Carbon Capture and Storage: What It Is and How It Works

What Is Carbon Capture?

Carbon capture refers to a variety of techniques that are used to trap the carbon dioxide (CO₂) produced by power plants and other industrial facilities, typically before it can be released into the atmosphere and contribute to global warming. Carbon dioxide that has been captured through one of these methods is either recycled for other purposes or stored where it cannot escape—a process known as carbon sequestration.

How Carbon Capture Works

There are several different technologies that are in use, or being developed, for carbon capture. They include:

Post-combustion carbon capture: In the widest use today, this technology collects smokestack emissions, called flue gases, before they can be released into the air. In one technique, called adsorption or absorption, the emissions are piped into a device called an absorber, where the carbon dioxide interacts with chemical solvents that absorb it, allowing it to be separated from the other component gases, which are then released. The carbon dioxide and the solvent are then separated so the solvent can be reused, after which the carbon dioxide is compressed for transportation and storage.

Pre-combustion capture: This process removes carbon dioxide from the fuel source before it has been fully burned.

Oxy-fuel combustion capture: In this form of capture, fuel is burned in an atmosphere of nearly pure oxygen, rather than ordinary air, which produces a highly concentrated form of carbon dioxide that is easier to collect.

Direct air capture: Unlike the first three methods, which all take place at the emissions source, direct air capture attempts to pull carbon dioxide out of the air wherever it may be found. To do that, giant fans suck air into a device called a collector, where the carbon dioxide is then separated out through means similar to post-combustion capture. This technique is largely still in the experimental stage.

Types of Carbon Storage

Once carbon dioxide has been successfully captured, the next question is, what to do with it? One option is storing, or sequestering it, where it can presumably do no harm to the atmosphere. There are two basic types of storage: geologic and biologic.

Geologic storage: In geologic storage, captured carbon dioxide is injected deep underground after it has been heated and pressurized into “supercritical” carbon dioxide. As the U.S. Department of Energy explains, supercritical CO₂ “has some properties like a gas and some properties like a liquid. In particular, it is dense like a liquid but has viscosity like a gas. The main advantage of storing CO₂ in the supercritical condition is that the required storage volume is substantially less than if the CO₂ were at ‘standard’ (room)-pressure conditions.” The CO₂ is trapped under layers of rock.  

Biologic storage: Biologic storage relies on natural processes to both capture and store carbon dioxide, such as through the planting of forests, where trees and other plants will absorb and retain it as well as produce oxygen through the process of photosynthesis.

Carbon Capture & Storage (CCS) vs. Carbon Capture, Utilization & Storage (CCUS)

Rather than simply trapping and burying carbon dioxide through a carbon capture and storage (CCS) process, some technologies allow it to be put to productive use—a process known as carbon capture, utilization, and storage (CCUS).

According to the Environmental Solutions Initiative at the Massachusetts Institute of Technology (MIT), some captured carbon dioxide is pumped into oil wells as a way to “flush out hard-to-extract oil.” In addition, it is used in some greenhouses to help grow plants. Other potential uses include “turning CO₂ into plastics, building materials like cement and concrete, fuels, futuristic materials like carbon fibers and graphene, and even household products like baking soda, bleach, antifreeze, inks, and paints.” None of these is in wide-scale production yet.

Advantages and Disadvantages of Carbon Capture

The major advantage of carbon capture is that it has the potential to slow and possibly reverse the accumulation of carbon dioxide in Earth’s atmosphere, which is a major cause of global warming, climate change, and all the dangers they pose.

The principal disadvantage at this point is cost—in particular, the cost of scaling up to the point where it will have much of an impact. In a 2023 report from the Intergovernmental Panel on Climate Change, carbon capture was rated as one of the least effective and most expensive means of reducing greenhouse gas emissions, ranking far below options such as wind, solar, geothermal, and nuclear power.

A related concern is that the emphasis on carbon capture is needlessly delaying the switchover from fossil fuels to renewable energy sources. As a 2021 article in the MIT Technology Review put it, “The noise, news, and hype are feeding a perception that carbon removal will be cheap, simple, scalable, and reliable—none of which we can count on.”

The advocacy group Food & Water Watch is more blunt: “Carbon capture and storage (CCS) is the fossil fuel industry’s biggest scheme yet to persuade people that the climate crisis can be solved while still depending on what they’re selling.” It calls CCS “bogus,” “snake oil,” “a scam,” and “a marketing ploy.”

History of Carbon Capture

Carbon capture dates back to at least the 1920s, when oil and gas drillers began to separate carbon dioxide from methane gas, which they could sell. But it seems to have caught on more broadly in the 1970s, when drillers started injecting it into oil wells to aid in the oil extraction process. This was known as enhanced oil recovery.

The idea gained some momentum in the 1980s and 1990s, as the environmental impact of carbon dioxide became more widely known. Even so, progress has been slow. Today, there are about 40 commercial CCUS facilities in operation worldwide, according to the International Energy Agency, plus “over 500 projects in various stages of development.”

The Future of Carbon Capture

While carbon capture has many critics, others see it as at least a useful interim measure. As the International Energy Agency puts it, CCUS systems “can be retrofitted to existing power and industrial plants, allowing for their continued operation. It can tackle emissions in hard-to-abate sectors, particularly heavy industries like cement, steel, or chemicals.” The organization says CCUS can also “remove CO₂ from the air to balance emissions that are unavoidable or technically difficult to abate.”

An opinion piece on the World Economic Forum website notes that, “Climate scientists claim that it is impossible to reach net-zero [carbon] targets without CCUS deployment on a wide global scale.” But, it adds, “The shortcomings of these technologies, including high costs and low efficiency, need to be addressed before CCUS can be deployed at scale and turned into an effective climate solution.”

In the U.S., the Infrastructure Investment and Jobs Act, passed in 2021, allocated more than $12 billion for CCUS projects—money that is gradually being spent. In August 2023, for example, the Department of Energy (DOE) announced that it was investing up to $1.2 billion in two commercial-scale direct air capture facilities, one in Louisiana and the other in Texas. The DOE said the investment “aims to kickstart a nationwide network of large-scale carbon removal sites to address legacy carbon dioxide pollution and complement rapid emissions reductions.” 

The Bottom Line

Carbon capture and storage (CCS) is one of the technologies that may aid in the fight against continued global warming. Advocates view it as a worthwhile stopgap measure, but critics question both its cost and its effectiveness.