Uncertainty assessment
ISO 14064-1:2018, clause 8.3
The organisation must assess the uncertainty of its GHG inventory, covering both activity data and emission factors.
Approach
- Give each source an uncertainty (±%) for its activity data and its emission factor. Base these on meter accuracy class, invoice versus estimate, or the uncertainty published with the factor.
- Combine the two for each source (error propagation, assuming they are
independent):
U_source = √(U_AD² + U_EF²) - Combine across sources, weighted by emissions:
U_total = √Σ(E_i × U_i)² / ΣE_i - For large or skewed uncertainties, use Monte Carlo simulation instead.
Qualitative rating
Where a number cannot be estimated, rate each source:
| Rating | Typical case |
|---|---|
| Low (< ±5%) | Billed, metered data with an official factor |
| Medium (±5–20%) | Partial estimates; average factors |
| High (> ±20%) | Spend-based; modelled or proxy data |
Use the results
Focus improvement work on sources that are both large and highly uncertain. Record planned improvements in the inventory management plan.