Direct Air Carbon Capture and Storage (DACCS): A Crucial Tool for Climate Mitigation

In the fight against climate change, the global community is urgently working to limit the rise in average global temperatures to a maximum of 1.5 °C. This ambitious target has led to the development of increasingly stringent climate policies in many countries. While these efforts are important, current mitigation strategies are likely to fall short, and the window of opportunity to achieve greenhouse gas neutrality is rapidly closing. As a result, growing attention is being directed toward technologies that enable negative emissions—the removal of carbon dioxide (CO₂) from the atmosphere and its long-term storage. Among these emerging solutions is a promising technological approach known as Direct Air Carbon Capture and Storage (DACCS).

What Is DACCS?

Direct Air Carbon Capture and Storage (DACCS) refers to a suite of technologies designed to extract CO₂ directly from ambient air and store it securely underground. The system includes two primary components: Direct Air Capture (DAC), which involves capturing CO₂ from the air, and Carbon Storage (CS), which involves transporting and permanently storing the captured CO₂. This approach is distinct from conventional carbon capture methods that focus on emissions from power plants or industrial sources; DACCS, in contrast, deals with CO₂ already present in the atmosphere, making it a vital tool for achieving negative emissions.

Various DAC technologies are currently under development, with differences in their operational principles, energy requirements, and maturity levels. Some rely on chemical sorbents, while others use physical adsorption techniques. Although not all are market-ready, many have shown considerable promise in pilot-scale trials. The transport of captured CO₂, whether by pipelines or containers, poses no significant technical challenges. There is ongoing discussion about repurposing existing natural gas pipelines to transport CO₂, which could reduce infrastructure costs.

Cost and Scalability of DACCS

While DACCS is technologically feasible, cost remains a critical factor. The actual cost of capturing CO₂ from the air can vary widely based on several factors, including the scale of deployment, technological improvements, and the availability of low-cost renewable energy. Some highly optimistic projections suggest that capture costs could be as low as EUR 40 per ton of CO₂ by 2050. However, average cost estimates are currently around EUR 200 per ton. Despite these costs, DACCS may still be more economical than other methods of reducing emissions in the long term.

Transport and storage costs are relatively minor compared to capture costs. Nevertheless, realizing the full cost-reduction potential of DACCS depends on making significant investments today to scale up capacity and drive innovation. Without such efforts, the technology may not be ready in time to deliver the volumes of negative emissions required to meet global climate goals.

Permanent CO₂ Storage: Technologically Advanced Options

The success of DACCS also depends heavily on the ability to store CO₂ permanently and safely. Geological storage is currently the most viable and technologically advanced method for long-term CO₂ storage. It involves injecting CO₂ into porous rock formations located more than 800 meters below the Earth’s surface. At such depths, pressure and temperature conditions cause CO₂ to enter a supercritical state, in which it behaves like both a gas and a liquid, making it easier to contain and store.

There are three main geological storage options:

• Saline Aquifers: These are porous rock formations filled with saltwater. When CO₂ is injected into these aquifers, it gradually dissolves into the brine and sinks to the bottom due to its higher density. Over extremely long time periods, a small portion of the CO₂ may mineralize with the surrounding rock. Saline aquifers offer the largest global and national storage potential and, due to their depth, typically do not compete with drinking water sources. However, they may compete with underground hydrogen storage in some cases.

• Depleted Oil and Gas Fields: These sites are attractive because they are well-characterized geologically, often already have infrastructure in place, and have proven to be leak-proof over decades of use. However, they are generally considered less technologically mature (with a Technology Readiness Level of 5–8 out of 10), though some successful storage projects have already been implemented.

• Coal Seams: These formations could theoretically store CO₂, but research is still ongoing, and the technology is not yet ready for large-scale deployment.

Another experimental storage method is in-situ mineralization, where CO₂ is injected into basalt or other reactive rock formations beneath the seafloor or deep underground. Over time, the CO₂ reacts with the rock to form solid minerals. While this method offers the advantage of permanent storage through mineralization, its technological maturity is low, and the potential storage capacity is not yet well understood. For now, it is not considered capable of handling the large volumes of CO₂ needed to meet climate targets.

Monitoring and Safety

To ensure the safety and effectiveness of underground CO₂ storage, a wide array of monitoring and surveillance technologies is available and continues to evolve. These include seismic imaging, pressure monitoring, and satellite-based observation systems. Together, they enable regulators and operators to track the movement and containment of CO₂ underground, and they are expected to become more cost-effective and comprehensive over time.

Conclusion

Direct Air Carbon Capture and Storage (DACCS) represents a critical pathway for achieving negative emissions and addressing the limitations of current climate mitigation strategies. While the technology is still developing, it holds great promise if supported by timely investments and policy decisions. As the need for CO₂ removal intensifies, DACCS could play a central role in stabilizing the climate by safely and permanently removing carbon from the atmosphere