Example
Multiplying litres of a fuel by an appropriate factor can estimate combustion emissions.
The catch
A factor must match the fuel, location, technology and reporting context.
Related terms
Reporting, Absolute emissions, Activity data, Base year, Carbon dioxide equivalent, Carbon footprint
In more depth
Emission factor, explained.
An emission factor is an average, so it can be right for a country and wrong for a particular site. The IPCC organises methods in tiers, from global default factors through country-specific values to direct measurement, and higher tiers take more effort but describe a source more faithfully. Factors also change. Grid electricity factors fall as coal plants close, so a company that keeps an old figure overstates its Scope 2 emissions.
Methane exposes the weakness most clearly. Measurement campaigns in oil and gas regions have found emissions well above estimates built from standard factors, partly because a single super-emitter can outweigh many ordinary sites. Record every factor with its source and year in the audit trail, and update it before comparing one year with the next.