CSRD vs GHG Protocol: What Changes When You Move from Voluntary to Mandatory Reporting

A significant number of European mid-caps have been producing voluntary GHG inventories for three to seven years — either in response to customer requests, CDP questionnaires, or internal target-setting processes. When CSRD enters into force for their company size category, the understandable assumption is that existing GHG Protocol reporting gives them a head start. That assumption is partially correct and significantly incomplete.

This article maps the key differences between a GHG Protocol-aligned voluntary inventory and a CSRD-compliant sustainability statement — not to discourage existing reporters, but to identify precisely which gaps need to be closed and in what order.

What the GHG Protocol Does Well

The GHG Protocol Corporate Standard (2004) and the Scope 3 Standard (2011) established the foundational methodology for corporate carbon accounting that is now used globally. ESRS E1 does not replace these standards — it explicitly references GHG Protocol methodology as the basis for Scope 1, 2, and 3 calculations. A company with a well-maintained GHG Protocol inventory already has:

• A defined organisational boundary (operational or equity share control approach)
• A methodology for Scope 1 (direct combustion, process emissions, fugitive emissions)
• Location-based and market-based Scope 2 calculations using appropriate emission factors
• At least some Scope 3 category calculations, commonly starting with Categories 1, 4, 6, and 11
• A historical data series that can serve as the base year for ESRS E1-4 GHG reduction targets

All of this is directly usable in the CSRD sustainability statement. The GHG methodology work does not need to be redone — it needs to be documented at a higher evidentiary standard, extended to cover additional ESRS E1 data points, and embedded in a broader disclosure architecture that GHG Protocol reporting alone does not address.

Gap 1: Double Materiality Assessment

The GHG Protocol has no materiality framework in the CSRD sense. Voluntary GHG reporters measure what they choose to measure, typically guided by what data is available and what stakeholders have asked for. CSRD requires that a formal double materiality assessment determine which sustainability topics are material — including whether climate is material from both an impact and a financial perspective — before the disclosure scope is defined.

For a company whose entire voluntary reporting programme has been built around GHG Protocol methodology, completing the double materiality assessment is typically the most unfamiliar piece of work in the CSRD transition. It requires a structured stakeholder process, a scoring framework, and documentation of methodology — all processes that sustainability teams focused on emissions accounting have rarely needed to build before.

Gap 2: Governance and Strategy Disclosures

The GHG Protocol is an accounting standard, not a disclosure framework. It specifies how to calculate emissions, not what to say about board oversight, transition strategy, or scenario analysis. CSRD through ESRS E1 requires disclosures on all of the following that the GHG Protocol simply does not address:

• E1-1: The transition plan — how the company intends to reach its climate targets, what capital will be redirected, and over what timeline
• E1-2: Climate-specific policies covering both adaptation and mitigation
• E1-3: Climate actions taken in the reporting period with associated expenditure
• E1-8: Financial effects of physical and transition risks — a quantified or semi-quantified scenario analysis output
• E1-9: Internal carbon pricing mechanisms, if in use

Bréchet Logistique SAS, a growing French freight company with around 420 employees, had been producing an annual GHG inventory since 2020 — covering Scope 1 (fleet fuel consumption), Scope 2 (depot electricity), and a partial Scope 3 (Category 4 upstream transport for third-party logistics). Their CSRD gap assessment in early 2025 found that the emissions data was largely ready for ESRS E1-6, but all five of the above governance and strategy disclosures were entirely absent. The emissions accounting was approximately 35% of the total CSRD preparation effort; the governance, strategy, and risk disclosures were the other 65%.

Gap 3: Assurance and Data Lineage

Voluntary GHG reporting does not require third-party assurance. CSRD does — limited assurance from the first filing year, with potential upgrade to reasonable assurance in later years. This changes the evidentiary standards for the emissions data itself.

Under voluntary reporting, it was acceptable to calculate Scope 2 using a grid emission factor from memory, without retaining the source reference. Under limited assurance, the auditor will ask: which database was used for the location-based Scope 2 factor, what version was it, and does the figure in the inventory match the factor in that database version applied to the consumption data on the underlying invoice? The calculation chain must be traceable and reproducible.

Similarly, for Scope 3, where a spend-based method was used, the auditor will ask: which emission factor database was applied, were the factors applied to EUR spend or local currency spend, and how were the spend figures extracted from the procurement system? None of these are difficult questions — but they require documentation that many voluntary reporters simply did not build into their processes when there was no audit obligation.

Gap 4: iXBRL Tagging and Digital Format Requirements

The GHG Protocol produces a number — or a table of numbers — that can be included in any document format. CSRD requires that the sustainability statement be embedded in the management report in XHTML format with iXBRL tags applied according to the ESRS XBRL taxonomy. This is a machine-readable format requirement that has no equivalent in voluntary GHG reporting.

The iXBRL tagging requirement means that specific data points in the ESRS E1 disclosure — including the GHG inventory figures — must be tagged with the correct ESRS taxonomy element codes so that they can be extracted and compared automatically by ESMA's ESEF reporting system and by investment analysis tools. Companies that produce their first CSRD sustainability statement as a nicely formatted PDF will need to convert it to XHTML and apply iXBRL tags before submission — a technical step that requires either specialist software or an external service provider.

What Stays the Same — and Why That Matters

We're not saying that GHG Protocol reporters are behind the curve on CSRD — existing GHG reporters have a substantial advantage over companies starting from zero. The emissions methodology, the historical data series, the familiarity with Scope 1/2/3 boundary questions, and the internal processes for collecting energy and procurement data are all directly transferable to the CSRD regime. The core accounting work is already done.

The gaps are additive, not replacements. CSRD builds on GHG Protocol methodology for the quantitative emissions figures, then adds a governance and strategy disclosure layer (ESRS E1-1 through E1-3), a risk quantification layer (E1-8), a Taxonomy alignment layer (Article 8 KPIs), a formal materiality process (ESRS double materiality), an assurance layer (limited assurance engagement), and a digital format requirement (iXBRL). For a team that has already invested years in building a credible GHG inventory, the most efficient path forward is treating the CSRD transition as an extension project, not a rebuild — closing the specific gaps identified above while retaining the existing emissions accounting methodology that already aligns with ESRS E1-6 requirements.