Emissions Verification: When and Why It Is Required

An investor has requested a third-party assurance statement to accompany the emissions report, and the deadline is six weeks away. This situation is increasingly familiar in 2026, as the CSRD rollout and SBTi targets require verified data. This article explains what verification means in practice, what ISO 14064-3 requires, and when verification becomes necessary.

What Verification Means in Emissions Accounting

Verification is an assessment carried out by an independent external expert body confirming that:

The calculation has been performed in accordance with the relevant standard (typically GHG Protocol and/or ISO 14064-1)
The data used is traceable to its original sources
Emission factors are documented with their sources
The reported figures are materially correct

The outcome is a written assurance statement that can be used as an annex to the sustainability report, in investor and customer communications, in EcoVadis or CDP responses, and as part of CSRD reporting.

Verification does not change the figures in the calculation. It states whether the numbers are justified and calculated in accordance with the standard. If the verifier identifies errors, they are corrected before the statement is issued.

Terminology varies: the process is also referred to as assurance, verification, and validation. English-language sources use the terms verification and assurance. ISO 14064-3 and ISAE 3410 use different words for the same activity, and the most important practical distinction is the form of the outcome: limited or reasonable assurance.

When Verification Becomes Necessary

Verification is rarely a direct statutory requirement for SMEs, but in practice it becomes necessary in several situations.

CSRD reporting. Large companies’ ESRS reporting requires at least limited assurance for climate-related data. Over time, the requirement may tighten to reasonable assurance. For SMEs, this requirement is reflected indirectly through the value chain.

SBTi target disclosure. When a company publishes a Science Based Targets commitment, third-party verification of the underlying figures is expected.

A major customer or investor requires it. In supply chains and investor communications, verified figures are increasingly a prerequisite for contracts or financing.

Pursuing a higher EcoVadis rating. Higher tiers (Gold, Platinum) require evidence of externally verified figures.

Internal reliability. In some cases, a company wants to confirm the reliability of its own figures before external reporting. This is often a prudent step before the first public report.

Baseline for emission reduction commitments. When a company commits to a reduction target (e.g. SBTi), the baseline year serves as the foundation against which progress is measured for years to come. Verification at this stage prevents having to revise the baseline and target trajectory later.

Limited Assurance vs. Reasonable Assurance

The two assurance levels differ in how deeply the verifier examines the data and in the language used in the statement.

Limited assurance is the lighter level. The verifier reviews the documentation, performs checks, and requests additional information. The statement is worded along the lines of “nothing has come to our attention that would cause us to believe that the figures are materially misstated.” This is the most common level for first-time verifications and in the early stages of CSRD.

Reasonable assurance is the more rigorous level. The verifier conducts deeper examination, sampling, and independent recalculation. The statement is worded along the lines of “in our opinion, the figures are presented fairly, in all material respects.” This is equivalent to an audit opinion and takes more time.

The practical difference shows up in two areas: workload (reasonable assurance is typically 1.5–3 times more labour-intensive) and data traceability requirements (reasonable assurance often requires supplier-level supporting documents where limited assurance accepts summaries).

ISO 14064-3: The Verification Process Standard

ISO 14064-3 defines the principles governing the verification of greenhouse gas statements. The standard rests on three main principles:

Materiality. Verification focuses on figures and processes that have a significant impact on the outcome. The materiality threshold is agreed in advance (e.g. 5% of total emissions).

Sampling. Not every supporting document is examined. The verifier selects a representative sample and checks its traceability to original sources.

Independence. The verifier must not have been involved in preparing the calculation. This is why a consultant who performs the calculation cannot verify that same calculation.

Documentation. The verifier maintains working papers demonstrating what was checked, how it was checked, and what conclusion was reached. This also forms the basis for accreditation.

The practical verification process typically proceeds as follows: proposal and scoping agreement → planning and materiality threshold setting → documentation request and review → sampling and traceability assessment → question and correction rounds → drafting of the statement. The total timeline is typically 4–8 weeks.

More information on our verification services page.

What Is Expected of the Company During Verification

The verifier typically requests the following materials.

Calculation methodology document. Standards applied, organisational boundary, scopes, categories, assumptions, and exclusions with justifications.

Data traceability. Fuel purchase invoices, electricity consumption records, vehicle mileage data, refrigerant service reports, business travel management reports. For spend-based categories: accounting source documents.

Emission factor documentation. Factors used with their sources, years, and versions. In practice this is a table linked to every line in the calculation.

Calculation formulas and working files. Excel models or equivalent, showing formulas and intermediate results.

Justification for boundary decisions. In particular, the materiality assessment for Scope 3 categories: why a given category has been excluded and on what basis.

If any of these is missing or unclear, verification will be delayed. This is the most common cause of schedule slippage.

The Most Common Reasons Verification Is Delayed

Incomplete data collection. Primary data has not been requested from suppliers in time, and the verifier cannot confirm figures based on summaries alone.

Unclear Scope 3 boundaries. Categories have been scoped without documented justification, or the materiality assessment has not been completed.

Undocumented emission factor selection. Factors have been applied, but the source, year, or version is missing.

Missing refrigerant data. Service reports have not been archived, and top-up quantities can no longer be traced to supporting document level.

Reporting period timing error. The financial year start and end dates do not match the data used.

Practical recommendation: allow 8 weeks from the planned report publication date, working backwards. If the process is started later, deadlines become tight and correction rounds remain superficial.

What the Assurance Statement Actually Says

The assurance statement is typically 1–3 pages. It includes:

The scope and boundary of the engagement (what was verified and what was not)
The standards applied (ISO 14064-3, ISAE 3410, GHG Protocol)
The materiality threshold applied in the work
The assurance conclusion at the applicable level (limited or reasonable)
Any observations and limitations

The statement is signed by the verifier and can be used as an annex to the report and in stakeholder communications. A separate certificate is not generally issued; the statement itself is the evidence.

The statement is typically written in English when the target audience is international. For domestic use it can also be issued in Finnish or bilingually.

Check your calendar for when an investor, parent company, or customer expects to receive a verified report, and count 8 weeks back from that date. That is the latest date by which the verification process must be initiated.

Frequently Asked Questions

Do the figures in a CSRD report need to be verified?

Yes, at minimum at the limited assurance level. The requirement applies to large companies on a phased basis and may tighten to reasonable assurance over time.

Who can verify an emissions calculation?

An independent expert body with competence in the GHG Protocol and ISO 14064-3 principles. For some purposes (e.g. CSRD), the verifier must be an accredited certification body or statutory audit firm.

Can the same party perform both the calculation and the verification?

No. The independence principle in ISO 14064-3 prohibits this. The party performing the calculation and the verifier are separate organisations, or at minimum separate teams with documented firewalls.

How long does the verification process typically take?

4–8 weeks, once the documentation is ready. Limited assurance at the shorter end, reasonable assurance at the longer end. Correction rounds can extend the timeline.

What is the difference between limited and reasonable assurance?

Limited assurance involves a lighter examination and a more cautious statement. Reasonable assurance involves deeper examination, broader sampling, and a positively worded opinion. Limited assurance is sufficient in the early stages of CSRD.

What does verification cost?

The cost depends on the size of the organisation, scope coverage, the state of the data, and the assurance level. Get in touch and we will provide an indicative estimate based on your specific situation.

Does your calculation need to be verified?

We perform verification in accordance with ISO 14064-3 principles, independently. The result is a statement you can stand behind.

Book a 30-minute scoping call · Learn about our verification service