How Does Carbon Capture Work?

In October 2024, the world emitted its billionth tonne of carbon dioxide since January 1st. That is not a typo. Humanity crosses that threshold every six to eight months. Even in the most optimistic scenarios where solar panels and wind turbines cover every viable rooftop and field, one stubborn fraction of global emissions resists easy elimination: the exhaust from cement kilns, steel furnaces, chemical plants, and the natural gas that heats millions of homes. Carbon capture and storage (CCS) aims to intercept that tail of emissions and pump it underground instead of into the sky, and according to the International Energy Agency, the technology is already operational at dozens of facilities worldwide.

The short answer

Carbon capture works by separating CO2 from other gases at the source of combustion or directly from ambient air, then compressing it into a dense fluid and injecting it deep underground into rock formations where it stays trapped for thousands of years. The technology exists today, is operational at dozens of plants worldwide, and can reduce industrial emissions that cannot easily be electrified. The problem is cost, scale, and the uncomfortable fact that most current CCS projects use the CO2 to extract more oil.

The full picture

The two ways to catch carbon

There are two main approaches, and they operate at very different scales of difficulty.

Point source capture intercepts CO2 at industrial facilities where it is already concentrated. A cement plant flue gas might contain 15 to 30% CO2; a natural gas power plant exhaust around 4 to 8%. These are thick concentrations compared to the 0.04% found in the open air. The most common technical approach is called amine scrubbing: the exhaust gas is passed through a solution of amine compounds that bind selectively with CO2. When the solution heats up, it releases the CO2 in a concentrated stream while the amines get recycled back into the absorber. This is the technology that has been used for decades in natural gas processing to remove CO2 and hydrogen sulfide from raw gas.

Direct air capture (DAC) pulls CO2 from the atmosphere anywhere on the planet. Because ambient air is so dilute, DAC requires much larger air contactors and significantly more energy. The leading DAC companies, including Climeworks and Carbon Engineering, use solid or liquid sorbent materials that bind CO2 from air passing through their systems. When the sorbent is heated (using waste heat, geothermal heat, or renewable electricity), it releases concentrated CO2 that can be compressed and stored.

The energy cost is the central challenge. Capturing a tonne of CO2 from ambient air currently requires roughly 1,500 to 2,000 kilowatt-hours of energy, according to the International Energy Agency. That is roughly equivalent to driving a gasoline car 7,000 kilometers. At current electricity prices, that translates to hundreds of dollars per tonne, though costs are expected to fall with scale and engineering improvements.

The three stages: capture, transport, storage

Once separated, the CO2 must get from wherever it was captured to wherever it will be stored. This involves three distinct steps.

Capture is the hardest and most expensive part. For point source capture, retrofitting an existing coal power plant with CCS can increase its cost of electricity by 30 to 70%, according to the IEA. For DAC, the cost per tonne has fallen from over $1,000 in the early 2010s to roughly $300 to $600 at the newest plants, but is still well above most carbon prices.

Transport is comparatively mundane. CO2 is typically transported as a supercritical fluid (neither fully liquid nor gas) through pipelines. Existing CO2 pipelines span thousands of kilometers in the United States, primarily serving enhanced oil recovery operations. Building new pipeline networks at scale is a permitting and financing challenge, not a technology gap.

Storage is where permanence becomes the goal. The CO2 is injected into deep geological formations, typically at depths of 1 to 3 kilometers. At those depths, the pressure keeps CO2 in a dense supercritical state. Several trapping mechanisms hold it in place: structural trapping (the CO2 is buoyant and rises until impermeable rock stops it), residual trapping (CO2 gets stuck in tiny pores in the rock like water in a sponge), solubility trapping (CO2 dissolves in the formation water), and mineral trapping (the CO2 slowly reacts with the rock to form solid carbonate minerals, which is permanent but takes centuries). A 2023 study in the journal International Journal of Greenhouse Gas Control estimated that properly selected and managed geological storage sites can retain over 99% of injected CO2 for 1,000 years.

What happens to the CO2 underground

Injecting CO2 into rock is not like filling an underground balloon. The subsurface is porous, like a tightly packed sand, with pores connected by narrow channels. When supercritical CO2 is injected, it flows through those channels and spreads through the formation. The primary risk is leakage through existing or induced fractures in the cap rock, the impermeable layer that seals the reservoir. This is why site selection matters enormously. Depleted oil and gas reservoirs have the advantage of proven storage capacity and existing well infrastructure, but they also contain old wells that could potentially leak. Saline aquifers offer enormous theoretical storage capacity, but are less well-characterized.

Some CO2 finds its way into a use: roughly 80% of all CO2 captured worldwide is used for enhanced oil recovery. In EOR, captured CO2 is injected into partially depleted oil fields to push remaining oil toward production wells, much like using waterflooding but more effectively. The CO2 is not consumed; most of it returns to the surface with the oil and gets recaptured and reinjected. Critics argue this makes CCS a tool for extending fossil fuel production rather than reducing atmospheric CO2. Proponents counter that the CO2 would otherwise be released, and that EOR provides an economic justification that makes some CCS projects financially viable without subsidy.

Why it matters

The Intergovernmental Panel on Climate Change estimates that limiting warming to 1.5 degrees Celsius requires removing 100 million to 1 billion tonnes of CO2 from the atmosphere per year by 2050, on top of dramatic emissions reductions. Current global CCS capacity is roughly 50 million tonnes per year, according to the IEA. Reaching even the lower end of that removal target means scaling up by a factor of 2,000 from today’s levels in under three decades.

The harder truth is that some industrial processes have no near-term alternative. Making cement requires heating limestone to roughly 1,450 degrees Celsius, a process that releases CO2 as a chemical byproduct (not just from burning fuel) and cannot easily be electrified. Steel production via a blast furnace similarly releases CO2 as part of the reduction chemistry. These sectors account for roughly 18% of global emissions. For them, carbon capture is not a nice-to-have option; it is the primary decarbonization pathway.

The US Inflation Reduction Act allocated $12.5 billion for carbon capture infrastructure, including a 45Q tax credit that pays up to $180 per tonne for DAC and $130 per tonne for point source capture. The EU Carbon Border Adjustment Mechanism and Canada’s investment tax credits have similarly shifted the economics. The question is no longer whether CCS can work; it is whether it can be built fast enough.

Common misconceptions

“Carbon capture is a way for oil companies to keep drilling.” This one is partly true and partly misleading. It is true that roughly 90% of current CCS operations are linked to enhanced oil recovery, and that EOR can extend fossil fuel production. But the two things are not the same. New standalone CCS projects built specifically for emissions reduction, including several now under construction in the US and Europe, are designed for permanent storage with no oil recovery. The technology itself is neutral; what matters is how it is used.

“The CO2 just leaks back out.” Properly selected geological storage is remarkably secure. According to the US Department of Energy’s Regional Carbon Sequestration Partnership program, which has been studying storage integrity for over two decades, carefully managed geological storage sites can retain over 99% of injected CO2 for periods exceeding 1,000 years. The 1% that might escape is not a sudden burst; it would be slow seepage through the overlying rock, and monitoring technologies can detect it well before it becomes significant.

“It is just a excuse to keep emitting.” This critique applies to specific projects and policy choices, not to the technology itself. Carbon capture does not reduce the incentive to cut emissions at the source; it provides a complementary tool for the hardest-to-abate sectors. A cement plant that installs CCS is still emitting less CO2 per tonne than one that does not. The concern about lock-in is a legitimate policy argument about where CCS investments should rank relative to demand reduction and electrification, but it does not make the technology ineffective.

Key terms

Amine scrubbing: A chemical process in which exhaust gases pass through a liquid solution of amine compounds that selectively bind to CO2. Heating the solution releases the concentrated CO2 while the amines are recycled.

Direct air capture (DAC): A technology that pulls CO2 directly from ambient air using solid or liquid sorbent materials, rather than from a concentrated point source like a smokestack.

Enhanced oil recovery (EOR): Injecting CO2 into partially depleted oil reservoirs to push remaining oil toward production wells. About 80% of global CCS capacity is used for EOR.

Geological storage: Injecting captured CO2 into deep underground rock formations such as depleted oil fields, saline aquifers, or unmineable coal seams, where it is trapped by impermeable cap rock and various trapping mechanisms.

Point source capture: Capturing CO2 from the concentrated exhaust stream of a specific industrial facility such as a power plant, cement kiln, or steel furnace.

Supercritical CO2: CO2 held at a pressure and temperature above its critical point, where it behaves as a dense fluid with properties of both a liquid and a gas. This is the form in which CO2 is typically transported through pipelines and injected underground.

45Q tax credit: A US federal tax credit that provides financial incentives for carbon oxide sequestration and utilization. The credit was expanded by the 2018 Bipartisan Budget Act and further extended by the Inflation Reduction Act.