Global carbon emissions hit a high of 36 billion metric tons last year. Efforts to reduce emissions are not on track to meet climate goals; hence, the increased interest in carbon capture. Direct air capture (DAC) involves removal of carbon dioxide from the atmosphere at any location for geologic storage or use, while traditional carbon capture and sequestration (CCS) captures CO2 directly from large point sources such as chemical plants, coal power plants, cement kilns or biomass plants. The CO2 is chemically separated from other plant emissions, highly compressed, and either stored geologically onsite or transported by pipeline (mostly), ship, rail or truck to be used in a range of applications such as enhanced oil extraction, or injected into deep geological formations such as depleted oil and gas reservoirs or saline aquifers. In the U.S., the 2021 Infrastructure Investment and Jobs Act included funding for several carbon capture demonstration projects, and the 2022 Inflation Reduction Act included significant tax credits for CCS ($60-80/metric ton), and even higher credits for DAC (up to $180 per metric ton).
One example of DAC outside the U.S. is a Climeworks plant in Iceland powered by geothermal energy, which captures up to 36,000 metric tons (one millionth of annual global emissions) of CO2 each year and stores it in bedrock. The plant has a series of bunker-like buildings with huge fans that suck air into bins containing chemical pellets that absorb carbon dioxide. The gas is released when the pellets are heated, mixed with water, and pumped more than a mile below the surface where extreme pressure turns it into a solid, essentially part of the rock, in a matter of years. Similarly, a plant in Texas being built by Occidental will have the potential to capture and sequester 500,000 metric tons of carbon dioxide per year. Most will be sequestered deep underground, but some will be pumped into the ground to extract oil that is otherwise too difficult to obtain. Occidental plans to build 100 facilities in the coming years. There are also several dozen point-source CCS projects in operation or under development in the U.S. at this time.
Carbon capture has been promoted as an important component in achieving net-zero emissions by mid-century; however, there are a number of issues. The cost per metric ton for DAC and CCS far exceeds the cost for other strategies such as renewable energy, electric vehicle and mass transit expansion and forest preservation, due to high equipment cost and extensive energy required for pressurization. There are safety concerns about the chemicals used and about CO2 leakage, particularly with long-distance pipeline transmission. Only certain states in the U.S. (including Illinois) are geologically suited for long-term CO2 storage. There are also concerns that enhanced oil extraction sequesters some carbon to produce more (as oil). In July 2024, S.B. 1289 passed the Illinois legislature and was signed by the governor to regulate and provide environmental and safety protections applicable to CCS projects in the state.
CCS is a developing technology. While time will tell whether it is worth the cost and issues, clearly action is needed to reduce carbon dioxide emissions ASAP.