CCS, or carbon capture and storage, removes carbon dioxide from industrial exhaust or the atmosphere and locks it away underground so it doesn’t contribute to climate change. Around 45 commercial CCS facilities operate globally, capturing more than 50 million metric tons of CO2 per year. The process works in three stages: capturing the CO2 at its source, transporting it to a storage site, and injecting it deep underground into rock formations where it stays permanently.
How CO2 Gets Captured
Most CCS systems grab CO2 from the exhaust gases of power plants, cement factories, steel mills, or chemical plants. The dominant method, called post-combustion capture, runs those exhaust gases through a chemical solvent, typically an amine-based liquid that bonds with CO2 and pulls it out of the gas stream. The solvent is then heated to release the concentrated CO2 for transport, and the solvent gets recycled.
A second approach, pre-combustion capture, converts fuel into a mix of hydrogen and CO2 before burning it. Because this process happens at high pressure and produces a gas stream that’s roughly 40% CO2 (compared to the much lower concentrations in regular exhaust), the separation equipment can be smaller and less expensive. A 2022 analysis from the National Energy Technology Laboratory found that adding pre-combustion capture to a coal gasification power plant raises electricity costs by about 37%, from 11.4 cents to 15.6 cents per kilowatt-hour.
A third method, oxy-fuel combustion, burns fuel in nearly pure oxygen instead of regular air. This produces exhaust that’s mostly CO2 and water vapor, making the CO2 easy to isolate by simply condensing the water out. The tradeoff: generating that pure oxygen stream requires significantly more energy than the other approaches, which drives up costs.
Direct Air Capture: A Different Approach
Unlike point-source CCS, which catches CO2 where it’s produced, direct air capture (DAC) pulls CO2 straight from the ambient atmosphere. This is far more energy intensive and expensive because atmospheric CO2 is extremely dilute compared to industrial exhaust. DAC matters because it can theoretically remove CO2 that’s already been emitted, not just prevent new emissions, but its high cost currently limits large-scale deployment.
Transporting CO2 to Storage Sites
Once captured, CO2 is compressed into a dense, supercritical fluid (a state between liquid and gas that behaves like a thick liquid) and moved through pipelines to a storage location. The U.S. Department of Transportation has regulated supercritical CO2 pipelines for decades and recently proposed new rules covering gaseous CO2 pipelines as well. These rules would require operators to install remote or automatic shut-off valves, train local emergency responders, provide CO2 detection equipment to first responders, and conduct detailed analyses of how CO2 vapor would disperse if a pipeline failed. CO2 can also be transported by ship or truck for shorter distances or in regions without pipeline infrastructure.
Where CO2 Gets Stored Underground
The final step is injecting compressed CO2 deep underground into rock formations that can hold it permanently. A suitable storage site needs four things: enough pore space in the rock to hold millions of metric tons of CO2, rock that’s permeable enough to accept injected fluid at a useful rate, at least one thick sealing layer (caprock) above the storage zone to prevent upward migration, and enough depth that pressure keeps the CO2 in its dense supercritical state.
Three types of formations are used most often:
- Saline formations are deep, porous rock layers filled with extremely salty water (brine). They span large underground volumes and represent the biggest potential storage capacity.
- Depleted oil and gas reservoirs are formations that already held hydrocarbons for thousands to millions of years, proving they have the right conditions to trap fluids long-term. The extracted oil or gas leaves behind porous space that can be filled with CO2.
- Basalt formations have chemical properties that can actually react with CO2 over time, potentially converting it into solid minerals and locking it in place even more permanently.
All storage complexes include sealing layers that separate stored CO2 from drinking water sources and the surface.
How Storage Sites Are Monitored
The primary risks of underground storage are CO2 migrating out of the intended formation and minor ground motion caused by injection pressure. Operators monitor for both using a layered system. Underground, they use seismic imaging, well-logging tools, downhole sensors, fluid sampling, and gravity measurements to track where the CO2 plume is moving and detect any faults or fractures. Near the surface, geochemical sensors check shallow groundwater and soil for signs of leakage, while surface displacement tools watch for subtle ground movement. Above ground, optical sensors, atmospheric tracers, and air-flow measurement techniques detect any CO2 that might reach the atmosphere.
What Captured CO2 Can Be Used For
Some captured CO2 gets put to use rather than simply stored, which is why you’ll sometimes see the acronym CCUS (carbon capture, utilization, and storage). The most common industrial use is enhanced oil recovery, where CO2 is injected into aging oil fields to push out hard-to-reach crude. Beyond that, captured CO2 is used in fertilizer production (as a feedstock for urea), beverage carbonation, municipal water treatment, fire suppression equipment, and precision cleaning of electronics. Newer applications are converting CO2 into building materials like cement and aggregate, plastics, chemicals, and synthetic fuels.
What CCS Costs
Capture costs vary enormously depending on how concentrated the CO2 source is. Industries that produce nearly pure CO2 streams, like natural gas processing, ammonia production, and ethanol production, can capture it for roughly $15 to $35 per metric ton. Power generation, cement, iron, steel, and hydrogen production have much more dilute exhaust streams, pushing capture costs to $50 to $120 per metric ton. Transportation and underground storage add further costs on top of capture. These cost differences explain why the first wave of CCS projects has concentrated in industries where capture is cheapest, while broader deployment in the power sector has been slower to take off.