GHG Verification Process & Timeline: Planning to Statement

Process Overview

GHG verification under ISO 14064-3 follows a structured, five-stage process that transforms raw GHG data into an independently assured statement. Each stage builds on the previous one, and together they ensure that the final verification conclusion is well-supported, defensible, and credible.

The five stages are:

1. Pre-Engagement: Scope definition, materiality agreement, timeline setting, and engagement formalisation
2. Planning: Risk assessment, verification plan development, team assignment, and sampling design
3. Execution: Document review, data testing, site visits (physical or remote), and interviews
4. Evaluation: Aggregation of findings, materiality assessment, and opinion formation
5. Reporting: Issuance of verification statement and management report

Understanding this process helps organisations prepare effectively, set realistic expectations for timelines and resource requirements, and engage productively with the verification team throughout the engagement.

Stage 1: Pre-Engagement

The pre-engagement stage establishes the foundation for the entire verification engagement. Decisions made at this stage—scope, materiality, assurance level—determine the nature and extent of all subsequent work.

Scope Definition

The scope defines what will be verified. Key elements to agree include:

• Reporting period: The financial or calendar year covered by the GHG inventory
• Emission categories: Which scopes are included (Scope 1 only, Scope 1+2, Scope 1+2+3, or specific Scope 3 categories)
• Organisational boundary: Which entities, sites, and facilities are within scope
• Criteria: The standard against which the inventory is verified (e.g., ISO 14064-1:2018, GHG Protocol)
• Intended users: Who will rely on the verification statement (regulators, investors, CDP, public)

Materiality and Assurance Level

The materiality threshold and assurance level are agreed between the verifier and the organisation based on the intended use of the statement and any scheme-specific requirements. Typical settings are 5% materiality for reasonable assurance and 5-10% for limited assurance.

Engagement Agreement

The pre-engagement stage concludes with a formal engagement agreement (or terms of reference) that documents the agreed scope, materiality, assurance level, timeline, fees, and the responsibilities of both parties. This agreement protects both the organisation and the verifier by setting clear expectations.

Timeline Setting

Establish key milestones including the submission deadline for the GHG inventory and supporting evidence, planned dates for site visits, the target date for the draft findings meeting, and the target date for verification statement issuance.

Stage 2: Planning

Planning translates the engagement agreement into a detailed verification plan. This stage is conducted by the verification team and determines where effort will be focused during execution.

Risk Assessment

The verification team assesses the risk of material misstatement for each significant emission source. Risk assessment considers inherent risk (complexity of quantification, data availability, magnitude of emissions) and control risk (quality of internal controls, data management maturity, prior verification history). High-risk areas receive more extensive testing.

Verification Plan

The verification plan specifies:

• Which emission sources will be tested and at what depth
• The sampling approach for data testing (statistical, judgemental, or key item)
• Which sites will be visited (if applicable) and the purpose of each visit
• The types of evidence to be gathered for each emission category
• The team assigned to the engagement and their responsibilities
• The detailed timeline for execution activities

Sampling Strategy

For organisations with multiple sites or large volumes of data, sampling is essential. The verification team designs a sampling strategy that provides sufficient coverage while managing effort. Factors influencing sample selection include the materiality of individual sites or data items, the homogeneity of sites and data, the assessed risk level, and the level of assurance required.

Stage 3: Execution

Execution is the most intensive stage and involves direct engagement with the organisation's data, systems, and personnel. The verifier gathers evidence to support the verification conclusion through a combination of document review, data testing, site activities, and interviews.

Document Review

The verifier reviews the GHG inventory report, quantification methodologies, emission factor documentation, organisational boundary documentation, and supporting policies and procedures. The review assesses completeness, compliance with the stated criteria, and consistency with prior periods.

Data Testing

Data testing is the core of the execution stage. Activities include:

• Recalculation: Independently recalculating emissions from source activity data using the organisation's declared methodology and emission factors
• Vouching: Tracing reported data back to source documents (invoices, meter readings, system outputs)
• Analytical procedures: Comparing reported data to prior periods, budgets, or benchmarks to identify anomalies
• Completeness checks: Verifying that all sites, months, and emission sources within scope are included
• Cut-off testing: Confirming that activity data relates to the correct reporting period

Site Visits

Site visits provide first-hand evidence that supports the verification conclusion. Activities during a site visit include:

• Facility walkthrough: Physical inspection of emission sources, metering equipment, fuel storage, and operational processes
• Meter verification: Checking calibration records, reading meters, and comparing to reported data
• Interviews: Speaking with operational staff responsible for data collection to understand processes and identify potential issues
• Process observation: Observing data collection and recording procedures in practice
• Document inspection: Reviewing original records that may not be available electronically

Remote Verification

Where site visits are not conducted, remote verification procedures include video conferencing and virtual facility tours, screen-sharing of data systems and records, electronic submission of scanned documents and evidence, real-time walkthrough of calculation spreadsheets, and remote interviews with site personnel.

Interviews

Interviews are conducted with key personnel including the GHG inventory manager, site-level data collectors, facilities and operations managers, finance staff (for spend-based Scope 3 data), and sustainability or ESG leadership. Interviews help the verifier understand data flows, identify potential weaknesses, and corroborate documentary evidence.

Stage 4: Evaluation

The evaluation stage brings together all the evidence gathered during execution and assesses its implications for the verification conclusion.

Findings Aggregation

The verifier aggregates all identified misstatements—factual errors, judgemental differences, and projected misstatements from sampling—into a summary schedule. Each finding is categorised by type, magnitude, and the emission source affected.

Materiality Assessment

The aggregate of uncorrected misstatements is compared to the materiality threshold. If the aggregate is below materiality, the verifier can issue an unqualified conclusion. If at or near materiality, additional procedures may be performed or the organisation may be asked to correct identified errors. If above materiality and errors remain uncorrected, the conclusion must be qualified or adverse.

Findings Categories

Draft Findings Meeting

Before finalising the conclusion, the verifier typically holds a draft findings meeting with the organisation to present identified misstatements, discuss observations and recommendations, give the organisation an opportunity to correct errors or provide additional evidence, and agree on the final content of the verification statement.

Stage 5: Reporting

The reporting stage produces the formal outputs of the verification engagement: the verification statement and the management report.

Verification Statement

The verification statement is the public-facing document that communicates the verifier's conclusion. It is typically 2-3 pages and includes identification of the GHG assertion, reporting period, and scope of verification; the criteria used (e.g., ISO 14064-1:2018); the level of assurance and materiality threshold; a summary of verification procedures; the verification conclusion (opinion); any qualifications or emphasis of matter; and the date, place, and signature of the lead verifier.

Management Report

The management report (confidential to the organisation) provides detailed information including a comprehensive description of procedures performed, specific findings with supporting detail, corrected and uncorrected misstatements, data quality observations, recommendations for improving GHG reporting and internal controls, and areas to focus on for future reporting periods.

Independent Review

Before the verification statement is issued, ISO 14065 requires an independent technical review. A qualified reviewer who was not involved in the execution of the engagement reviews the verification documentation, findings, and conclusion to ensure quality and consistency. This is an internal quality assurance step within the verification body.

Typical Timelines

Verification timelines vary based on complexity, scope, and data readiness. The following provides typical ranges for different scenarios.

Timeline Breakdown by Stage

For a standard engagement (4-6 weeks total):

• Pre-engagement: 1-2 weeks (overlaps with organisation preparing evidence)
• Planning: 3-5 working days
• Execution: 1-2 weeks (including site visits if applicable)
• Evaluation and draft findings: 3-5 working days
• Organisation response to findings: 3-5 working days
• Final reporting and independent review: 3-5 working days

Cost Factors

GHG verification costs are primarily driven by verifier time (person-days), which is influenced by several factors.

Key Cost Drivers

• Organisation complexity: More sites, entities, and countries increase effort
• Scope coverage: Adding Scope 3 categories significantly increases the volume of data and methodologies to verify
• Level of assurance: Reasonable assurance typically requires 50-100% more verifier time than limited assurance
• Site visits: Physical site visits add travel costs and on-site verifier days
• Data quality: Poor data quality and documentation increases the time needed for evidence gathering and query resolution
• First-time verification: First-year engagements typically require more effort than recurring verifications as the verifier builds understanding
• Scheme-specific requirements: Regulatory schemes (EU ETS, California) have specific requirements that may increase scope

Indicative Cost Ranges

Tips for a Smooth Verification

Based on our experience conducting hundreds of GHG verification engagements, these practices consistently lead to smoother, faster, and more cost-effective verifications.

Before the Engagement

• Prepare your evidence pack early: Compile all activity data, emission factors, calculation workbooks, and supporting documents before the verifier starts
• Conduct an internal review: Have someone other than the preparer review the inventory for errors, completeness, and consistency
• Document your methodology: Write down how each emission source was quantified, including data sources, emission factors, and assumptions
• Organise your data: Use a logical folder structure with clear file naming conventions

During the Engagement

• Respond promptly to queries: The single biggest factor in verification delays is slow query resolution. Aim to respond within 2-3 working days
• Designate a single point of contact: One person who coordinates all communication with the verifier
• Be transparent about limitations: If data quality is poor for a particular source, explain why and what steps you plan to take. Verifiers appreciate honesty
• Correct errors promptly: When the verifier identifies errors, correct them quickly to avoid them accumulating toward materiality

After the Engagement

• Act on recommendations: The management report contains valuable insights for improving your next inventory
• Start early next year: Use the findings to improve data collection processes throughout the year, not just at reporting time
• Maintain the relationship: Continuing with the same verification body (subject to rotation policies) builds efficiency as the verifier develops understanding of your organisation

The best verification engagements are characterised by well-prepared organisations, responsive communication, and a shared commitment to data quality. Verification is not an adversarial process—it is a collaborative assurance mechanism that benefits everyone.

Frequently Asked Questions

How long does a GHG verification engagement take?

A typical GHG verification engagement takes 4-8 weeks from kick-off to statement issuance. Simple, single-site organisations with good data quality may complete in 3-4 weeks. Complex, multi-site organisations or first-time verifications may require 8-12 weeks. The timeline depends on data readiness, number of sites, scope complexity, and responsiveness to verifier queries.

How much does GHG verification cost?

GHG verification costs typically range from USD 5,000 to USD 50,000+ depending on organisation size, number of sites, scope complexity, the level of assurance, and whether site visits are required. Single-site SMEs seeking limited assurance on Scope 1 and 2 may pay USD 5,000-10,000. Large multinational organisations with full Scope 3 coverage at reasonable assurance can expect USD 25,000-50,000+.

Are site visits always required for GHG verification?

Site visits are not always mandatory but are strongly recommended for reasonable assurance engagements and for material sites. For limited assurance, remote verification may be acceptable if sufficient documentary evidence can be provided. The decision depends on the assessed risk, materiality of site-level emissions, the level of assurance, and whether the site has been visited in prior years.

What happens if the verifier finds errors in my GHG data?

If errors are identified, the verifier will communicate them as findings and give the organisation an opportunity to correct the data before the statement is issued. Corrected errors are noted in the verification documentation but do not affect the final opinion. If material errors remain uncorrected, the verifier may issue a qualified or adverse opinion.

Can GHG verification be done remotely?

Yes, remote verification has become increasingly common and accepted, particularly for limited assurance engagements. Remote verification uses video conferencing, screen-sharing, electronic document exchange, and virtual site tours. However, for reasonable assurance—especially for first-time verifications or high-risk sites—physical site visits are typically expected.