With the effects of climate change, manifest in the increasing number of storms and wildfires, among others, becoming increasingly palpable, the need to pare greenhouse gas (GHG) emissions through the deployment of clean and low-carbon technologies, such as renewable energy and electric vehicles, has become paramount. The current climate change and decarbonization efforts are inadequate to crimp global temperature rise beneath 1.5º C annually and halt the pace at which climate change is harming the environment.
To meet the Paris Accord climate goals, the adoption of CO2 removal systems – solutions that eliminate carbon directly from the air – has become imperative. Carbon-removal solutions are expected to be adopted at a billion-ton scale by 2050 to slow the build-up of CO2 in the atmosphere, as well as eliminate residual emissions that are otherwise uneconomical to contain. Several carbon-removal solutions have the potential to drastically curb carbon emissions. The ones that have gained widespread traction are afforestation and tree-planting, as they augment the ability of the soil to sequester and squirrel away carbon. Another promising technological solution is direct air capture (DAC), expected to be part of the larger carbon-removal solution portfolio in the future.
DAC technologies extract carbon directly from the air, which is then either permanently sequestered in underground geological formations or used in industrial applications, such as oil exploration (enhanced oil recovery), food processing or production of synthetic fuels. DAC has primarily two approaches: liquid and solid capture. Liquid systems pass air captured from the atmosphere through chemical solutions to remove and capture CO2 while returning the remaining air constituents to the atmosphere. Solid technology uses solid sorbent filters that bind with CO2 captured from the air and release the remaining captured constituents into the atmosphere.
DAC offers several benefits over its counterparts. It occupies less real estate and, hence, can be installed in an existing industrial site, while other technologies require stand-alone industrial space for deployment. For example, bioenergy with carbon capture and storage – another carbon-removal solution that converts organic materials (such as trees) into energy – occupies 2,900-17,600 square feet to capture one metric ton of CO2, while DAC plants require 0.5-15 square feet. This is a significant cost advantage as land rates, particularly industrial land rates, have touched new peaks, due to elevated inflation.
DAC plants can be built near geological storage sites or industrial sites with existing CO2 pipelines. This eliminates the need for stand-alone CO2 pipelines – one of the largest barriers to carbon capture and storage currently. This feature of DAC offers a material cost advantage compared to other technologies.
However, DAC comes with a few challenges. The biggest drawback is the low technology readiness levels and scarce investments in an unproven technology. Only 19 DAC plants are operating worldwide, capturing less than 0.01 mn. ton CO2/year. Scaling this technology to a billion-ton level would require billions of dollars of capital infusion every year. DAC is also energy-intensive, requiring significant energy to power the fans of DAC plants. Sourcing energy from fossil-fuel-based sources would exacerbate the problem of GHG emissions. Moreover, the technology is expensive, with the cost of captured CO2 at US$200-600 per ton. In contrast, regulatory support and incentives are offered to the tune of US$50-100 per ton of CO2 captured. The technology needs to be scaled up quickly to reduce the overall cost to capture CO2.
DAC, like most clean and promising energy technologies, is not expected to have a significant impact initially. Although the technology has shown promise, it would need collaborative effort from governments and business leaders, regulatory support and technological innovation. With a comprehensive and holistic implementation strategy, DAC can achieve its full potential and help usher in a carbon-based circular economy that can hasten the transition to a carbon-free world.