GHG verification and ISO 14064-3

What is ISO 14064-3?

ISO 14064-3 is part 3 of the ISO 14064 series on greenhouse gases. It specifies how verifiers and validators plan and carry out engagements on greenhouse gas statements and reach an opinion, for organisations, projects or products. Its 2019 edition replaced the 2006 version, with engagements started after 30 April 2023 required to use it under the accreditation bodies' transition rules. See the GHG Protocol explained.

How does ISO 14064-3 fit with the other ISO standards?

• ISO 14064-1: quantifying and reporting an organisation's greenhouse gas emissions and removals, similar to the GHG Protocol Corporate Standard.
• ISO 14064-2: quantifying emission reductions and removal enhancements from projects.
• ISO 14064-3: verifying and validating the resulting statements.
• ISO 14065 and ISO/IEC 17029: requirements for the bodies that perform verification and validation, used by accreditation bodies.
• ISO 14066: competence of verification and validation teams.
• ISO 14064-5: guidance on remote activities, published in February 2026.

In July 2026, the GHG Protocol and ISO agreed to combine their corporate accounting standards, including ISO 14064-1, into a single standard, planned for publication in the fourth quarter of 2028.

How does a GHG verification work?

The verifier agrees the objective, criteria, scope and level of assurance; understands the organisation, its sources and its data systems; sets materiality; assesses the risk of material misstatement; prepares a verification plan and sampling plan; gathers evidence through site visits, interviews, document review, recalculation and tests of data and controls; evaluates misstatements, which the company may correct; and issues a verification statement with its opinion. An independent reviewer within the verification body checks the work before the opinion is issued. See building a GHG inventory.

ISO 14064-3 in practice: verifying a manufacturer's emissions

A manufacturer's draft scope 1 and 2 statement shows 102,400 tonnes. The verifier, engaged for reasonable assurance, sets materiality at 5% of the total and visits the two largest sites.

The verifier finds diesel counted twice at one site, 3,000 tonnes, and refrigerant top-ups left out, 1,200 tonnes, and the company corrects both, giving 100,600 tonnes. Two smaller differences remain uncorrected: a meter estimate overstating emissions by 900 tonnes and an outdated factor understating them by 600. Together they total 1,500 tonnes in absolute terms, well below materiality of about 5,030 tonnes, and are not qualitatively significant, so the verifier issues an unmodified reasonable assurance opinion. See refrigerants and fugitive emissions.

What levels of assurance does ISO 14064-3 offer?

Reasonable assurance, a positive opinion that the statement is materially correct, or limited assurance, a conclusion that nothing has come to the verifier's attention suggesting it is not. Emissions trading schemes generally require reasonable assurance: in the EU ETS, accredited verifiers check operators' annual emissions reports under the EU's Accreditation and Verification Regulation, applying ISO 14065. Voluntary reports often start with limited assurance. See limited and reasonable assurance.

How does ISO 14064-3 compare with ISSA 5000 and ISAE 3410?

ISO 14064-3 is used mainly by verification bodies accredited by national accreditation bodies, such as engineering and certification firms. ISSA 5000 and ISAE 3410 come from the IAASB and are used mainly by audit firms, though ISSA 5000 is open to other providers meeting its quality management and ethics requirements. All three support limited and reasonable assurance; ISSA 5000 covers all sustainability information, while ISO 14064-3 and ISAE 3410 cover greenhouse gas statements. CARB's proposals for SB 253 accept ISO 14064-3, ISSA 5000, ISAE 3000 with ISAE 3410, the AICPA attestation standards and AA1000AS. See ISSA 5000 and ISAE 3000 and ISAE 3410.

When is an ISO 14064-3 verification enough?

It is enough for emissions trading schemes that require it, for carbon credit projects under programmes that rely on it, for voluntary reports and questionnaires such as CDP, and, under CARB's proposals, for SB 253. It is not enough under the CSRD, where the whole sustainability statement must be assured by the statutory auditor or, where a member state allows it, an independent assurance services provider, though an existing emissions verification can make that engagement easier. See getting ready for sustainability assurance.

This guide is general information. It is not tax or legal advice for your situation.