3. Choice of Method

The choice of estimation method is country-specific and determined by the level of detail in the activity data available.

Decision trees for selecting the methods for estimating CO₂ and non-CO₂ emissions are included in the IPCC Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories.

3.1. CO₂ Emissions
It is possible to estimate national CO₂ emissions by accounting for the carbon in fuels supplied to an economy. Statistics on the production, imports, exports, and stock changes for fuels is more likely to be available in many countries than detailed end use consumption statistics. Therefore, CO₂ emissions from fuel combustion can be calculated accurately at a highly aggregated level, provided that complete fuel consumption statistics and their typical carbon contents are available. These data provide a sound starting point for the estimation of CO₂ emissions from energy use. Estimates of CO₂ emissions then require adjustments for unoxidized, carbon stored in products, and international bunker fuels.

Supply data for commercial fuels is generally available at the national level. Official international databases (e.g. IEA) also include data that are directly supplied by the countries themselves. However, because fuel qualities and carbon content factors may differ markedly between countries, national inventories should use local energy data and factors where available.