Greenhouse gas accounting in 2025 and beyond: assurance is here, standards are converging, and Scope 3 remains the stress point

Greenhouse gas inventories have moved from voluntary metrics to assured, decision-relevant information on climate impacts. 2025 was the first year when listed companies subject to the EU sustainability reporting directive (CSRD) had to publish ESRS‑compliant sustainability statements with limited assurance alongside their financials. This moves GHG inventories from voluntary narratives into the realm of attestable information, changing how finance, sustainability, and audit teams build evidence files and internal controls. 

Based on the first-year outcome, audit reports across sectors converged on the same message: Scope 3 disclosures carry more inherent limitations than Scopes 1–2 because value‑chain data are less available, less precise, and often sit outside the company’s direct control. The risk of not detecting a material misstatement is ordinarily higher for “value chain information” and companies should expect auditors to keep probing Scope 3 estimates in the next filing cycle. Auditors also stress that forward‑looking statements - transition plans, targets, scenarios - are inherently uncertain; there is a substantial, unavoidable risk that outcomes will diverge from assumptions. None of this, however, diminishes the disclosures’ utility. It simply clarifies where the weak points are and where assurance effort will intensify.

Two structural shifts are now shaping what comes next. First, ISO and the GHG Protocol announced a strategic partnership in September 2025 to align and co‑develop a unified global suite of GHG standards. For practitioners juggling the ISO 1406X family and the GHG Protocol’s Corporate, Scope 2 and Scope 3 frameworks, a single language promises less mapping work and more consistent verification - though timelines for joint outputs have not yet been published. Second, the GHG Protocol’s Scope 2 revision entered public consultation in October 2025. The proposal keeps dual reporting (location‑ and market‑based) but tightens claims by requiring hourly matching of energy certificates and limiting market-based accounting to electricity that is actually available and deliverable to the company’s location. In practice, that would narrow the use of some market instruments: virtual power purchase agreements (VPPAs) would need to be deliverable to the buyer’s grid region, and many contracts that work under annual matching may not qualify without more granular time and grid alignment. PPAs, certificates and residual mixes would all require finer‑grained data and clearer contract attributes. These proposals are still subject to negotiations and are expected to be finalized by the end of 2027, but the direction is already clear: more precise alignment in time and place, and a higher bar for supporting evidence.

To meet these challenges, companies should treat GHG data like financial data: assign clear ownership, use controlled and versioned methodologies, ensure full traceability from raw activity data through emission factors to final totals, and maintain an auditable record of all changes. On Scope 3, prioritize the categories that drive the emissions, push for supplier‑specific inputs, and label estimates transparently so your evidence file stands up to limited assurance. On Scope 2, map energy instruments and contracts against the proposed hourly‑matching and deliverability criteria and assess whether your certificates can support that granularity.