Carbon accounting
Carbon Accounting: UK Guide to GHG Emissions Measurement
Carbon accounting — also called GHG accounting — is the measurement, monitoring and reporting of greenhouse gas emissions using standardised methods.
The global standard is the GHG Protocol; the UK regulatory anchors are SECR, UK SRS S2 (proposed mandatory 2027) and IFRS S2.
What carbon accounting is
Carbon accounting is the measurement, monitoring and reporting of greenhouse gas (GHG) emissions using standardised methods.
The global standard is the GHG Protocol Corporate Standard, developed by the World Resources Institute and World Business Council for Sustainable Development. 97% of disclosing S&P 500 companies used the GHG Protocol to report emissions in 2023.
Corporate carbon accounting categorises emissions into three scopes — Scope 1 (direct), Scope 2 (purchased energy) and Scope 3 (other indirect, across 15 value-chain categories) — and produces a corporate GHG emissions inventory that is increasingly central to regulatory disclosure, investor reporting and procurement requirements.
This page is the technical reference for carbon accounting under UK regulatory conditions: definitions, scopes, methodology, the UK regulatory anchors (SECR, UK SRS S2, IFRS S2, ESOS), software, assurance, and how to start.
For the regulatory deep-dives, see UK SRS S2, IFRS S2, SECR, and the GHG Protocol standard pages. For software choice, see the carbon reporting software comparison.
"97% of disclosing S&P 500 companies used GHG Protocol standards to report their emissions to CDP in 2023. Carbon accounting is no longer a niche sustainability function — it is becoming a core financial-grade reporting discipline."Green Central Banking, May 2026
Scope 1, Scope 2, Scope 3 — the GHG Protocol classification
The GHG Protocol Corporate Standard defines three scopes of corporate emissions.
Scope 1 covers direct emissions from owned or controlled sources.
Scope 2 covers indirect emissions from purchased electricity, steam, heating and cooling.
Scope 3 covers all other indirect emissions in the value chain, across 15 categories.
The scopes are mutually exclusive within a company — but one company's Scope 3 contains other companies' Scope 1, 2 and 3.
This is why supplier engagement and primary-data collection are central to high-quality Scope 3 reporting.
| Scope | What it covers | Common UK examples | Reporting status |
|---|---|---|---|
| Scope 1 | Direct emissions from owned or controlled sources | Gas heating, fleet vehicles, on-site refrigerants, process emissions, biogenic CO₂ | Mandatory under SECR, UK SRS S2 (when mandatory), IFRS S2 |
| Scope 2 | Indirect emissions from purchased energy | Grid electricity, district heating/cooling, purchased steam | Mandatory under SECR, UK SRS S2, IFRS S2 (location-based gross required) |
| Scope 3 | All other indirect emissions in the value chain (15 categories) | Purchased goods, business travel, use of sold products, financed emissions | Voluntary under SECR; UK SRS S2 comply-or-explain from 1 Jan 2028; IFRS S2 required where material |
The GHG Protocol Corporate Value Chain (Scope 3) Standard defines 15 categories grouped into upstream (1–8) and downstream (9–15) 1.
Upstream: 1. Purchased goods and services. 2. Capital goods. 3. Fuel- and energy-related activities. 4. Upstream transportation and distribution. 5. Waste generated in operations. 6. Business travel. 7. Employee commuting. 8. Upstream leased assets.
Downstream: 9. Downstream transportation and distribution. 10. Processing of sold products. 11. Use of sold products. 12. End-of-life treatment of sold products. 13. Downstream leased assets. 14. Franchises. 15. Investments (financed emissions).
Category 15 — financed emissions — is particularly relevant to asset managers, commercial banks and insurance, and is the subject of December 2025 ISSB targeted amendments. See UK SRS Scope 3 reporting for the operational detail.
How a corporate carbon inventory is built
Building a corporate carbon inventory follows the same five GHG Protocol principles: Relevance, Completeness, Consistency, Transparency, and Accuracy.
The practical sequence: set the organisational boundary (equity-share, financial-control, or operational-control), set the operational boundary (which scopes), collect activity data, apply emission factors, calculate, quality-check, and disclose.
Most UK first-time inventories take 8–16 weeks for a single entity; multi-entity groups with material Scope 3 take 4–9 months end-to-end.
Carbon accounting in the UK regulatory framework
UK companies typically need carbon accounting outputs for at least one of four regulatory anchors.
SECR has been mandatory since 2019 for ~11,900 large quoted, large unquoted and large LLP entities.
UK SRS S2 is proposed mandatory for ~500 UK-listed companies under FCA CP26/5 from 1 January 2027.
IFRS S2 is the underlying global standard.
ESOS audits are mandatory every four years for large UK undertakings.
The same underlying carbon inventory generally feeds all four — what differs is the disclosure wrapper, the connectivity to financials and the assurance expectations.
| Regulation | Who it covers | Carbon-accounting requirement | Status |
|---|---|---|---|
| SECR | ~11,900 large quoted, large unquoted, large LLPs | Scope 1 + Scope 2 + energy use + intensity ratio | Mandatory since 2019 |
| UK SRS S2 | ~500 UK-listed issuers (UKLR 6/16/22) | Scope 1 + 2 + 3 (15 categories); industry metrics; financed emissions for financials | Voluntary now; proposed mandatory 1 Jan 2027 under FCA CP26/5; Scope 3 comply-or-explain from 1 Jan 2028 |
| IFRS S2 (global) | Jurisdictional adoption; UK adopts as UK SRS S2 | Same as UK SRS S2 | Effective 1 Jan 2024; jurisdictional |
| ESOS | Large UK undertakings (250+ employees or turnover/balance sheet thresholds) | Energy-use audit every four years; not GHG inventory per se | Phase 4 audit period 6 Dec 2023–5 Dec 2027 |
UK preparers generally use the UK Government GHG Conversion Factors for company reporting, published annually by DESNZ. The dataset covers electricity, fuels, refrigerants, water, waste and transport.
For Scope 3 categories outside the DESNZ dataset, the GHG Protocol Scope 3 Calculation Guidance is the operational manual, supplemented by third-party databases (Ecoinvent, DEFRA, IEA, Carbon Trust). The choice of factor source must be disclosed transparently per the GHG Protocol's transparency principle.
Carbon accounting software
Most UK preparers above SECR thresholds use carbon accounting software to manage data collection, calculation and disclosure.
Software choice depends on size, regulatory perimeter and Scope 3 ambition.
Enterprise multi-framework platforms (Workiva, IBM Envizi, Microsoft Sustainability Cloud) suit groups reporting under CSRD/ISSB/SEC simultaneously.
Verdantix 2026 Green Quadrant Leaders include Cority, Sphera, Sweep, Watershed and Persefoni.
Specialists include SINAI for CFO-led carbon pricing, Emitwise for AI-driven Scope 3, and Persefoni for financed emissions.
We maintain a 15-platform comparison guide that maps software fit to UK regulatory perimeter.
Assurance over carbon accounting
Assurance over carbon accounting is increasingly expected, even where not yet mandated.
Under FCA CP26/5 and UK SRS S2, no mandatory assurance is proposed in the initial phase — in-scope listed companies must disclose whether they have obtained third-party assurance (disclose-or-explain), but they do not have to obtain it.
UK practitioners use ISSA (UK) 5000 as the relevant assurance standard.
The FRC's Interim Sustainability Assurance Register is the live oversight mechanism (mid-2026).
Mandatory assurance is under separate UK Government consultation with no fixed date.
Sustainability assurance practitioners look for audit-ready evidence: a documented organisational and operational boundary, traceable activity data with source evidence, transparent factor selection, calculation traceability from raw data through to disclosed figure, year-on-year consistency, and a quality-management process that catches errors before disclosure.
See sustainability assurance for the full UK assurance framing.
Carbon accounting — Frequently Asked Questions
The most common UK carbon accounting questions, with every answer linking to a primary source or the matching dedicated page.
Topics: what carbon accounting is, the three scopes, UK mandatory status, emission factors, location vs market-based Scope 2, software choice, cost, connectivity to financials, and assurance.
What is carbon accounting?
Carbon accounting (also called GHG accounting) is the measurement, monitoring and reporting of greenhouse gas emissions using standardised methods 1.
The global standard is the GHG Protocol Corporate Standard, developed by the World Resources Institute and World Business Council for Sustainable Development. Corporate carbon accounting categorises emissions into three scopes: Scope 1 (direct), Scope 2 (purchased energy) and Scope 3 (other indirect, across 15 value-chain categories). 97% of disclosing S&P 500 companies used the GHG Protocol to report emissions in 2023 2.
What is the difference between Scope 1, 2 and 3 emissions?
Scope 1 covers direct GHG emissions from sources a company owns or controls — fuels burned on-site, fleet vehicles, fugitive refrigerants. Scope 2 covers indirect emissions from purchased electricity, steam, heating and cooling. Scope 3 covers all other indirect emissions in the value chain.
The GHG Protocol Corporate Value Chain (Scope 3) Standard defines 15 categories under Scope 3, with Category 15 (financed emissions) particularly relevant to financial institutions — see UK SRS Scope 3 reporting 3.
Is carbon accounting mandatory in the UK?
Partially. Streamlined Energy and Carbon Reporting (SECR) has been mandatory since 2019 for ~11,900 large UK companies (quoted, large unquoted and large LLPs above the qualifying thresholds).
UK SRS S2 (climate-related disclosures, adopted from IFRS S2) is proposed mandatory for UK-listed companies from 1 January 2027 under FCA CP26/5 4, with Scope 3 comply-or-explain from 1 January 2028. ESOS audits are mandatory every four years for large UK undertakings.
What emission factors should UK companies use?
UK companies preparing SECR or UK SRS S2 disclosures generally use the UK Government GHG Conversion Factors for company reporting, published annually by DESNZ 5.
The dataset covers grid electricity, fuels, refrigerants, water, waste, transport and several other categories. For Scope 3 categories that fall outside the DESNZ dataset, the GHG Protocol Scope 3 Calculation Guidance is the operational manual, and many companies use third-party databases (Ecoinvent, DEFRA, IEA, Carbon Trust).
What is the difference between location-based and market-based Scope 2 accounting?
Location-based Scope 2 emissions are calculated using grid average emission factors for the local electricity grid. Market-based Scope 2 emissions reflect the specific electricity products an entity has chosen — including renewable energy certificates, power purchase agreements, or supplier-specific factors.
The GHG Protocol Scope 2 Guidance (2015) requires companies to report both figures where market-based instruments are in use. UK SRS S2 and IFRS S2 require Scope 2 disclosure on a location-based gross basis, with contractual-instrument information disclosed where relevant.
What carbon accounting software should I use?
Software choice depends on your size, regulatory perimeter, and Scope 3 ambition. We maintain a 15-platform comparison covering enterprise multi-framework platforms (Workiva, IBM Envizi, Microsoft Sustainability Cloud), Verdantix 2026 Green Quadrant Leaders (Cority, Sphera, Sweep, Watershed, Persefoni), and specialists.
See the full carbon reporting software comparison guide.
What does carbon accounting cost?
The cost varies dramatically with scope and approach. A first-year SECR-scope inventory for a single-entity mid-market company built in-house with templated DESNZ factors might cost £8,000–£25,000 in consultancy time.
A multi-entity Scope 1+2+3 inventory aligned with UK SRS S2 and supported by enterprise carbon accounting software typically costs £75,000–£250,000 in year one, with significant reductions in steady state. Software licences add £15,000–£150,000+ per year depending on platform tier — see the platform comparison. We do not publish vendor pricing — quotes are bespoke.
How does carbon accounting connect to financial statements?
IFRS S2 (and UK SRS S2) require connectivity between climate disclosures and the financial statements — same reporting entity, same reporting period, consistent assumptions 6.
In practice this means carbon accounting can no longer sit only in the sustainability function: finance teams need to be able to trace the emissions calculation back to the same trial balance the financial statements draw on, and to explain any deltas. See the UK SRS compliance guide.
Do I need third-party assurance on my carbon accounting?
Not under SECR alone. Under FCA CP26/5 and UK SRS S2, no mandatory assurance is proposed in the initial phase — in-scope listed companies must disclose whether they have obtained third-party assurance (disclose-or-explain), but they do not have to obtain it.
UK practitioners use ISSA (UK) 5000 as the relevant assurance standard. Mandatory assurance is under a separate UK Government consultation with no fixed date. See sustainability assurance.
Related guides & references
Best Carbon Reporting Software (2026) — 15 Platforms Compared
Comparison of 15 UK + global carbon accounting and ESG reporting platforms, with SECR / UK SRS S2 fit assessed per vendor.
GHG Protocol — Corporate Standard and Scope 3
The global standard underpinning all corporate carbon accounting, including the 15 Scope 3 categories and the 2015 Scope 2 Guidance.
UK SRS S2 — Climate-related Disclosures
The UK adoption of IFRS S2. Proposed mandatory for listed companies from 1 January 2027 under FCA CP26/5.
SECR — Streamlined Energy and Carbon Reporting
Mandatory UK energy and carbon reporting for ~11,900 large companies since 2019. Often the first carbon accounting deliverable.
Primary sources: 1, 2, 3, 4, 5.
For the dedicated UK SRS framework page, see What is UK SRS. For implementation pathway, see the UK SRS compliance guide.