And so with that in mind, there’s a lot of opportunities out there in terms of low carbon heat, like geothermal for instance, that could couple well to that type of technology for direct air capture. One thing you have to be careful, and this is part of the work that we’re doing in my group, is responsible citing of these.
There’s this concept that a direct air capture plant, you can put it anywhere. I would argue with that. It goes back to what we talked about before, which is the C02 has to go somewhere. And you don’t want to necessarily spend a lot in the transportation of the C02. The other piece is it requires a lot of energy to do direct air capture. To capture 100 million tons of C02 per year can take anywhere from 300-500 megawatt power plant. So it’s a lot of energy.
And depending on what the choice is of the energy, can — may lead to more emissions back into the atmosphere. So coupling to things like geothermal, but asking yourself first, is that geothermal not better spent replacing a coal-fired power plant. So as long as that low carbon energy resource is in an area where maybe there’s not a population center or the energy couldn’t be better suited to displace fossil in the first place, the thing about geothermal in particular is that sometimes it’s too low of quality in terms of the working fluid. The temperature is not high enough to produce electricity. And so in those kinds of situations, direct air capture could couple well.
Stone: So let’s look at the economics of this for just a moment. So right now it’s quite expensive. I’ve read it’s around $600 per ton, are some of the estimates, to remove a ton of carbon dioxide from the atmosphere. How cheap does it need to be to start to create some critical mass for this technology work and ramp up?
Wilcox: Yeah, I think today there are some incentives in place. There’s in the State of California something called the Low Carbon Fuel Standard that is trading up to about $200 per ton of C02. And so if the C02 for instance is used for enhanced oil recovery, that qualifies for that fuel standard. There’s also a federal tax credit called 45Q, which pays up to $35 per ton of C02 if the C02 is used for enhanced oil recovery, and up to $50 per ton if the C02 is used for geologic storage.
So if you look at EOR in particular, $200 plus $35 is $235, so the question is, can we get direct air capture to be kind of lower than this number so that we can maybe close the gap, is the goal. Today it’s true, Climeworks publicly says that it’s about $600 per ton of C02, but they also state that they have a path in the next five years of potentially getting done to $200 per ton.
I think if we could get the cost down to $200 a ton in the next five to ten years, that that would be — that could make some impact. And potentially if we can deploy on the millions of tons scale over this same timeframe, maybe we could get as low as $100 by mid-century, and then these kinds of technologies would play a significant role in the second half of the century.
Stone: So the situation with direct air capture and any negative emissions technology kind of recalls what happened in the early days of wind and solar. You had these technologies, had a lot of potential benefit, a lot of potential use, but the economics didn’t really work out. So we’re obviously trying to make those more and more economic at this point. There are a few projects, new projects that have been announced with direct air capture, one involving Occidental Petroleum out in Texas. It looks like it may be a way to actually start to scale up. Can you tell us more about what’s going on out there?
Wilcox: Sure. So Occidental has partnered with Carbon Engineering, and they are designing a plant to build in the Permian Basin in Texas, that will remove on the order of 100 million tons of C02 per year. And what they ultimately are doing with the C02 is using it for enhanced oil recovery. So to give you a little bit of background on what enhanced oil recovery is, first I’ll say the first project took place in the Permian Basin in Texas in 1972.
And ultimately what you’re doing is, it’s called a tertiary recovery method. So already in the reservoir, the oil and gas reservoir, they’ve essentially recovered as much oil as they can, and now they’re still — this residual oil that they would like to still remove, the carbon dioxide in its super critical form is a solvent. We use it for decaffeinating tea and coffee and other applications. But at the temperature and pressure conditions of the subsurface where the oil is, it has properties that allow it to be mixable or mixing. It can easily mix with the oil.
And in doing that it changes the properties of the oil. Its viscosity, its surface tension, its density. And it makes that oil easier to recover. And so what happens in one of these projects is that you have an injection well where you inject the C02 and then you have a production well. In the production well, you’re producing oil, but C02 will also be produced. At the surface you separate the C02, and you reinfect it.
And you keep reinfecting it to get as much oil out as you can out of that C02, because today oil operators are paying for the C02. Up to $40 per ton of C02 is what they pay depending on what the price of oil is. And so because it costs something, they don’t want to just leave it in the ground. They want to use it for enhancing oil recovery as much as they can.
Stone: So they recycle it?
Wilcox: So they’re recycling it over and over again. And so that’s basically the process. But today, 84% of the C02 is actually sourced from natural C02 that’s in the earth. So just like oil and gas has been stored in the earth for millions of years, there are reservoirs of high purity C02 in various regions. Some in Colorado, and in other parts of the Southwest, and also in the Gulf Coast. And so pipeline infrastructure has been developed such that that natural C02 can be brought to the enhanced oil recovery sites.
Stone: So they’re taking out C02 from under the surface specifically to use it for — ?
Wilcox: For EOR, yeah.
Stone: For EOR, okay.
Wilcox: So the first step would be to stop doing that obviously. And then to think about, well where are there nearby anthropogenic sources of C02. C02 that’s produced from a power plant for instance, that could be captured and transported to these sites. And so that, capturing C02 from a point source is always going to be cheaper than capturing C02 from the atmosphere. These point sources are anywhere from 100-300 times more concentrated in C02 than is in the atmosphere, which really translates in the end to less energy required to do the separation, and less capital also. Because that really is about the contacter of the unit and how much C02 you’re capturing.
And so ultimately it would be — the first step would really be to stop using natural C02 for enhanced oil recovery and using anthropogenic C02. And there will be some cases where maybe there’s not enough anthropogenic C02, in which case a company might use direct air capture as well. The market for this today, so how much C02 is used for EOR in the US every year, it’s roughly 70 million tons of C02 that’s used for EOR. And so again, roughly 60 million tons is the runway we’re looking at, that we could imagine coupling to anthropogenic C02 emissions instead of naturally sourcing it from the earth. So it’s an opportunity.
Stone: So there’s obviously a lot of potential there, but we’re nowhere near the scale that we need at this point to actually make a difference for the climate. And this kind of recalls the situation we had once upon a time with wind and solar. High costs, not a whole lot of it out there, we needed to ramp it up. How do we ramp it up in the case of direct air capture?
Wilcox: Sure. So just taking solar or photovoltaics as an example, and it’s not clear whether that’s the best model to compare to direct air capture, we can talk about that after. But in its first significant decade of deployment, photovoltaics increased by about 180 times in its first decade. A good rule of thumb for installed energy increases is typically a factor of ten over a decade. So that was significant.
And there was a study that came out of MIT, I guess it was last December, that talked about that and how that happened. And that 60% of that increase was really due to government incentives and policies that were in place for that, and only 40% were in the technological advances of photovoltaics. And so just looking at that model of growth, if we had that kind of growth with direct air capture we would get to the gigaton scale that we need to by mid-century.
I think enhanced oil recovery could be an interesting transition, but again if we look at that scale, right now the market is that there’s 60 million tons. We’re not doing a million tons of direct air capture globally at this point, it’s on the order of thousands of tons. That if you look at what Climeworks’s efforts add up to. And so —
Stone: Climeworks is a Swiss company involved in direct air capture?
Wilcox: That’s right. So Climeworks is a company out of Switzerland. They have fourteen plants globally. And when you add up all of their efforts, it’s on the order of thousands of tons of C02 in terms of direct air capture. And so it’s still on the order of thousands of tons. We need to make the next step to get to millions of tons and then gigatons by mid-century. But I also feel that with enhanced oil recovery, although it is a transition, but it’s not necessarily the right answer to couple to direct air capture for all cases.
I think direct air capture will couple to some extent, but I also think we’re kind of missing a step. The first step would be to first avoid as much C02 from entering the atmosphere to begin with. So again, if you look at all of the enhanced oil recovery opportunities in the Gulf Coast or in the Permian Basin, you first should look at those power plants or industrial emitters of C02 and see if they’re not most suited for doing it in the first place, like avoiding the carbon emissions to begin with.
Because those processes will always be lower in cost because they’re more concentrated streams of C02. But there may not be enough to satisfy the market that’s needed, in which case direct air capture will play some role in that. But I wouldn’t say that you would want to use that entire market just for direct air capture. I think that ultimately though what is going to scale to gigatons, we don’t know the answer of what we have to build, what we’re going to need in order to really go from millions of tons to gigatons.
But what we do know is that there is enough geologic storage in the earth to put that C02 back in the earth. There is absolutely gigatons of storage in the earth in reliable formations that exists, and we know how to do that today. And we know how to do that because of all of the experience we’ve had injecting C02 in the subsurface through enhanced oil recovery. Again, with the first project in 1972, and each year regardless of the fact that it’s mostly naturally sourced C02, the operators have experience injecting C02 in the earth into these formations.
And they’re monitoring the leakage and verification of that storage every year since the start of these projects. So we’ve got about 50 decades of experience putting carbon dioxide in the earth in a safe way. So I think with all of that experience — will lend itself to transitioning from opportunities that are on the millions of tons scale in terms of EOR, to gigaton scale. And gigaton scale is really just dedicated geologic storage projects.
Stone: So you really emphasize the point of that we’ve got enough space underground to store all of this carbon dioxide. And let me ask you an extremely naive question here if I may. I have this image in my head that at some point in the future we’re going to have an earthquake, okay? And a big crack is going to open up in the ground and all of this carbon dioxide is going to escape out. I know it’s not that simple, I know there’s some chemistry behind that, but can you explain to me and to the listeners why that carbon dioxide once it’s in the ground is going to be there permanently? And obviously this is an issue because one of the major concerns is, will this escape. And there’s monitoring that has to go on at these sites, etcetera, to make sure the carbon dioxide doesn’t get out. Why is it permanent, how does it work?
Wilcox: So again, leaning on the expertise and the history of the enhanced oil recovery business really, those sites are fairly safe in terms of reliable, durable storage because they’ve been storing oil and gas for millions of years. And so typically there’s either fault mechanisms or — like so physical faults, or even low permeability cap rocks that have been keeping the oil and gas, and even the natural sourced C02 that I talked about in the Rocky Mountains in the Colorado Basin. They’ve been trapping these fluids in the subsurface for millions of years. And so in those sites in particular, we understand how that storage took place, and we’re simply — to put it simply, taking oil out and putting carbon in.
Stone: And these aren’t just big open spaces underground where there’s just a lot of carbon dioxide, it’s actually mixed into the minerals, into the — if you could explain that for me?
Wilcox: Sure. So a lot of the EOR projects, the formations are greater than 2,000 feet in the earth. So they’re pretty deep. And then the other part is that it’s not like you have these large voids in the earth.
Stone: It’s not a cavern under there.
Wilcox: These are sandstones or carbonate rocks, and the pore spaces within these rocks are — the sizes of the pore spaces are on the order of microns. So like, you know, your hair, one strand of your hair. Very small pores. And they’re dictated really by the grain size of the rock itself. And so it’s all of these little pores that have been storing oil and gas and have these trapping mechanisms, and the C02 will be trapped by those same mechanisms.
Now not all formations that we could sequester C02 in will be depleted oil and gas formations. Some may be saline aquifers in which case more characterization and understanding of those systems needs to take place, which is why there should be more research in this field. It’s not done, because the earth is very heterogeneous and these formations are different. And some of the ones that we don’t know as much about will need more characterization than the ones that we do know a lot about that have been storing oil and gas.
Stone: One of the things that you’ve researched in the past that’s very interesting is this concept of stacked storage. And this being an opportunity to actually take existing oil and gas drilling and production sites, and actually using multiple layers of the subsurface to actually store a whole lot of carbon dioxide. Can you tell us a little more about that? What the opportunity may be, and if there are any limitations?
Wilcox: Sure. So stack storage is really how you just described it, where the formations in the earth are stratified, so there are these different layers. And you could imagine that if you’re an oil operator, that your focus is really about using C02 to enhance the recovery of oil. But the formation doesn’t just have pore spaces that have oil and gas, there’s pore spaces maybe even at different layers in the earth but within the same formation that have only salt water in them.
And so if you have all the expertise in place and the human capital in place to drill wells that recover oil and inject C02, you can also have wells that solely inject C02. One thing I’ll say is that this then leads to the question of, if I store more carbon in the earth than the equivalent carbon of the oil that I get out, what does that mean? Is there such a thing as carbon neutral oil for instance, is that possible?
With this approach, it could be possible. So if you — but keep in mind that it means that you have some dedicated storage of C02 at that site as well. Just from a purely chemical physics perspective, one thing is true, is that if you have original oil in place and you simply want to displace that oil with super critical C02, the carbon atom density of super critical C02 will never be greater than the carbon atom density of the oil. It’s just that’s not the case.
So in order to put more carbon in the ground than carbon that you get out, and by the way, what does that even mean, carbon you get out? There’s energy associated with recovering the oil. You have to refine it, that takes energy. You have to transport it, that takes energy and subsequent carbon emissions. And oh, by the way, what do we do with oil today? We burn it. And we put the C02 back in the air. So all that carbon has to be added up, and in order for that oil to have a neutral footprint, you need to put more carbon than that back in the earth.
Stone: And you say you can’t put that carbon back into the same space and exceed the amount that you took out.
Wilcox: Not in the same space, that’s right. That’s right. So there needs to be pore space in the subsurface dedicated for C02, not for oil
Stone: That would be the stacked storage?
Wilcox: Yeah, that could be stacked storage as a way to think about that. And then there’s the question, what about legacy emissions? So remember we talk about C02 EOR as being a tertiary method of recovery. But the primary method is drilling a well and getting oil out of the ground. But at some point, you know, you have to pressurize the system to push more oil out. So secondary approaches are like water flooding for instance, or thermal approaches, to get more oil out.
And so C02 EOR typically is taking place pretty late in the project, right? So you’ve already -- that formation has already produced a lot of oil. One thing I think would be interesting is to look at if energy companies could kind of quantify, what are the historical emissions associated with that formation, and what would it take to offset those historical emissions.
So many people say, “Oh it’s the energy company’s fault,” you know? And it’s like, well it’s everybody’s fault. We make decisions too, right? Day to day. And it’s like, well imagine — sure, if they were part of the problem, they could also be part of the solution, right? And so through something like stacked storage, we could actually potentially capture historical emissions at a given formation as well which I think would be interesting.
Stone: Jennifer, what’s your take on the recent proposal from Republicans in the House of Representatives to plant a trillion trees to address climate change and remove carbon dioxide from the atmosphere? Is this realistic?
Wilcox: Well, so it’s going to be — going back to there’s going to be — it’s a portfolio. Planting trees is one aspect of a broad range of solutions that we need to tackle, that we need to do all of the above. So just to reiterate, there’s storage in planting biomass for instance, and using that to displace coal-fired power plants with biomass energy coupled to carbon capture and storage. There’s direct air capture of course, there’s mineralization of C02. Like all of these things need to play a role.
And the other thing that we’ve noticed too is recently that some of these things are becoming sources of C02. And we’ve seen that for instance in the bushfires in Australia. And also in the California fires too. And so relying on just one option, and — I think is a gamble, you know? And a safer bet is putting a little bit of investment and deployment in each of these things. There’s not one answer. And that’s why it’s so difficult.
Stone: Some corporations have come out in the last few weeks with some pretty bold pledges to go carbon neutral or carbon negative using some of these technologies and solutions that we’ve spoken about. What’s your feeling about those?
Wilcox: Yeah, it’s amazing. I hope it’s real. So a lot of companies are talking about — most are actually talking about achieving carbon neutrality by a certain timeframe. I think Microsoft is really the one that’s also talking about dealing with its legacy emissions. So one thing we have to keep in mind is that even if your aim is to go carbon neutral, it’s hard. So you have to really think about, well what does that mean?
If you’re an airline, and you want to carbon neutral for instance, are you only talking about the supply chain? For instance, the fuel? That’s a different story. You want carbon neutral fuel, and that’s your goal. But what about all the other aspects that go into that industry, you know? And drawing the box a little bit bigger in terms of the responsibility of the emissions associated with that.
There are sectors that are just very, very difficult to avoid. And transportation fuel is one of them. And biofuels are only going to play so much of a role because the do compete with land for food production. And so we have to really ask this question of, what is it going to take to be carbon neutral. And in the sectors that are difficult to avoid, that’s when negative emissions will probably start to play a more significant role. Of course a company like Microsoft who is pledging to also negate legacy emissions, there’s going to have to be negative emissions projects taking place in order to deal with past emissions, historical emissions.
But even now in companies that are pledging to just go neutral, there are parts of their -- whether it’s energy, whether it’s liquid fuels, that are really difficult. Or even the embodied emissions and materials, the infrastructure of iron and steel and cement. All of these emissions are very, very difficult to avoid. And that’s where negative emissions could also have impact and play a role. But we need to be able to get these projects deployed so that we can learn by doing, and hopefully decrease costs, and deploy more to get to the scale that we need to.
Stone: It sounds like that’s the real key right there, right? Scaling it and doing what we need at this point to make that happen.
Stone: Jennifer, thanks for talking.
Wilcox: Thanks for having me.