Building a GHG inventory: data and controls

What is a GHG inventory?

A GHG inventory lists a company's emissions sources within its boundaries, the activity data and emission factors for each, and the resulting emissions in tonnes of CO2 equivalent by scope: scope 1 from sources it owns or controls, scope 2 from purchased energy, and scope 3 from its value chain. It is the basis for every emissions figure the company publishes, from its sustainability statement to its target progress. See calculating scope 1 and 2 emissions.

How do you build a GHG inventory?

1. Set the organisational boundary, using equity share or control, and the operational boundary of scopes and categories. See organisational boundaries.
2. List every emissions source at every site, including small ones such as refrigerants and backup generators.
3. Name a data owner for each source and agree the source system, timing and format.
4. Collect activity data, estimating gaps with a documented method.
5. Select emission factors and global warming potentials, recording their source and version. See emission factors.
6. Calculate in a controlled tool, with locked formulas and change logs.
7. Review: completeness, reconciliations, year-on-year variances and approval.
8. Document everything in an inventory management plan and keep the evidence.

Where does the data come from?

Fuel and electricity come from supplier invoices and meter readings; fleet fuel from fuel card reports; refrigerants from maintenance contractors' service logs; business travel from travel agency and expense systems; and scope 3 purchases from the ledger or supplier data. Periods should match the reporting year, so readings that straddle the year-end are apportioned. Where data are missing, such as for a site that has not sent its bills, a company estimates from comparable sites or prior periods and records the estimate for review once actual data arrive. See scope 3 supplier-specific data.

A GHG inventory in practice: a retailer's data and controls

A retailer with 300 stores maps each source to an owner and a key control.

Its review compares each source with the prior year and requires an explanation for any change above 10%.

Three sources exceed the 10% trigger. The electricity fall is supported by the new renewable tariff contract and its certificates; the refrigerant rise by service logs for two major leaks, now an action item; and the travel rise by the agency's confirmation that its 2025 report missed one booking channel, which the retailer judges below its recalculation threshold and discloses. See refrigerants and fugitive emissions.

Which controls do assurance providers expect?

Controls that are designed sensibly and operate in practice: reconciliations of activity data to invoices or the ledger, checks that every site has reported, reviews of variances, approval of new or changed emission factors, restricted access and change logs in the calculation tool, and sign-off by someone independent of the preparer. Under ISSA 5000, a limited assurance practitioner understands these controls, and a reasonable assurance practitioner usually tests them. ESRS 2 asks companies to describe their risk management and internal controls over sustainability reporting. See ISSA 5000 and getting ready for sustainability assurance.

What should the inventory management plan contain?

The boundaries and the reasons for them; the list of sources; methods, emission factors and global warming potentials with their versions; data owners and timetables; estimation methods; the base year and recalculation policy; controls and review steps; known limitations and planned improvements. ISO 14064-1 calls this GHG information management and requires procedures for it. The plan is the first document a verifier asks for. See base year recalculation.

How should uncertainty be handled?

Every figure carries uncertainty, from measurement, from emission factors and from estimates. The GHG Protocol provides guidance and a tool for assessing it, and companies should at least identify the sources with large emissions and high uncertainty, such as scope 3 spend-based figures, and prioritise improving them. IFRS S1 and the ESRS require disclosure of significant measurement uncertainty and the estimates behind it. See the spend-based method.

This guide is general information. It is not tax or legal advice for your situation.