GHG Protocol vs ISO 14064 vs IFRS S2: Which Sustainability Standard Does Singapore Actually Use?

Why There Are Three Frameworks for the Same Thing

The short answer is that each framework was created by a different institution, for a different purpose, at a different point in time. That they now converge around the same underlying data — greenhouse gas emissions — reflects the fact that the field has matured around a common technical foundation, not that three separate systems are asking you for three separate sets of numbers.

The GHG Protocol came first, created in 2001 by the World Resources Institute (WRI) and the World Business Council for Sustainable Development (WBCSD). Its purpose was practical: give businesses a consistent, credible methodology for measuring and managing their greenhouse gas emissions. At the time, there was no global standard. Different companies were calculating emissions differently, using different boundaries and different emission factors, making comparisons meaningless. The GHG Protocol solved that problem.

ISO 14064 arrived in 2006 (updated in 2018) as the International Organization for Standardization's formalisation of the GHG Protocol approach into an auditable international standard. ISO 14064-1 covers organisational-level GHG inventories — exactly what most businesses need when they talk about "measuring our carbon footprint." The ISO framework adds more specificity around documentation requirements, boundary setting, and verification procedures, making it suitable for formal third-party audit and assurance.

IFRS S2 is the most recent arrival: published in June 2023 by the International Sustainability Standards Board (ISSB), a body under the IFRS Foundation that also sets global accounting standards. IFRS S2 is explicitly a disclosure standard for investors. It does not reinvent the accounting methodology — it mandates the use of GHG Protocol as the underlying calculation basis — but it adds four structured disclosure pillars (governance, strategy, risk management, and metrics and targets) designed to give investors standardised, comparable information about climate-related risks and opportunities.

These three frameworks are not alternatives. They are layers. Understanding the stack is the key to understanding what Singapore actually requires.

GHG Protocol: The Foundation That Everything Else Builds On

The GHG Protocol is best understood as the engineering standard of carbon accounting. It establishes the fundamental concepts and methodology that underpin almost every corporate sustainability report in the world.

The most important contribution of the GHG Protocol is the Scope 1/2/3 categorisation. Scope 1 emissions are direct emissions from sources owned or controlled by the organisation. Scope 2 emissions are indirect emissions from purchased electricity. Scope 3 emissions are all other indirect emissions in the value chain — upstream (suppliers) and downstream (customers, end-of-life). This three-part structure is now so universally adopted that it has become the lingua franca of corporate emissions reporting worldwide.

The GHG Protocol also establishes the activity-based calculation methodology: you measure a physical activity (litres of diesel consumed, kWh of electricity purchased) and multiply it by a published emission factor (kg CO2e per litre, kg CO2e per kWh) to arrive at your emissions in tonnes of CO2 equivalent (tCO2e). It defines the concept of a base year, organisational boundaries (equity share vs. operational control approaches), and the treatment of biogenic emissions.

The GHG Protocol is not a certification. There is no "GHG Protocol certified" status for organisations. It is a methodology — a set of rules and approaches that you apply when calculating your emissions. This is an important distinction: you can be ISO 14064-1 certified (meaning an auditor has verified your GHG inventory against the standard), but you cannot be "GHG Protocol certified."

For Singapore businesses, the practical significance is this: whatever reporting framework you end up using — whether you are reporting to SGX under IFRS S2, or producing a GRI 305 report for stakeholder communications, or seeking ISO 14064-1 verification for a client tender — the underlying calculation methodology is GHG Protocol. The emission factors you use (Singapore's grid emission factor, DEFRA emission factors for fuels) slot into the GHG Protocol framework. Getting the GHG Protocol calculation right is the foundation on which everything else rests.

ISO 14064: The Auditable International Standard

ISO 14064 takes the GHG Protocol methodology and formalises it into a three-part international standard:

ISO 14064-1 (Organisation level): the standard that governs GHG inventories at the company or facility level. This is what most businesses need. It specifies requirements for design, development, management, reporting, and verification of GHG inventories. ISO 14064-1 is what an assurance provider or third-party auditor uses when they are verifying your Scope 1 and Scope 2 emissions figures.

ISO 14064-2 (Project level): applies to GHG emission reductions or removal enhancement projects — essentially, carbon credits or offset projects. Relevant if you are developing or investing in carbon offset projects, less so for standard corporate emissions reporting.

ISO 14064-3 (Validation and verification): sets out the requirements and guidance for GHG verifiers conducting validation or verification of GHG assertions. This is the standard your assurance provider operates under when they review your emissions figures.

For Singapore's purposes, ISO 14064-1 is the relevant standard for organisational GHG inventories, and it is explicitly accepted by SGX as a valid methodology for sustainability reporting. When an SGX-listed company needs external assurance on its Scope 1 and Scope 2 emissions (mandatory from FY2029), the assurance engagement will typically reference ISO 14064-3 as the verification standard.

The practical difference between using GHG Protocol alone and using ISO 14064-1 is one of documentation rigour and auditability. ISO 14064-1 requires more explicit documentation of boundary decisions, data quality assessments, and uncertainty management. This additional rigour is exactly what assurance providers need to do their work efficiently — and it is what VerityOS's evidence vault is designed to support.

IFRS S2: The Investor Disclosure Standard

IFRS S2 is where investor-facing sustainability reporting converges with the GHG Protocol methodology. Published by the ISSB in 2023 alongside IFRS S1 (general sustainability disclosures), IFRS S2 is specifically designed to give investors standardised, comparable information about an organisation's exposure to climate-related risks and opportunities.

The four disclosure pillars of IFRS S2 are:

Governance: how the organisation's board and management oversee climate-related risks and opportunities. Who has responsibility? How is it structured? What processes are in place for escalation and oversight?

Strategy: the actual and potential effects of climate-related risks and opportunities on the organisation's business model, strategy, and financial planning — including scenario analysis for physical risks (flooding, heat stress) and transition risks (carbon pricing, policy changes, technology shifts).

Risk management: the processes the organisation uses to identify, assess, prioritise, and monitor climate-related risks and how these processes are integrated into the overall enterprise risk management framework.

Metrics and targets: including the emissions data (Scope 1, Scope 2, Scope 3) calculated using GHG Protocol methodology, emissions intensity metrics, progress against climate targets, and climate-related financial metrics where applicable.

The critical point for Singapore is that SGX has aligned its sustainability reporting requirements with IFRS S2. SGX-listed companies reporting from FY2025 onwards are producing IFRS S2-aligned disclosures. This means the GHG Protocol Scope 1 and Scope 2 emissions data is feeding directly into the Metrics and Targets pillar of an IFRS S2 disclosure.

IFRS S2 also has a specific requirement that is easy to miss: for Scope 2 emissions, it requires disclosure of both location-based (using the grid average emission factor) and market-based (using supplier-specific or instrument-specific factors, such as RECs or PPAs) figures where available. For Singapore businesses relying on the Energy Market Authority's published grid emission factor, the location-based figure is the primary disclosure — but companies with renewable energy certificates or power purchase agreements need to also calculate the market-based figure.

GRI 305 and the Singapore Picture

The Global Reporting Initiative (GRI) Standards sit alongside the IFRS S2 framework as an alternative or complementary disclosure approach. GRI is designed for a broader multi-stakeholder audience — not just investors, but employees, communities, regulators, NGOs, and civil society.

GRI 305 (Emissions) is the specific GRI standard that governs greenhouse gas disclosures. It requires disclosures of:

305-1: Direct (Scope 1) GHG emissions. 305-2: Energy indirect (Scope 2) GHG emissions, both location-based and market-based. 305-3: Other indirect (Scope 3) GHG emissions. 305-4: GHG emissions intensity. 305-5: Reduction of GHG emissions.

GRI 305 uses GHG Protocol as its accounting methodology — exactly like IFRS S2. The emissions figures you calculate under GHG Protocol feed equally into a GRI 305 disclosure or an IFRS S2 disclosure. The difference is the surrounding framework and the audience.

SGX's Sustainability Reporting guidelines allow companies to use GRI as an alternative or complement to IFRS S2 in certain circumstances. Many Singapore companies with international operations or global clients produce reports that cross-reference both — the investor community follows IFRS S2, while international procurement teams and sustainability-focused stakeholders often follow GRI. Producing data that is simultaneously GRI 305-compliant and IFRS S2-aligned is straightforward when the underlying GHG Protocol calculations are done correctly, because the source data is the same.

How They Relate to Each Other: The Singapore Stack

The clearest way to understand how these frameworks relate is as a three-layer stack:

For a Singapore SME whose primary purpose is producing a credible sustainability report in response to client or commercial pressure: focus on getting the GHG Protocol calculations right (Layer 1), document them to ISO 14064-1 standard so you are assurance-ready (Layer 2), and structure the output in an IFRS S2-aligned format so listed-company clients recognise it (Layer 3).

For a Singapore SME whose primary purpose is responding to a supplier questionnaire from an MNC client: your Scope 1 and Scope 2 figures, calculated using GHG Protocol methodology and documented with evidence, are what they need. The exact framework label matters less than the quality and completeness of the underlying calculation.

What a Singapore Business Should Actually Do

The practical answer depends on your situation:

If you are an SGX-listed company, your reporting obligation is clear: IFRS S2-aligned disclosure from FY2025, with external assurance required from FY2029. Use GHG Protocol as your calculation methodology, structure disclosures across the four IFRS S2 pillars, and ensure your Scope 1+2 data is documented to ISO 14064-1 standard so your assurance provider can work efficiently. GRI 305 cross-referencing is valuable if you report to international stakeholders.

If you are an unlisted SME facing client pressure or pursuing the EnterpriseSG sustainability reporting grant, you should use GHG Protocol as your calculation methodology and ISO 14064-1 as your documentation standard. If your clients are listed companies, structuring your outputs to be IFRS S2-legible (i.e., providing Scope 1, Scope 2, and ideally Scope 3 data in a clear structured format) will make you more useful to their sustainability teams.

If you are planning for the future, the trajectory is clear. ISSB standards (IFRS S1 and S2) are being adopted across Asia-Pacific regulatory frameworks. Singapore is aligned. The direction of travel is IFRS S2 as the baseline disclosure standard, with GHG Protocol as the mandated calculation methodology underneath it. Building your emissions infrastructure on GHG Protocol today means you are building on the foundation that everything else requires.

Platforms like VerityOS handle the methodology compliance layer automatically — emission factors are version-controlled in the database, every entry is linked to a source document, and the calculation approach is GHG Protocol-based. This means the reports you produce are simultaneously GHG Protocol-compliant, ISO 14064-1-ready for assurance, and formatted for IFRS S2 alignment, without requiring your team to be experts in the technical specifications of each framework.