GHG Protocol or ISO 14064? Which is the Right Choice and When?

When preparing a corporate carbon inventory, the first critical decision is which standard to follow. This decision determines calculation boundaries, data collection systems, report format, and verification approach. Two names come up together in most projects: GHG Protocol and ISO 14064.

In this article, we compare both standards in detail, explaining when to choose which and how they can be used together.

What is GHG Protocol?

GHG Protocol (Greenhouse Gas Protocol) is a framework developed by the World Resources Institute (WRI) and the World Business Council for Sustainable Development (WBCSD) that forms the foundation of corporate greenhouse gas accounting. It has been developing since 1998 and is the most widely used reference worldwide.

Several standards and guidelines exist under the GHG Protocol umbrella:

Corporate Accounting and Reporting Standard: Forms the foundation of corporate inventory. Covers Scope 1 and Scope 2 emissions.
Scope 2 Guidance: Provides detailed guidance for purchased electricity, heat, and steam emissions.
Corporate Value Chain (Scope 3) Standard: Addresses value chain emissions in 15 categories.
GHG Protocol for Cities: For city-level inventory.
Product Life Cycle Standard: For product-based calculations.

GHG Protocol is freely accessible. It works on a principles basis: relevance, completeness, consistency, transparency, and accuracy.

What is ISO 14064?

ISO 14064 is a standard published by the International Organization for Standardization (ISO) that provides requirements and guidance for greenhouse gas inventories. It consists of three parts:

ISO 14064-1: Requirements and guidance for the design, development, management, and reporting of organization-level greenhouse gas inventories.
ISO 14064-2: Quantification, monitoring, and reporting of project-level greenhouse gas emission reductions or removals.
ISO 14064-3: Requirements for the verification and validation of greenhouse gas statements.

ISO 14064 is a standard that must be purchased. It works on a requirements basis: "shall" statements specify conditions that must be met for compliance.

Key differences

Structure and flexibility

GHG Protocol offers principles and guidance. It leaves flexibility to companies on how things are done. ISO 14064 defines requirements. It is more prescriptive and specific.

This difference is reflected in practice: GHG Protocol says "organizational boundary can be determined using one of financial control, operational control, or equity share approaches." ISO 14064 presents these approaches similarly but defines more detailed expectations for documentation and justification.

Scope definitions

GHG Protocol clearly defines the Scope 1, Scope 2, and Scope 3 distinction, and this terminology has become standard worldwide. CDP, SBTi, GRI, and many reporting frameworks use this terminology.

ISO 14064 uses direct emissions and indirect emissions distinction. It classifies indirect emissions as energy-related indirect emissions and other indirect emissions. It does not directly use Scope 3's 15-category structure.

Verification approach

ISO 14064-3 contains detailed requirements for verification. The independence and competence of the verification body, verification plan, evidence collection, findings, and opinion types are clearly defined. Accreditation bodies (e.g., TÜRKAK) accredit verification bodies according to ISO 14064-3.

GHG Protocol strongly recommends verification but does not provide detailed requirements on how it should be done. ISO 14064-3 or ISAE 3410 (Assurance Engagements on Greenhouse Gas Statements) is generally referenced for verification.

When to use which?

GHG Protocol is preferred when:

Reporting to frameworks like CDP, SBTi, GRI, TCFD
Scope 3 work will be set up in detail (15-category structure)
Comparability with international companies is important
Inventory is being prepared for the first time and guidance needs are high
Freely accessible resources are preferred

ISO 14064 is preferred when:

Accredited verification is mandatory or preferred
Regulation or tender specifications require ISO
Project-based emission calculation will be done (ISO 14064-2)
Formal certification is required
Customer or investor expects ISO compliance

Can they be used together?

Yes, and this is common practice. Many companies adopt the following approach:

Build inventory using GHG Protocol methodology (Scope 1-2-3 structure, calculation guidelines)
Prepare documentation compliant with ISO 14064-1 requirements (procedures, policies, controls)
Obtain accredited verification according to ISO 14064-3

The two standards do not conflict; they complement each other. While GHG Protocol provides more detailed calculation guidance, ISO 14064 provides the management system and verification structure.

Implementation recommendations

At project start: Identify target stakeholders and reporting frameworks. Will you report to CDP, do you need ISO certification, or both?

In methodology selection: Use GHG Protocol guidelines for calculation methodology. Follow the category structure for Scope 3.

In documentation: Check ISO 14064-1 requirements. Document topics such as organizational boundary, materiality, uncertainty, and recalculation policy.

In verification: Obtain verification from an accredited body under ISO 14064-3. Assurance level (limited or reasonable) should be determined according to expectations.

Accreditation bodies and assurance

The competence of verification bodies is assured through the accreditation system. ISO 17029 defines general principles and requirements for the verification and validation of greenhouse gas statements. This standard is used together with ISO 14064-3 and forms the basis for accreditation of verification bodies.

In Turkey, TÜRKAK (Turkish Accreditation Agency) accredits verification bodies under ISO 14064-3. Verification from an accredited body provides a higher level of confidence for stakeholders. Regulations or customer requirements may require accredited verification.

Practical recommendations for dual compliance

To work in compliance with both standards, follow these steps:

Use GHG Protocol guidelines as the methodology foundation
Apply ISO 14064-1 documentation requirements as a checklist
Document inventory management procedures in writing
Create uncertainty assessment and recalculation policy
Obtain verification from an accredited body according to ISO 14064-3

This approach ensures both compliance with frameworks like CDP and SBTi and formal verification certification.

Conclusion

Standard selection should be made according to the project's purpose. Reporting target, verification expectations, and stakeholder requirements shape this decision. In most cases, the best approach is to use both standards together: combining GHG Protocol's calculation guidance with ISO 14064's management system and verification structure.

GHG Protocol or ISO 14064? Which is the Right Choice and When?