Climate
IPCC default factor
Definition
An IPCC default factor is a representative average value, published in the IPCC Guidelines for National Greenhouse Gas Inventories and its Emission Factor Database, that links an activity level (such as fuel burned or fertiliser applied) to the quantity of a greenhouse gas emitted or removed. Using default factors with activity statistics constitutes the Tier 1, least data-intensive, estimation approach.
References
Overview
What it means
Compiling a greenhouse gas inventory requires multiplying "activity data" by an emission factor for every source category. The IPCC provides globally averaged defaults so that any country can produce a complete inventory without original measurement. Tier 1 applies these defaults; Tier 2 uses country-specific factors; Tier 3 uses facility-level measurement or modelling.
Defaults are deliberately conservative in coverage but carry higher uncertainty.
How it is used
National inventory compilers use Tier 1 defaults for minor source categories while reserving higher-tier methods for key categories. Corporate and project-level carbon accountants also draw on IPCC defaults where commercial databases lack a factor, for example in AFOLU calculations and small-country inventories.
Why it matters
Default factors make global emissions reporting possible and comparable: without them, many countries could not report at all. But their generic nature means they can misrepresent local conditions, so guidance recommends moving significant sources to higher tiers as capacity allows. **Note:** Candidate 1540 ("IPCC emissions factor") merges here as the same concept.
Related methodological entry: Key category analysis (this batch).