Why the next evolution of GHG accounting matters for mandatory climate reporters 

For many entities reporting under Australia’s mandatory climate disclosure regime, the initial focus has been on governance, scenario analysis and establishing Scope 1 and 2 emissions baselines, with most entities relying on transitional relief to defer Scope 3 reporting in year one. However, with Scope 3 disclosures becoming mandatory from the second reporting year for Group 1 entities under AASB S2, attention is now shifting toward data quality, category screening, boundary setting and methodological rigour, as well as the implications for transition planning and decarbonisation strategy. Proposed refinements to AASB S2 reinforce this direction by signalling stronger expectations around materiality assessment, governance and the prioritisation of material Scope 3 categories. 
AASB S2 requires entities to disclose absolute gross Scope 3 emissions explain the methodologies and assumptions used, and assess all 15 Scope 3 categories across the value chain to determine material emissions sources, with the Greenhouse Gas Protocol (GHG Protocol) remaining the primary measurement framework. At the same time, the GHG Protocol is undergoing its most significant review since 2011, with proposed revisions pushing the market away from high-level proxy estimates toward more granular, traceable and decision-useful value chain data. Together, these developments signal increasing regulator, investor and assurance expectations around transparency, comparability and auditability of Scope 3 disclosures. 

The big shift: Scope 3 is becoming a financial reporting issue 

Historically, Scope 3 reporting has tolerated a high degree of estimation uncertainty because primary supplier data was limited, methodologies were still evolving and value chain transparency was relatively immature. As a result, many organisations relied heavily on spend-based emission factors, industry averages and broad proxy assumptions to calculate emissions across their value chain. That landscape is now shifting rapidly. The proposed revisions to the GHG Protocol suggest the era of “acceptable approximation” is narrowing, with a clear market shift toward more decision-useful, auditable and financially relevant emissions data. 
The proposed revisions place greater emphasis on improving the comparability and transparency of estimation methods and data hierarchies, alongside stronger requirements for data quality, traceability and methodological consistency. They also introduce clearer inventory boundary-setting rules, including specified quantitative limits for inventory exclusions, revise the treatment of investments and financed emissions, and propose a new Category 16 to capture additional value chain activities and climate-related impacts not adequately addressed under the existing 15-category framework. 
The practical implication is significant, signalling that increasingly, Scope 3 reporting is being treated less like sustainability storytelling and more like core financial reporting infrastructure, requiring governance, controls and evidentiary support comparable to financial data. 

Why this matters now for AASB S2 reporters 

“Comply first, improve later” will not hold for long 

Many reporting entities are currently focused on producing their first compliant disclosures. That is understandable. But regulators, auditors and investors are already signalling that maturity expectations will increase quickly over the next reporting cycles. The proposed GHG Protocol changes reinforce that direction by placing greater emphasis on methodological consistency, transparent assumptions and better underlying activity data. 

This creates three immediate pressures for reporters.

1. Finance teams becoming more deeply involved in emissions reporting

As climate disclosures move into mainstream reporting, finance functions are increasingly being asked to validate controls, estimation logic and audit readiness. Scope 3 inventories can no longer sit solely within ESG teams using disconnected spreadsheets and external assumptions. Organisations will need controlled data environments, documented methodologies, governance over assumptions and emission factors and stronger linkage between operational activity and financial data.

2. Supplier engagement is becoming a strategic capability

Most organisations are still relying on spend-based estimates to cover a material share of their Scope 3 footprint, with access to timely and reliable supplier-specific data proving challenging. The direction of travel from both AASB S2 and the evolving GHG Protocol suggests that entities relying exclusively on secondary data may face increasing stakeholder challenge to their disclosed Scope 3 inventories. Leading organisations are slowly shifting to annual supplier surveys to target material spend buckets and are contemplating more targeted measures, including supplier emissions clauses in procurement as well as digital collection platforms and data exchange mechanisms.

3. Transparency and defensibility will matter more than “perfect” numbers

Reporters will increasingly be expected to demonstrate not just what their emissions are, but how they were calculated, where uncertainty exists and whether the underlying approach is reasonable. As scrutiny increases, organisations relying heavily on opaque proxy data, inconsistent methodologies or poorly documented assumptions may face growing challenges from auditors, regulators and investors, particularly where Scope 3 emissions are material to transition risk (e.g., carbon cost pass through), capital allocation or stated decarbonisation commitments. 

Balancing effort against outcomes is critical to ensure “no regret” near-term actions 

For organisations preparing for AASB S2, the central question is how to build a Scope 3 reporting approach, which stands up under future regulatory and assurance maturity. Whilst the 2026 ‘Whole-of-Government Regulatory Reform Agenda provides some refinement to scope reporting, including clearer boundaries around supplier information requests and reducing burden across the value chain, there is no fundamental shift or retreat in the need for reporters to comprehensively consider their Scope 3 emissions. 

What reporters should do next 

Treat Scope 3 as a transformation programme, not a disclosure workstream 

The organisations likely to mature fastest are those embedding Scope 3 into procurement, finance, risk and operational processes rather than managing it as a standalone ESG exercise. 

Prioritise “high-materiality, high-influence” categories 

Rather than trying to perfect all 15 categories simultaneously, focus on the categories that are both financially material and operationally influenceable. For many organisations, that means the prioritisation of categories such as ‘purchased goods and services’, ‘capital goods’, ‘use of sold products’ and ‘investments and financed emissions’. 

Build an assurance-ready methodology now 

Even where assurance requirements remain phased, reporters should prepare for future scrutiny by clearly documenting methodologies and boundaries, emission factor selection and application logic, data hierarchy approaches, estimation methodologies and assumptions and governance frameworks and controls. This approach will help identify gaps and enable early action, reducing future remediation effort as expectations tighten. 

Design for evolving standards 

One of the clearest messages from the current market direction is that emissions accounting standards are still evolving. Organisations should therefore avoid building rigid reporting architectures tied to a single methodology assumption. As the GHG Protocol evolves, AASB S2 reforms and regulatory interpretations mature, organisations with flexible data models, strong traceability and governance frameworks will be best positioned. 

The bottom line 

The next phase of climate reporting will not be defined by whether organisations disclose Scope 3 emissions; that expectation is already established. The differentiator will be whether organisations can demonstrate that their emissions data is robust enough to support transition planning, capital allocation, supplier engagement and financial decision-making.