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Discussions of carbon removal sometimes use a confusing variety of terms, which are connected to one another in complicated ways. This glossary defines key terminology and acronyms related to carbon removal and explains some of the relationships between the terms.

If you're looking for more than just definitions of carbon removal-related terms, start with our What Is Carbon Removal? Fact Sheet or our Carbon Removal Explainer.

Biochar

Biochar is a charcoal-like substance produced by burning organic material (also called biomass) at temperatures of 300–600°C in an oxygen-limited environment. Biochar can store large amounts of carbon for up to a thousand years, in contrast to the very rapid release of carbon that occurs from the burning or natural decomposition of biomass.

Bioenergy with Carbon Capture and Storage (BECCS)

Bioenergy with carbon capture and storage (BECCS) is a carbon removal technique that depends on two technologies. Biomass (organic material, which extracts carbon dioxide from the atmosphere as it grows) is converted into heat, electricity, or liquid or gas fuels (the “bioenergy” step), and the carbon emissions from this process are captured and stored in geological formations or the deep ocean, or embedded in long-lasting products (the “carbon capture and storage” step). BECCS is sometimes referred to as bioenergy with carbon capture and sequestration. See our BECCS Fact Sheet for more information.

Carbon Capture

Carbon capture includes any process for capturing carbon dioxide, whether from the atmosphere or from a smokestack or other concentrated source of carbon dioxide emissions. This term is sometimes used ambiguously to refer to carbon removal and carbon capture and sequestration, despite the important differences between those two activities. See also carbon capture and sequestration, carbon capture and use, carbon removal.

Carbon Capture and Sequestration (CCS)

Carbon capture and sequestration (CCS) usually refers to the process of capturing carbon dioxide emissions from a point-source, such as the flue of a gas-fired power plant, and injecting the captured carbon dioxide into geological reservoirs. CCS on a fossil fuel power plant reduces carbon emissions but does not remove carbon dioxide from the atmosphere. It therefore does not count as a form of carbon removal. On the difference between CCS and carbon removal, see our Carbon Removal Explainer. See also carbon capture, carbon capture and use.

Carbon Capture and Use (CCU)

Carbon capture and use (CCU) refers to the two-step process of capturing carbon dioxide and using it to make valuable products or provide valuable services. For example, carbon dioxide can be used to carbonate beverages or make synthetic fuels, cement, carbon fibers, and much more. The term is used for the use of carbon captured from the atmosphere and for the use of carbon captured from flue gas via conventional carbon capture and sequestration (CCS). CCU only counts as carbon removal in cases where the carbon dioxide is captured from the atmosphere and stored for long periods of time (e.g., in long-lived products, such as cement). See our Carbon Removal Explainer for more on the relationship between CCU, carbon removal, and carbon capture and sequestration.

Carbon Capture and Use or Sequestration (CCUS)

Carbon capture and use or sequestration (CCUS) is an umbrella term covering both carbon capture and use (CCU) and carbon capture and sequestration (CCS). It often refers to CCU or CCS associated with fossil fuels or cement, rather than to carbon removal.

Carbon Dioxide Removal (CDR)

Carbon dioxide removal (CDR) is a widely used synonym for carbon removal. See also carbon drawdown, negative emissions technologies.

Carbon Drawdown

Carbon drawdown is usually used as a synonym for carbon removal. It sometimes refers specifically to the use of carbon removal to reduce the atmospheric concentration of carbon dioxide, as opposed to simply slowing its increase.

Carbon Neutral

Carbon neutral describes a country, company, process, etc., that does not emit more carbon dioxide than it captures. An entity could be carbon neutral because it does not emit any carbon dioxide in the first place, but "carbon neutral" more often refers to an entity or process that emits some carbon dioxide but removes just as much carbon dioxide from the atmosphere via carbon removal. See also net zero emissions.

carbon removal

Carbon removal is the two-step process of capturing carbon dioxide (CO₂) from the atmosphere and locking it away for decades or centuries in plants, soils, oceans, rocks, saline aquifers, depleted oil wells, or long-lived products like cement. See our What Is Carbon Removal? Fact Sheet or our Carbon Removal Explainer for more information. See also carbon dioxide removal (CDR), carbon drawdown, negative emissions technologies (NETs).

CCS

CCS is an acronym that stands for carbon capture and sequestration.

CCUS

CCUS is an acronym that stands for carbon capture and use or sequestration.

CDR

CDR is an acronym that stands for carbon dioxide removal.

Direct Air Capture (DAC)

Direct air capture (DAC) is a process of capturing carbon dioxide directly from the ambient air (as opposed to capturing from point sources, such as a cement factory or biomass power plant) using specially designed machines. In these machines, chemicals bind with carbon dioxide in the air. The carbon dioxide is then separated from those chemicals to produce a stream of concentrated carbon dioxide, which can be sequestered or used to make valuable products. The chemicals are then reused to capture more capture dioxide. When the captured carbon dioxide is sequestered or used in long-lived products, DAC counts as a form of carbon removal. See also direct air capture with carbon storage (DACCS), direct air capture and use (DAC+U), carbon capture and use.

Direct Air Capture with Carbon Storage (DACCS)

Direct air capture with carbon storage (DACCS) refers specifically to the two-step process of using direct air capture to capture carbon dioxide from the atmosphere and then sequestering it, as opposing to using it in short-lived products. DACCS counts as a form of carbon removal. See our DACCS Fact Sheet for more information. See also direct air capture and use (DAC+U).

Direct Air Capture and Use (DAC+U)

Direct air capture and use (DAC+U) refers specifically to the two-step process of using direct air capture to capture carbon dioxide from the atmosphere and then using it to make products, such as carbonated beverages, synthetic fuels, or cement; or to provide services, such as enhanced oil recovery. If the captured carbon dioxide is used in long-lived products, such as cement, DAC+U counts as a form of carbon removal. For more on when carbon capture and use counts as carbon removal, see our Carbon Removal Explainer. See also carbon capture and use.

Enhanced Oil Recovery (EOR)

Enhanced oil recovery (EOR) is the process of injecting compressed carbon dioxide into declining oil wells to increase oil production from the well. The injected carbon dioxide could come from processes that capture carbon dioxide from the ambient atmosphere, such as direct air capture. Using carbon dioxide captured from the atmosphere would reduce the overall lifecycle emissions of the oil produced through EOR. Under most circumstances, however, burning oil produced with EOR still contributes more carbon dioxide to the atmosphere than it removes.

Greenhouse Gas Removal (GGR)

Greenhouse gas removal (GGR) is an unbrella term covering both carbon dioxide removaland the capture and storage of other kinds of greenhouse gases, such as methane. There are currently very few proposals to capture greenhouse gases other than carbon dioxide.

Lifecycle Emissions

Lifecycle emissions include all of the carbon dioxide emissions and removals associated with an activity or with the production and use of an energy carrier, such as electricity or jet fuel. For instance, the lifecycle emissions of corn ethanol include not just the carbon dioxide emitted by burning the ethanol, but also the carbon dioxide removed from the atmosphere as the corn grows; the carbon dioxide emitted during the harvesting, transporting, and processing of the corn; et cetera. Calculating the lifecycle emissions of a product or activity requires making choices about how to define the boundaries of the system used to produce and consume the product or conduct the activity. This means that different analyses can produce very different estimates of the lifecycle emissions for the same product or activity.

Natural Climate Solutions

Natural climate solutions involve conserving, restoring, or better managing ecosystems to remove carbon dioxide from the atmosphere. Examples include allowing forests to regrow, restoring mangroves and other wetlands, and switching to restorative agricultural practices, such as cover crop roation, that support healthy soils. These ecosystems capture carbon dioxide from the air and sequester it in plants, soils, and sediments.

Nature-Based Solutions

Nature-based solutions is a synonym for natural climate solutions.

Negative Emissions

Negative emissions refers to removing carbon dioxide (or other greenhouse gases) from the atmosphere. The "negative" in "negative emissions" means "less than zero." See also lifecycle emissions, negative emissions technologies (NETs), net negative emissions, net zero emissions.

Negative Emissions Technologies (NETs)

Negative emissions technologies (NETs) are technologies for implementing carbon dioxide removal. They are called negative emissions technologies because their lifecycle emissions are below zero, meaning that they remove more carbon dioxide from the atmosphere than they emit. Some people include practices such as restorative agriculture as negative emissions technologies, while others restrict the terms to engineered approaches to carbon dioxide removal, such as BECCS or direct air capture with carbon storage (DACCS).

Net Negative Emissions

A country, company, etc. or a process produces net-negative emissions if it removes more carbon dioxide from the atmosphere than it emits. For instance, if a country emits one billion tons of carbon dioxide per year but uses carbon removal to remove two billion tons of carbon dioxide per year, the country would have net negative emissions. See also net zero emissions, negative emissions, negative emissions technologies (NETs).

Net Zero Emissions

Net zero emissions is usually used as a synonym for carbon neutrality. A country, company, or other entity reaches net zero emissions when it is carbon neutral. See also net negative emissions.

Soil Carbon Sequestration

Soil carbon sequestration, also known as "restorative agriculture" or "regenerative agriculture," includes various ways of managing land, especially farmland, so that soils absorb and hold more carbon. See our Soil Carbon Sequestration Fact Sheet for more information. See also natural climate solutions.

Last updated April 15, 2020.