Direct Air Capture Pros and Cons

Smoke of chimney writing CO2 in the sky

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The amount of carbon dioxide (CO2) coming from the burning of fossil fuels is considered by the Intergovernmental Panel on Climate Change (IPCC) to be the largest human-generated contributor to the warming of the planet since the 1700s. As the impacts of the climate crisis become more disruptive to human and natural systems, the need to find multiple pathways to slow warming has become more urgent. One tool that shows promise for helping in this effort is direct air capture (DAC) technology

While DAC technology is currently fully functional, several issues make its widespread implementation difficult. Constraints like costs and energy requirements as well as the potential for pollution make DAC a less desirable option for CO2 reduction. Its larger land footprint when compared to other mitigation strategies like carbon capture and storage systems (CCS) also put it at a disadvantage. However, the urgent need for effective solutions to atmospheric warming as well as the possibility of technological advances to improve its efficiency could make DAC a useful long-term solution. 

What Is Direct Air Capture?

Direct air capture is a method of removing carbon dioxide directly from the Earth’s atmosphere through a series of physical and chemical reactions. The pulled CO2 is then captured into geologic formations or used to make long-lasting materials like cement or plastics. While DAC technology has not been widely deployed, it has the potential to be part of the toolkit of climate change mitigation techniques.

Advantages of Direct Air Capture

As one of the few strategies for removing CO2 that has already been released into the atmosphere, DAC has several advantages over other technologies. 

DAC Reduces Atmospheric CO2

One of the most obvious advantages of DAC is its ability to reduce the amount of CO2 that is already in the air. CO2 only makes up about 0.04% of the Earth’s atmosphere, yet as a potent greenhouse gas, it absorbs heat and then slowly releases it again. While it does not absorb as much heat as other methane and nitrous oxide gases, it has a greater effect on warming because of its staying power in the atmosphere.

According to NASA climate scientists, the most recent measurement of CO2 in the atmosphere was 416 parts per million (ppm). The rapid rate of increase in CO2 concentrations since the beginning of the industrial age and especially in more recent decades has led experts at the IPCC to warn that drastic steps must be taken to keep the Earth from warming more than 2 degrees Celsius (3.6 degrees Fahrenheit). It is very likely that technologies like DAC will need to be part of the solution to keep dangerous temperature increases from happening. 

It Can Be Employed in a Wide Variety of Locations

Unlike CCS technology, DAC plants can be deployed in a larger variety of locations. DAC does not need to be attached to an emissions source such as a power plant in order to remove CO2. In fact, by placing DAC facilities close to locations where the captured CO2 can then be stored in geologic formations, the need for extensive pipeline infrastructure is eliminated. Without a long network of pipelines, the potential for CO2 leaks is greatly reduced.

DAC Requires a Smaller Footprint

The land use requirement for DAC systems is much smaller than carbon sequestration techniques like bioenergy with carbon capture and storage (BECCS). BECCS is the process of turning organic material such as trees into energy like electricity or heat. The CO2 that is released during the conversion of biomass into energy is captured and then stored. Because this process requires growing organic material, it uses a large amount of land to grow plants to pull CO2 from the atmosphere. As of 2019, the land use required for BECCS was between 2,900 and 17,600 square feet for every 1 metric ton (1.1 US tons) of CO2 per year; DAC plants, on the other hand, only require between 0.5 and 15 square feet.  

It Can Be Used to Remove or Recycle Carbon

After the CO2 is captured from the air, DAC operations aim to either store the gas or use it to create long-lived or short-lived products. Building insulation and cement are examples of long-lived products that would bind up the captured carbon for an extended time. Using CO2 in long-lived products is considered a form of carbon removal. Examples of short-lived products created with captured CO2 include carbonated beverages and synthetic fuels. Because the CO2 is only stored in these products temporarily, this is considered a form of carbon recycling.

DAC Can Achieve Net-Zero or Negative Emissions

The advantage of creating synthetic fuels from captured CO2 is that these fuels could take the place of fossil fuels and essentially create net-zero carbon emissions. While this does not reduce the amount of CO2 in the atmosphere, it does keep the total CO2 balance in the air from increasing. When carbon is captured and stored in geologic formations or cement, the levels of CO2 in the atmosphere are reduced. This can create a negative emissions scenario, where the amount of CO2 being captured and stored is greater than the amount being released. 

Disadvantages of Direct Air Capture

While there is hope that the main barriers to widespread implementation of DAC can be overcome quickly, there are several significant drawbacks to using the technology, including cost and energy use.

DAC Requires Large Amounts of Energy

In order to drive air through the part of a DAC plant that contains the sorbent materials that capture the CO2, large fans are used. These fans require large amounts of energy to operate. High energy inputs are also necessary to produce the materials required for DAC processes and to heat sorbent materials for reuse. According to a 2020 study published in Nature Communications, it is estimated that the amount of liquid or solid sorbent DAC requires to meet the atmospheric carbon reduction goals outlined by the IPCC may reach between 46% and 191% of the total global energy supply. If fossil fuels are used to provide this energy, then DAC will have a more difficult time becoming carbon neutral or carbon negative. 

It's Currently Very Expensive

As of 2021, the cost of the removal of a metric ton of CO2 ranges between $250 and $600. Variations in cost are based on what type of energy is used to run the DAC process, whether liquid or solid sorbent technology is used, and the scale of the operation. It’s difficult to predict the future cost of DAC because many variables must be considered. Since CO2 is not very concentrated in the atmosphere, it takes a lot of energy, and therefore is very expensive to remove. And because right now there are very few markets willing to purchase CO2, cost recovery is a challenge.  

Environmental Risks

CO2 from DAC must be transported and then injected into geologic formations to be stored. There is always a risk that a pipeline will leak, that groundwater will be polluted in the process of injection, or that the disruption of geologic formations during injection will trigger seismic activity. Additionally, liquid sorbent DAC uses between 1 and 7 metric tons of water per metric ton of CO2 captured, while solid sorbent processes use around 1.6 metric tons of water per metric ton of CO2 captured. 

Direct Air Capture Can Enable Enhanced Oil Recovery

Enhanced oil recovery uses CO2 that is injected into the oil well to help pump out otherwise unreachable oil. In order for enhanced oil recovery to count as either carbon neutral or carbon negative, the CO2 used must come from DAC or from the burning of biomass. If the amount of CO2 injected is not less than or equal to the amount of CO2 that will be released from the burning of the oil that is recovered, then using CO2 for enhanced oil recovery can end up doing more harm than good.

View Article Sources
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