ISAE 3410 — Assurance Engagements on Greenhouse Gas Statements: A Practical Guide for European Auditors

Key Takeaways

ISAE 3410 is the profession's first subject-specific standard for environmental assurance, and its legacy extends far beyond its formal lifespan.
The core competencies it builds — understanding emission scopes, quantification methods, the distinction between scientific and estimation uncertainty, the need for multidisciplinary teams, and site visit judgment — are permanent requirements for climate-related assurance.
While ISSA 5000 will formally replace ISAE 3410 from December 2026, the transition is more of an expansion (from GHG-specific to all sustainability) than a replacement of knowledge.
For European firms building sustainability assurance practices, deep GHG competence built through ISAE 3410 experience is the essential foundation upon which CSRD assurance capability is constructed.
Every CSRD sustainability statement includes climate disclosures under ESRS E1 — every assurance engagement on a sustainability report will require GHG expertise.

Why ISAE 3410 Matters

Greenhouse gas emissions reporting has moved from voluntary disclosure to regulatory requirement across Europe and globally. The EU Emissions Trading System (EU ETS), the Corporate Sustainability Reporting Directive (CSRD), national climate legislation, and investor expectations all demand reliable emissions data — and with that demand comes the need for independent assurance. ISAE 3410 is the subject-specific standard that governs assurance engagements on greenhouse gas (GHG) statements, providing the specialised framework practitioners need when the subject matter involves emissions quantification.

For European audit firms, GHG assurance is both a current revenue stream and a bridge to the broader sustainability assurance market. While ISAE 3410 will be withdrawn when ISSA 5000 becomes effective for periods beginning on or after 15 December 2026, the standard remains directly relevant today for standalone GHG assurance engagements and provides essential conceptual foundations that carry directly into ISSA 5000 practice. Understanding ISAE 3410 is not just about current compliance — it is about building the GHG-specific expertise that sustainability assurance demands.

Scope and Fundamental 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, emission deductions, and emissions offsets) 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, customers, or the public

The Emissions Framework

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

Scope	Definition	Examples	Quantification Complexity
Scope 1	Direct emissions from sources owned or controlled by the entity	Combustion in boilers/furnaces, vehicle fleet, chemical process emissions, fugitive emissions from refrigerants	Moderate — direct measurement or calculation from fuel consumption data
Scope 2	Indirect emissions from purchased electricity, heat, steam, or cooling	Electricity consumption at all facilities, district heating	Lower — calculation from energy consumption and grid emission factors
Scope 3	All other indirect emissions in the entity's value chain	Business travel, employee commuting, purchased goods, waste disposal, use of sold products, investments	High — relies on estimates, third-party data, industry averages, and modelling

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, metering equipment, and fuel records. Scope 2 verification is relatively straightforward (energy bills x 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. 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:

Framework	Context
GHG Protocol Corporate Standard	Global voluntary standard, widely adopted
ISO 14064-1	International standard for organisational-level GHG quantification
EU ETS Monitoring and Reporting Regulation (MRR)	Mandatory for EU ETS installations
ESRS E1 (Climate change)	CSRD sustainability reporting standard
National schemes	UK Streamlined Energy and Carbon Reporting (SECR), French Bilan Carbone, Dutch NEa requirements
Entity-developed criteria	Must be evaluated for suitability by the practitioner

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:

Ethical and independence requirements are met
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.
Preconditions — the subject matter is appropriate, suitable criteria exist, and sufficient evidence can be obtained
Scope — which emissions are covered (all scopes? specific facilities? specific gases?)
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, environmental scientists to assess quantification methodologies, and IT specialists to evaluate emissions data systems. 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. Scientific uncertainty is disclosed in the GHG statement and referenced in the assurance report but is not something the practitioner can reduce through assurance procedures.

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

Materiality for GHG assurance engagements is determined 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:

The entity's operations, facilities, and processes that generate emissions
The organisational and operational boundaries applied
The types and sources of emissions within scope
The quantification methods used (direct measurement, calculation, estimation)
The data collection and reporting systems
The internal controls over emissions data
The emission factors and global warming potentials applied
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
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 essential
For limited assurance, site visits may not always be necessary but the practitioner must evaluate whether procedures performed at head office provide sufficient evidence
Factors affecting the decision include: the nature of emissions (process emissions require more on-site understanding than purchased electricity), the complexity of the entity's operations, the quality of centralised data systems, and the risk of material misstatement at specific facilities

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 essential 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. Conducting the engagement entirely from head office risks missing fundamental measurement or completeness issues.

Specific Procedures

The practitioner considers procedures for:

Emissions Component	Typical Procedures
Activity data (fuel consumption, electricity use, production volumes)	Agree to source records (invoices, meter readings, production logs), test mathematical accuracy, evaluate completeness
Emission factors	Evaluate appropriateness of factors used, verify source (IPCC, national inventories, EU MRR defaults), check whether entity-specific factors are available and should be used
Calculations	Recalculate emissions from activity data x emission factors x GWP, verify unit conversions, check aggregation
Scope 2 methods	Evaluate whether location-based or market-based method is applied correctly, verify contractual instruments for market-based approach
Scope 3 estimates	Evaluate methodology and assumptions, assess data sources, test key estimates, consider sensitivity of results to assumption changes
Completeness	Evaluate whether all relevant sources and facilities are included, consider acquisitions/disposals during the period
Comparative information	Evaluate consistency of methods, appropriate restatement for structural changes

Reporting

Report Content

The assurance report must include:

Element	Content
Title	Clearly identifies as an independent assurance report
Addressee	As appropriate for intended users
GHG statement identification	Identifies the specific GHG statement covered
Applicable criteria	Identifies the criteria used (GHG Protocol, ISO 14064-1, EU MRR, etc.)
Inherent uncertainty reference	Mandatory — draws attention to uncertainty inherent in GHG quantification
Responsibility paragraphs	Entity's responsibility for the GHG statement; practitioner's responsibility
Summary of procedures	Particularly important for limited assurance — describes the nature of work performed
Conclusion	Positive form (reasonable assurance) or negative form (limited assurance)

Illustrative Conclusions

Reasonable assurance: "In our opinion, the GHG statement of [Entity] for the year ended [date] is prepared, in all material respects, in accordance with [applicable criteria]."

Limited assurance: "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]."

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:

Standalone standard — ISSA 5000 does not require separate compliance with ISAE 3000, unlike ISAE 3410
Broader scope — ISSA 5000 covers all sustainability information, not just GHG. GHG assurance under ISSA 5000 is one element of broader sustainability assurance
Double materiality — ISSA 5000 introduces double materiality concepts relevant to CSRD reporting
Value chain considerations — Enhanced guidance on Scope 3 and value chain emissions data
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), the Dutch Climate Act (Klimaatwet), 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, energy, 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, SEPA, and DAERA. 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 energy, cement, steel, 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

Frequently Asked Questions

What is the difference between scientific uncertainty and estimation uncertainty in ISAE 3410?

Scientific uncertainty is inherent in the science of quantifying GHG emissions — emission factors carry inherent uncertainty ranges regardless of reporting quality. Estimation uncertainty arises from the entity's measurement, data collection, and calculation processes, including metering accuracy, data gaps, and use of industry averages. The practitioner's assurance procedures focus on estimation uncertainty, while scientific uncertainty is disclosed and referenced in the assurance report.

Does ISAE 3410 still apply after ISSA 5000 becomes effective?

No. ISAE 3410 will be formally withdrawn when ISSA 5000 becomes effective for sustainability assurance engagements on sustainability information reported for periods beginning on or after 15 December 2026. However, ISAE 3410 continues to apply for engagements on GHG statements for periods beginning before that date. Early adoption of ISSA 5000 is permitted.

Are site visits required for ISAE 3410 engagements?

For reasonable assurance engagements involving Scope 1 emissions from complex processes, site visits are typically essential. For limited assurance, site visits may not always be necessary but the practitioner must evaluate whether head-office procedures provide sufficient evidence. Factors include the nature of emissions, complexity of operations, quality of centralised data systems, and the risk of material misstatement at specific facilities.

What are the three scopes of GHG emissions covered by ISAE 3410?

Scope 1 covers direct emissions from sources owned or controlled by the entity (e.g., combustion, vehicle fleets, process emissions). Scope 2 covers indirect emissions from purchased electricity, heat, steam, or cooling. Scope 3 covers all other indirect emissions in the entity's value chain, including business travel, purchased goods, waste disposal, and use of sold products. The practitioner's procedures and required expertise vary dramatically by emission scope.