The two most widely used carbon accounting systems in the world are becoming one. The Greenhouse Gas Protocol and the International Organization for Standardization announced on July 29 that they will combine their corporate carbon accounting standards into a single, harmonized global standard, with an integrated public consultation on the future standard planned for Q2 2027. For companies that report emissions, buy carbon credits, or verify inventories, this ends a decades-old split between the framework used for corporate reporting and the one used for auditing and verification.

The consolidation is the most consequential step yet in the strategic partnership the two organizations signed in September 2025, and it was identified as a key milestone in the COP30 Action Agenda for harmonizing global greenhouse gas accounting.

What Is Actually Being Merged

The single co-branded corporate standard will bring together the GHG Protocol’s Scope 1, Scope 2, Scope 3, and Actions and Market Instruments (AMI) standards with ISO’s 14064-1 standard. Until now, these have evolved in parallel: corporate sustainability teams typically built inventories on the GHG Protocol, while verifiers and assurance providers worked to the ISO 1406X family. Companies operating across jurisdictions often had to translate between the two, duplicating work and creating inconsistencies in reported figures.

The reach of what is being unified is hard to overstate. In 2023, 97% of S&P 500 companies that disclosed through CDP used the GHG Protocol, while ISO 14064 underpins verification practice and regulatory assurance frameworks, including limited assurance under the EU’s CSRD. A single standard collapses that translation layer into one rulebook.

Existing standards remain in effect until the co-branded standards are published, with transition periods to be defined. The timeline companies should hold is the Q2 2027 consultation, which will be the first look at the combined text.

Scope 2: 1,100 Responses and Still No Consensus

Alongside the merger announcement, GHG Protocol published the results of its public consultation on the Scope 2 standard, which governs how companies account for purchased electricity. The consultation drew nearly 1,100 responses from 56 countries and surfaced a wide range of views on how companies should account for renewable energy purchases, alongside broad support for improving the accuracy, comparability, and integrity of electricity emissions accounting.

Rather than forcing a single answer, the organization said multiple reporting approaches are being explored, reflecting different theories of change represented in the feedback. Any further proposals will go through the Technical Working Group and the Independent Standards Board before adoption.

This matters well beyond electricity procurement. Scope 2 market-based accounting is the template for how contractual instruments, from renewable energy certificates to power purchase agreements, enter a corporate inventory. How the merged standard treats these instruments will shape the rules for every other market instrument a company holds.

The AMI Workstream Is Where Carbon Credits Will Live

For carbon market participants, the most consequential piece is the Actions and Market Instruments standard. GHG Protocol released preliminary feedback from its Request for Information on AMI, which will be synchronized with Scope 2 development, and the proposal on the table introduces a “multi-statement” reporting approach with three distinct components:

  • Physical emissions: emissions from a company’s own operations and value chains.
  • Market-based emissions: emissions tied to market instruments such as commodity certificates and mitigation-related contractual agreements.
  • GHG impact statement: the emissions impact of a company’s actions and investment decisions, measured using consequential methods.

According to GHG Protocol, public feedback shows strong support for this approach. The structural implication for credit buyers is significant: under a multi-statement model, instruments such as carbon credits would be reported in a dedicated statement rather than blended into the physical inventory. That would formalize a clear line between what a company emits, what it contracts, and what its actions deliver, a line that buyers, auditors, and regulators have been arguing over for years.

Why One Standard Changes the Market Plumbing

A unified standard is not just a reporting convenience. Carbon credit claims, net-zero targets, and disclosure regimes from CSRD to ISSB all rest on the same accounting foundation. When that foundation comes in two dialects, every claim carries translation risk: a tonne accounted for under one framework may not read the same under the other.

A single co-branded standard, developed with ISO’s technical experts embedded in the GHG Protocol working groups and ISO sitting as an Observing Entity on the Independent Standards Board, gives regulators and assurance providers one reference point. That tends to raise the bar for weak claims while lowering compliance costs for companies that report across multiple jurisdictions. It also supports implementation of carbon border adjustment mechanisms, which depend on consistent methodologies for embedded emissions.

What to Watch Before the 2027 Consultation

Three markers will show how disruptive the merger will be. First, the Q2 2027 consultation draft itself: the treatment of market-based instruments in the combined text will determine how credits and certificates appear in corporate accounts for the next decade. Second, the Scope 2 outcome: whether the final standard lands on one reporting approach or legitimizes several will set the integrity floor for electricity claims. Third, transition periods: companies with multi-year assurance contracts and credit-linked claims should track how long existing standards remain valid once the co-branded text is published.

The direction is no longer in question. Carbon accounting is converging on a single global rulebook, and the rules for how carbon credits appear in corporate climate accounts will be written inside it. Buyers and developers who want a say in that text now have a date: Q2 2027.