Climate & Environment
Tier 1/2/3 Method
The IPCC's three levels of inventory methodology — from default emission factors to facility-specific measurement.
Definition
The tier structure is the IPCC's graded approach to greenhouse gas inventory methods: Tier 1 applies default emission factors to basic activity data; Tier 2 uses country- or region-specific factors for key categories; Tier 3 uses facility-level data and detailed models or direct measurement. Higher tiers reduce uncertainty but demand more data and capacity, and good practice requires higher tiers for a country's key (largest or fastest-growing) source categories.
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