Direct Air Capture: Can Machines Scrub the Sky Clean?

01 The Chemistry of Pulling Carbon From Thin Air

Direct air capture (DAC) is the use of chemical or physical processes to extract carbon dioxide directly from ambient air. If the extracted CO2 is then sequestered in safe long-term storage, the overall process is called direct air carbon capture and sequestration (DACCS), achieving carbon dioxide removal. Systems that engage in such a process are referred to as negative emissions technologies.

The fundamental challenge is one of concentration. Atmospheric CO2 currently sits near 420 parts per million, meaning that for every million molecules of air, only about 420 are CO2. To capture one ton of carbon dioxide, a DAC facility must move roughly two thousand tons of air through its collectors. This dilution problem is the central engineering hurdle that distinguishes DAC from point-source carbon capture, which intercepts concentrated exhaust gases at industrial smokestacks.

Two dominant technical approaches have emerged. Liquid solvent systems use aqueous hydroxide solutions to chemically bind CO2, releasing it when heated to roughly 900 degrees Celsius. Solid sorbent systems use amine-functionalized filter materials that adsorb CO2 at ambient temperature and release it when heated to around 100 degrees Celsius. Each method trades energy intensity against capture efficiency, and the choice between them shapes the entire cost structure of a DAC plant.

02 Why Dilution Makes Everything Expensive

Carbon dioxide removal (CDR) is a process in which carbon dioxide is removed from Earth's atmosphere by deliberate human activities and durably stored in geological, terrestrial, or marine reservoirs, or in products. CDR is increasingly integrated into climate policy as an element of climate change mitigation strategies. Achieving net zero emissions will require first and foremost deep and sustained cuts in emissions, and then, in addition, the use of CDR.

The thermodynamic penalty of working with dilute CO2 is severe. While point-source capture deals with flue gas at 10 to 15 percent CO2 concentration, DAC operates at 0.04 percent. The energy required to separate a gas scales inversely with its initial concentration, which means DAC demands substantially more energy per ton captured than any smokestack system. Industry estimates place the energy cost of DAC between 8 and 12 gigajoules per ton of CO2, compared to 2 to 4 gigajoules for post-combustion point-source capture.

This energy budget translates directly into cost. Current DAC prices range from 600 to 1,000 dollars per ton of CO2, though companies like Climeworks project costs falling to 200 to 300 dollars per ton as plants scale. By comparison, nature-based solutions such as reforestation can sequester carbon at 20 to 50 dollars per ton. The gap is narrowing, but it remains the most significant barrier to deployment at climate-relevant scales.

03 The Plants Already Running

Climeworks AG is a Swiss company specializing in direct air capture and sequestration technology. The company's plants filter CO2 directly from the ambient air through an adsorption-desorption process that removes CO2 from the air permanently. Their Orca facility in Iceland, operational since 2021, was the world's first commercial DAC plant, with a nameplate capacity of 4,000 tons of CO2 per year. The larger Mammoth facility, brought online in 2024, targets 36,000 tons annually at full capacity.

These Icelandic plants leverage geothermal energy and partner with the Carbfix mineralization project, which injects dissolved CO2 into basalt formations where it mineralizes into solid carbonate rock within approximately two years. This geological permanence is a critical advantage over biological storage, which can re-release carbon through fire, decay, or land-use change.

Other players include Carbon Engineering, a Canadian firm whose liquid solvent system is being commercialized through partnerships with Occidental Petroleum. Their plants in the Permian Basin of Texas aim to capture up to 500,000 tons annually, though some captured CO2 is used for enhanced oil recovery rather than purely sequestration. This dual-use pathway has drawn criticism from climate advocates who question whether DAC serves as a genuine climate tool or a production subsidy for fossil fuel extraction.

04 The Energy Math That Decides Everything

The energy source powering a DAC plant determines whether it achieves net-negative emissions or merely relocates carbon from a smokestack to the atmosphere. A DAC facility running on fossil grid electricity could consume more carbon in its energy supply than it captures from the air, producing a net-positive emissions outcome. This is why the geographic siting of DAC plants is not incidental but existential.

Iceland's geothermal basalt combination offers an ideal pairing: abundant clean energy and reactive rock for mineralization. The United States Permian Basin offers abundant solar and wind resources but also a fossil fuel infrastructure that complicates the climate narrative. Companies must demonstrate that their energy supply is additional, meaning new renewable capacity built to serve the DAC plant rather than diverted from grid decarbonization.

The scale question compounds the energy question. Removing one gigaton of CO2 per year, roughly 2.5 percent of current annual emissions, would require approximately 8 to 12 exajoules of energy annually. That is comparable to the total electricity consumption of the European Union. DAC at climate-relevant scale is not a small add-on to the energy system; it is a parallel energy system in its own right.

05 Carbon Capture and Storage: The Sibling Technology

Carbon capture and storage (CCS) is a process by which carbon dioxide from industrial installations or natural sources is separated before it is released into the atmosphere, then transported to a long-term storage location. The CO2 is captured from a large point source, such as a natural gas processing plant, and is typically stored in a deep geological formation. Around 80 percent of the CO2 captured annually is used for enhanced oil recovery, a process by which CO2 is injected into partially depleted oil reservoirs to extract more oil and is largely left underground.

CCS and DAC are frequently conflated in public discourse but serve fundamentally different functions. CCS prevents emissions from entering the atmosphere by intercepting concentrated industrial exhaust. DAC removes CO2 that has already dispersed, addressing historical and distributed emissions. CCS is cheaper per ton but cannot address the vast majority of emissions from transport, agriculture, and buildings, which are diffuse and not amenable to point-source capture.

The enhanced oil recovery linkage is the political fault line. When captured CO2 enables additional oil extraction, the net climate benefit depends on whether the oil produced displaces dirtier supply or adds to total consumption. Climate advocates argue that EOR-linked capture is a subsidy for continued fossil extraction dressed in climate language. Industry argues that using captured CO2 productively accelerates the learning curve for capture technology before pure storage markets mature.

06 Policy, Markets, and the Voluntary Carbon Gate

The voluntary carbon market has become a primary revenue stream for DAC developers. Corporations purchasing carbon removal credits to meet net-zero commitments pay a premium for DAC credits because the permanence and measurability of geological storage are more robust than many nature-based alternatives. Microsoft, Stripe, and Shopify have collectively committed hundreds of millions of dollars to DAC purchases, effectively subsidizing the technology's early-stage cost curve.

Government policy is now entering the equation. The United States Inflation Reduction Act expanded the 45Q tax credit to 180 dollars per ton for DAC with geological sequestration, substantially improving project economics. The European Union's Carbon Removal Certification Framework is developing standards for durable removal credits, though implementation details remain under negotiation. These policy mechanisms are essential because the social cost of carbon, which internalizes climate damages, is not yet reflected in market prices for removal.

07 Scaling From Pilots to a Climate-Relevant Industry

The IPCC estimates that limiting warming to 1.5 degrees Celsius requires removing between 100 and 1,000 gigatons of CO2 over the twenty-first century, with most scenarios relying on a combination of afforestation, soil carbon, bioenergy with CCS, and direct air capture. DAC's share in these scenarios is modest in the near term but grows substantially after 2050, reflecting the time needed to reduce costs and build energy infrastructure.

The scaling challenge is not merely building more plants. It is building the entire supply chain: sorbent materials, heat exchangers, geological characterization and injection infrastructure, monitoring and verification systems, and the renewable energy generation to power it all. Each DAC plant is a small industrial ecosystem, and replicating it thousands of times requires industrial learning curves that historically take decades.

Carbon sequestration is a natural process of storing carbon in a carbon pool, playing a crucial role in effectively managing the global carbon cycle and limiting climate change by reducing the amount of carbon dioxide in the atmosphere. There are two main types of carbon sequestration: biologic and geologic. DAC targets geologic sequestration, leveraging the permanence of deep-rock mineralization to lock carbon away for millennia rather than the decades-to-centuries timescale of biological storage. The question is whether human industry can match the speed and reliability of geology at the scale climate science demands.