Greenhouse gas (GHG) accounting is the systematic process of identifying, quantifying and reporting emissions associated with an organisation, activity, product or project. It helps researchers, institutions and industry understand where emissions originate and how they change over time.
Carbon accounting commonly covers carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O) and other greenhouse gases. Results are often expressed as carbon dioxide equivalent (CO₂e), allowing different gases to be compared using an appropriate global warming potential.
For organisational inventories, the Greenhouse Gas Protocol distinguishes three categories, known as emission scopes.
| Category | Definition | Illustrative sources |
|---|---|---|
| Scope 1 | Direct emissions from sources owned or controlled by the organisation | On-site fuel combustion, company vehicles, process emissions, refrigerant leaks |
| Scope 2 | Indirect emissions from generation of purchased or acquired energy consumed by the organisation | Purchased electricity, steam, heating and cooling |
| Scope 3 | Other indirect emissions occurring in the organisation's value chain | Purchased goods, transport, business travel, use and disposal of sold products |
Scope classification depends on organisational boundaries and the reporting framework. Scope 3 includes upstream and downstream categories and should not be confused with Scope 2 purchased energy.
An emissions inventory begins by defining the reporting period, organisational boundary and operational activities included in the assessment.
Activity data, such as fuel consumed, electricity purchased or transport distance, are combined with suitable emission factors. Where available, reliable direct measurements can complement calculated estimates.
Consistent boundaries and documented assumptions are essential for comparing results between reporting periods and identifying opportunities to reduce emissions.
Simplified educational illustration of the three scopes; it does not represent every emissions category or accounting boundary.
A common calculation approach multiplies measured or estimated activity data by an appropriate emission factor. For inventories covering multiple gases, each gas can then be converted to CO₂e using its applicable global warming potential.
Example: 10,000 kWh of electricity × 0.40 kg CO₂e/kWh = 4,000 kg CO₂e (4 tonnes CO₂e).
The electricity emission factor in this example is hypothetical and is used only to illustrate the calculation. Actual factors depend on the location, reporting year, energy source and selected accounting method.
Data quality, measurement units, emission factor sources and assumptions should be documented. Avoiding double counting within the inventory is essential, particularly when analysing value-chain emissions.
Carbon accounting supports emissions inventories, environmental assessments, academic research and the evaluation of industrial decarbonisation measures.
Reporting frameworks such as the GHG Protocol provide established approaches for organisational inventories, while ISO 14064-1 sets requirements and guidance for organisation-level quantification and reporting.
Well-documented inventories can help identify major emissions sources, evaluate changes over time and support transparent communication of results.
Gathering consistent energy, fuel, process and value-chain activity information.
Checking data completeness, units, calculation methods and supporting evidence.
Using inventory results to prioritise and evaluate practical emissions reductions.
CO2.SERVICES provides educational information on carbon accounting, greenhouse gas emissions and related technologies. Additional scientific publications, technical reports and research notes are available through the Euro-Eurasia Environmental Science & Education Foundation (EEESEF).
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