Deep dive: Carbon accounting & MRV — what's working, what's not, and what's next

Carbon accounting and measurement, reporting, and verification (MRV) have undergone a fundamental transformation over the past three years, driven by overlapping regulatory mandates, investor demands for auditable emissions data, and a maturing technology ecosystem. Yet the field remains marked by sharp contradictions: sophisticated satellite-based methane detection coexists with spreadsheet-driven Scope 3 estimates; mandatory disclosure frameworks demand precision that current data infrastructure cannot reliably deliver; and the proliferation of carbon accounting platforms has created a fragmented market where identical activities produce materially different emissions figures depending on which tool and methodology an organization selects. This deep dive assesses what is genuinely working in carbon accounting and MRV, where persistent gaps remain, and which developments will shape the discipline over the next two to three years.

Why It Matters

The regulatory landscape for carbon accounting has shifted from voluntary best practice to enforceable obligation across the UK and the broader European market. The UK's Streamlined Energy and Carbon Reporting (SECR) framework, which already requires quoted companies and large unquoted companies to disclose energy use and carbon emissions, is being supplemented by the Transition Plan Taskforce (TPT) disclosure framework, endorsed by the Financial Conduct Authority for premium-listed companies from 2026. The EU's Corporate Sustainability Reporting Directive (CSRD), which applies to approximately 50,000 companies including UK subsidiaries of EU parent companies and UK firms with significant EU operations, mandates detailed emissions disclosure aligned with European Sustainability Reporting Standards (ESRS) beginning with fiscal year 2024 reports.

For UK sustainability leads, these requirements create an immediate operational challenge: producing emissions data that is sufficiently granular, consistent, and auditable to satisfy multiple overlapping frameworks. A 2025 survey by the Carbon Trust found that 68% of UK companies subject to SECR reported "significant difficulty" in producing Scope 3 emissions inventories that met their auditor's evidence requirements. The International Financial Reporting Standards (IFRS) Foundation's International Sustainability Standards Board (ISSB) standards, specifically IFRS S1 and S2 effective for annual reporting periods beginning January 2025, add another layer of requirements for companies reporting under IFRS-aligned jurisdictions.

The financial stakes extend beyond compliance. Institutional investors managing over $130 trillion in assets through the Glasgow Financial Alliance for Net Zero (GFANZ) have committed to aligning portfolios with net zero by 2050, requiring portfolio-level carbon accounting that depends entirely on the quality of company-level disclosures. Carbon pricing mechanisms, including the UK Emissions Trading Scheme (UK ETS) and the EU Carbon Border Adjustment Mechanism (CBAM), create direct financial consequences for emissions measurement errors. And the voluntary carbon market, valued at approximately $1.7 billion in 2025, depends on MRV systems that can credibly quantify emission reductions and removals.

What's Working

Scope 1 and 2 Accounting Has Reached Maturity

Direct emissions (Scope 1) and purchased electricity emissions (Scope 2) accounting are now well-established disciplines with robust methodologies, reliable data sources, and strong auditor consensus. The GHG Protocol Corporate Standard, supplemented by the Scope 2 Guidance published in 2015, provides a widely accepted framework that most UK companies can implement with existing data. Natural gas and fuel consumption records from utility invoices, combined with government-published emission factors from the Department for Energy Security and Net Zero (DESNZ), enable Scope 1 calculations with uncertainty ranges of 3 to 5% for most organisations.

Scope 2 accounting benefits from increasingly granular electricity grid data. The UK's half-hourly settlement data, available through suppliers and the Balancing Mechanism Reporting System, enables temporal matching of electricity consumption to grid carbon intensity at 30-minute resolution. Companies using location-based methods can apply DESNZ grid average factors, while those opting for market-based approaches can leverage Renewable Energy Guarantees of Origin (REGOs) and Power Purchase Agreements with documented emission factor claims. The Electricity Maps platform and National Grid ESO's Carbon Intensity API provide real-time carbon intensity data that supports operational decision-making beyond annual reporting.

Satellite and Remote Sensing MRV Has Scaled

The most transformative development in MRV has been the operational deployment of satellite-based emissions monitoring at scale. MethaneSAT, launched in March 2024, provides methane detection at 100-meter resolution across oil and gas producing regions globally, identifying super-emitter events that ground-based monitoring consistently missed. The European Space Agency's Copernicus Atmosphere Monitoring Service (CAMS) delivers CO2 and methane concentration data with global coverage, while commercial providers including GHGSat and Kayrros offer facility-level methane quantification with detection thresholds below 100 kilograms per hour.

For UK-relevant applications, satellite MRV has proven particularly valuable in three areas: verifying methane emissions from North Sea oil and gas operations, where satellite observations revealed emissions 50 to 100% higher than operator self-reports in a 2024 analysis by the National Physical Laboratory; monitoring land-use change emissions in global agricultural supply chains, supporting Scope 3 Category 1 (purchased goods and services) calculations for UK food retailers and manufacturers; and providing independent verification of emission reduction claims in voluntary carbon market projects, where a 2025 study by Sylvera found that 35% of forestry-based carbon credits had overestimated sequestration relative to satellite-derived biomass estimates.

Digital MRV Platforms Have Consolidated

The carbon accounting software market has matured through consolidation, with a smaller number of enterprise-grade platforms emerging from a fragmented field of over 200 providers that existed in 2023. Persefoni, Watershed, and Sphera have established themselves as leaders for large enterprises, offering automated data ingestion from ERP systems (SAP, Oracle, Workday), supplier engagement modules for Scope 3 data collection, and audit trails that satisfy ISAE 3410 limited assurance requirements. Plan A, Normative, and Emitwise have carved positions serving UK and European mid-market companies with platforms designed specifically for CSRD and SECR compliance.

These platforms have solved several previously manual workflows: automated utility data extraction from smart meters and supplier portals; activity-based emission factor matching using machine learning classification of spend data; supplier-specific emission factor integration through APIs connecting to CDP, EcoVadis, and supplier portals; and automated calculation of location-based and market-based Scope 2 using time-matched grid intensity data. For organisations that previously relied on consultant-built spreadsheets updated annually, these platforms represent a step-change in data currency, auditability, and internal accessibility.

What's Not Working

Scope 3 Remains Fundamentally Unreliable

Despite significant investment in tools and methodologies, Scope 3 emissions accounting remains the weakest link in corporate carbon inventories. The core problem is structural: Scope 3 requires quantifying emissions across value chains where reporting organisations have limited visibility and no operational control. A 2025 analysis by the Carbon Disclosure Project found that Scope 3 estimates for identical companies varied by 40 to 200% across different calculation approaches, reflecting the compounding uncertainty introduced by spend-based emission factors, industry-average proxies, and allocation methodologies.

The most common UK approach, spend-based calculation using Defra or Exiobase environmentally extended input-output (EEIO) factors, converts procurement spend into estimated emissions using sector-average intensity data. This method captures relative scale but cannot reflect supplier-specific performance, geographic variation in energy mix, or process-level differences. A UK retailer sourcing cotton textiles from both Bangladesh and Turkey will calculate identical Scope 3 emissions per pound spent, despite the substantial difference in grid carbon intensity and manufacturing efficiency between the two countries.

Supplier-specific data collection offers better accuracy but faces persistent challenges. Response rates to CDP Supply Chain Programme questionnaires averaged 54% for UK-headquartered requesting companies in 2025, meaning nearly half of supplier emissions remain estimated. Small and medium enterprises, which comprise the majority of most supply chains, lack the resources and expertise to calculate their own emissions, creating a data gap that no amount of downstream pressure can fully resolve.

Emission Factor Databases Are Fragmented and Outdated

The accuracy of any carbon accounting exercise depends on the quality of emission factors applied to activity data, and the current ecosystem of emission factor databases has significant limitations. UK organisations commonly reference three to five different sources: DESNZ conversion factors (updated annually, focused on UK energy and transport), Defra EEIO factors (based on economic modelling with 2 to 3 year lags), IPCC default factors (global averages insufficient for country-specific calculations), supplier-specific factors from CDP or product declarations, and commercial databases from ecoinvent or GaBi/Sphera.

These sources frequently conflict. A 2024 comparison by the University of Cambridge Institute for Sustainability Leadership found that emission factors for the same activity (e.g., one tonne of steel produced in the UK) varied by 15 to 45% depending on the database selected. The discrepancy arises from differences in system boundaries (cradle-to-gate versus cradle-to-grave), allocation methods (mass, economic, or energy-based), vintage of underlying data, and geographic specificity. Until the field converges on a unified, continuously updated emission factor infrastructure, carbon accounting results will remain methodology-dependent rather than reflecting actual physical emissions.

Assurance Standards Are Immature

The demand for third-party assurance of sustainability disclosures has outpaced the development of robust assurance standards and competent assurance providers. The International Auditing and Assurance Standards Board (IAASB) released its proposed International Standard on Sustainability Assurance (ISSA 5000) in 2024, but the standard is not expected to be finalised until late 2026. In the interim, assurance providers apply varying interpretations of ISAE 3000 (Revised) and ISAE 3410, producing inconsistent levels of scrutiny across engagements.

The practical consequence is that "limited assurance" of emissions data, the level most commonly obtained by UK companies, provides substantially less confidence than financial statement audits. Limited assurance engagements typically involve reviewing methodology documentation, testing a sample of data inputs, and assessing the reasonableness of emission factor selections, but do not require the comprehensive testing and corroboration procedures characteristic of reasonable assurance. A 2025 survey by the Financial Reporting Council found that 42% of UK sustainability assurance engagements were performed by providers without financial audit backgrounds, raising questions about technical competence and professional scepticism.

What's Next

Regulatory Convergence Will Force Standardisation

The most significant near-term development is the convergence of disclosure frameworks around ISSB standards. The UK government confirmed in its 2025 Green Finance Strategy that it will endorse IFRS S1 and S2 as the basis for UK sustainability disclosure requirements, with mandatory adoption for premium-listed companies from fiscal year 2027. This convergence will reduce the current burden of multi-framework reporting but will also raise the bar for data quality, as ISSB standards require disclosure of Scope 3 emissions with sufficient granularity to inform investor decision-making.

The EU's CSRD and ESRS standards will continue to apply to UK companies with EU operations, creating a dual-reporting requirement that sustainability leads must manage. However, the EFRAG-ISSB interoperability guidance published in 2025 provides mapping between ESRS E1 (Climate Change) and IFRS S2, reducing but not eliminating the reconciliation effort. UK companies should prepare for a regulatory environment where baseline ISSB compliance is mandatory and ESRS compliance is required for EU-facing operations.

AI-Powered Scope 3 Will Move From Estimation to Measurement

Machine learning approaches to Scope 3 accounting are advancing rapidly, offering the potential to replace spend-based estimation with activity-based measurement at scale. Platforms including Watershed, Persefoni, and Plan A are deploying AI models that classify procurement transactions into specific activity categories, match transactions to supplier-specific or product-specific emission factors, and flag anomalies that indicate data quality issues. Early deployments report 25 to 40% improvements in Scope 3 accuracy compared to pure spend-based methods, though validation against measured emissions remains limited.

The most promising development is the emergence of product-level carbon footprint databases that use lifecycle assessment (LCA) data, supply chain tracing, and AI-driven inference to generate emission factors at SKU or commodity level rather than sector-average level. The Pathfinder Framework, developed by the World Business Council for Sustainable Development (WBCSD), provides a standard for exchanging product carbon footprint data between trading partners, and adoption by major UK retailers and manufacturers is accelerating. If product-level data achieves sufficient coverage, it could fundamentally resolve the Scope 3 accuracy problem by replacing top-down estimation with bottom-up aggregation of supplier-provided, product-specific emissions data.

Continuous Monitoring Will Replace Annual Reporting

The current paradigm of annual emissions inventories compiled retrospectively is giving way to continuous monitoring and real-time carbon accounting. IoT sensors, smart meters, and automated data pipelines enable organisations to track emissions on daily or weekly cycles rather than reconstructing annual totals from invoices and estimates. The UK's mandatory half-hourly electricity settlement, combined with APIs providing real-time grid carbon intensity, makes continuous Scope 2 accounting technically feasible today.

For Scope 1, the deployment of continuous emissions monitoring systems (CEMS) in industrial facilities, combined with connected fleet telematics and building management system data feeds, enables near-real-time direct emissions tracking. The regulatory trajectory supports this shift: the UK ETS already requires quarterly emissions reporting for covered installations, and the Transition Plan Taskforce framework emphasises forward-looking metrics that require more frequent data updates than annual reporting cycles can support.

Carbon Accounting KPIs: Benchmark Ranges

Metric	Below Average	Average	Above Average	Top Quartile
Scope 1 & 2 Data Coverage	<80%	80-90%	90-97%	>97%
Scope 3 Categories Reported	<5 of 15	5-8 of 15	8-12 of 15	>12 of 15
Supplier-Specific Scope 3 Data	<10%	10-25%	25-50%	>50%
Emission Factor Currency	>3 years old	2-3 years	1-2 years	<1 year
Assurance Level	None	Limited (partial)	Limited (full)	Reasonable
Reporting Cycle Frequency	Annual	Semi-annual	Quarterly	Monthly or continuous
Time to Produce Annual Inventory	>6 months	4-6 months	2-4 months	<2 months

Action Checklist

• Audit current carbon accounting methodology against ISSB (IFRS S2) and ESRS E1 requirements to identify compliance gaps
• Evaluate Scope 3 calculation approach: transition from spend-based EEIO to hybrid methods incorporating supplier-specific data for top 20 suppliers by emissions
• Assess carbon accounting platform options, prioritising automated data ingestion, audit trail functionality, and multi-framework reporting capability
• Establish data quality metrics and governance processes including emission factor version control, data completeness tracking, and anomaly detection
• Engage with top suppliers through CDP Supply Chain Programme or direct data requests to improve Scope 3 accuracy for material categories
• Plan for third-party assurance, engaging assurance providers early to understand evidence requirements and remediate data gaps before reporting deadlines
• Investigate continuous monitoring capabilities for Scope 1 and 2 to move toward real-time carbon accounting and reduce annual inventory compilation burden
• Monitor WBCSD Pathfinder Framework adoption and product carbon footprint data availability in your supply chain for future Scope 3 improvement

FAQ

Q: What is the most reliable method for calculating Scope 3 emissions for a UK company? A: Use a hybrid approach combining supplier-specific data for your largest emission sources (typically purchased goods and services, upstream transportation, and use of sold products) with EEIO-based estimates for the remainder. Prioritise direct engagement with your top 20 suppliers by procurement spend, as these typically account for 60 to 80% of Scope 3 emissions. Apply DESNZ conversion factors for UK-based activities and ecoinvent or GaBi factors for international supply chain segments. Accept that current Scope 3 estimates carry 30 to 50% uncertainty and document methodology assumptions transparently.

Q: How should UK companies prepare for ISSB disclosure requirements? A: Begin by mapping your current SECR and TCFD disclosures against IFRS S2 requirements, identifying gaps in governance, strategy, risk management, and metrics sections. The most common gaps are: quantified Scope 3 emissions across all material categories, climate scenario analysis using specified pathways, and transition plan disclosure with interim targets. Engage your auditor or assurance provider to understand evidence requirements at least 12 months before your first mandatory reporting period.

Q: What level of assurance should we target for our emissions disclosures? A: For UK premium-listed companies, limited assurance of full Scope 1 and 2 emissions is the current market standard and regulatory expectation. Reasonable assurance, comparable to financial audit, is expected to become the regulatory requirement by 2028 to 2030 but is currently achieved by fewer than 10% of UK reporters. Scope 3 assurance is typically limited to methodology review rather than data verification, reflecting the inherent uncertainty in value chain emissions. Invest in data infrastructure and audit trails that will support the transition to reasonable assurance as requirements escalate.

Q: How do we reconcile differences between SECR, CSRD, and ISSB reporting requirements? A: Start with ISSB (IFRS S2) as your baseline, as UK regulation is converging on this standard. Map ESRS E1 requirements against your ISSB disclosure to identify additional EU-specific disclosures (such as pollution, water, and biodiversity metrics required under ESRS but not ISSB). SECR requirements are a subset of both ISSB and ESRS, so ISSB-compliant disclosures will satisfy SECR. Use a single carbon accounting platform that supports multi-framework output from a unified data model to avoid maintaining parallel calculations.

Q: What is the cost of implementing enterprise carbon accounting? A: For a UK mid-market company (250 to 5,000 employees), expect annual costs of 50,000 to 150,000 pounds for carbon accounting software, 20,000 to 60,000 pounds for third-party assurance, and 1 to 2 FTE equivalents for internal management. Large enterprises with complex supply chains should budget 150,000 to 500,000 pounds annually for platforms, 50,000 to 150,000 pounds for assurance, and 3 to 5 FTE equivalents. Initial setup costs in year one are typically 50 to 100% higher than ongoing annual costs due to data infrastructure buildout and methodology development.

Sources

• Carbon Trust. (2025). UK Corporate Carbon Reporting: Challenges and Best Practices Survey 2025. London: Carbon Trust.
• Carbon Disclosure Project. (2025). Global Supply Chain Report 2025: Scope 3 Data Quality and Coverage. London: CDP Worldwide.
• Financial Reporting Council. (2025). Sustainability Assurance in the UK: Market Assessment and Quality Review. London: FRC.
• University of Cambridge Institute for Sustainability Leadership. (2024). Emission Factor Databases: Harmonisation Challenges and Recommendations. Cambridge: CISL.
• Sylvera. (2025). State of Carbon Credits 2025: Satellite-Verified Performance Assessment. London: Sylvera Ltd.
• World Business Council for Sustainable Development. (2025). Pathfinder Framework Version 2.1: Guidance for Product Carbon Footprint Data Exchange. Geneva: WBCSD.
• HM Government. (2025). Green Finance Strategy: UK Sustainability Disclosure Standards Roadmap. London: HM Treasury.