Greenhouse gas (GHG) accounting: Scope 1, 2 and 3

Why GHG accounting requires more than calculation

GHG accounting is often treated as a reporting exercise. In practice, weak GHG inventories usually fail because of poor data boundaries, unclear assumptions, inconsistent activity data, missing Scope 3 logic, weak supplier evidence, inappropriate emission factors, or insufficient documentation.

For enterprise organisations, these weaknesses create real risk. They affect sustainability reporting, procurement decisions, carbon reduction targets, product carbon footprint work, ESG disclosures, customer requirements, and verification readiness.

DEISO approaches GHG accounting as a technical execution and data-governance process. The objective is not only to estimate emissions, but to produce an inventory that can be reviewed, explained, improved, and used for decision-making.

Scope 1, Scope 2, and Scope 3 coverage

DEISO supports full GHG inventory development across organisational and value-chain emissions — or Scope 3 on its own, when that is what your customers or reporting require.

For many organisations, Scope 3 is the highest-risk area because it requires structured supplier data, defensible estimation logic, category-level screening, data-quality evaluation, and clear prioritisation.

The 15 Scope 3 categories

The GHG Protocol Scope 3 Standard organises value-chain emissions into 15 categories. DEISO screens all 15 for relevance before deciding where detailed data collection is worth the effort.

Scope 3 screening and calculation methods

Every Scope 3 project starts with relevance screening of all 15 categories, using less specific data to find the categories that matter most for your emissions, risks, and reduction opportunities. Detailed data collection then focuses where it adds value.

• Spend-based method — procurement spend multiplied by economic emission factors; useful for screening and where physical data is unavailable
• Average-data method — physical quantities such as tonnes or kilometres multiplied by secondary emission factors
• Supplier-specific method — product- or company-level emissions data provided by your suppliers
• Hybrid method — a combination of supplier-specific data and secondary data, the usual approach for material categories

The method used for each category is documented and scored for data quality, so you can see where accuracy can improve in future reporting years.

How DEISO builds the inventory

DEISO’s GHG accounting work is built to produce a structured and review-ready emissions inventory — not a superficial spreadsheet output.

The process typically includes organisational boundary definition, operational boundary mapping, data request design, activity data collection, supplier data structuring, emission factor selection, calculation methodology, uncertainty and data-quality review, documentation, hotspot identification, and reduction pathway support.

Where data gaps exist, DEISO applies transparent estimation logic and documents assumptions clearly so the organisation can improve its data maturity over time.

The result is a GHG inventory that supports internal decision-making, regulatory framework alignment, customer disclosure, ESG reporting, carbon management, and future verification preparation.

Organisational boundaries, base year, and Scope 2 methods

• Consolidation approach — equity share, financial control, or operational control, chosen to match your reporting obligations and applied consistently
• Base year and recalculation policy — a documented base year and clear rules for recalculating it after acquisitions, divestments, or methodology changes
• Scope 2 dual reporting — location-based results from grid averages, and market-based results reflecting contractual instruments such as energy attribute certificates and power purchase agreements

Methodology, standards alignment, and documentation

DEISO structures GHG accounting work to support alignment with recognised GHG inventory principles and reporting expectations — relevance, completeness, consistency, transparency, and accuracy.

Depending on the organisation’s needs, DEISO supports inventory development, methodology documentation, data-quality review, emission factor justification, Scope 3 category mapping, internal control documentation, and review-readiness preparation.

The documentation layer is critical. A GHG inventory must be explainable. Each major data source, assumption, boundary decision, calculation method, and emission factor selection should be traceable and defensible.

This is where DEISO’s technical review approach adds value — identifying weaknesses before they become reporting, assurance, or stakeholder-confidence risks.

Standards, reporting frameworks, and emission factors

Scope 3 data structuring and supplier engagement

Scope 3 emissions are often the most complex part of corporate GHG accounting. Organisations may need to collect data from suppliers, map spend or physical activity data, classify purchased goods and services, evaluate upstream and downstream transportation, assess waste treatment routes, and estimate end-of-life emissions.

DEISO supports Scope 3 work through structured category mapping, supplier data request design, data-quality scoring, estimation logic, supplier response review, and prioritisation of high-impact categories.

The objective is to move Scope 3 from a vague disclosure requirement into a managed technical system that supports procurement decisions, supplier engagement, carbon reduction planning, and product-level carbon work.

GHG accounting for carbon management and decarbonisation

A GHG inventory should not stop at reporting. When structured correctly, it becomes a management system for carbon reduction.

DEISO helps organisations identify emissions hotspots, prioritise reduction opportunities, evaluate data gaps, structure reduction initiatives, and connect GHG accounting outputs with PCF, LCA, EPD, ESG reporting, procurement strategy, and sustainability performance management.

This helps leadership teams move from annual reporting toward operational carbon management.

Common GHG accounting risks DEISO helps resolve

Organisations often face avoidable risks in GHG accounting, including incomplete Scope 3 boundaries, inconsistent data collection, weak supplier evidence, unclear activity data, duplicated emissions, inappropriate emission factors, missing documentation, lack of audit trail, and poor connection between GHG inventory outputs and real reduction actions.

DEISO supports clients by identifying these issues early and stabilising the inventory before it is used for disclosure, target-setting, customer communication, procurement decisions, or third-party review.

Verification readiness

DEISO is not a verification body. DEISO prepares your inventory to be traceable, documented, and ready for third-party verification to ISO 14064-3, and coordinates with the verifier during the process.

Third-party verification fees are not covered by DEISO. Verification is carried out by an independent verifier and paid by the client directly.

What you receive

DEISO’s GHG accounting engagements may include a full Scope 1–3 GHG inventory, emissions calculation workbook, data collection templates, Scope 3 category mapping, supplier data request structure, emission factor documentation, data-quality assessment, hotspot analysis, methodology report, management summary, and review-readiness recommendations.

The exact outputs depend on the organisation’s boundary, sector, available data, reporting objectives, and intended use of the inventory.

Who this service is for

This service is for organisations that need technically defensible GHG accounting for corporate reporting, ESG disclosure, supply-chain requirements, customer requests, decarbonisation planning, procurement strategy, product carbon footprint development, EPD preparation, or internal carbon management.

It is especially relevant when emissions data must be reliable enough to support decision-making, withstand internal review, and prepare for external scrutiny.

Engage DEISO for GHG accounting and Scope 3 execution

When your organisation needs more than a basic emissions estimate — Scope 1, 2, and 3 GHG accounting through structured execution, technical review, data governance, and verification-ready documentation. Emissions inventories that are clear, defensible, and useful for carbon management.