ISAE 3410: Assurance Engagements on Greenhouse Gas Statements

Why ISAE 3410 matters

The first GHG assurance engagement at most mid-tier firms looks identical to a financial statement audit done by people who have never seen a meter. The team requests activity data, recalculates emissions × emission factors, ties the result to the disclosure, and signs off. Then the second-year review surfaces the gaps. No site visit at the largest emitting facility. No assessment of whether the entity used a location-based or market-based Scope 2 method consistently. No documentation of why the chosen emission factors were the right ones. In our experience this is exactly how a GHG file becomes a tick box exercise. The standard is not the problem. The standard is ISAE 3410, and most of what goes wrong in practice is already addressed in its requirements.

For European audit firms, GHG assurance is both a current revenue stream and a bridge to the broader sustainability assurance market. ISAE 3410 will be withdrawn when ISSA 5000 becomes effective for periods beginning on or after 15 December 2026. Until then, the standard remains directly relevant for standalone GHG assurance engagements, and the GHG-specific knowledge it requires carries straight into ISSA 5000 practice. Building the capability now is not just about current compliance.

ISAE 3410 is the IAASB’s subject-specific standard for assurance engagements on greenhouse gas statements. It governs both reasonable and limited assurance, requiring practitioners to evaluate emission quantification methods and assess whether the GHG statement is free from material misstatement within the inherent uncertainty of emissions measurement.

• Why ISAE 3410 matters
• Scope and key concepts
• Engagement acceptance
• Key technical concepts
• Performing the engagement
• Reporting
• The transition to ISSA 5000
• European jurisdiction implementations
• Relationship with other standards

Scope and key concepts

ISAE 3410, approved by the IAASB in March 2012, deals with both limited assurance and reasonable assurance engagements to report on an entity’s GHG statement. It operates alongside ISAE 3000 (compliance with both standards is required).

What is a GHG statement?

A GHG statement reports an entity’s greenhouse gas emissions (and, where applicable, removals and emission deductions) for a period. It may be:

• A standalone document
• Part of a broader sustainability report
• Included in an entity’s annual report
• Filed with a regulator (such as the EU ETS competent authority)
• Published voluntarily to inform investors or customers

The emissions framework

GHG emissions are categorised into three scopes, following the GHG Protocol framework that underlies most reporting requirements:

Scope determines work effort. The practitioner’s procedures and required expertise vary dramatically by emission scope. Scope 1 emissions from a manufacturing facility may require engineering expertise and site visits to verify process emissions and fuel records. Scope 2 verification is relatively straightforward (energy bills × emission factors). Scope 3 is the most challenging. Data often comes from third parties, estimation methodologies vary widely, and the practitioner must evaluate the reasonableness of assumptions rather than verify source data directly. The ciferi Scope 3 emissions estimator structures this estimation by GHG Protocol category and generates the calculation documentation that assurance files require. Plan the engagement team accordingly.

Applicable criteria

The GHG statement is prepared against applicable criteria (the rules and methods used to quantify emissions). Common criteria frameworks include:

The practitioner must evaluate whether the criteria are suitable. They must be relevant, complete, reliable, neutral, and understandable to intended users.

Engagement acceptance

Before accepting, the practitioner evaluates:

1. Ethical and independence requirements. These must be met.
2. Competence. The engagement team has (or can obtain) sufficient expertise in GHG quantification, relevant industries, and assurance skills. Multidisciplinary teams are common, combining audit professionals with environmental scientists or engineers.
3. Preconditions. The subject matter is appropriate, suitable criteria exist, and sufficient evidence can be obtained.
4. Scope. Which emissions are covered (all scopes? specific facilities? specific gases?).
5. Level of assurance. Reasonable or limited (may be determined by regulation, contract, or entity preference).

ISAE 3410 explicitly recognises that GHG assurance engagements often require multidisciplinary teams. The practitioner may need engineers to evaluate process emissions and environmental scientists to assess quantification methodologies. ISA 620 (using experts) principles apply.

Key technical concepts

Scientific uncertainty vs. estimation uncertainty

ISAE 3410 draws an important distinction that practitioners must understand:

Scientific uncertainty is inherent in the science of quantifying GHG emissions. Emission factors (the conversion ratios used to calculate emissions from activity data) are based on scientific measurements that carry inherent uncertainty. For example, the emission factor for natural gas combustion has a scientific uncertainty range. This uncertainty exists regardless of the quality of the entity’s reporting. It is a property of the underlying science.

Estimation uncertainty arises from the entity’s measurement, data collection, and calculation processes. This includes uncertainty from metering equipment accuracy, data gaps requiring estimation, allocation of shared emissions, extrapolation from sample data, and use of industry average factors instead of entity-specific data.

The practitioner’s assurance procedures focus on estimation uncertainty (evaluating whether the entity’s data collection, quantification methods, and calculations are reasonable and applied consistently). The entity discloses scientific uncertainty in the GHG statement, and the practitioner references it in the assurance report, but assurance procedures cannot reduce it.

The assurance report must reference uncertainty. ISAE 3410 requires the assurance report to include a reference to the inherent uncertainty of GHG quantification, regardless of what disclosures appear in the GHG statement. This is an unusual feature. It ensures users understand that even a “clean” assurance opinion does not mean the emissions figure is precise, only that it is free from material misstatement within the inherent limitations of GHG measurement science.

Materiality

The practitioner determines materiality for GHG assurance engagements by reference to the information needs of intended users. Key considerations:

• Materiality is the same for both reasonable and limited assurance engagements. The level of assurance affects work effort, not the materiality threshold.
• Materiality may be set as a percentage of total reported emissions (commonly 5-10% for reasonable assurance, though there is no prescribed threshold)
• Different components of a GHG statement may warrant different materiality considerations (for example, a 5% error in Scope 1 emissions from a regulated facility may be more material than the same percentage error in Scope 3 business travel estimates)
• Qualitative factors also matter. Errors affecting compliance with regulatory thresholds (such as EU ETS surrender obligations) may be material regardless of their quantitative size

Performance materiality

As in financial statement audits, the practitioner may set performance materiality below materiality to reduce the risk that the aggregate of uncorrected and undetected misstatements exceeds materiality.

Performing the engagement

Understanding the entity and its emissions

The practitioner must understand:

1. The entity’s operations, facilities, and processes that generate emissions
2. The organisational and operational boundaries applied
3. The types and sources of emissions within scope
4. The quantification methods used (direct measurement, calculation, estimation)
5. The data collection and reporting systems
6. The internal controls over emissions data
7. The emission factors and global warming potentials applied
8. Changes from prior periods

Risk assessment and response

For reasonable assurance, the practitioner:

• Identifies and assesses risks of material misstatement
• Designs and performs procedures to respond to assessed risks
• Tests controls over emissions data (where the practitioner intends to rely on controls)
• Performs detailed testing of activity data, emission factors, and calculations
• Performs analytical procedures
• Evaluates the completeness of emissions reported

For limited assurance, the practitioner:

• Performs procedures primarily consisting of inquiry and analytical procedures
• Considers the process used to prepare the GHG statement
• Evaluates whether the entity’s data collection systems can produce reasonable quantification
• Must perform additional procedures when the practitioner becomes aware that the GHG statement may be materially misstated (the “trigger point”)

The “trigger point” is a critical ISAE 3410 concept: in a limited assurance engagement, if during the course of inquiry and analytical procedures the practitioner identifies indicators that the GHG statement may be materially misstated, the practitioner must perform additional procedures sufficient to either confirm or dispel the concern. The practitioner cannot simply note the concern and issue a qualified conclusion. They must investigate further.

Site visits

ISAE 3410 provides extensive guidance on whether site visits are necessary:

• For reasonable assurance, the practitioner must consider whether site visits are needed, and for engagements involving Scope 1 emissions from complex processes, site visits are typically required
• For limited assurance, site visits may not always be necessary but the practitioner must evaluate whether procedures performed at head office provide sufficient evidence
• The nature of emissions (process emissions require more on-site understanding than purchased electricity) and the complexity of the entity’s operations both push toward more on-site work
• The quality of centralised data systems and the risk of material misstatement at specific facilities push the other way and may justify a head-office approach

Don’t skip site visits for industrial emitters. For entities with significant Scope 1 process emissions (manufacturing, chemical processing, oil and gas), site visits are practically required even for limited assurance. Understanding the physical processes, metering equipment, and data flows at the facility level is often the only way to evaluate whether the quantification methodology is appropriate and the reported data is reasonable. Running the engagement entirely from head office risks missing basic measurement or completeness issues. This is also the work that nobody enjoys scheduling, but skipping it is how the file gets flagged.

Specific procedures

The practitioner considers procedures for:

Reporting

Report content

The assurance report must include:

Illustrative conclusions

For reasonable assurance, the typical conclusion reads: “In our opinion, the GHG statement of [Entity] for the year ended [date] is prepared, in all material respects, in accordance with [applicable criteria].”

For limited assurance, the conclusion takes a negative form: “Based on the procedures we have performed and the evidence we have obtained, nothing has come to our attention that causes us to believe that the GHG statement of [Entity] for the year ended [date] is not prepared, in all material respects, in accordance with [applicable criteria].”

Whichever form applies, the file should tell a story about how the team got there. Reviewers want to see why each emission factor was chosen, why each scope boundary was drawn where it was, and why the team accepted (or rejected) management’s estimates for the harder Scope 3 categories.

The transition to ISSA 5000

Timeline and implications

In May 2025, the IAASB formally approved the withdrawal of ISAE 3410. The withdrawal aligns with ISSA 5000’s effective date:

• ISSA 5000 is effective for sustainability assurance engagements on sustainability information reported for periods beginning on or after 15 December 2026
• ISAE 3410 continues to apply for engagements on GHG statements for periods beginning before 15 December 2026
• Early adoption of ISSA 5000 is permitted

What changes under ISSA 5000

For GHG-specific assurance, the key changes are:

1. Standalone standard. ISSA 5000 does not require separate compliance with ISAE 3000, unlike ISAE 3410.
2. Broader scope. ISSA 5000 covers all sustainability information, not just GHG. GHG assurance under ISSA 5000 is one element of broader sustainability assurance.
3. Double materiality. ISSA 5000 introduces double materiality concepts relevant to CSRD reporting.
4. Value chain considerations. Enhanced guidance on Scope 3 and value chain emissions data.
5. Qualitative disclosures. ISSA 5000 addresses assurance on narrative sustainability disclosures that accompany GHG data.

What carries forward

The core GHG-specific knowledge from ISAE 3410 (understanding emission scopes, quantification methods, emission factors, scientific vs estimation uncertainty, site visit considerations) carries directly into ISSA 5000 practice. Practitioners who have built ISAE 3410 competence have a significant head start on ISSA 5000 implementation.

Build GHG expertise now. Even though ISAE 3410 will be withdrawn, the GHG-specific knowledge it requires is permanent. Climate reporting is expanding, not contracting. Every CSRD sustainability statement includes climate disclosures under ESRS E1. Every assurance engagement on a sustainability report will require GHG expertise. Investing in ISAE 3410 capability today builds the foundation for ISSA 5000 practice tomorrow.

European jurisdiction implementations

Netherlands

Dutch practice has extensive GHG assurance experience driven by the EU ETS (administered by the Nederlandse Emissieautoriteit, NEa) and voluntary reporting under the CO₂ Performance Ladder scheme. The NEa requires verification of emissions reports from EU ETS installations, with verifiers accredited under the EU Accreditation and Verification Regulation. While EU ETS verification follows its own regulatory framework rather than ISAE 3410 directly, many Dutch practitioners apply ISAE 3410 principles for voluntary GHG assurance alongside their EU ETS verification practice. For CSRD first-wave companies, Dutch auditors are providing limited assurance on ESRS E1 climate disclosures (including GHG emissions) under ISAE 3000/3410. The NBA has published practice guidance on GHG assurance engagements. Dutch multinationals with extensive global operations face particular challenges in obtaining reliable Scope 3 data across international value chains.

Germany

Germany has a large population of EU ETS-regulated entities, particularly in manufacturing and chemicals. The Deutsche Emissionshandelsstelle (DEHSt) administers EU ETS compliance. German verifiers follow the EU Accreditation and Verification Regulation for EU ETS, while voluntary GHG assurance engagements apply IDW PS 3410 (aligned with ISAE 3410). German practitioners face particular complexity with the Brennstoffemissionshandelsgesetz (BEHG, national emissions trading for heating and transport fuels), which creates additional GHG reporting obligations beyond EU ETS. For CSRD sustainability assurance, German Wirtschaftsprüfer are providing limited assurance on climate disclosures under ISAE 3000/3410. The IDW has published guidance on applying assurance standards to sustainability information including GHG data. Germany’s industrial base means that Scope 1 process emissions (often the most technically complex to verify) feature prominently in German GHG assurance engagements.

United Kingdom

The UK has its own UK ETS (replacing participation in EU ETS post-Brexit) administered by the Environment Agency and SEPA. UK ETS verification follows UK-specific regulations. For voluntary and regulatory GHG reporting under the Streamlined Energy and Carbon Reporting (SECR) framework and the Task Force on Climate-related Financial Disclosures (TCFD) recommendations (mandatory for premium-listed companies and large private companies), ISAE (UK) 3410 provides the assurance framework. The FRC has signalled increasing expectations for climate-related assurance quality. UK practitioners benefit from the relatively mature market for climate disclosures, with many FTSE companies having obtained GHG assurance for several years under voluntary frameworks before mandatory requirements emerged.

France

France has been a pioneer in mandatory GHG reporting through the Bilan Carbone and Bilan des émissions de gaz à effet de serre (BEGES) requirements under the Code de l’environnement, which predates CSRD. Large French entities have been required to report Scope 1 and 2 emissions (and encouraged to report Scope 3) since 2010. GHG verification has historically been performed by both commissaires aux comptes and organismes tiers indépendants (OTIs) accredited by COFRAC. The dual-provider model for sustainability assurance under CSRD continues this tradition. NEP 9090 provides French-specific guidance for environmental assurance engagements. French practitioners have significant experience with the industrial emissions verification required under the EU ETS, particularly for the cement, steel, energy, and chemical sectors concentrated in France’s industrial regions.

Relationship with other standards

• ISAE 3000. ISAE 3410 operates within the ISAE 3000 framework. Compliance with both is required.
• ISSA 5000. Will replace ISAE 3410 for sustainability assurance from December 2026 (ISAE 3410 to be withdrawn).
• ISA 720. When a GHG statement is included in the annual report, the financial statement auditor reads it as other information.
• ISA 620. The practitioner may use experts (environmental engineers, climate scientists) for GHG assurance.
• ISA 540. Concepts of estimation uncertainty from ISA 540 are adapted for GHG-specific estimation challenges.
• ESRS E1. The CSRD climate change reporting standard provides criteria for GHG disclosures subject to assurance.

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Frequently asked questions

Further reading and source references

• IAASB Handbook 2024: The authoritative source for the complete ISAE 3410 text.
• ISAE 3000 (Revised): The foundation assurance standard that ISAE 3410 operates alongside.
• ISSA 5000: The new standalone sustainability assurance standard effective December 2026, which will replace ISAE 3410.
• GHG Protocol Corporate Standard: The most widely adopted criteria framework for GHG quantification.
• ISO 14064-1: International standard for organisational-level GHG quantification and reporting.
• EU ETS Monitoring and Reporting Regulation (MRR): Mandatory criteria for EU ETS installations.