Carbon Credit Double Counting Explained: Corresponding Adjustments and Article 6

A carbon credit represents one tonne of emissions reduced or removed, and it is only worth something if that tonne is counted once. Double counting happens when the same reduction is claimed by two parties at the same time. The most common case is a project in one country whose credits are sold abroad, where both the host country and the buyer count the tonne toward their own climate targets. Avoiding that outcome is one of the main design problems of the carbon market, and it has become more urgent as countries and companies build targets around the same emission reductions.

The problem in plain terms. Countries report emissions and reduction progress under the Paris Agreement through their nationally determined contributions. Companies report under their own net zero or offsetting claims. If a credit generated inside a country is sold to a company abroad and both sides keep the reduction, the world has only one tonne of real benefit but two tonnes of claimed benefit. The gap is invisible in the project's own accounts, which is why it needs rules that operate at the level of national accounts and transfers.

What a corresponding adjustment does. A corresponding adjustment is the accounting step that resolves the problem. When a host country authorises credits for international transfer, it adds the transferred reduction back to its emissions in the accounts it reports, so it can no longer count that tonne toward its own target. The acquiring party can then claim the reduction toward its own goal, and the tonne is counted once in total. The mechanism depends on the host country taking this step, on a clear record that the adjustment was made, and on the credit being labelled as authorised. Without the adjustment, a transferred credit is still the same physical tonne, but it has a double claim attached to it.

Article 6 and the new rules. Article 6 of the Paris Agreement sets out the legal basis for international transfers. Article 6.2 covers bilateral or multilateral cooperation in which countries trade mitigation outcomes, known as internationally transferred mitigation outcomes, and it requires corresponding adjustments for those transfers. Article 6.4 creates a centrally supervised crediting mechanism, which is intended to succeed the Clean Development Mechanism and carries its own rules for authorisation, adjustment and issuance. The rules are still being developed and applied, so the practical position differs between countries, registries and methodologies, and buyers should check the current guidance for the specific credits they are considering.

Why registries and serial numbers matter. A registry does more than record that a credit was issued. It tracks each unit from issuance through transfer to retirement, and it records any authorisation or adjustment attached to that unit. A retirement recorded in the registry is the point at which a credit is used up for a claim, which is why the registry entry is the evidence buyers and auditors look for. Credits that carry no authorisation record or that show a claim by the host country create a risk that the buyer's claim will be challenged.

The two sides of the claim. Buyers face a different question from host countries. A company that retires a credit to back a claim of carbon neutrality, or to meet an offsetting obligation, needs to know whether the credit has been adjusted and whether the claim it wants to make is allowed under the framework it reports against. A host country that issues credits needs to know whether it can still count the reduction toward its own target. Where both sides would count the same tonne, the claim fails for one of them. Many disputes in the voluntary market have come down to exactly this question of who is entitled to the claim.

What to check before you buy. A short checklist helps. First, is the credit labelled as authorised for international transfer, and by which host country? Second, is there a recorded corresponding adjustment, and is it visible in the registry? Third, does the claim you intend to make match the framework that governs the credit, whether that is a national target, a compliance scheme or a voluntary standard? Fourth, is the credit issued under a methodology whose rules on adjustment are clear? If any of these answers is unclear, the safer course is to ask the seller for the authorisation and adjustment records before you retire the credit, not after.

The bottom line. Double counting is not a technicality. It decides whether a carbon credit represents a reduction that the world can count once, or a claim that two parties hold on the same tonne. Corresponding adjustments, transparent registries and clear claim rules are the tools that keep the claim honest. For anyone buying or selling credits, the practical lesson is to treat the authorisation record as part of the product, as important as the methodology and the project itself.