Glossary
Short answer
Plain-English definitions of carbon market terms, from additionality to vintage. Related terms link to each other, and every definition cites the primary source it is based on.
By HowToBuyCarbonCredits editorial team · Last reviewed
Use the A–Z bar to jump to a letter. Each entry gives a short definition first, then any detail a buyer needs, and the “Related” chips take you to connected terms on this page. Where several bodies use a term differently, the definition follows the standard or UN body named in its footnote, such as the IPCC glossary.Source 1
New to the topic? Start with what a carbon credit is, then read how to verify carbon credits before you buy.
120 terms in plain English.
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A unit issued in the registry of the Paris Agreement Crediting Mechanism (Article 6.4) for a registered activity, each representing one tonne of CO2e reduced or removed.Source 2Source 3
There are two types. Mitigation contribution A6.4ERs are not authorised by the host country, so no corresponding adjustment applies and the mitigation counts towards the host's NDC. Authorised A6.4ERs are authorised for NDC use and/or other international mitigation purposes and are subject to corresponding adjustment. At issuance, 5% of an activity's A6.4ERs go to the Adaptation Fund (least developed countries and small island developing states may opt out) and 2% are cancelled to contribute to overall mitigation of global emissions.
A carbon crediting program run as a nonprofit enterprise of Winrock International. It registers emission reduction and removal projects, oversees their independent verification and issues serialized credits on a public registry.Source 4Source 5
ACR says it established the world's first carbon registry in 1996. It operates in both voluntary and compliance markets; the markets it lists include California's cap-and-invest program, Washington State's cap-and-invest program and the International Civil Aviation Organization (ICAO). Credit purchases are agreed directly between buyer and seller, or on an approved linked exchange, and the parties then record the transfer or retirement on the ACR Registry.
A credit is additional if the emission reduction wouldn't have happened without the money from selling credits.Source 6Source 7Source 1
Additionality is one of the ICVCM's ten Core Carbon Principles, and the IPCC lists it among the key tests of an offset's environmental integrity. If a project would have gone ahead anyway, its credits don't represent extra climate benefit. Programs assessed by the ICVCM must, among other checks, confirm that the activity isn't already required by host-country law and that carbon-credit revenue was considered when the project was planned.
The IPCC greenhouse gas inventory category that combines agriculture with land use, land-use change and forestry (LULUCF), covering emissions and removals from farming, forests and other land.Source 1
The IPCC notes that land-related emissions estimated in global models are not always directly comparable with LULUCF figures in national inventories, because countries and modellers define human-caused CO2 removals differently.
A permit issued under an emissions trading system that gives the holder the right to emit one tonne of CO2e. Companies surrender allowances to cover their reported emissions.Source 8Source 9
Allowances are mostly sold at auction, some are given free, and they can be traded. They differ from offset credits: an allowance is a slice of the cap, while an offset credit comes from a project outside the capped sectors. In California, offsets are typically slightly cheaper than allowances bought at state auctions, which is one reason the program limits their use.
Carbon project activities that increase carbon stored in woody vegetation, and sometimes soils, by planting, sowing or helping natural regrowth. They remove CO2 from the atmosphere.Source 10Source 1
The IPCC defines afforestation as turning land that has not historically held forest into forest, and reforestation as restoring forest on land that was once forested but converted to another use. Verra's revegetation category covers woody vegetation that does not meet those forest definitions. Because stored carbon can be lost, for example through fire, Verra holds credits in a pooled buffer account to cover unforeseen losses.
The part of the Paris Agreement that lets countries cooperate on their climate targets, including by trading emission reductions with each other.Source 3Source 11
It has three tracks. Article 6.2 covers bilateral or multilateral deals in which countries transfer mitigation outcomes (ITMOs). Article 6.4 sets up a crediting mechanism, operated centrally through the UNFCCC, that credits reductions by public and private actors. Article 6.8 covers non-market approaches that involve no trading. At COP29 in Baku, countries adopted further guidance aimed at fully operationalising Article 6.
The part of Article 6 that lets countries cooperate bilaterally or in groups and transfer emission reductions to each other as ITMOs, with corresponding adjustments to avoid double counting.Source 11Source 3
Deals are agreed between participating countries rather than run by a central UN body. ITMOs can count toward the buying country's NDC or, if the host country authorises it, toward other international mitigation purposes. At COP29 countries added detailed guidance on authorisation, first transfers, registries and reporting, and agreed no further negotiation of the guidance until its review resumes in 2028.
A carbon crediting mechanism under the Paris Agreement, known as PACM and run centrally through the UNFCCC, that registers projects and issues credits called A6.4ERs for emission reductions and removals.Source 12Source 3
It is supervised by the Article 6.4 Supervisory Body, under the authority of the meeting of the Parties to the Paris Agreement (CMA). Host countries can authorise A6.4ERs for use toward other countries' NDCs or other international purposes, in which case corresponding adjustments apply, or leave them unauthorised as mitigation contribution units. Afforestation and reforestation projects and programmes of activities from the Clean Development Mechanism (CDM) could request to transition into it, with a deadline of 31 December 2025.
A credit for emissions prevented, such as by protecting a forest, rather than removed from the air.Source 13Source 14
The ICVCM separates emission reductions (a net cut in human-caused emissions from sources) from removals (CO2 taken out of the atmosphere and stored). The difference matters for net-zero claims: the SBTi Corporate Net-Zero Standard requires residual emissions to be neutralised by removing carbon and storing it permanently, so avoidance credits can't be used for that. They can still fund mitigation beyond a company's own targets.
A historic reference point, either a single year or an average over several years, against which a company tracks its greenhouse gas emissions over time and measures progress towards targets.Source 15
The GHG Protocol requires companies to set a base-year recalculation policy. Base-year emissions are recalculated for significant structural changes, such as acquisitions or divestments, or for changes in calculation methodology, so comparisons stay like for like. They are not recalculated for organic growth or decline.
The emissions that would have happened without the project. Credits are counted against it.Source 13Source 15
The ICVCM calls this the baseline scenario: what is predicted or assumed to happen without the incentive of carbon credits, holding everything else constant. Each credit equals the gap between baseline emissions and what happens under the project, adjusted for leakage. Because the baseline can't be observed directly, the assumptions behind it decide how many credits a project earns, and a baseline set too high leads to over-crediting.
Capturing and storing the CO2 produced when biomass is used for energy. Whether it removes CO2 from the atmosphere overall depends on the total emissions of its supply chain.Source 1
The IPCC describes BECCS as carbon capture and storage technology applied to a bioenergy facility and lists it among carbon dioxide removal methods, with the caveat about supply chain emissions.
Climate action or investment a company makes outside its own value chain, such as funding projects that avoid, reduce or remove emissions, on top of cutting its own emissions.Source 14Source 16
SBTi recommends BVCM in addition to, not instead of, near-term and long-term science- based targets. BVCM is not counted in a company’s scope 1, 2 or 3 inventory and does not count toward its value-chain targets. Buying high-quality carbon credits is one way to do it.
A stable, carbon-rich material made by heating biomass with little oxygen and used as a soil amendment. It locks up carbon that would otherwise return to the air as the biomass decomposed, so it counts as carbon removal.Source 1
The IPCC distinguishes biochar from charcoal by how it is used: biochar goes into soil to improve soil functions and to cut greenhouse gas emissions from biomass that would otherwise decompose quickly. The IPCC lists it among carbon dioxide removal methods.
Carbon stored by coastal and marine ecosystems, mainly mangroves, tidal marshes and seagrasses, in their plants and especially their soils and sediments.Source 1Source 17
These ecosystems bury carbon quickly per unit of area. If they are degraded or lost, most of that carbon is likely to return to the atmosphere. Blue carbon credits come from projects that conserve or restore these habitats, which can also protect coasts from storms and support food security.
A reserve of credits set aside to cover losses, such as a forest fire reversing stored carbon.Source 18Source 7
Projects whose stored carbon could be released again, such as forestry and other land-use projects, deposit part of their credits into a shared reserve that the program can cancel to compensate for reversals. Under Verra's VCS, the share is set with its AFOLU Non-Permanence Risk Tool, which scores risks including fire. The ICVCM requires CCP-Eligible programs to run a pooled buffer holding either at least 20% of credits issued to contributing projects or an amount proportional to each project's reversal risk.
The permanent removal of a carbon credit from a registry for a reason other than a buyer's claim, for example to correct over-issuance, compensate for a reversal or convert the credit into another type of unit.Source 10Source 19Source 20
Registries keep cancellation and retirement apart. Verra's VCS definitions describe retirement as a credit being used by its owner in a claim, while cancellation takes credits out of circulation for other purposes, such as converting them into another kind of greenhouse gas credit or compensating for excess issuance. Isometric gives cancelled credits their own 'Canceled' status, used for example after erroneous over-issuance or a reversal, and buffer pool credits may be cancelled to cover a reversal. If you are buying credits to support a claim, the registry entry to look for is a retirement, not a cancellation.
The design behind most emissions trading systems: a regulator sets a limit (cap) on total emissions and lets covered companies trade the allowances that make up that cap.Source 8Source 9
The EU ETS and California’s program both work this way. Some cap-and-trade programs let covered companies use a limited quantity of approved offset credits toward their obligation; California, for example, caps offsets at a small percentage of each company’s compliance obligation.
The maximum total of net CO2 emissions humanity can release while limiting global warming to a given level with a given probability. The term is also used for global accounts of carbon sources and sinks.Source 1
The IPCC distinguishes the Total Carbon Budget, counted from pre-industrial times, from the Remaining Carbon Budget, counted from a recent date. The budget is used up when annual net CO2 emissions reach zero. How much other climate forcers such as methane are cut affects the size of the budget.
A tradeable certificate, issued by a crediting program, that represents one tonne of carbon dioxide equivalent reduced or removed from the atmosphere and is tracked in a registry by a unique serial number.Source 13Source 6
The tonne is calculated as the difference between the project's emissions or removals and its baseline scenario, adjusted for leakage. A credit can be used only once: when a buyer claims it, the registry retires it so it can't be sold again. Credits differ in quality, which is why the ICVCM's Core Carbon Principles set a threshold covering additionality, permanence, robust quantification and no double counting.
A third-party assessment of how likely a carbon credit, or the project behind it, is to deliver the climate benefit it claims, looking at risks such as additionality, permanence and leakage.Source 21Source 22
The UK government sees a role for carbon credit rating agencies in giving extra assurance at project level, because the ICVCM does not assess how each project is implemented. Respondents to its 2025 consultation broadly supported ratings as a complement to programme and methodology standards, but called for clearer disclosure of rating criteria and noted that agencies can reach different results for similar projects.
Human activities that take CO2 out of the atmosphere and store it durably in geological, land or ocean reservoirs, or in products. Natural CO2 uptake not caused by people does not count.Source 1Source 10
The IPCC lists methods including afforestation, reforestation, biochar, bioenergy with carbon capture and storage (BECCS), direct air carbon capture and storage (DACCS), enhanced weathering and ocean alkalinity enhancement. Verra's definitions also exclude the growth of natural forests and the maintenance of declining carbon stocks from counting as removals. Credits from CDR are removal credits, which differ from credits for avoided or reduced emissions.
A measure of the total carbon dioxide emissions caused, directly and indirectly, by an activity, or built up across the life-cycle stages of a product. A household footprint covers home energy, transport, food and other consumption.Source 1Source 15
Under the GHG Protocol Corporate Standard, a company's inventory must report absolute emissions; intensity ratios are optional. Knowing the footprint is the starting point for deciding how much to reduce first and how many credits, if any, to buy for what remains.
A claim that the CO2 emissions linked to a company, product or event have been balanced by CO2 removals or offsets over a set period. Its meaning depends on which emissions are counted and which rules apply.Source 1Source 23
The IPCC notes that carbon neutrality may cover the full lifecycle, including scope 3, or only emissions under the subject's direct control, depending on the scheme. Offset-based claims are restricted: under Directive (EU) 2024/825, applied by EU member states from 27 September 2026, businesses may not claim a product has a neutral, reduced or positive climate impact on the basis of offsetting. The directive still allows businesses to advertise investments in carbon credit projects if the information isn't misleading.
A reduction, avoidance or removal of greenhouse gas emissions that one party pays for to counterbalance its own emissions elsewhere. In practice, this usually means buying and retiring carbon credits.Source 1Source 14Source 23
The IPCC notes that offsets need integrity rules such as additionality, appropriate baselines, permanence, and avoiding leakage and double counting. Offsetting isn't the same as cutting your own emissions: the SBTi doesn't count carbon credits as reductions toward science-based targets, and EU rules applied from 27 September 2026 ban claims that a product has a neutral, reduced or positive climate impact based on offsetting. Reduce first, then offset what remains.
The process of storing carbon in a carbon pool, a reservoir such as geological formations, land, the ocean or products. It is the storage that follows removing CO2 from the atmosphere.Source 1Source 24Source 6
How long the carbon stays stored matters to buyers. The ICVCM's Core Carbon Principles require that, where there is a risk of reversal, measures are in place to address the risk and compensate for any reversals.
Anything (a process, activity or mechanism) that takes a greenhouse gas, an aerosol or a gas that forms one out of the atmosphere. The IPCC uses the definition from the UNFCCC treaty text.Source 1
A sink is different from a pool, the reservoir where carbon is held. When people deliberately enhance biological sinks, the IPCC counts the result as anthropogenic removals, alongside engineered approaches.
A tax set per tonne of CO2 or CO2e emitted, usually charged on fossil fuels. It fixes the price of emitting but not the total amount of emissions.Source 25Source 1
A carbon tax and an emissions trading system are the two main forms of explicit carbon pricing. The tax gives emitters price certainty, while an ETS gives certainty over total emissions and lets the market find the price.
A standard-setting body that writes rules and methodologies for carbon projects, registers projects and issues credits, often through its own registry. Verra's Verified Carbon Standard is one example.Source 26Source 6Source 21Source 27
The ICVCM assesses programmes against its Core Carbon Principles, which require effective governance, a registry that tracks credits, public transparency and robust independent validation and verification. Only programmes that are CCP-Eligible can use the CCP label, and only on credits from approved categories.
A mark from the ICVCM showing a credit comes from a category of credits and a crediting program that it has assessed and approved against its Core Carbon Principles.Source 6Source 13
The ICVCM assesses carbon-crediting programs and categories of credits separately. A category groups credits from the same type of activity, issued under the same program using the same version of the same methodology. Only CCP-Eligible programs can tag credits from CCP-Approved categories with the label. The ICVCM says the label is meant to help buyers tell apart credits that represent real, verifiable climate impact. Its reviews look at categories, not individual projects, so project-level checks still matter.
A credit issued under the Kyoto Protocol’s Clean Development Mechanism, equal to one tonne of CO2 reduced or avoided by a project in a developing country.Source 28Source 3
Countries with Kyoto commitments could use CERs to meet part of their targets. COP29 decisions set out procedures for transitioning some CDM activities and CERs to the Paris Agreement’s Article 6.4 mechanism. When buying older CERs, check the vintage and whether the activity has transitioned.
Improved cooking devices and fuels that cut emissions by burning fuel more efficiently or switching to lower-emission fuels. Carbon projects deploy them in homes, institutions and small businesses and earn credits for the reductions.Source 29Source 30
Credits depend on estimates of how much fuel the stoves save and how much they are used. In March 2025 ICVCM approved three cookstove methodologies (Gold Standard's Metered & Measured Energy Cooking Devices, Gold Standard's TPDDTEC v4.0 and Verra's VM0050) as meeting its Core Carbon Principles, on condition that projects use the most robust tools available for estimating fuel consumption and monitoring usage.
The Kyoto Protocol mechanism, set out in its Article 12, under which emission-reduction projects in developing countries earned saleable credits called CERs.Source 28Source 3
Industrialised countries could use CERs toward part of their Kyoto targets. The first CDM project was registered in 2005 in Brazil. Under Paris Agreement rules, some CDM activities can transition to the Article 6.4 mechanism with host-country approval.
A US nonprofit carbon crediting program and registry that develops project protocols and issues and tracks credits called Climate Reserve Tonnes (CRTs) for voluntary and compliance carbon markets.Source 31Source 32
The Reserve began as the California Climate Action Registry, created by the State of California in 2001. In California and Washington it acts as an approved Offset Project Registry for the compliance programs, and in Chile and Tamaulipas its credits can be used by regulated entities. Every CRT carries a unique serial number that encodes the project, vintage and issuance batch, which you can look up in its public registry.
Positive effects of a climate project beyond cutting or removing emissions, such as cleaner air, jobs, biodiversity or coastal protection.Source 1Source 33
Some standards verify these benefits separately. Gold Standard projects must show verified contributions to at least three Sustainable Development Goals, and Verra VCUs can carry extra labels for community and biodiversity benefits, which can raise their price.
A common unit that expresses different greenhouse gases as the amount of carbon dioxide with the same warming effect over a chosen time period. One carbon credit represents one tonne of CO2e.Source 1Source 15Source 13
Each gas is converted using a metric, most often its global warming potential over 100 years (GWP100), which countries use for reporting under the Paris Agreement. The IPCC cautions that equal amounts of CO2e don't have identical effects on every aspect of climate change, so the choice of metric and time horizon matters.
A statement that the credits a company bought counterbalance, or "net out", emissions from its own operations or value chain. A "carbon neutral" claim is the typical example.Source 16Source 23
Compensation claims face growing scrutiny and regulation. From 27 September 2026, EU consumer law bans claims, based on offsetting, that a product has a neutral, reduced or positive greenhouse gas impact. Companies can still describe their investment in carbon credit projects if they do so without misleading consumers.
A carbon market created by law, in which regulated companies must surrender allowances, or in some schemes eligible offset credits, to cover their emissions. The EU Emissions Trading System is one example.Source 8Source 31
The EU ETS uses a cap-and-trade design: a cap limits total emissions from covered installations and operators, the cap falls each year, and each allowance gives the right to emit one tonne of CO2e; allowances are auctioned and can be traded. Some compliance schemes also accept offset credits: the Climate Action Reserve, for example, acts as an approved Offset Project Registry for the California and Washington programs.
A statement that a company has funded climate action beyond its value chain, such as through carbon credits, without saying this cancels out its own emissions.Source 16
SBTi contrasts contribution claims with compensation claims, which present credits as netting out a company’s emissions. A contribution claim describes the support as a contribution to global or national mitigation efforts. Claims should still be accurate, transparent and backed by clear reporting.
An accounting entry under Article 6 of the Paris Agreement: the country that transfers an emission reduction adds it back to its own emissions total, and the country using it subtracts it, so it is counted once.Source 11Source 3Source 13
The rule prevents the same tonne from counting toward two countries' nationally determined contributions (NDCs). It applies to authorised ITMOs, including Article 6.4 credits that a host country has authorised. For voluntary buyers it matters because, without one, the host country may also count the reduction toward its own target; the ICVCM calls this double claiming.
ICAO's global scheme that requires airlines to offset CO2 emissions from international flights between participating countries above a baseline, set at 85% of 2019 levels from 2024.Source 34Source 13
CORSIA stands for the Carbon Offsetting and Reduction Scheme for International Aviation. It runs in phases: a pilot phase (2021 to 2023), a first phase (2024 to 2026) and a second phase (2027 to 2035). Country participation is voluntary until the second phase, which covers all ICAO states except those exempted. During the pilot phase the baseline was 2019 emissions. Airlines meet their obligations by buying and cancelling eligible emissions units from crediting programs approved by the ICAO Council.
The period during which a project's verified emission reductions or removals can be issued as carbon credits. Programmes set its length and whether, and how, it can be renewed.Source 26Source 35Source 10
The ICVCM requires programmes to define the length of crediting periods, including the total across all renewals, and to reassess the baseline scenario at each renewal. It also expects aggregate crediting periods to be short enough to allow ambition to increase over time. Under Verra's VCS, the crediting period does not include any potential renewals.
The use of digital tools such as remote sensing, smart sensors, machine learning and mobile apps to collect, process and analyse the data used to monitor, report and verify carbon projects.Source 36Source 37
Verra began a DMRV pilot programme in 2023 to test such platforms in its VCS Program and to draft guidance on how they should be built and certified. It lists possible benefits, such as more standardisation and lower cost and time, and risks, such as greater data or method uncertainty and reduced transparency.
A chemical process that captures CO2 directly from ambient air. When the captured CO2 is then stored, the combined process (DACCS) is a form of carbon dioxide removal.Source 1Source 38
The IPCC separates direct air capture, which produces a stream of captured CO2, from direct air carbon dioxide capture and storage (DACCS), which adds storage. For removal credits, the storage step is what matters. Registries focused on carbon removal, such as Isometric, list direct air capture among the pathways they certify.
When the same tonne of emission reduction or removal is counted more than once toward climate goals, through double issuance, double claiming or double use.Source 6Source 39
Avoiding it is one of the ICVCM Core Carbon Principles. Registries help by giving each credit a unique serial number so it can be traced from issuance to retirement. When buying, check that credits are retired in your name and not also claimed elsewhere.
How long the carbon behind a credit stays out of the atmosphere. Removals stored in geological reservoirs or minerals can last centuries to millennia; carbon stored in forests and soils faces a higher risk of reversal.Source 40Source 19
The Oxford Principles say credits used against residual emissions should increasingly come from removals with durable storage and a low risk of reversal. Some standards set minimum durability: Isometric’s default threshold is 1,000 years where a protocol does not specify one.
A number that converts an activity, such as litres of fuel burned or kilowatt-hours of electricity used, into the greenhouse gas emissions it causes.Source 1Source 15Source 41
Emission factors are usually averages built from measurement data, so they estimate rather than measure an activity's actual emissions. Governments publish sets of them: the UK's greenhouse gas conversion factors, for example, let organisations calculate emissions from energy use, transport, waste and more. Footprint calculators multiply activity data by factors like these, so the factors chosen shape how many tonnes you might decide to offset.
Emissions expressed per unit of physical activity or economic value, such as tonnes of CO2 per unit of electricity generated, rather than as an absolute total.Source 15Source 1
The GHG Protocol Corporate Standard requires companies to report absolute emissions; intensity ratios are an optional extra that helps compare performance over time or between businesses of different sizes. Because intensity can fall while total emissions rise, check both when a company describes its progress. The IPCC glossary treats emissions intensity and emission factor as the same coefficient.
A government scheme that caps the total greenhouse gas emissions of covered emitters and issues tradable allowances, so a market sets the carbon price.Source 42Source 8
Each covered company must hand in allowances for its emissions and can buy extra or sell spare ones. Because the cap fixes the quantity, an ETS gives certainty over the emissions outcome while the market sets the price; a carbon tax does the reverse. ETS allowances belong to compliance markets and are a different instrument from voluntary carbon credits.
A carbon removal method that grinds silicate rock into fine particles and spreads it on land, often farmland, to speed up the natural chemical reactions that draw CO2 out of the air.Source 1Source 43
Natural weathering takes thousands of years; grinding the rock increases its surface area so it reacts faster. Puro.earth published the first crediting methodology for it and describes the storage as lasting 1,000+ years. It may also improve soil fertility.
The European Union’s Emissions Trading System, a cap-and-trade carbon market launched in 2005 that covers power, industry, aviation and, since 2024, maritime emissions.Source 8
It runs in all EU countries plus Iceland, Liechtenstein and Norway, and covers about 40% of EU greenhouse gas emissions. The cap falls each year. Companies monitor and report emissions annually and must surrender one allowance per tonne of CO2e or face heavy fines. EU allowances are compliance instruments, not voluntary carbon credits.
An agreement in which a buyer and seller set the quantity of something, such as carbon credits, to be delivered at a future date, with the price agreed in advance or fixed at delivery.Source 44Source 45
The US Commodity Futures Trading Commission notes that forward contracts are negotiated directly between the parties, unlike standardised exchange-traded futures, and that each party carries the risk that the other defaults. In carbon removal, Puro.earth describes buyers securing future supply through offtake contracts, while spot purchases meet immediate needs.
A quantified list of an organisation's greenhouse gas emissions and their sources, prepared within a defined boundary and organised by scope.Source 15Source 24
Under the GHG Protocol Corporate Standard, companies set organisational and operational boundaries, must report scope 1 and scope 2, may report scope 3, and track emissions against a base year. Credits do not reduce the inventory: the VCMI Claims Code says credits behind its claims are not counted as internal emission reductions.
A set of widely used standards, built on a partnership between the World Resources Institute and the World Business Council for Sustainable Development, for measuring and reporting greenhouse gas emissions from organisations, value chains, products and mitigation projects.Source 46Source 47
Its Corporate Standard covers the seven Kyoto Protocol gases and was supplemented in 2015 by the Scope 2 Guidance. The Corporate Standard states that it should not be used to quantify reductions from mitigation projects for use as offsets or credits; the GHG Protocol for Project Accounting covers that. GHG Protocol reports that in 2023, 97% of disclosing S&P 500 companies reported to CDP using it.
A measure of how much warming a given mass of a greenhouse gas causes over a chosen period, compared with the same mass of carbon dioxide.Source 1Source 41
GWP combines how long a gas stays in the atmosphere with how strongly it traps heat. The value depends on the time horizon: under the Paris Agreement rulebook, countries report using 100-year values (GWP100) from the IPCC's Fifth Assessment Report or a later one. Different IPCC reports give different values, so check which set a footprint or methodology uses; the UK's 2026 government conversion factors, for example, use AR4 values for some categories and AR5 values for others.
A not-for-profit based in Geneva, Switzerland, that runs the Gold Standard for the Global Goals, a standard for certifying climate and sustainable development projects. It issues credits called Verified Emission Reductions (VERs).Source 48Source 39Source 49
Gold Standard says every project it certifies makes verified contributions to at least three UN Sustainable Development Goals, always including SDG 13 (climate action). Its Impact Registry is where credits are issued, held, transferred and retired, with a unique serial number for each credit, and it also shows certified SDG impacts.
A gas in the atmosphere that absorbs and emits heat radiation, which causes the greenhouse effect. Carbon dioxide, methane and nitrous oxide are among the main examples.Source 1Source 47
The IPCC names water vapour, carbon dioxide, nitrous oxide, methane and ozone as the primary greenhouse gases, and lists human-made gases such as sulphur hexafluoride, hydrofluorocarbons, chlorofluorocarbons and perfluorocarbons. Corporate reporting under the GHG Protocol covers seven gases: CO2, methane, nitrous oxide, HFCs, PFCs, SF6 and nitrogen trifluoride. Different gases are compared in CO2-equivalent terms.
The amount of CO2 emitted per unit of electricity by the power plants supplying a grid. It is used to estimate emissions from electricity use and the reductions from projects that displace grid power.Source 50Source 51
Corporate scope 2 reporting under the location-based method uses grid-average factors. For credits from projects that displace grid electricity, the UNFCCC's CDM tool calculates a 'combined margin': a weighted average of the operating margin (existing plants whose output the project would affect) and the build margin (future plants whose construction it would affect).
An independent, non-profit governance body that sets a global quality threshold for carbon credits, the Core Carbon Principles, and assesses crediting programs and methodologies against it.Source 52Source 6
It emerged in 2021 after the Taskforce on Scaling Voluntary Carbon Markets gained the backing of more than 250 organisations. Its ten Core Carbon Principles cover governance, emissions impact (additionality, permanence, robust quantification and no double counting) and sustainable impact. Programs that pass its assessment become CCP-Eligible and can apply the CCP label to credits from categories it has approved.
A forest carbon project type that changes how an existing forest is managed to keep or increase its carbon stocks above a baseline.Source 53
Credits depend on the gap between actual carbon stocks and the modelled baseline, so baseline assumptions matter. Climate Action Reserve’s U.S. Forest Protocol also requires natural forest management practices and more than 10% tree canopy cover.
Funding interventions inside a company's own value chain, often with suppliers such as farmers, that reduce or remove scope 3 emissions while benefiting communities and ecosystems. It differs from buying credits on the voluntary carbon market.Source 21
The UK government describes insetting as an emerging term, most associated with forest, land and agriculture (FLAG) supply chains. It notes that the GHG Protocol recommends inventory accounting for insetting, where the impact shows up as lower emission factors in the value chain rather than as separate tradable units, to reduce the risk of double counting.
A price per tonne of carbon that an organisation sets for itself and uses in decisions, such as testing investments against future carbon costs, even where no law requires it.Source 54
A common form is a 'shadow price', a notional cost per tonne built into capital decisions to surface risks and opportunities. Companies use it to prepare for future carbon regulation and carbon prices that could raise their costs.
The Intergovernmental Panel on Climate Change: the UN body that assesses the science of climate change, its impacts and risks, and options for adaptation and mitigation. It reviews published research rather than doing its own.Source 55
It was created in 1988 by the World Meteorological Organization (WMO) and the UN Environment Programme (UNEP), and its members are governments. It has three Working Groups and a Task Force on National Greenhouse Gas Inventories, which develops methods for calculating and reporting national emissions and removals.
A carbon crediting program and registry, founded in 2022, that certifies durable carbon removal. Under its current standard it issues carbon dioxide removal credits and emission reduction credits, each for one net tonne of CO2e.Source 19Source 20Source 38
Each Isometric credit is publicly visible on its registry with a unique serial number, credit type, durability, the protocol version used and its ownership history. A credit starts as Active and becomes Retired when used for a claim, or Canceled, for example to compensate for over- issuance or a reversal. Buyers retire credits through the Isometric Registry, which issues a retirement certificate.
The step in which a carbon crediting program creates new credits in a project's registry account, after an independent body has verified the emission reductions or removals the project achieved.Source 10Source 20
Credits are issued for results that have already been verified, not for promised future outcomes: Verra's verification is an ex-post check of what happened during a monitoring period, and Isometric issues credits once a verified removal has taken place. Each issued credit gets a unique serial number and a vintage. Isometric notes that the vintage year (when the removal or reduction happened) is often, but not always, the year of issuance, because reporting and verification take time.
An internationally transferred mitigation outcome: an emission reduction or removal that one country authorises for transfer to another country or for other international uses under Article 6.2 of the Paris Agreement.Source 11
Under the UNFCCC guidance adopted at CMA.3, ITMOs must be real, verified and additional, are measured in tonnes of CO2 equivalent (or another metric the countries agree), and must represent mitigation from 2021 onward. They can count toward another country's nationally determined contribution (NDC) or, if authorised, toward other international mitigation purposes. The countries involved apply corresponding adjustments so the same tonne isn't counted twice. Article 6.4 credits become ITMOs once authorised.
REDD+ forest protection accounted for and credited across a whole jurisdiction, such as a country or state, rather than one project area. Individual projects can be "nested" within it.Source 56Source 57
Verra’s Jurisdictional and Nested REDD+ (JNR) Framework and ART TREES are jurisdictional methodologies. In November 2024 the ICVCM approved both for the CCP label, noting they operate at a much larger scale than project-based REDD+.
A 1997 treaty under the UNFCCC that set legally binding emission targets for developed countries listed in its Annex B. Its Article 12 created the Clean Development Mechanism for projects in developing countries.Source 58Source 3
It entered into force on 16 February 2005. Annex B Parties agreed to cut emissions of six greenhouse gases by at least 5% below 1990 levels in 2008–2012, and a second period (2013–2020) was agreed in 2012 through the Doha Amendment. Under the CDM, projects in developing countries earned Certified Emission Reductions (CERs); some CDM activities may transition to the Paris Agreement's Article 6.4 mechanism.
A project that collects methane-rich gas from decomposing landfill waste and destroys it by flaring or burning it for energy, earning credits for the methane kept out of the air.Source 59Source 60
Landfill gas is roughly half methane, a far more potent greenhouse gas than CO2. Under protocols such as Climate Action Reserve’s, only methane destroyed beyond what regulations already require is credited, so legal requirements affect additionality.
When a project's emission cuts are partly cancelled out by emissions rising elsewhere because of the project, such as logging moving to an unprotected forest nearby.Source 13Source 1
The ICVCM describes several types: activity-shifting (emissions move location, such as farming displaced by tree planting), market (less timber or another product from the project area leads to more production elsewhere), ecological (effects on hydrologically connected areas) and upstream or downstream emissions. Credit calculations must deduct leakage, so a methodology that underestimates it leads to over-crediting.
A document from a host country's designated Article 6 authority that authorises a project's mitigation outcomes for specified uses, such as other countries' NDCs, and commits the host to apply corresponding adjustments.Source 61Source 3
Under Verra's Article 6 Label Guidance, an LoA should state the authorised uses ('all uses', or one or more of NDC use, international mitigation purposes and other purposes), the 'first transfer' condition and the host's commitment to corresponding adjustments. Verra applies an Article 6 Label only to VCUs covered by an LoA uploaded to its registry. If a credit is sold as 'authorised', the LoA is the document to ask to see.
A method for compiling and evaluating the inputs, outputs and potential environmental impacts of a product or service across its whole life cycle, from raw materials to end of life.Source 58Source 62
The IPCC glossary definition builds on ISO standards. The GHG Protocol Product Life Cycle Standard applies the approach to greenhouse gases, treating a product's life cycle as linked stages from raw material acquisition or generation to end-of-life.
A way of calculating scope 2 emissions using the average emission factor of the grid where electricity is consumed, for a defined area such as a country or region, regardless of the contracts a company holds.Source 51
The GHG Protocol Scope 2 Guidance says the method reflects the average emissions intensity of the grids where energy is used, and that grid-average factors should not be adjusted for contractual claims. Companies with operations in markets offering contractual instruments must report both location-based and market-based totals.
A way of calculating scope 2 emissions from purchased electricity using emission factors from the contracts a company holds, such as energy attribute certificates, power purchase agreements or supplier-specific rates.Source 51
Where a company has no contractual information that meets the GHG Protocol's Scope 2 Quality Criteria, it uses a 'residual mix' factor representing untracked or unclaimed energy. Companies with operations in markets that offer such contracts must report scope 2 both ways, market-based and location-based, which the guidance calls dual reporting.
A greenhouse gas that is the main component of natural gas. Human sources include hydrocarbon fuels, livestock farming and rice paddies; it also forms naturally where organic matter decays without oxygen, as in wetlands.Source 1Source 35
The IPCC classes methane as a short-lived climate forcer: such gases stay in the atmosphere for hours to about two decades, far less than CO2, but significantly affect warming while they do. Credits from methane projects are expressed in CO2e, and the ICVCM requires programmes to disclose the global warming potential values used for that conversion.
The rulebook a project must follow to calculate its emission reductions or removals, covering eligibility, the project boundary, the baseline, additionality and monitoring.Source 63Source 13Source 7
Each crediting program publishes methodologies for specific sectors and project types. Under Verra's VCS, methodologies go through public consultation and review by independent experts before use. Because the methodology sets how a credit's numbers are calculated, the ICVCM assesses credits by category, which includes the methodology version, and requires programs to be able to review, suspend or withdraw methodologies found to overestimate reductions or removals.
The process of measuring emissions or removals, reporting the results in a set format, and having them independently checked. It is how a project shows that the reductions behind its credits happened.Source 1Source 13
The IPCC glossary describes measurement as collecting data over time (for example field measurements, remote sensing or interviews), reporting as formal reporting in agreed formats, and verification as formally checking those reports. In carbon crediting, verification is a periodic, independent third-party check by an accredited validation and verification body (VVB) before credits are issued.
A country's climate plan under the Paris Agreement, setting out how it intends to cut its emissions and, for some countries, how it will adapt and what support it needs or offers.Source 58Source 61
Article 4.2 of the Paris Agreement requires each Party to prepare, communicate and maintain successive NDCs. NDCs matter to credit buyers because of Article 6: when a host country authorises credits for use by others, it commits to a corresponding adjustment and does not use those authorised outcomes towards its own NDC, so the same reduction is not counted twice.
Actions that protect, sustainably manage or restore natural or modified ecosystems to address societal challenges such as climate change, while also benefiting people and biodiversity.Source 1
A state in which the greenhouse gases an entity or the world emits are balanced by the amount it removes from the atmosphere over a set period.Source 1Source 14
For companies, the SBTi Corporate Net-Zero Standard defines net zero as cutting scope 1, 2 and 3 emissions to zero or a residual level in line with 1.5°C pathways, then neutralising any remaining emissions by removing carbon and storing it permanently. Under that standard, carbon credits don't count as reductions toward targets, so a company can't reach net zero by buying credits instead of cutting emissions.
The risk that carbon stored by a project will later be released. Standards assess it to decide how many credits a project must set aside in a buffer pool.Source 18Source 6
Verra’s AFOLU Non-Permanence Risk Tool scores internal, external and natural risks and adds them into a risk rating, with a minimum of 12. A higher rating means more buffer credits; projects rated above 60 fail the analysis and cannot be credited.
A contract in which a buyer commits to purchase credits that a project will produce in the future, often before it is certified. It gives the supplier expected revenue it can use to raise finance.Source 64Source 45
Puro.earth also calls these agreements advance market commitments and says they help carbon removal suppliers secure debt and equity financing, while buyers gain early access to future credits. Credits are delivered to the buyer only after they are issued; Puro.earth offers a service in which supplier and buyer register agreed deliveries before issuance so the credits reach the buyer when they are issued.
When a project is issued more credits than the emission reductions or removals it actually achieved, for example because its baseline was set too high or its leakage was underestimated.Source 7Source 13
Each credit should stand for one tonne of CO2 equivalent, so over-crediting means buyers claim impact that didn't happen. The ICVCM requires methodologies to be conservative enough that reductions are likely not overestimated and very unlikely to be very significantly overestimated. Programs must be able to review, suspend or withdraw methodologies shown to overestimate, and can cancel credits to compensate for earlier excess issuance.
Four University of Oxford principles, first published in 2020 and revised in 2024, on how organisations should use carbon offsets in a way that supports net zero.Source 40
In short: cut your own emissions first and use only high-integrity credits; shift toward carbon removals for residual emissions by the net zero target date; favour removals with durable storage and a low risk of reversal; and support new and integrated approaches. They describe how an offsetting portfolio should shift over time.
An international climate treaty adopted in December 2015 at COP21 in Paris under the UNFCCC. Its goals include holding warming well below 2°C above pre-industrial levels and pursuing efforts to limit it to 1.5°C.Source 58Source 1Source 3
It entered into force on 4 November 2016. Each Party prepares successive nationally determined contributions (NDCs). Article 6 lets countries cooperate on their NDCs, both through transfers of mitigation outcomes between countries (Article 6.2) and through a crediting mechanism (Article 6.4). That is why some carbon credits now carry information about host-country authorisation and corresponding adjustments.
A benchmark set for a whole class of activities, such as emissions per unit of output, that a project must beat to count as additional or that sets its crediting baseline, instead of a project-by-project assessment.Source 10Source 35
Verra calls this a performance method, one type of standardised method, and expresses benchmarks in tonnes of CO2e per unit of output or input, or as a sequestration metric. The ICVCM requires standardised approaches to be set at a suitable level of aggregation, published with their data, reviewed regularly (for example every three years) and checked at validation.
How long the carbon behind a credit stays out of the atmosphere. Credits carry a risk if stored carbon can be released again, for example when a protected forest burns.Source 6Source 7Source 18
The ICVCM's permanence principle requires reductions or removals to be permanent or, where reversal is possible, backed by measures that address the risk and compensate any reversal. It treats carbon stored in forests, soils, wetlands and other biological reservoirs as having a material reversal risk. For these, CCP-Eligible programs must require monitoring for at least 40 years from the start of the first crediting period (or to the end of the crediting period, if later) and keep a pooled buffer reserve.
The company or organisation that designs and runs a carbon project, documents it under a crediting program's rules and holds the rights to the reductions or removals it generates. Verra calls this party the project proponent.Source 10Source 32Source 20
Verra's definitions say a project proponent has overall control of, and responsibility and accountability for, the project and must be able to show both the right to operate it and the right to its reductions and removals. The Climate Action Reserve assigns each project developer an ID that appears in its credit serial numbers. Carbon removal registries such as Isometric use the term supplier for the party that removes CO2 and sells it to buyers.
A Nasdaq-backed carbon removal standard and registry that certifies durable carbon removal and issues CO2 Removal Certificates (CORCs), each confirming one tonne of CO2 durably removed from the atmosphere.Source 65Source 66Source 45
Puro.earth certifies only removals, not avoided or reduced emissions, under the Puro Standard, and labels durability as 100+, 200+ or 1,000+ years. CORCs are issued to the supplier in the Puro Registry and retired once the buyer applies them to a climate claim. Buyers can purchase CORCs on the spot market or secure future supply through offtake agreements.
A change in the balance of energy entering and leaving the atmosphere caused by something like a greenhouse gas. For flights, the term covers extra warming from contrails, nitrogen oxides and water vapour on top of the CO2.Source 1Source 41Source 67
The UK government's 2026 conversion factors recommend multiplying a flight's CO2 by 1.7 as a central estimate of these effects, while stressing that the multiplier is highly uncertain. The European Commission cites an EASA finding that non-CO2 effects made up about two-thirds of aviation's net climate forcing in 2018. Flight calculators differ on whether they apply such an uplift, which changes a flight's footprint and the number of credits needed to cover it.
Reducing emissions from deforestation and forest degradation, plus conserving forest carbon stocks, managing forests sustainably and enhancing forest carbon stocks, as defined under UNFCCC decisions.Source 1Source 57
REDD+ credits can come from individual projects or from whole jurisdictions. In November 2024 ICVCM approved three REDD+ methodologies as meeting its Core Carbon Principles: ART's TREES v2.0, Verra's VM0048 and Verra's Jurisdictional and Nested REDD+ (JNR) Framework v4.1. Credits issued under them are eligible for the CCP label.
An online database, run by or for a carbon crediting program, that records projects and every credit issued, who holds each credit, and when it is transferred, retired or cancelled.Source 10Source 5Source 39
Registries are how credits are tracked. The Verra Registry gives public access to project and credit information, and Verra treats a credit recorded in a holder's account as prima facie evidence of that holder's entitlement to it. At ACR, credits are bought and sold directly between buyer and seller or on a linked exchange, and the parties then record the transfer or retirement on the ACR Registry. Gold Standard calls its Impact Registry the 'source of truth' for its credits. A retirement record on the registry, not an invoice, is the evidence that your credits were used.
A requirement that a carbon project's reductions or removals go beyond what laws and regulations already require. An activity that is legally mandated, where that mandate is enforced, cannot earn credits for meeting it.Source 10Source 35
Verra and the ICVCM treat all laws in high-income countries as enforced. Elsewhere, a law that is not systematically enforced need not rule a project out, but the ICVCM requires authoritative, up-to-date evidence of non-enforcement. Regulatory surplus is one part of showing additionality.
A credit for carbon dioxide taken out of the atmosphere and stored, for example in trees, soils, rock formations or products, rather than for emissions that were prevented.Source 13Source 1Source 14
The ICVCM defines a removal as human-caused removal of CO2 from the atmosphere with durable storage in land-based or geological reservoirs or in products. The IPCC's list of removal methods includes afforestation, biochar, bioenergy with carbon capture and storage (BECCS) and direct air capture with storage. Storage in forests and soils can be reversed, so those credits rely on monitoring and buffer pools. The SBTi Corporate Net-Zero Standard requires residual emissions to be neutralised by removing and permanently storing carbon.
A tradable certificate that represents the environmental attributes of one megawatt-hour of renewable electricity delivered to the grid.Source 68
RECs and carbon offsets are different instruments. A REC covers 1 MWh of renewable generation and backs claims about using renewable electricity; an offset represents one tonne of emissions avoided, reduced or removed.
Emissions that remain after all available reduction measures consistent with 1.5°C pathways have been applied. Under net-zero standards they must be balanced by permanently removing carbon from the atmosphere.Source 24Source 14
The SBTi Corporate Net-Zero Standard expects most companies to cut emissions by at least 90% through long-term targets and then neutralise residual emissions by removing carbon and storing it permanently. A company cannot claim net-zero until it has met its long-term target across all scopes and neutralised what is left.
The permanent removal of a carbon credit from circulation on a registry to show that its owner has used it in a claim. A retired credit cannot be sold, transferred or used again.Source 10Source 20Source 39
Verra's VCS rules define retirement as taking a credit out of circulation because its owner has used it in a claim, and treat it separately from cancellation, which removes credits for other reasons. On the Isometric Registry a retired credit can no longer be updated and a retirement certificate is issued, which prevents the same tonne being counted twice. A retirement can be made for the account holder or for a named beneficiary. When you buy credits, ask for the public registry record of the retirement, including the serial numbers.
The release back into the atmosphere of carbon that a credited project had stored, for example through a forest fire or a leak from storage.Source 6Source 19
The ICVCM Core Carbon Principles require that, where there is a risk of reversal, measures exist to address that risk and compensate for any reversal. Standards usually do this through a buffer pool: when a reversal happens, credits are cancelled from the buffer.
Rules that aim to stop carbon projects from harming people or nature, so that a project cutting emissions does not create new social or environmental damage.Source 6Source 69
The ICVCM Core Carbon Principles require crediting programs to have clear guidance, tools and compliance procedures so that projects meet or exceed widely established social and environmental safeguard practice while delivering positive sustainable development impacts.
A charity that writes standards for corporate emissions targets, such as the Corporate Net-Zero Standard, and, through a subsidiary, validates the targets companies submit.Source 70Source 14
It began as a collaboration between CDP, the UN Global Compact, We Mean Business Coalition, WRI and WWF. Under its Corporate Net-Zero Standard, carbon credits do not count as reductions toward a company’s science-based targets; they can only be used to neutralise residual emissions or to fund mitigation beyond those targets.
A company greenhouse gas reduction target set in line with what climate science says is needed, typically using SBTi criteria and pathways.Source 71Source 14
SBTi requires near-term scope 1 and 2 targets to align with 1.5°C pathways. Companies can have targets validated through SBTi Services. Buying carbon credits does not count as progress toward these targets; credits must be reported separately from the GHG inventory.
Greenhouse gas emissions from sources a company owns or controls, such as fuel burned in its boilers, furnaces and vehicles, or gases released from its own production processes.Source 15Source 14
Scope 1 is one of three scopes in the GHG Protocol Corporate Standard, which requires companies to account for and report scopes 1 and 2 at a minimum. Direct CO2 from burning biomass is reported separately rather than in scope 1. Cutting these emissions comes before offsetting: under the SBTi Corporate Net-Zero Standard, carbon credits don't count as reductions toward targets.
Indirect greenhouse gas emissions from generating the electricity, steam, heat or cooling that a company buys and uses. They physically occur where the energy is generated, not at the company's site.Source 47Source 72Source 15
The GHG Protocol's Scope 2 Guidance, added in 2015, standardises how companies measure these emissions and is required reading for companies following the Corporate Standard. Scope 2 is usually calculated from metered electricity use and an emission factor, which may be supplier-specific or based on the local grid.
All other indirect emissions in a company's value chain, from sources it doesn't own or control, such as producing the materials it buys, transporting fuels and the use of products it sells.Source 15Source 73Source 14
The GHG Protocol's Scope 3 Standard, released in 2011, sorts these emissions into 15 categories upstream and downstream of a company's operations, and the GHG Protocol says most corporate emissions come from scope 3 sources. Under the SBTi Corporate Net-Zero Standard, companies must cut scope 1, 2 and 3 emissions to zero or a residual level before neutralising what remains.
A unique code that a registry gives each carbon credit it issues, so the credit can be traced from issuance through every transfer to retirement and is not counted twice.Source 32Source 39
Serial numbers usually encode information about the credit. The Climate Action Reserve's format includes the issuing registry, unit type, country, project ID, project type, project developer ID, vintage year and batch number, and credits are issued in batches with a start and end number. Gold Standard's Impact Registry generates a unique serial number for every credit it issues. Asking for the serial numbers of credits retired on your behalf lets you check them yourself on the public registry.
Carbon held in soil organic matter. Soil carbon projects change farming practices to increase it, removing CO2 from the atmosphere.Source 1Source 74
Soil carbon programs, such as Climate Action Reserve’s Soil Enrichment Protocol, set rules to quantify, monitor and verify the extra carbon. They may also credit cuts in other emissions, such as nitrous oxide from fertiliser.
A market where a product is paid for and delivered immediately. For carbon credits, a spot purchase means buying credits available for delivery now, rather than agreeing to take future credits under a forward or offtake contract.Source 44Source 75
A forward contract, by contrast, fixes delivery of a set quantity at a future date. In the US, the CFTC regulates derivatives but cannot broadly regulate spot commodity markets; it can still act against fraud and manipulation in them, and has warned about fraud in carbon spot markets, including 'ghost' credits listed on registries.
The 17 global goals agreed by the United Nations in the 2030 Agenda for Sustainable Development, covering poverty, hunger, health, education, clean energy, climate action and more.Source 1Source 69
Carbon projects often report which SDGs they support. Gold Standard requires certified projects to show verified positive contributions to at least three SDGs, one of which must be SDG 13, Climate Action.
The United Nations Framework Convention on Climate Change: a 1992 treaty whose ultimate objective is stabilising greenhouse gas concentrations at a level that prevents dangerous human interference with the climate. The Kyoto Protocol and Paris Agreement implement it.Source 1Source 58
It was opened for signature at the 1992 Earth Summit in Rio de Janeiro and entered into force in March 1994; the IPCC glossary records 197 Parties as of September 2020. Its Conference of the Parties (COP), made up of the Parties that have ratified or acceded to it, is the convention's supreme body.
An independent assessment of a carbon project's design by a VVB, checking that it follows the crediting program's rules and that its assumptions and methods for estimating future results are reasonable.Source 10Source 6
Validation looks forward, at the project as designed; verification later checks the reductions or removals that actually happened. Under Verra's rules the VVB records its findings in a validation report. ICVCM's Core Carbon Principles require crediting programs to have robust independent third-party validation and verification.
An organisation that sets guidance on how companies can credibly use carbon credits and communicate that use, mainly through its Claims Code of Practice.Source 76
VCMI's Claims Code expects a company to set near-term, science-aligned emission reduction targets consistent with net zero by 2050 and then buy high-quality carbon credits representing reductions or removals outside its value chain. It is aimed at companies, but VCMI also presents it as a reference for buyers of goods and services, investors and regulators judging climate claims. VCMI published a separate Scope 3 Action Code of Practice in April 2025.
Guidance from the Voluntary Carbon Markets Integrity Initiative on how companies can use carbon credits alongside science-aligned emission cuts, and how to describe that use credibly.Source 76Source 77
Companies must meet foundational criteria, including near-term reduction targets, before claiming. The Silver, Gold and Platinum Carbon Integrity claims require retiring high- quality credits equal to at least 10%, 50% or 100% of remaining emissions. VCMI defines high-quality credits as those meeting the ICVCM Core Carbon Principles. Credits cannot count toward within-value-chain targets.
The carbon credit issued by Verra’s Verified Carbon Standard (VCS) Program. Each VCU represents a reduction or removal of one tonne of CO2e by a project.Source 33
Issuance and retirement records are public on the Verra Registry. Only registry account holders, not individuals, can hold VCUs, and VCUs can only be retired on an individual’s behalf by an entity that holds a registry account. VCUs can carry extra labels, such as for community and biodiversity benefits.
The name Gold Standard uses for the carbon credits it issues. Each Gold Standard VER equals one tonne of CO2e reduced, avoided, removed or sequestered, as verified under its rules.Source 39Source 78
Each issued credit has a unique serial number on the Gold Standard Impact Registry, which tracks it from issuance to retirement. Some Gold Standard VERs are labelled as eligible for CORSIA or authorised under Article 6, which affects how they can be used.
A periodic independent audit, by a VVB, of the emission reductions or removals a project has already achieved during a monitoring period. Credits are issued for the verified amount.Source 10Source 6
In Verra's VCS Program, verification is an ex-post assessment based on historical data that decides whether the project's claim is materially correct and follows the rules. It differs from validation, which assesses the project's design. Each Verified Carbon Unit represents a tonne of reductions or removals verified by a VVB.
A greenhouse gas crediting program operated by Verra. Projects certified under its rules can be issued Verified Carbon Units (VCUs), each representing one tonne of CO2e reduced or removed.Source 27Source 10
Under the VCS Program, independent validation/verification bodies (VVBs) audit projects against the program rules and the methodology they apply, and the Verra Registry records each VCU from issuance to retirement. Version 5.0 of the VCS Program Definitions was issued on 16 December 2025. When you buy VCUs, the project ID and serial numbers let you look the credits up on the public Verra Registry.
The calendar year in which the emission reduction or removal behind a credit took place. It is not necessarily the year the credit was issued.Source 13Source 11
Verification happens after the reductions or removals occur, so credits are often issued after their vintage year. Vintage can affect what a credit may be used for: for example, ITMOs under Article 6.2 must represent mitigation from 2021 onward.
The decentralised market in which companies and other private buyers choose to buy and sell carbon credits, each representing one tonne of greenhouse gas reduced or removed, rather than doing so to meet a legal obligation.Source 79
The Integrity Council for the Voluntary Carbon Market (ICVCM) describes the market as driven by voluntary, private initiatives and not regulated by governments or financial authorities. It stresses that companies' priority must be to cut emissions in their own value chains, with credits used for emissions they cannot yet cut. ICVCM's Core Carbon Principles aim to set a common quality benchmark for credits sold in this market.
An independent auditing organisation approved by a carbon crediting program to validate project designs and verify the emission reductions or removals that projects report.Source 27Source 10Source 6
Verra describes VVBs as independent third parties that audit projects to confirm they meet the program's requirements, apply methodologies correctly, comply with local laws and avoid negative impacts on stakeholders. Credits are issued only for amounts a VVB has verified. ICVCM's Core Carbon Principles require crediting programs to have robust independent third-party validation and verification.
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