What is direct air capture, and how does it work?

Direct air capture is a process that uses machines to extract CO2 from ambient air and convert it into a concentrated form that can be stored or used for other purposes. Three main types of DAC technologies are currently in use or under development:

• Adsorption-based DAC: This method uses solid materials, such as activated carbon or zeolites, that can bind CO2 molecules from the air. The materials are then heated or exposed to low pressure to release CO2, which can be compressed and transported. This is the technology used by Climeworks, an ETH Zurich spin-off that operates a plant in Iceland that captures 4,000 metric tons of CO2 per year¹.
• Absorption-based DAC: This method uses liquid solvents, such as amines or sodium hydroxide, that can dissolve CO2 from the air. The solvents are then regenerated by heating or applying an electric current to release CO2, which can be compressed and transported. This is the technology used by Carbon Engineering, a Canadian company that plans to build a large-scale plant in the US that can capture 1 million metric tons of CO2 per year.
• Calcination-based DAC: This method uses solid materials, such as calcium oxide or magnesium oxide, that can react with CO2 from the air to form carbonates. The carbonates are then heated to high temperatures to decompose into CO2 and metal oxides, which can be recycled. This is the technology used by Skytree, a Dutch company that has developed a prototype device that can capture 150 kg of CO2 per day³.

What are the benefits and drawbacks of direct air capture?

Direct air capture has several advantages over other carbon removal methods, such as afforestation, bioenergy with carbon capture and storage (BECCS), or enhanced weathering. Some of these advantages are:

• DAC can capture CO2 from any location, regardless of the source or concentration of emissions. This makes it suitable for capturing emissions that are hard to avoid or reduce, such as those from aviation, agriculture, or industry.
• DAC can operate continuously and independently of weather conditions, unlike biological methods that depend on land availability, water supply, and seasonal variations.
• DAC can produce pure CO2 that can be used for various applications, such as synthetic fuels, carbonated beverages, or enhanced oil recovery. This can create new revenue streams and incentives for carbon removal.

However, DAC also faces several challenges and limitations, such as:

• DAC is still very costly and energy-intensive, compared to other carbon removal methods or emission reduction measures. According to a recent study by ETH Zurich researchers, the cost of removing 1 tonne of CO2 from the air in 2050 will be between 230 and 540 US dollars, which is twice as high as previous estimates. The energy consumption of DAC will also be significant, requiring up to 1% of global energy demand in 2050.
• DAC is still at an early stage of development and deployment, and its scalability and feasibility are uncertain. There are only a few operational DAC plants in the world, and their capacity is very small compared to global emissions. The technical, economic, and social barriers to scaling up DAC are still unknown and need to be addressed.
• DAC is not a substitute for emission reduction, but a complement. DAC can only offset a fraction of the current and future emissions, and it cannot reverse the existing impacts of climate change. Therefore, it is essential to continue reducing emissions from all sources and sectors and to adopt other mitigation and adaptation strategies.

How can we make direct air capture more affordable and efficient?

To make direct air capture more attractive and viable, several actions and innovations are needed, such as:

• Improving the performance and reducing the cost of DAC technologies by developing new materials, processes, and designs that can enhance the capture efficiency, selectivity, and durability and lower the energy and material requirements.
• Increasing the demand and value of CO2 by creating new markets and policies that can incentivize and reward carbon removal and utilization, such as carbon taxes, credits, or subsidies, and by expanding the applications and products that can use CO2 as a feedstock or a resource.
• Integrating DAC with renewable energy sources, such as solar, wind, or geothermal, that can provide low-carbon and low-cost electricity and heat for the DAC process and reduce its environmental footprint and dependence on the grid,
• Collaborating and coordinating among different stakeholders, such as researchers, entrepreneurs, investors, policymakers, and consumers, can support and accelerate the development and deployment of DAC and ensure its safety, sustainability, and social acceptance.

Direct air capture is a promising technology that can help slash carbon emissions and combat climate change. However, it is not a silver bullet, and it needs to be improved and scaled up, along with other solutions, to achieve the global climate goals.