Refer to the tables in Part I of the Synthesis and Assessment (S&A) report to see which categories are “key” and see which methodology each Party has applied.

Remember that it is good practice to use both the Reference Approach and at least a top-down Sectoral Approach to estimate CO₂ emissions from a key category, and to correct for oxidation and stored carbon. A more rigorous bottom-up Tier 2 or 3 approached is preferable to a Tier 1 approach if the required data are available and believed to be accurate.

For the Tier 1 Sectoral Approach, total CO₂ is summed across all fuels (excluding biomass) and all sectors. For Tier 2 and 3, the Detailed-Technology-Based Approach, total CO₂ emissions are summed across all fuels and sectors, plus combustion technologies (e.g., stationary and mobile sources). The Tier 2 and 3 approaches provide more disaggregated emission estimates, but also require more data to apply.

Refer to Sections 2.1.1.1, p. 2.8 of the IPCC Good Practice Guidance for a further description of Tier 1 and 2 approaches for estimating CO₂ emissions from fuel combustion, and for guidance on choosing an appropriate method for the different subcategories.

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