Quantification methodology
ISO 14064-1:2018, clause 6
General approach
For most sources:
Emissions (tCO₂e) = Activity data × Emission factor × GWP
Where the factor is already in CO₂e, no separate GWP step is needed.
Hierarchy of methods
Use the most accurate method that is practical. Record the method used for
each source in activity-data.csv (method_tier column).
| Tier | Method | Example |
|---|---|---|
| A | Direct measurement | Continuous emissions monitoring |
| B | Supplier-specific or primary activity data × specific factor | Fuel invoices × fuel-specific factor; supplier-specific electricity factor |
| C | Primary activity data × published average factor | kWh from meters × national grid factor |
| D | Estimated or modelled activity data × average factor | Floor-area estimate of energy use |
| E | Spend-based (EEIO) | £ spend × kgCO₂e/£ |
Global warming potentials
Selected GWP set: IPCC AR_ (100-year). Use one set throughout, and record it in the GHG report. If the set changes, recalculate the base year.
Calculation rules
- Hold all calculations in version-controlled files. Never hard-code numbers in a report.
- Use the same units throughout. Convert at the activity-data stage.
- Every row of activity data must reference an evidence ID (see data quality).
- Estimates and extrapolations, such as a missing month of meter data, must
be flagged (
is_estimate = TRUE) with the method described.