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What is the most efficient way to remove CO2 from the atmosphere?

We don’t yet know how carbon removal technologies will compare at scale, and there is probably no one “best” method in all times and places.

 

April 7, 2025

The most important fuel for today’s climate change is the carbon dioxide (CO2) humans are adding to our atmosphere. To stabilize our climate, we urgently need to cut that planet-warming pollution. But maybe you’ve also heard of strategies to pull some of that CO2 back out of the air. Already, people are rolling out carbon removal plans as low-tech as planting more trees, and as involved as building big machines to suck CO2 from the sky.

You might ask: Which of these strategies is the most efficient?

“It’s a very good question with a very simple answer: depends,” says Angelo Gurgel, a principal research scientist with the MIT Center for Sustainability Science and Strategy and the MIT Energy Initiative.

If by “most efficient” we mean “least pricey,” the big CO2-sucking machines are likely not our best bet. These “direct air capture” (DAC) systems use chemical reactions to isolate CO2 from the atmosphere. The CO2 can then be locked away underground for the long term.1

Thanks in part to its high energy demands, DAC is quite costly. To give a rough idea: The operator of the largest DAC plant working today is currently charging individual customers $1,000 per ton of CO2 removed from the air.2

As DAC matures, the price is expected to fall—perhaps in the not-too-distant future, as multiple plants are in various stages of planning and construction. But just how far the price can come down is hotly debated. Some scientists are optimistic that DAC could one day capture CO2 for $100-$300 a ton;3 in their research, Gurgel and his colleagues conclude that $380-$660 is a more plausible range.4

There are cheaper ways to take CO2 out of the air. One possibility, Gurgel says, is bioenergy with carbon capture and sequestration (BECCS). BECCS relies on the power of plants to absorb CO2 as they grow. Normally, that CO2 would just reenter the air when the plants die and decompose, but BECCS has a technological workaround. The plant material is used to make electricity or fuels, and the CO2 released by those processes is captured and stored underground.

Like DAC, BECCS is in its infancy, but there are good reasons to think it could be cheaper. For one thing, it’s a lot easier to pull CO2 from a concentrated stream, as you would with BECCS, than to extract it from the air. It’s hard to know how much BECCS would cost at scale, but research by Gurgel and his colleagues suggests it could eventually remove CO2 from the air for $260 a ton or less.4

But in another way, BECCS may be far less efficient than DAC. Growing crops for BECCS takes a lot of land. At the scale needed to make a dent on climate change, the space might be hard to find—and clearing it can pose risks for natural ecosystems, or drive up food prices if other crops get pushed out.

Can we get more cost-efficient still? Among the cheapest strategies, Gurgel says, are tree-planting and storing carbon in farm soils. At the lowest estimates, these methods could eventually cost just dollars per ton of CO2.3 But they add a new trade-off: Making sure the carbon stays put is a challenge. For instance, if we plant a new forest to absorb CO2, but then disease or wildfire kills those trees, the carbon goes right back into the atmosphere.

There are also costs that are harder to measure than dollars or acres of land. Consider enhanced rock weathering, which aims to speed up the slow, natural Earth process that moves carbon from the air and stores it in minerals. A common approach is to crush rocks and spread them out, accelerating the chemical reactions that draw down CO2. As with all kinds of carbon removal, it’s not clear what enhanced weathering would cost on a large scale, but Gurgel’s research suggests it could be cheaper than DAC and probably doesn’t need as much dedicated land as BECCS.

But although enhanced weathering may turn out to be both reasonably cost-efficient and reasonably land-efficient (at least by carbon removal standards), it’s not very rock-efficient. When Gurgel and his colleagues modeled a scenario that used a mix of removal options to control climate change, they found that their model eventually called for mining 25 billion tons of rock a year for weathering: about three times the world’s coal production today.4 Researchers are also unsure of the environmental and health effects of mining and spreading so many rocks.5

The best carbon removal strategy, Gurgel believes, isn’t a single strategy at all—it’s a mix. According to his model, using several options keeps costs down while limiting pressure on land and energy resources.4 That flexibility also means countries and regions can think locally—How much land is available for BECCS? How cheap is clean electricity for DAC?—and pursue the strategy that makes the most sense for them.

Plus, many of these strategies are in their infancy, and gauging how they will evolve over time is challenging. Keeping our options open hedges against uncertainty, Gurgel says. “It’s like in the financial sector. A diversified portfolio is much safer than a concentrated investment in one or a few assets.”

And, lest we forget, the most important investment in that portfolio is not CO2 removal at all; it’s keeping climate pollution out of the air in the first place.6 If we’re building large amounts of new clean energy, using it to power DAC has to be measured against using it to… well, run our homes and businesses on clean energy. If we care about forests as a climate solution, planting new trees has to be compared with protecting those we already have. In the search for the most efficient measures to deal with climate change, Gurgel says, we are still far from the point where CO2 removal of any kind is the cheapest or easiest option.

 

Thank you to Stephen Anthony Murphy of London, U.K., for the question.

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Footnotes

1 Gambhir, Ajay, and Tavoni, Massimo. “Direct air carbon capture and sequestration: how it works and how it could contribute to climate-change mitigation.” One Earth 1 (2019). https://doi.org/10.1016/j.oneear.2019.11.006.

2 “CO2 removal plans for individuals.” Climeworks. (2025). Accessed 27 March 2025.

3 Fuss, Sabine, et al. “Negative emissions—part 2: costs, potentials and side effects.” Environmental Research Letters 13 (2018). https://doi.org/10.1088/1748-9326/aabf9f. 

4 Chiquier, Solene, et al. “Integrated assessment of carbon dioxide removal portfolios: land, energy, and economic trade-offs for climate policy.” Environmental Research Letters 20 (2025). https://doi.org/10.1088/1748-9326/ada4c0.

5 See, e.g.: Levy, Charlotte, et al. “Enhanced rock weathering for carbon removal—monitoring and mitigating potential environmental impacts on agricultural land.” Environmental Science & Technology 58 (2024). https://doi.org/10.1021/acs.est.4c02368. 

6 See, e.g.: Zickfeld, Kirsten, et al. “Net-zero approaches must consider Earth system impacts to achieve climate goals.” Nature Climate Change 13 (2023). https://doi.org/10.1038/s41558-023-01862-7; Ho, David T. “Carbon dioxide removal is not a current climate solution—we need to change the narrative.” Nature 616 (2023). https://doi.org/10.1038/d41586-023-00953-x; Dooley, Kate, et al. “Carbon removals from nature restoration are no substitute for steep emission reductions.” One Earth 5 (2022). https://doi.org/10.1016/j.oneear.2022.06.002.

Madison Goldberg
by Madison Goldberg, MIT Climate Portal Writing Team
Angelo Gurgel
featuring guest expert Angelo Gurgel, Principal Research Scientist, MIT Center for Sustainability Science and Strategy and MIT Energy Initiative
Related MIT Groups
More Resources for Learning
MIT Climate Portal: "How much carbon dioxide would we have to remove from the air to counteract climate change?"
MIT News: "Smart carbon dioxide removal yields economic and environmental benefits"
National Oceanic and Atmospheric Administration: "Carbon dioxide removal: NOAA State of the Science factsheet"
Stephen M. Smith et al.: "The State of Carbon Dioxide Removal 2024—2nd Edition"
David T. Ho, Nature: "Carbon dioxide removal is not a current climate solution—we need to change the narrative"
Topics
Carbon Removal

Want to learn more?

Listen to this episode of MIT's "Today I Learned: Climate" podcast on carbon dioxide removal.

LHF: [00:00:00] Hello, and welcome to Today I Learned: Climate, the show where you learn about climate change from real scientists and experts. I’m your host Laur Hesse Fisher of the MIT Environmental Solutions Initiative. We’ve had people ask us, OK, if climate change is caused by adding too much CO2 in the atmosphere, can we just suck it back out? Won’t that solve our climate change problem?

To answer this question, we spoke with someone who would know.

NM: [00:00:27] My name is Niall Mac Dowell. I'm a professor at Imperial College London, and I've been working for carbon management for about 15 years, particularly, recently, with a focus on greenhouse gas removal, or taking CO2 out of the atmosphere.

LHF: [00:00:40] Prof. Mac Dowell shared with us that this is actually pretty tricky to do at a large scale.

To understand why… well... think about the sky. Maybe you can even see it right now. That’s our atmosphere, and even though you can’t see them, there’s a whole mix of gases swirling around up there: nitrogen, oxygen, argon, water vapor … and CO2 is just one of them.

 So Prof. Mac Dowell asked us to imagine that each molecule of CO2 in the atmosphere is a red marble, and every other molecule is a blue marble.

NM: [00:01:19] So if you imagine a bucket of marbles and if we have a hundred marbles and all of the marbles are red and you're given the task of getting five red marbles. It's already easy. You just grabbed five red marbles. There's no work to do.

 If we imagine now the atmosphere, the air, it's not a hundred marbles, it's a million marbles and of this million, only about 400 of them are red, and everything else is blue. So you can spend a lot of energy, you will have to do a lot of work to search through all the blue marbles to find the red marbles. [skip] For every million tons of CO2 that you want to recover from the atmosphere, you will have to handle — you have to physically move — between 5 and 7 billion — with a B — tons of air, and a ton of air is as heavy as a ton of rock. So it's a big effort.

LHF: [00:02:10] Wow. So, is this really possible?

NM: [00:02:14] Yeah, sure. It's technically eminently feasible. As we've discussed, it requires a lot of energy, it takes a lot of work, to sort through all of the atmospheric marbles to find the carbon, but you can totally do it.

LHF: [00:02:29] And, in fact, people are doing it. Or, at least, trying it out. The technology is called “direct air capture,” because you’re capturing CO2 directly out of the air. There’s a company with three facilities in Europe, there’s a different company with one up in Canada, there’s an oil company testing it out in Texas.

NM: [00:02:50] Every time I turned around, there's news of some, somebody else, you know, proposing a DAC pilot, pilots can come in many shapes and sizes.

LHF: [00:02:59] So if I were to tour the facility, what would it look like?

NM: [00:03:03] When this has been trialed in different places — you're  talking about a bank of units, a bit like shipping containers. So say, you know, two meters by two meters, this kind of thing. And that has a big fan on it, and that fan is sucking air through and it's just sucking the air through and blowing it over some kind of contactor, which will react with the CO2 and that's directly pulling the carbon out of the atmosphere.

LHF: [00:03:28] What is the contactor? Is that a chemical solution of some kind?

NM: [00:03:33] Yeah. So very simply CO2 is an acid. So, whatever you want it to react with, will want to be some kind of base or a caustic or an alkaline material.

LHF: [00:03:44] OK so you have this, like, chemical solution that acts like a sponge, pulling out the CO2 from the air. But then, you gotta wring the sponge and get the CO2 out.

NM: [00:03:56] So you do that simply by adding energy. So if it's in the liquid form, you have to effectively boil it out. And this allows you to recover a pure string of CO2, which you can compress, transport and store.

LHF: [00:04:09] Once you have all this extracted CO2, you have to put it somewhere where it won’t go back up in the atmosphere.

NM: [00:04:17] So this is typically underground. In Texas, for example, people are talking about having direct air capture technologies to directly transport the CO2 into oil fields that are right nearby.

LHF: [00:04:29] If you want to know more about storing CO2 underground or using it to produce other things like building materials, check out our episode 7 from season 2 on carbon capture, which is about capturing the CO2 out of the smokestacks of manufacturing and power plants.

But shipping containers with big fans isn’t the only idea we have to take CO2 out of the atmosphere.

NM: [00:04:54] So. The important thing about greenhouse gas removal or carbon dioxide removal is that it's a portfolio of different approaches, some of which rely on engineered technologies — so this is direct air capture or some forms of what's known as enhanced weathering, so that's reacting CO2 with crushed rock, or bioenergy with carbon capture and storage pathways — so that could be turning biomass into heat, power, mobility, and then you capture whatever CO2 you can.

There are ways in which we can improve and change the management of our natural environment. So one good example of that, one really important example of that, is afforestation. So turning a landscape into a forest and carbon sink, and similarly changing the way in which we manage peatlands wetlands, wetland restoration.

LHF: [00:05:49] Put a pin in those last two —in our next episode, we’ll talk all about using forests to take CO2 out of the atmosphere.

Okay, let’s back up. The bottom line is that it really is possible to take CO2 out of the air. And that’s… sort of an intoxicating thought. Because if there’s one thing we’ve seen on this show, it’s that stopping our CO2 emissions [which Prof. Mac Dowell is going to call “mitigation,” “mitigating climate change”] requires us to change the way we get energy, the way we build, the way we travel, the way we grow food. So is carbon removal the easier way out of climate change?

NM: [00:06:32] In my personal opinion? No.

Greenhouse gas removal through any pathway, whether it's direct air capture, bioenergy with CCS, afforestation, or any other options, is not an alternative to mitigation.

LHF: [00:06:47] Why is that?

NM: [00:06:49] Very simply, most mitigation will be cheaper, just simply more cost-effective than greenhouse gas removal.

We are at, I think, the very early days of developing direct air capture technology. You know, the basic science is sort of there, right? We know how to capture the CO2.

The problem is that what we need to do is be actively removing lots of CO2 at the million tons per year scale minimum.

I mean, the analogy I think is that it's a bit maybe like saying we need to be able to break the sound barrier and Orville and Wilbur right now just managed to get their, you know, the first plane flying for 10 meters or whatever it was, you know, that's sort of where we are.

So it's far too early to rule anything out, but putting all your faith in the manifestation of some kind of technical unicorn, which will very, very cheaply reverse the impact of climate change, I think is brave. And I wouldn't do it.

LHF: [00:07:53] And this is the central challenge with carbon removal. If you look at it as an economist would -- how much it costs to remove or avoid a ton of CO2 --- direct air capture isn’t yet cheaper than pretty much any other option: building wind and solar, even capturing and storing CO2 from smokestacks is cheaper.

 So if it’s so expensive to take CO2 out of the atmosphere, and so much cheaper to avoid putting it there in the first place, why invest in CO2 removal at all? Well, it’s because a whole lot of CO2 has already accumulated in the atmosphere, and that CO2 is going to be warming the Earth for a long time—so we will need to remove it if we’re going to keep global warming in check.

In fact, almost every scenario scientists have come up with for how to keep global warming at relatively safe levels has large-scale carbon removal by the end of the century as one of the key tools in our toolkit.

NM: [00:08:57] We have to mitigate as fast as we can with every tool in our arsenal. And we will also very likely have to think about greenhouse gas removal options as well.

We will need everything. We need renewable energy. We need fuel switching. We need nuclear power. We need demand reduction. We need carbon capture and storage, and we will need all forms of greenhouse gas removal as and when they get going.

LHF: [00:09:24] We’re going to stay on this subject in our next episode, and talk about another way to suck out that CO2, using nature. But for now, I want to thank Prof. Mac Dowell for joining us, and remind you that you can always check out our website or Twitter @TILclimate for a bunch of resources we’ve pulled together: fun facts, other websites, our sources, and educator guides so teachers can use this podcast to introduce climate change in the classroom. As always, email us your questions at tilclimate@mit.edu, and thanks for listening.

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