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Greenhouse Gases

Sucking carbon dioxide from air in Iceland

The world’s largest direct-air-capture plant opens, but questions remain about its value

by Alex Scott
June 3, 2024 | A version of this story appeared in Volume 102, Issue 17
A low, gray building with a mountain of volcanic rock in the background.

Credit: Halldor Kolbeins/Getty Images | Climeworks has built its new Mammoth plant next to a geothermal energy facility in an active volcanic area of Iceland.


In brief

The Swiss company Climeworks has started up the world’s largest direct-air-capture (DAC) facility, in Iceland. The company mounts solid amine-containing compounds in containers to remove up to 36,000 metric tons (t) of carbon dioxide from the air each year. It dissolves the captured CO2 in water and pumps it underground, where it reacts with basalt rock to form a solid carbonate material. Climatologists agree that we need to take billions of metric tons of CO2 out of the atmosphere annually by 2050 to help prevent runaway climate change. But some climate experts say investing in DAC is less cost effective than investing in renewable energy to replace fossil fuels and thus prevent CO2 emissions in the first place. Nevertheless, Climeworks and a raft of other companies are attracting substantial funding for DAC projects. The new plant in Iceland will go some way toward demonstrating whether the technology can work at scale.

Blizzard-whipped glaciers, lava-spewing volcanoes, kilometer upon kilometer of rough, black basalt rocks, and almost constant darkness in winter. This is Iceland, the location of the world’s first industrial-scale plant to suck carbon dioxide from the air and store it underground. Last month, with this winter’s snow barely melted, the Swiss company Climeworks started up the facility, saying it can remove 36,000 metric tons (t) of CO2 every year.

The company is using an approach known as direct air capture, or DAC, which strips air of CO2, a greenhouse gas present in the atmosphere at just 0.04%. Other carbon capture methods go after emissions from factories and power plants, which contain CO2 at higher concentrations. Climeworks’ co-CEO and cofounder Jan Wurzbacher says society needs to remove about 10 billion t of CO2 from the air annually by 2050 to help prevent runaway climate change.

The new plant, located on the Hellisheiði lava plateau and called Mammoth, is the first in the world to remove CO2 from the air on a large scale. In all, Climeworks aims to remove 1 billion t of the greenhouse gas annually in 25 years.

“We have started scaling up now . . . because otherwise we won’t have any chance by 2050 to remove that much,” Wurzbacher told journalists during a recent tour of the plant.

But not everyone accepts DAC’s effectiveness at combating climate change. Some climate experts say we would do better for the climate by taking the money needed to build and run a DAC plant and spending it on renewable energy instead.

More than 100 companies around the world are developing DAC technology. All of them still have much to prove. A failure by the Iceland plant to perform to Climeworks’ expectations would set back adoption of DAC. Although scientists are developing a plethora of other CO2 removal technologies, none appear to match DAC’s combination of scalability and investor commitment.

Climeworks’ technology

Iceland may be the best place in the world to build a DAC plant. Some parts of the country, a small, volcanic island in the middle of the Atlantic Ocean and close to the Arctic Circle, are inhospitable. Known as the Land of Ice and Fire, Iceland is blessed with an abundance of geothermal energy. It also is mostly made of basalt rock, which turns out to be an ideal medium for storing CO2.

Climeworks marries Icelandic geology with what it says is cutting-edge technology for extracting CO2 from the air and locking it underground.

A long pipe extends away from the viewer and turns at a right angle; two pipes snake toward the viewer to the right. In the background is a mountain of volcanic rock.
Credit: Heida Helgadottir/Bloomberg via Getty Images
The Mammoth plant uses geothermal energy to capture carbon dioxide, which is then injected into water before being pumped underground.

Like many other DAC companies, Climeworks uses amine compounds, which are weak bases, to adsorb the slightly acidic CO2. But whereas some firms pump CO2 into an aqueous amine solution, Climeworks captures CO2 on a solid, granular material to which the amines—which the company isn’t disclosing—have been covalently bonded. It has added channels in the granular material to create a large surface area where the contact can occur.

“Think of it as a sponge, a highly porous material with a high internal surface area,” Wurzbacher said. The 12 amine-holding containers that are already set up in Hellisheiði collect a total of around 600 kg of CO2 per hour. The whole facility is powered by electricity from an adjacent geothermal energy plant.

One of the more dramatic features of the Iceland facility is the array of giant fans on the back of the containers. Because CO2 is present in the atmosphere at a concentration of only about 421 ppm, the fans are needed to pull air into the containers to create sufficient contact with the amines.

“They suck in air for about an hour and a half. Then the door closes, it seals, and then we send steam through a filter to regenerate that filter and sweep the CO2 out,” Doug Chan, Climeworks’ chief operating officer, said as he shepherded a group of journalists out of the cold and into the new plant. Inside was a maze of pipes, pumps, and compressors. One of Chan’s responsibilities is to ensure that the Mammoth facility is running at full capacity with the installation of a further 60 amine containers by year-end.

Once the CO2 has been captured, it is separated from the steam, cooled, and purified. The gas is then temporarily held in a giant balloon suspended between the facility’s ceiling and the separation equipment. From here, Carbfix, an Icelandic technology firm, takes over, injecting the 99.99% pure CO2 into water under 20 bar of pressure.

The inside of a factory with a large, cylindrical balloon near the ceiling and above a long pipe.

Credit: Alex Scott/C&EN
Captured carbon dioxide is separated from steam, cooled, and purified and temporarily placed in a large buffer balloon before being injected into water.

“This is about four times the pressure that you would inject CO2 into water in your home SodaStream,” said Bergur Sigfusson, chief system development officer at Carbfix. Unlike in a carbonated drink, the CO2 is fully dissolved, and no bubbles emanate from the water, he said. About 20 t of water is required to dissolve 1 t of CO2.

Just outside the Climeworks plant, the CO2-rich water is pumped 350 m underground through a steel pipe. Beyond the pipe, the well hole extends a further 350 m. Once underground, the water finds its way into myriad pores and cracks in the volcanic basalt rock.

A large pipe extends from the ceiling of the facilty to the floor.
Credit: Alex Scott/C&EN
Pipes engineered to expand and contract in the extreme Icelandic climate bring steam to the Mammoth plant from a nearby geothermal facility.

Because the water is rich in CO2, it is denser than the surrounding water and has no tendency to rise. It is also slightly acidic and dissolves some of the calcium, magnesium, and iron compounds in the rock to form a solution. This solution slowly reacts with the CO2 and within 2 years forms solid carbonate materials, said Sandra Ósk Snæbjörnsdóttir, chief scientist at Carbfix. “And then we have locked the CO2 away for millennia.”

Snæbjörnsdóttir codeveloped the sequestration process in 2016 alongside scientists including the late Wallace S. Broecker, a professor of geology at Columbia University who is credited with coining the phrase global warming.

The Mammoth project is the biggest test yet of Carbfix’s technology. “We are achieving a thousandfold scale-up already in a couple of years,” Snæbjörnsdóttir said. Unlike in some gas-phase CO2 storage systems, no plug or caprock is required to contain the CO2. The storage capacity of the basalt underneath the Climeworks plant is “unlimited,” said Ólafur Elínarson, Carbfix’s head of communications and community.

Water for the process is circulated back into the Climeworks facility. “We measure the concentration of CO2 in this water continuously,” Sigfusson said. Carbfix also uses computer models to understand where the CO2 is underground.

The Climeworks-Carbfix process has secured third-party verification from the environmental auditing firm DNV. “That is really important because we don’t want this to turn out to be like the wild, wild west with anybody saying, ‘Hey, I’m burying CO2 by this method,’ ” Elínarson said.

Climeworks’ ambition to be the first to scale DAC has echoes of Tesla’s push to mainstream electric vehicles, Chan said. He should know: until 2022, Chan was a manufacturing director for the car company. Chan said he joined Climeworks because of his desire to solve a new set of “difficult problems with the objective of scaling and creating a new global industry.”

The company’s goal of capturing 1 billion t of CO2 annually will doubtless present Chan with plenty of problems, not least because it would require 27,778 plants the size of Mammoth. But co-CEO and cofounder Christoph Gebald said that Climeworks and the wider DAC industry are already planning a series of DAC plants much bigger than Mammoth and that as soon as 2030, the nascent DAC sector will require up to 25 GW of renewable energy—equivalent to about 3% of the world’s clean energy capacity.

We are achieving a thousandfold scale-up already in a couple of years.
Sandra Ósk Snæbjörnsdóttir, chief scientist, Carbfix

Advancing amine chemistry

Climeworks is banking on improving its amine sorbents’ selectivity to help it increase CO2 capture without new capacity or additional energy. Each container currently captures about 500 t per year of CO2. By replacing the granular sorbents the company uses today with structured sorbents, it will be able to double its CO2 collection capacity, Wurzbacher said.

“This is because those structured adsorbents are much faster in both adsorption and desorption,” he said. Climeworks has about 500 employees, of which 30 are chemists working on different aspects of sorbents, including synthesis, scale-up, characterization, emissions, and quality, the company says.

A worker kneels in front of a panel with multiple huge fans mounted on it.
Credit: Climeworks.
Climeworks has attached huge fans to its containers to increase the number of carbon dioxide molecules coming into contact with its amine compounds.

Industry has been using aqueous monoethanolamine (MEA) for many years to remove CO2 from the smokestacks of industrial plants and has great potential for use in DAC, according to a 2023 study led by Ahmed Sodiq of Hamad Bin Khalifa University. BASF is one of the biggest suppliers of MEA for capturing CO2 from smokestacks, but the German firm says it does not have DAC companies among its customers.

Many DAC developers around the world are now advancing plans to commercialize their technologies based on a variety of liquid or solid sorbents, including amines. Radically different sorbent chemistries are also emerging, such as a peptide-guanidine system that can be regenerated with mild heat. Radu Custelcean and colleagues at Oak Ridge National Laboratory are developing that approach.

The Canadian DAC firm Carbon Engineering, purchased in 2023 by Occidental Petroleum for $1.1 billion, has developed an aqueous potassium hydroxide sorbent that reacts with CO2 in the air to form carbonate salts, which are then sent to a calciner to energetically release the CO2. “However, this regeneration energy is huge, and it is what makes solid sorbent application in DAC more attractive than the liquid-based sorbents,” Sodiq and colleagues say in his study. Aqueous MEA also has the potential to consume less thermal energy in regeneration than aqueous hydroxides, the authors say.

Unlike Climeworks, Carbon Engineering is considering using its captured CO2 as a raw material, combining it, for example, with green hydrogen to produce synthetic fuels for airlines. Carbon Engineering is also looking at using CO2 from DAC to push oil and gas out of depleted wells, a practice called enhanced oil recovery.

Other DAC developers have yet to put all their efforts into one sorbent. The US firm CarbonCapture claims its technology can accommodate a variety of amines, metal-organic frameworks, and other novel materials that can be fitted in sorbent cartridges that permit fast and easy upgrades. The company disclosed in March that it had raised $80 million in series A financing from investors, including Amazon’s Climate Pledge Fund and Aramco Ventures.

The cost problem

Our climate and CO2

For a 50% chance of limiting global warming to 1.5 °C above preindustrial levels, total carbon dioxide emissions from fossil fuels from now to 2050 must be limited to 250 giga-metric tons (Gt). The world is currently emitting almost 40 Gt per year. Thus, other levers will be required.

Carbon lever: Agriculture

Mitigation method: Make changes to agriculture, forestry, and food production.

Potential annual change in carbon emissions (Gt): +4 to –5

Carbon lever: Land biosphere

Mitigation method: Ensure nature on land is intact.

Potential annual change in carbon emissions (Gt): –11

Carbon lever: Ocean biosphere

Mitigation method: Ensure stable oceans.

Potential annual change in carbon emissions (Gt): –11

Carbon lever: CO2 removal technologies

Mitigation method: Deploy carbon capture and storage.

Potential annual change in carbon emissions (Gt): –5 to –10

Sources: Climeworks; Intergovernmental Panel on Climate Change; Nat. Clim. Change 2023, DOI: 10.1038/s41558-023-01848-5.

One of the sector’s biggest challenges remains the development of a sorbent that enables the capture and storage of CO2 at a low cost and with minimal energy consumption. Building the Mammoth plant itself cost more than $100 million; capturing and storing CO2 adds around $600 for each metric ton. Climeworks aims to bring that figure down to $300 by 2030 and $200 by 2050.

To meet its cost-of-production goals, Climeworks aims to improve its amine chemistry, automate the construction of its containers, and use economies of scale, Wurzbacher said. Even then, the company’s capture cost will be well above the current price of CO2 emission allowances of less than $100 per metric ton of CO2 under the European Union’s Emissions Trading System. The program is considered one of the best indicators today of the price of carbon.

Despite the high cost of capture and storage, Climeworks is already attracting customers. It has sold credits for one-third of the CO2 that the new plant will capture over its 25-year lifetime to companies including Microsoft, Lego, and the Swiss watchmaker Breitling. More than 20,000 private individuals have also purchased CO2 removal credits from Climeworks.

The market for DAC is likely to strengthen as policymakers seek to accommodate carbon capture technologies. California is mulling legislation that would require heavy polluters to purchase a certain amount of carbon removal, and European legislators are considering incorporating carbon removal into the Emissions Trading System, Gebald said.

DAC doubters

Although Climeworks has been able to attract leading brands as customers, some climate experts and environmental organizations say DAC is counterproductive in the fight against climate change. “Despite the fact that many countries are incorporating technofixes like direct air capture into their net zero plans, it is far from certain that they could ever scale to meet such demands, or more importantly, whether they even should,” the environmental organization OceanCare says in a recent press release that singles out Climeworks.


“DAC is counterproductive,” Mark Z. Jacobson, a professor of civil and environmental engineering at Stanford University, said in a 2023 CleanTech Talk podcast episode hosted by CleanTechnica. Jacobson calculates that the overall energy, health, and climate costs of DAC are six to seven times as great as those of simply replacing fossil fuels with renewable electricity.

“It’s not even close,” he said. “So long as we have a source of combustion—or any source of CO2 that can be replaced or fixed with renewable electricity—direct air capture is useless. It has no benefit whatsoever.” Jacobson said he suspects that DAC is advancing so readily, despite evidence that it does not have a net benefit, because of lobbying by the oil and gas industry.

Wurzbacher acknowledges that DAC could be in competition for renewable energy in some locations, but at other sites—such as in Iceland—he does not see a conflict.

But even in Iceland, DAC uses renewable electricity that could be replacing fossil fuels, Jacobson tells C&EN in an email. “Iceland still uses lots of imported coal for industry, and that coal use is increasing. 1 kWh of geothermal electricity replacing coal reduces 3–7 times the CO2—from coal mining and combustion—as the exact same 1 kWh of geothermal electricity running DAC,” he writes.

The US policy think tank Alliance for Innovation and Infrastructure says it is more prudent to capture carbon from point sources than from air and says any captured carbon would be better used in a product rather than stored underground. “It doesn’t make sense to lock away the carbon when you can use it for other things, like our infrastructure,” says Benjamin Dierker, the alliance’s executive director.

So long as we have a source of combustion—or any source of CO2 that can be replaced or fixed with renewable electricity—direct air capture is useless. It has no benefit whatsoever.
Mark Z. Jacobson, professor of civil and environmental engineering, Stanford University

In the right locations and in optimal applications—such as the production of CO2-consuming concrete—CO2 from DAC could be mineralized to provide clear environmental and financial benefits, says Diego A. Santamaria Razo, who covers low-carbon technologies for Boston Consulting Group. Such concrete could complement standard concrete and reduce its associated CO2 emissions, Santamaria Razo says, noting that an average European plant producing 800,000 t of cement annually might emit about 700,000 t of CO2. There is no single technology that will solve the CO2 problem on its own, but DAC could contribute, Santamaria Razo says. “It’s just one of the many solutions that should be available.”

Wurzbacher has nothing against such concepts, but he argues that underground sequestration is necessary because other applications have yet to show they can be scaled. “I don’t see an application adding value, to be honest, at the level of 10 gigatons per year,” he said. Meanwhile, capturing CO2 and using it to make plastics or aviation fuel adds value but does not remove CO2 permanently from the atmosphere, he said.

Likewise, Wurzbacher said, the world’s efforts to reduce emissions from power plants, the steel and cement industries, vehicles, and the like are not enough. That is also the finding of a 2022 report by the Intergovernmental Panel on Climate Change. It states that we need to actively remove between 3 billion and 12 billion t of CO2 from the atmosphere every year by 2050 in addition to making unprecedented emission reductions.

Thirty years ago, emission reduction would have been the way to go. “But today we are already here,” Wurzbacher said. The global climate has warmed on average by 1.48 °C since the late 19th century.

DAC projects grow

Despite questions about the benefits of DAC, adoption appears to be underway. Climeworks and other companies are already seeking to establish DAC plants around the world that are substantially larger than the one in Iceland. Test projects are operating in Canada, Europe, Kenya, and Oman. In the US, Climeworks is studying projects in Louisiana, North Dakota, and California and is on course to secure between $500 million and $600 million under the government’s Inflation Reduction Act (IRA).

Direct Air Capture
How the full process from CO2 capture to storage works in Iceland.
A diagram shows that a geothermal power plant provides electricity and steam to a direct-air-capture facility, which uses a filter to separate carbon dioxide from ambient air. Steam and CO2 go from the filter to the rest of the plant, and then CO2-rich water undergoes high-pressure pumping and is sent underground, where it is turned into stone.
Credit: Yang H. Ku/C&EN/Shutterstock

Occidental has secured $500 million from the IRA fund to build a DAC hub in south Texas. A further 19 early-stage DAC projects have secured lower levels of funding from the IRA. Under the Bipartisan Infrastructure Law, the US has also agreed to provide companies with $3.5 billion to scale DAC.

A shadow over Climeworks’ ambition to make Iceland a DAC and CO2 storage hub is that the hot rocks providing the company with its geothermal energy also come with a threat. Climeworks’ Hellisheiði site sits in an area of volcanic activity, close to a fault line in the earth’s crust. A few weeks before the facility started up, a volcanic eruption along a fault line west of Hellisheiði released lava that forced all 3,000 inhabitants of the town of Grindavík to evacuate.

But Climeworks’ immediate concern is to build out the facility and run it efficiently. With an abundance of geothermal energy, the potential for CO2 storage, and a growing concentration of technical expertise, Iceland may well be the best place in the world for DAC. If the technology cannot prove its worth there, it may not be worth building anywhere.


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