A plain-English guide to how companies measure, verify and report their greenhouse gas emissions under the GHG Protocol, CSRD and related standards.
Carbon accounting, defined
Carbon accounting is the systematic process of measuring, tracking and reporting the greenhouse gas emissions caused by a company's operations, value chain and products. Think of it as financial accounting, but the "currency" being counted is climate impact instead of money.
Companies emit many different greenhouse gases - carbon dioxide (CO2), methane, nitrous oxide and a family of fluorinated gases - and each warms the planet by a different amount. To make them comparable, every gas is converted into CO2 equivalents (CO2e): one number that expresses the total climate impact, whether it's reported in kilograms or tonnes. That single unit is what makes emissions addable, benchmarkable and reportable across companies and industries.
Where financial accounting produces a P&L and a balance sheet, carbon accounting produces a carbon inventory: a line-by-line record of what was emitted, where, and under which methodology. Modern carbon accounting is auditable, comparable across years, and increasingly subject to third-party assurance.
Why carbon accounting matters in 2026
Three forces have moved carbon accounting from a voluntary exercise into a core finance and reporting workflow.
01
Customers
The largest EU companies are legally required to report their value-chain emissions, so they request emission information from their suppliers. To keep those requests manageable for smaller businesses, the EU created a simplified standard - the Voluntary SME Standard (VSME) - which is essentially a lighter version of the full corporate reporting rules. Disclosing your emissions quickly and credibly is now a sales enabler in most B2B markets.
02
Capital
Lenders, investors and rating agencies price climate risk. Reliable emissions data is a prerequisite for green finance, transition loans, sustainability-linked credit terms and inclusion in ESG indices - regardless of whether a company falls under any reporting mandate.
03
Regulation
The EU's Corporate Sustainability Reporting Directive (CSRD) requires large companies (more than 1,000 employees and over €450M turnover) to disclose their emissions with mandatory third-party assurance. Other internationally recognised sustainability regulations are live or phasing in - such as ISSB-based rules in Australia, Japan, Singapore and Brazil, and California's SB 253 for large companies doing business in the state.
The practical consequence: for most mid-market companies, the pressure to produce audit-grade emissions data comes from customers and banks first, and regulators second. Either way the data quality requirement is high - your numbers feed directly into someone else's regulated report, so they must stand up to the same scrutiny.
The GHG Protocol and Scopes 1-3
The Greenhouse Gas Protocol is the de facto global standard for corporate carbon accounting. It is aligned with ISO 14064-1 and forms the basis for most reporting frameworks and initiatives that reference corporate emissions - including the CDP questionnaire, the Science Based Targets initiative (SBTi) and CSRD/ESRS E1. It splits emissions into three categories, or scopes.
Scope 1
Direct emissions
Direct emissions from sources a company owns or controls, including fuel combustion in company facilities, company-owned or leased vehicles, industrial process emissions and fugitive refrigerant leaks.
Scope 2
Indirect emissions from purchased energy
Indirect emissions from purchased electricity, steam, heat and cooling. Reported two ways in parallel: the location-based method uses the average emission intensity of the local grid, while the market-based method reflects the specific electricity contracts and instruments (such as renewable energy certificates or power purchase agreements) a company has chosen.
Scope 3
Other indirect emissions across the value chain
All other indirect emissions in the value chain, split into upstream categories (purchased goods and services, capital goods, transportation, business travel and employee commuting) and downstream categories (use of sold products, end-of-life treatment, investments and leased assets). Scope 3 typically makes up more than 70% of a company's footprint.
Three methodologies are used across a carbon inventory, often in combination - from quick screening to audit-ready numbers.
1Screening
Spend-based
The spend-based method multiplies what a company spends with a supplier (in EUR or USD) by an economic emission factor for that sector. It is fast to implement and useful for a first-year screening across the full value chain, but it is insensitive to individual supplier performance - buying from a low-carbon supplier looks identical to buying from a high-carbon one.
2Audit-ready
Activity-based
The activity-based method multiplies physical activity data - such as kilowatt-hours of electricity, litres of diesel, tonne-kilometres of freight or kilograms of steel - by an emission factor tied to that activity. This is the expected standard for material categories in audit-ready reporting, and the direction assurance providers push toward.
3Best-in-class
Supplier-specific
The supplier-specific method uses each supplier's own product-level carbon footprint (PCF), ideally with third-party verification. It is required for credible reduction claims and for downstream customers running their own Scope 3 reduction programmes.
CSRD, ESRS E1 and the wider regulatory picture
The CSRD is the EU's flagship sustainability reporting law - and it changed significantly in early 2026. The Omnibus I Directive, in force since March 2026, narrowed its scope and simplified its requirements.
Who reports
EU companies with more than 1,000 employees and more than €450 million in net turnover. Listed SMEs are no longer in scope. Non-EU groups are covered above €450M of EU turnover.
When
The first wave (former NFRD companies) is already reporting. Companies originally due to start in 2026 now publish their first reports in 2028, covering financial year 2027.
What
Simplified ESRS with roughly 60% fewer mandatory datapoints. Climate (ESRS E1) remains the anchor: gross Scope 1, 2 and material Scope 3 for the reporting and base year, methodology and boundary, reduction targets (including 1.5°C alignment) and a transition plan. Carbon credits are disclosed separately.
Assurance
Sustainability statements are subject to mandatory limited assurance, with an EU limited assurance standard due by July 2027.
Value-chain cap
In-scope companies gathering Scope 3 data may not demand more from suppliers with 1,000 or fewer employees than what is covered by the voluntary SME standard (VSME).
Beyond the EU, ISSB-based climate disclosure is mandatory or phasing in across Australia, Japan, Singapore, Brazil, Hong Kong and other markets, and the UK's ISSB-based standards are due to follow (SECR already requires energy and carbon reporting from large UK companies). California's SB 253 requires large companies doing business in the state to report Scope 1 and 2 emissions from 2026 and Scope 3 from 2027. All share the same foundations: GHG Protocol methodology, a documented audit trail, and Scope 3 disclosure where material.
How to run carbon accounting in practice
Six steps take a company from a blank spreadsheet to an assured CSRD/ESRS E1 disclosure.
01
Set the boundary
Decide between operational control, financial control or equity share, and document which entities and facilities are included.
02
Collect activity data
Gather activity data from across the business: energy meters, fuel receipts, purchase ledgers in the ERP, expense records, travel bookings and logistics data. Automating the flow of ERP data into the carbon inventory is the single biggest time saver.
03
Apply emission factors
Match every transaction to the most specific emission factor available (UK Government/DEFRA, EPA, EEIO databases or supplier-specific PCFs) and record the factor version used, so an auditor can retrace the calculation.
04
Review and challenge
A sustainability analyst (in-house or advisory) reviews outliers and reclassifies items that were assigned to the wrong category before the numbers are locked.
05
Report and assure
Produce the disclosure required by your framework (CSRD/ESRS E1, ISSB, CDP or a customer questionnaire), feed the SBTi progress report and hand the inventory to the external auditor with a full audit trail.
06
Reduce and, if needed, compensate
Prioritise reductions on Scope 1, 2 and the top Scope 3 hotspots. High-integrity carbon credits address residual emissions, disclosed separately from gross numbers.
Common pitfalls
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Spend-based Scope 3 for years on end
Fine for year one, dangerous by year three - reductions become invisible because the number tracks spend, not physical emissions.
!
Double counting between Scope 1 and Scope 3
Fuel burned in vehicles the company owns or leases belongs in Scope 1. Category 6 (business travel) covers vehicles the company does not control - employee-owned cars used for work, rental cars and flights - so the same trip should never appear in both scopes.
!
Ignoring the market-based Scope 2 view
CSRD requires both location- and market-based numbers, not one or the other.
!
Netting off carbon credits
Gross emissions must be reported in full before any carbon credits are considered. Credits are disclosed as a separate line item and are never subtracted from the reported footprint.
!
No audit trail
Auditors need to trace every tonne back to a source document and an emission factor version. Screenshot-and-spreadsheet workflows fail assurance.
Frequently asked questions
What is carbon accounting in simple terms?+
Carbon accounting is the process of measuring, tracking and reporting the greenhouse gas (GHG) emissions caused by a company's operations, value chain and products, expressed in tonnes of CO2 equivalent (tCO2e).
What is the difference between Scope 1, 2 and 3 emissions?+
Scope 1 covers direct emissions from sources a company owns or controls (e.g. company vehicles, on-site combustion). Scope 2 covers indirect emissions from purchased electricity, steam, heat and cooling. Scope 3 covers all other indirect emissions in the value chain, from purchased goods and services to business travel, use of sold products and investments.
Which standard should companies use for carbon accounting?+
The Greenhouse Gas Protocol (GHG Protocol) is the de facto global standard. It is aligned with ISO 14064-1 and forms the basis for most other corporate carbon reporting frameworks, which are generally structured around how GHG Protocol reporting works - including the CDP questionnaire, the Science Based Targets initiative (SBTi) and the European Sustainability Reporting Standards (ESRS E1) under CSRD.
Is carbon accounting mandatory?+
For the largest companies, yes. The EU's CSRD requires companies with more than 1,000 employees and over €450 million in turnover to disclose Scope 1, 2 and material Scope 3 emissions under ESRS E1, with limited assurance. ISSB-based rules apply in Australia, Japan, Singapore, Brazil and other markets, and California's SB 253 covers large companies doing business in the state. Most mid-market companies fall outside these direct mandates - but sit inside the value chains of companies that don't, which is where the data requests come from.
Does the EU Omnibus mean smaller companies no longer need carbon accounting?+
No. The 2026 Omnibus reform reduced the number of companies required to file a CSRD report, but it did not remove Scope 3 reporting for those that remain in scope. Those companies still need value-chain emissions data, which means suppliers will continue receiving data requests. Omnibus standardised these requests around the voluntary SME standard (VSME) rather than eliminating them. For most mid-market companies, carbon accounting is now driven by customer contracts, bank financing and tenders rather than a direct filing obligation.
What is the difference between carbon accounting and carbon offsetting?+
Carbon accounting measures a company's greenhouse gas emissions and creates the baseline for setting targets and reducing impact. Carbon offsetting, or the use of carbon credits, is used separately from emissions reductions: the credits do not reduce a company's reported emissions, but allow companies to take responsibility for residual emissions by financing verified climate projects.
How accurate does carbon accounting need to be?+
Accuracy should match the decision the number is used for. Spend-based estimates are often enough to screen emissions and identify hotspots, while activity data, such as kWh, litres or tonne-kilometres, and supplier-specific emission factors are needed for audit-ready reporting and credible target-setting.
