Article 6 of the Paris Agreement explained: international carbon markets and double counting
Article 6 is the Paris Agreement accounting system for international carbon markets. Learn how Article 6.2, Article 6.4, double counting, CORSIA and voluntary credits connect.
Article 6 is the Paris Agreement's accounting system for international carbon markets. Its first credits were approved for issuance in February 2026, but most voluntary carbon market credits still sit outside the Article 6 framework.
Article 6 implementation is moving quickly. This article reflects the state of play as of 8 June 2026, while the SB64 United Nations climate meetings in Bonn are running from 8 to 18 June 2026. Check the UNFCCC (United Nations Framework Convention on Climate Change) Article 6 pages and registry documents for the latest official updates before relying on compliance details.
Related guides
Start with the Paris Agreement guide, then read CORSIA explained, how carbon credits work, the voluntary carbon market in 2026, carbon credit quality and COP31 Antalya 2026.
On 26 February 2026, the UN carbon market announced that the first credits had been approved for issuance under the Paris Agreement Crediting Mechanism (PACM). The project was a clean-cooking programme in Myanmar, distributing efficient cookstoves that reduce harmful air pollution and lower pressure on local forests. A portion of the credits was authorised for use in the Republic of Korea, meaning those units can be transferred for use by Korean entities and reflected in Korea's national climate accounting. The remainder stays with Myanmar and can contribute to Myanmar's own Nationally Determined Contribution (NDC).
The language matters. These credits were approved for issuance under Article 6.4. That is different from saying Article 6 is now a fully mature carbon market. As of June 2026, the mechanism has moved from rulebook to early operation, but the registry, project pipeline, authorisation practice and country-level accounting systems are still developing.
The Myanmar example also shows why Article 6 is different from the older carbon market architecture. According to the UNFCCC announcement, the approved credit volume was around 40% lower than the same project would have received under the Clean Development Mechanism (CDM), because the Article 6.4 process applied updated values and more conservative calculations. That is the design intent: each credited tonne should more credibly represent a real tonne of emissions reduction or removal.
Article 6 is now live enough to matter, but immature enough to be misunderstood. It matters for aviation through CORSIA (Carbon Offsetting and Reduction Scheme for International Aviation), for companies buying voluntary credits, for countries selling mitigation outcomes, and for investors trying to understand where the next carbon market bottlenecks may appear.
Quick answer
| Question | Short answer |
|---|---|
| What is Article 6? | The carbon market chapter of the Paris Agreement. It sets rules for countries to cooperate on emissions reductions and transfer some mitigation outcomes internationally. |
| What problem does it solve? | Double counting. The same emissions reduction should not be claimed by both the host country and the buyer country or company. |
| What is a corresponding adjustment? | An accounting adjustment made by the host country so an internationally transferred reduction is not also counted toward that host country's own NDC. |
| What is Article 6.2? | The country-to-country route. Countries make bilateral or multilateral agreements and transfer Internationally Transferred Mitigation Outcomes (ITMOs). |
| What is Article 6.4? | The central UN-supervised crediting mechanism, now called the Paris Agreement Crediting Mechanism. |
| Are most voluntary carbon market credits Article 6-authorised? | No. Most voluntary carbon market (VCM) credits still operate outside Article 6 and do not come with host-country corresponding adjustments. |
| Why does CORSIA depend on Article 6? | CORSIA requires eligible credits to have host-country Letters of Authorisation (LoAs). Those authorisations rely on countries having Article 6 systems in place. |
What Article 6 is
Article 6 is the part of the Paris Agreement that allows countries to cooperate voluntarily in meeting their climate targets. It was included in the agreement adopted at COP21 in Paris in December 2015. The detailed rules were only agreed at COP26 in Glasgow in November 2021, after years of difficult negotiations.
There are three main parts:
| Mechanism | What it does | Carbon market relevance |
|---|---|---|
| Article 6.2 | Allows countries to transfer mitigation outcomes through bilateral or multilateral cooperation. | High. This is the route for ITMOs, country agreements and many authorised carbon credit transfers. |
| Article 6.4 | Creates a central UN-supervised crediting mechanism, the PACM. | High. This is the successor to the CDM and the route for Article 6.4 Emission Reductions (A6.4ERs). |
| Article 6.8 | Covers non-market cooperation such as technology transfer, capacity building and adaptation support. | Lower for credit buyers. It matters politically, but it does not create tradeable carbon credits. |
Most carbon market debate focuses on Article 6.2 and Article 6.4. Article 6.8 matters for climate diplomacy and non-market cooperation, but it is not the route through which companies, airlines or countries buy and retire credits.
Why Article 6 exists: the double-counting problem
The Paris Agreement works through national climate targets called Nationally Determined Contributions. Each country sets, updates and reports progress against its own NDC. That makes international cooperation possible, but it creates an accounting problem.
Suppose a solar project in Country A reduces emissions by 10,000 tonnes of CO2. Country B pays for the project and wants to count the reduction toward its own climate target. If Country A also counts the same 10,000 tonnes toward its own NDC, the world has recorded 20,000 tonnes of progress even though only 10,000 tonnes of emissions reduction occurred.
Article 6 is designed to stop that. When a host country authorises an emissions reduction for international transfer, it applies a corresponding adjustment to its national accounts. In simple terms, the host country subtracts the transferred reduction from its own progress so that another country or authorised buyer can use it without double counting.
Plain-English version
Article 6 does not magically make a carbon credit high quality. It tries to make sure that, if a credit is transferred internationally, the same tonne is not claimed twice.
This is why Article 6 matters for voluntary carbon markets. A company may buy a credit verified by a private standard such as Verra, Gold Standard, American Carbon Registry or Climate Action Reserve. That verification may say something useful about the project methodology. It does not automatically mean the host country has authorised the credit for international use or applied a corresponding adjustment.
Why the rules took six years
Article 6 was agreed in principle in Paris in 2015, but the implementation rules proved hard to settle. The core dispute was not whether cooperation should be allowed. It was who could claim the benefit of a traded emissions reduction.
At COP24 in Katowice in 2018, negotiators failed to finalise the rules. Brazil and other host-country interests wanted flexibility around whether exported reductions needed full corresponding adjustments. Buyer countries and environmental groups pushed for stricter accounting. The issue remained unresolved.
At COP25 in Madrid in 2019, the same problem blocked agreement again. The political split was deeper than a technical accounting dispute. Host countries wanted to preserve the value of mitigation projects on their territory. Buyer countries wanted units they could use without being accused of double claiming. Environmental groups wanted a rulebook that did not inflate global climate progress.
The breakthrough came at COP26 in Glasgow in 2021. Parties agreed that corresponding adjustments are required when mitigation outcomes are used toward another country's NDC or for other international mitigation purposes, including CORSIA. The compromise also allowed some CDM activities to transition into the new system under defined conditions.
That compromise made Article 6 operational in law, but not instantly operational in practice. Countries still needed designated national authorities, registries, reporting systems, authorisation procedures and technical guidance. That is why the gap between Glasgow in 2021 and the first Article 6.4 credit approval in 2026 matters.
How Article 6.2 works
Article 6.2 is flexible by design. Countries can create bilateral or multilateral arrangements and agree what kinds of mitigation outcomes can be transferred. Those outcomes are called Internationally Transferred Mitigation Outcomes. The units do not all need to look the same, because the rules allow countries to define cooperation in different ways as long as the required accounting, reporting and review rules are followed.
Examples include Japan's Joint Crediting Mechanism, Switzerland's bilateral agreements with partner countries, and Singapore's agreements with countries in the Asia-Pacific region. These arrangements are not identical. Some support energy projects, some support waste or industrial projects, and some are designed around future supply for aviation or corporate buyers.
According to the Article 6 Implementation Partnership's May 2026 update, more than 100 bilateral arrangements had been formalised under Article 6.2, with 64 parties engaged in bilateral cooperation. The number of agreements is growing faster than the number of completed transfers. That distinction is important. Signing an agreement is easier than issuing, authorising, transferring, recording and reporting an ITMO.
The practical bottleneck is implementation infrastructure. Countries need clear authorisation rules, designated national authorities, domestic registries, links to the Article 6 database, and systems to make corresponding adjustments in their national accounts. Without that infrastructure, a bilateral agreement can exist on paper without creating usable credit supply.
How Article 6.4 works
Article 6.4 is the central UN-supervised mechanism. It is governed by the Article 6.4 Supervisory Body, which approves methodologies, registers projects, accredits verifiers and oversees the issuance of Article 6.4 Emission Reductions.
The easiest way to understand Article 6.4 is as the stricter successor to the Clean Development Mechanism under the Kyoto Protocol. The CDM created a large project pipeline and years of institutional experience, but it was also criticised for over-crediting, weak additionality tests and limited environmental integrity. Article 6.4 is designed to keep the useful parts of a UN crediting mechanism while applying tighter accounting and stronger sustainable development requirements.
In 2025, the Article 6.4 Supervisory Body adopted methodological standards for baseline-setting, additionality, leakage, suppressed demand, and non-permanence and reversals. It also made the Sustainable Development Tool mandatory for PACM projects, requiring projects to address sustainable development and environmental safeguards rather than only carbon accounting.
The February 2026 Myanmar clean-cooking approval was therefore more than a symbolic first. It showed the mechanism applying a more conservative crediting approach than the CDM. The UNFCCC stated that the updated Article 6.4 calculations reduced the approved credit volume by around 40% compared with the amount that would have been issued under older CDM parameters.
Authorised units versus contribution units
One nuance is easy to miss: not every Article 6.4 unit has the same claim value.
Article 6.4 can create units authorised for international use. Those units require a host-country authorisation and a corresponding adjustment. They can support claims where the buyer needs the host country not to count the same mitigation outcome, for example certain CORSIA uses or Paris-aligned international mitigation claims.
Article 6.4 can also create mitigation contribution units. These are not authorised for international transfer in the same way. They can support climate finance or contribution claims, but they do not carry the same corresponding-adjustment-backed accounting effect. They are still Article 6.4 units, but they are not interchangeable with authorised units for every claim.
| Unit type | Host-country authorisation | Corresponding adjustment | Typical claim strength |
|---|---|---|---|
| Authorised Article 6.4 unit | Yes | Yes | Stronger for international mitigation claims and compliance uses where authorisation is required. |
| Mitigation contribution unit | No, not for transfer in the same accounting sense | No | Better suited to contribution claims rather than offsetting another party's target. |
For buyers, this means "Article 6.4" alone is not enough. The due-diligence question is whether the unit is authorised, whether a corresponding adjustment applies, and what claim the buyer wants to make.
The CDM wind-down
The Clean Development Mechanism is being wound down on a defined timetable. UNFCCC CDM registry guidance says issuance requests end on 30 June 2026. Transfer and cancellation transactions under the CDM end on 31 December 2026.
That matters because many project developers, countries and buyers are moving legacy project activity into the Article 6.4 system. The CDM is not simply disappearing overnight. Some activities can transition if they meet the new requirements, receive host-country approval and pass the relevant Article 6.4 processes.
The risk is that buyers treat any old CDM-linked credit as automatically Paris-aligned. It is not. The practical question is whether the project has transitioned, whether the unit is issued under the new mechanism, and whether the claim being made matches the unit's status.
The voluntary carbon market gap
The voluntary carbon market grew while Article 6 was still unresolved. Companies bought credits for carbon neutrality claims, net zero strategies, climate contribution claims and brand commitments. Standards such as Verra's Verified Carbon Standard, Gold Standard, American Carbon Registry and Climate Action Reserve became the main architecture for voluntary credit issuance.
Those standards can provide useful project-level controls. They may assess methodology, additionality, permanence, leakage, monitoring and verification. But private standard verification is not the same as host-country authorisation under Article 6.
That leaves three broad categories of credits in the market:
| Category | Authorisation | Corresponding adjustment | Typical use | Main risk |
|---|---|---|---|---|
| Article 6-authorised credits | Host country has authorised international use | Yes | CORSIA, country transfers, stronger Paris-aligned claims | Supply is limited and documentation must be checked carefully. |
| Private-standard VCM credits without Article 6 authorisation | Private standard, not necessarily host country | No | Voluntary offsetting or contribution claims | Double-counting risk is not eliminated at national-accounting level. |
| Legacy CDM credits | Kyoto-era mechanism | Generally not in the Paris Article 6 sense | Limited legacy uses | Paris-aligned claim credibility is contested unless transitioned appropriately. |
This does not mean every non-authorised voluntary credit is worthless. It means buyers need to be clearer about the claim. A contribution claim can be different from an offsetting claim. A credit used to fund mitigation can be different from a credit used to say an emissions footprint has been neutralised. Article 6 makes those distinctions harder to blur.
Why CORSIA makes Article 6 urgent
CORSIA is the most immediate demand-side test for Article 6. The aviation scheme requires eligible emissions units to meet strict criteria, and for the 2021-2026 compliance period, host-country Letters of Authorisation are central to eligibility. A Letter of Authorisation is the document that connects a credit to the host country's Article 6 accounting process.
According to the International Air Transport Association (IATA), only ten countries had issued Letters of Authorisation as of April 2026. That is a small supply base for a global aviation scheme. IATA has estimated Phase 1 demand at roughly 146 to 236 million eligible emissions units, with a cancellation deadline of 31 January 2028 for the 2024-2026 compliance period.
The result is a supply bottleneck. Airlines need eligible units. Project developers need host-country authorisations. Host countries need Article 6 systems that can issue those authorisations and account for corresponding adjustments. Until that machinery becomes more common, Article 6-authorised credits are likely to remain scarce relative to potential demand.
| Scenario | What drives it | Likely market effect |
|---|---|---|
| Low-demand pressure | Slower aviation growth, faster sustainable aviation fuel uptake, more eligible supply. | LoA-backed credit premiums may stay contained. |
| Base-case pressure | Phase 1 demand lands within the IATA 146 to 236 million unit range, with authorisations expanding gradually. | Eligible credits command a visible premium over ordinary VCM credits. |
| High-demand pressure | Strong aviation growth, slow authorisation expansion, limited eligible programme supply. | CORSIA demand becomes a major driver of Article 6-authorised credit pricing. |
This is why Article 6 is not only a legal-accounting topic. It can affect carbon credit prices, project development priorities, airline compliance costs and the negotiating power of host countries that can issue authorisations reliably.
Where Article 6 stands in June 2026
By June 2026, Article 6 has moved beyond negotiation but remains early in implementation.
- Article 6.4 has approved its first credits for issuance: the Myanmar clean-cooking project was the first public proof point under the PACM.
- Bilateral Article 6.2 activity is expanding: more than 100 bilateral arrangements had been formalised by May 2026, according to the Article 6 Implementation Partnership.
- The CDM transition is time-bound: CDM issuance requests end on 30 June 2026, with transfers and cancellations ending on 31 December 2026.
- CORSIA is forcing the authorisation question: airlines need eligible units, but Letters of Authorisation remain limited.
- Most voluntary credits remain outside Article 6: the voluntary carbon market has not suddenly become an Article 6 market.
- COP31 will matter: parties are expected to keep refining guidance for Article 6.4, methodologies, transitions and registry operation.
The practical picture is mixed. The architecture is real. The first credit approval is real. The country-to-country agreement pipeline is real. But the volume of fully authorised, corresponding-adjustment-backed units remains much smaller than the volume of credits traded in the wider voluntary market.
What companies and buyers should check
This section is for general information only. It is not legal, regulatory, procurement or investment advice. Article 6 rules, host-country authorisation procedures, CORSIA eligibility and voluntary carbon market claim guidance can change. Buyers should take specialist advice before relying on a credit for compliance or public claims.
If a company is buying credits, Article 6 turns the due-diligence question from "which standard issued this?" into "what claim can this credit safely support?"
Has the host country authorised the credit?
Ask whether there is a Letter of Authorisation or equivalent host-country approval for international use. If there is no authorisation, the credit may still have voluntary-market value, but it is not an Article 6-authorised credit.
Will a corresponding adjustment be applied?
Authorisation is the permission. The corresponding adjustment is the accounting. Buyers should understand whether the host country will adjust its national accounts and how that adjustment will be documented.
Which claim is being made?
A CORSIA compliance claim, an offsetting claim, a net zero claim and a climate contribution claim are not the same thing. The credit's authorisation status needs to match the claim.
Is the unit an authorised Article 6.4 unit or a contribution unit?
Both can sit under Article 6.4, but they do not carry the same accounting treatment. If the buyer needs a corresponding-adjustment-backed claim, the distinction is central.
What evidence does the seller provide?
Look for project documentation, registry identifiers, host-country authorisation, retirement records, vintage, methodology and claim guidance. A vague statement that a credit is "Paris-aligned" is not enough.
For a practical quality screen, read our carbon credit quality checklist. For business buyers, the carbon offsetting guide for UK businesses explains how to match credits, claims and procurement risk.
Frequently asked questions
Does Article 6 replace Verra or Gold Standard?
No. Article 6 is a Paris Agreement accounting framework. Private standards can still issue credits, and some private-standard credits may seek host-country authorisation for Article 6 use. The key question is whether a specific credit is authorised and adjusted, not whether the underlying standard still exists.
Are Article 6 credits automatically high quality?
No. Article 6 authorisation addresses national-accounting and double-counting risk. Credit quality still depends on the project type, baseline, additionality, permanence, leakage, monitoring and safeguards.
Can companies still buy ordinary voluntary carbon credits?
Yes, but they should be careful about the claim. Non-authorised credits may support contribution-style claims more safely than claims that imply a tonne has been fully neutralised in Paris-aligned national accounting.
Why are Letters of Authorisation so important for CORSIA?
CORSIA eligibility depends on host-country authorisation for relevant units. Without a Letter of Authorisation, a credit may be high quality by some voluntary-market criteria but still not eligible for CORSIA compliance.
What is the difference between Article 6.2 and Article 6.4?
Article 6.2 is country-led and flexible, built around cooperative approaches and ITMOs. Article 6.4 is centralised and UN-supervised, built around the Paris Agreement Crediting Mechanism and Article 6.4 Emission Reductions.
Conclusion
Article 6 is not a side issue in climate diplomacy. It is the accounting layer that determines whether international carbon market claims can be reconciled with national climate targets.
The first Article 6.4 credits being approved for issuance in February 2026 is a real milestone. The expanding Article 6.2 agreement pipeline is also real. So is the pressure from CORSIA, where airlines need eligible, authorised units for Phase 1 compliance. But none of that means the whole voluntary carbon market has become Article 6-compliant overnight.
The market now has a clearer integrity split. Some credits are authorised, adjusted and suitable for stronger international mitigation claims. Many credits remain private-standard voluntary credits without host-country corresponding adjustments. Some legacy credits are nearing the end of their old-system life. The important work is knowing which is which.
For companies, airlines, investors and policymakers, Article 6 is becoming the line between carbon credits that only exist inside private registries and credits that connect to the Paris Agreement's national-accounting system. That distinction will shape credibility, eligibility, pricing and procurement risk for years.