GHG Protocol and ISO join forces: What the harmonization of CO₂ standards means for companies

Anyone who has ever been faced with the decision to create a carbon footprint knows the dilemma: GHG Protocol or ISO 14064? Both standards have their justification, both have their specific strengths. The GHG Protocol is considered the de facto standard for corporate accounting and is recognized by most international initiatives such as CDP or Science Based Targets. The ISO standards, on the other hand, offer the advantage of formal certification and are established in many regulatory contexts.

On 9 September 2025, both organizations announced a strategic partnership to end this fragmentation. The aim is to develop a harmonized global standard that combines the practical experience of the GHG Protocol with the standardization expertise of ISO.

The starting point: two standards, one goal

The GHG Protocol was developed in 2001 by the World Resources Institute and the World Business Council for Sustainable Development and has established itself as a quasi-standard for corporate accounting. It provides clear guidelines for the categorization of emissions into Scope 1 (direct emissions), Scope 2 (indirect emissions from purchased energy) and Scope 3 (all other indirect emissions along the value chain).

The ISO standards, in particular ISO 14064, were developed as international standards and offer the advantage of a formal structure for verification and certification. They are divided into three parts: ISO 14064-1 for organizational assessments, ISO 14064-2 for project assessments and ISO 14064-3 for validation and verification.

In practice, this parallelism often led to uncertainties. Companies had to decide or even use both standards in parallel, which could lead to additional work and inconsistent results. There were different approaches to the treatment of Scope 3 emissions in particular, which made comparability difficult.

The Scope 3 problem: why harmonization is particularly important here

Scope 3 emissions are the crux of every CO₂ balance sheet. They usually make up the largest part, but are the most difficult to record. This is because it covers all indirect emissions along the value chain - from the raw materials purchased to the disposal of the products sold.

The GHG Protocol solves this with 15 fixed categories: "purchased goods", "business travel", "use of products sold" and so on. Clearly structured, but not very flexible. ISO 14064 is more methodical and gives companies more leeway in terms of categorization.

So far, so good. The problem arises when companies in the same supply chain use different standards. The steel producer calculates according to ISO, its customer according to the GHG Protocol. The data does not match, even though the same emissions are involved.

In addition, the two standards have different ideas about what data quality is sufficient and how the calculation should be carried out. The GHG Protocol recognizes primary, secondary and generic data. ISO 14064 has similar gradations, but names them differently and evaluates them differently in some cases.

The result? Depending on the standard, companies arrive at different results - for identical activities. This adds to the uncertainty, especially for Scope 3 emissions, where the data situation is often thin anyway.

Harmonization could change this. Uniform categories, uniform calculation methods, uniform data standards. This would not only improve comparability, but also reduce the effort involved. This would be a major step forward, especially for product carbon footprints, where data from hundreds of suppliers has to flow together.

And another side effect: with uniform standards, Scope 3 accounting can be better digitized. Automatic data exchange instead of manual Excel acrobatics - that would make life easier for many sustainability managers.

What harmonization means in concrete terms

The planned harmonization aims to combine the strengths of both systems. The GHG Protocol contributes its broad market acceptance and practical applicability, while ISO contributes its expertise in standardization and auditing. The result should be a uniform standard that offers both the flexibility of the GHG Protocol and the robustness of the ISO standards.

In terms of practical application, this initially means a standardization of methodologies. Different definitions for emission categories, different approaches to the allocation of emissions or differing data quality requirements are to be harmonized.

The new partnership will also improve consistency between company, product and project balances. Until now, there have been different approaches here, which could lead to confusion. A harmonized standard should close these gaps and offer a consistent methodology across all accounting levels.

Effects on companies and their accounting practices

For companies that already prepare CO₂ balance sheets, harmonization brings several benefits. The most obvious is the reduction in complexity and duplication of effort. Instead of having to choose between different standards or even using both in parallel, there will be a clear path in future.

The comparability of balance sheets will improve significantly. Until now, it was often difficult to assess whether different results were due to different business models or different accounting approaches. A uniform standard will create clarity here.

This is particularly relevant for companies that operate in international supply chains. If suppliers and customers use the same standard for accounting, the aggregation of data along the value chain is considerably simplified. This is particularly important for the calculation of Scope 3 emissions, which often make up the largest proportion of the overall balance sheet.

There are also advantages for companies that have their balance sheets verified externally. Combining the practical experience of the GHG Protocol with the auditing expertise of ISO should lead to more robust and consistent verification processes.

The difference between accounting and certification

An important point that often leads to confusion: The preparation of a balance sheet in accordance with the GHG Protocol or ISO does not automatically mean that it is certified. For official certification, the balance sheet must be audited by an accredited, independent body.

Accredited certification bodies are organizations that have been formally authorized by national accreditation authorities - in Germany the DAkkS (German Accreditation Body) - to carry out certifications. These bodies must pass regular audits and prove their competence. Examples are TÜV Süd, TÜV Rheinland, DEKRA, DQS or DNV Business Assurance.

The process typically works like this: A company prepares its balance sheet according to a recognized standard, then commissions an accredited certification body to audit it. This body checks the methodology, data quality, completeness and plausibility of the results. A certificate is only issued if all criteria are met.

This process remains in place even after harmonization. The advantage will be that the auditors will be able to assess according to uniform criteria, which should improve the consistency and quality of the certifications.

Timetable and transition phase

There is not yet a specific date for the completion of harmonization. Such processes are complex and time-consuming, as they require intensive coordination between various stakeholders. Experts assume that full integration will take several years.

Until then, both standards will continue to exist in parallel. Companies do not have to change over immediately and can continue with their established processes. However, it is advisable to follow developments and adapt to the new standards at an early stage.

The transition phase also offers the opportunity to review and optimize existing accounting processes. Companies can use this time to improve their data collection, digitize processes or train their employees.

Impact on the organizations themselves

Both organizations will continue to exist as a result of the partnership. It is not a takeover or merger, but a strategic cooperation. ISO and GHG Protocol will contribute their respective strengths and develop new standards together.

The GHG Protocol will continue to play its role as a practical guide for companies, while ISO will contribute its expertise in formal standardization and certification. The future standards will be developed and published under a common branding.

This division of labor makes sense: ISO has decades of experience in developing international standards and has established processes for consultation and coordination. The GHG Protocol, on the other hand, has proven itself as a practical standard and is recognized by a large number of initiatives and organizations.

Regulatory implications

The harmonization comes at a good time. With the EU taxonomy, the Corporate Sustainability Reporting Directive (CSRD) and similar regulations worldwide, the requirements for climate reporting are constantly increasing. A uniform standard can ensure greater clarity and efficiency here.

Many regulations already refer to recognized standards such as the GHG Protocol or ISO standards. A harmonized standard would simplify these references and create legal certainty. Companies would no longer have to ask themselves which standard is accepted by which regulation.

A uniform standard is also helpful for the development of future regulations. Regulators can refer to established methods instead of having to develop their own standards. This reduces fragmentation and facilitates the international harmonization of climate regulations.

The partnership between the GHG Protocol and ISO marks an important step towards a standardized, globally accepted approach to carbon accounting. For companies, this means less complexity, better comparability and ultimately more efficient climate management processes. It will still take some time until full implementation, but the direction is clear: the time of parallel standards is coming to an end.