Corresponding adjustments under Article 6 of the Paris Agreement are the matching accounting entries that two countries must make when a carbon credit is transferred between them, so that the same tonne of emission reductions is never counted twice toward national climate targets. The selling country adds the transferred amount back onto its reported emissions; the buying country subtracts the same amount from its own. The rules sit in Decision 2/CMA.3, adopted at the Glasgow climate conference, and apply to every transfer of mitigation outcomes between countries under Article 6.1UNFCCC. Decision 2/CMA.3 – Guidance on Cooperative Approaches Referred to in Article 6 Paragraph 2 of the Paris Agreement
The Double-Entry Logic
Every nationally determined contribution (NDC) is a country’s formal pledge to cut emissions by a specific amount over a defined period.2UNFCCC. The Paris Agreement When a country sells a credit representing a verified reduction, that reduction leaves its domestic balance sheet. The seller adds the transferred amount back into its reported emissions, acknowledging it can no longer count that reduction toward its own target. The buyer subtracts the same amount, reflecting the newly acquired reduction.1UNFCCC. Decision 2/CMA.3 – Guidance on Cooperative Approaches Referred to in Article 6 Paragraph 2 of the Paris Agreement
The math is symmetrical. One country’s addition offsets the other’s subtraction, so the transaction itself doesn’t change global emissions on paper. The environmental benefit exists exactly once in the global books. Without the adjustment, both sides could claim the same reduction and the world would appear to have cut twice as many emissions as actually disappeared from the atmosphere.
When an Adjustment Is Required
The underlying asset is an internationally transferred mitigation outcome, or ITMO. Article 6.2 defines ITMOs as mitigation results that countries voluntarily transfer between themselves to help meet their climate targets.3UNFCCC. Paris Agreement Full Text An ITMO might represent tonnes of CO2 equivalent reduced by a wind farm or removed by a reforestation project. ITMOs can also be measured in non-greenhouse-gas metrics such as megawatt-hours of renewable energy or hectares of planted forest, though these must eventually be converted into a CO2 equivalent for accounting purposes.4UNFCCC. Article 6.2 Reference Manual
A corresponding adjustment is triggered at the moment of “first transfer,” which is the initial point at which an ITMO moves between countries or is authorized for a specific use. Decision 2/CMA.3 requires adjustments in every scenario where mitigation outcomes cross borders, whether the reductions fall inside or outside the selling country’s NDC.1UNFCCC. Decision 2/CMA.3 – Guidance on Cooperative Approaches Referred to in Article 6 Paragraph 2 of the Paris Agreement Even a reduction generated in a sector the seller never pledged to cut still triggers an adjustment when transferred internationally. The rule closes what would otherwise be an easy loophole.
Authorization Comes First
Before any ITMO can be transferred, the host country must formally authorize the transaction. Authorization is a legal act that specifies whether the reduction will be used toward another country’s NDC, for other international mitigation purposes, or both. The Paris Agreement requires that both the transfer and use of ITMOs be voluntary and authorized by participating countries.3UNFCCC. Paris Agreement Full Text A country cannot simply generate reductions and have foreign buyers claim them without explicit governmental approval.
Uses Beyond Another Country’s NDC
Some ITMOs are authorized for “other international mitigation purposes” rather than for a partner country’s NDC. The most prominent example is the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA), where airlines buy credits to offset emissions from international flights. When a country authorizes mitigation outcomes for CORSIA, it must still apply a corresponding adjustment at first transfer, so the reduction isn’t simultaneously counted toward the host country’s climate target.1UNFCCC. Decision 2/CMA.3 – Guidance on Cooperative Approaches Referred to in Article 6 Paragraph 2 of the Paris Agreement
How Countries Calculate the Adjustment
The calculation depends on whether an NDC spans multiple years or targets a single year. Decision 2/CMA.3 sets out two approaches, and once a country picks one, it must stick with it for the entire NDC period.1UNFCCC. Decision 2/CMA.3 – Guidance on Cooperative Approaches Referred to in Article 6 Paragraph 2 of the Paris Agreement
Multi-Year NDC Targets
Countries with multi-year targets set an emissions trajectory or budget covering the full implementation period. They apply adjustments annually based on the actual quantity of ITMOs transferred or acquired that year, then tally the cumulative total at the end of the period. Annual tracking produces a year-by-year record reviewers can compare against the original trajectory.
Single-Year NDC Targets
Countries aiming at a single target year face a different problem. A snapshot of one year can be distorted if trades were front-loaded or back-loaded. Decision 2/CMA.3 gives these countries two options. The first mirrors the multi-year approach: the country builds an indicative multi-year trajectory and applies annual adjustments throughout. The second is an averaging method, where the country totals all ITMOs transferred and acquired across the entire NDC period, divides by the number of elapsed years, and applies that average as the adjustment in the target year.1UNFCCC. Decision 2/CMA.3 – Guidance on Cooperative Approaches Referred to in Article 6 Paragraph 2 of the Paris Agreement Averaging prevents a country from dumping credit purchases into the target year to hit its goal while running high emissions in every other year.
Voluntary Market Credits: A Boundary Worth Knowing
Article 6 only mandates corresponding adjustments for credits a host country explicitly authorizes for international transfer or use. Credits sold on the voluntary carbon market without host country authorization fall outside the formal ITMO system and do not trigger an adjustment.
The practical tension is real. A company might buy a voluntary credit from a project in a developing country and claim it offsets corporate emissions, while the host country still records that same reduction in its national inventory and counts it toward its NDC. No corresponding adjustment happens because the credit was never authorized under Article 6. Some host countries have responded by restricting or banning exports of voluntary credits from their territory. Anyone assessing a credit should know: an authorized ITMO with a corresponding adjustment carries a stronger claim to integrity, but the international rules have not required adjustments for the voluntary market, and it isn’t clear they ever will.
How Adjustments Are Reported and Tracked
Corresponding adjustments do not happen quietly in the background. Countries document every transaction through a layered reporting framework that produces an audit trail.
The Initial Report
Before joining its first cooperative approach, a country submits an initial report to the UNFCCC. The report describes the cooperative approach, the country’s chosen adjustment method (trajectory or averaging), the quantification of its NDC, and how it will safeguard environmental integrity. It is effectively the country’s entry ticket into the Article 6.2 system.
Biennial Transparency Reports
Ongoing reporting flows through the biennial transparency report, or BTR, submitted every two years. The first BTR was due by December 31, 2024.5UNFCCC. Biennial Transparency Reports Each BTR contains standardized tables showing the ITMOs authorized, transferred, acquired, and used during the reporting period. Every ITMO must carry a unique identification code, a vintage year, the sector in which the mitigation occurred, the quantity in CO2 equivalent, and its authorization status. Countries must also explain how their adjustments avoid double counting and remain consistent with achieving their NDC.1UNFCCC. Decision 2/CMA.3 – Guidance on Cooperative Approaches Referred to in Article 6 Paragraph 2 of the Paris Agreement Errors in sector classification, quantity, or vintage year can delay review and cast doubt on the adjustment itself. Each entry must be backed by supporting evidence, including project verification documents and authorization letters.
The International Registry
Two digital systems sit at the center of Article 6 accounting. The centralized accounting and reporting platform (CARP) handles the submission of reports, templates, and authorization records. Nested within the CARP is the international registry, managed by the UNFCCC secretariat, which tracks each ITMO from issuance through to final use or cancellation.6UNFCCC. International Registry and Additional Registry Services
Each ITMO in the registry receives a unique identifier recording its country of origin, vintage year, cooperative approach, and authorization scope. Countries that opt into the international registry get their own section containing accounts that track who currently controls each ITMO. Public and private entities can be authorized to open accounts within a country’s section, enabling corporate participation. The registry also auto-populates reporting information into BTR templates.7UNFCCC. Article 6.2 of the Paris Agreement As of mid-2025 the registry is operational, though some identity verification features remain provisional.
Technical Expert Review
After a BTR is submitted, a technical expert review team examines whether the reported adjustments line up with the data, methods, and international rules. Reviewers compare the seller’s reported additions against the buyer’s reported subtractions, check that the chosen method was applied consistently, and verify that required data fields are populated. When the numbers reported by partner countries do not match, reviewers flag the inconsistency and request clarification. Review teams are expected to complete their work within 12 months of starting the review.8UNFCCC. Technical Expert Review of Biennial Transparency Reports Once the review concludes, the adjustment is officially recorded and the country’s emissions balance is updated.
What Happens If a Country Gets It Wrong
The system’s ambition outruns its enforcement. Article 6 and its implementing decisions set detailed accounting rules, but the tools for punishing errors or bad faith are limited. If an automated consistency check or a technical expert review finds a country’s reported ITMOs “inconsistent” with achieving its NDC, the strongest response available under current rules is a request that the country not use those ITMOs. A request, not a binding prohibition.
The system leans on good faith reporting and reputational incentives rather than penalties. Countries that miss BTR deadlines or apply incorrect adjustments face scrutiny from review teams and diplomatic pressure, not formal sanctions. For anyone participating in the carbon market, this means the integrity of any given ITMO ultimately rests on the credibility of the host country and the rigor of the underlying verification, not on a centralized body with the power to void transactions.