Full definition
PRG in French (Potentiel de Réchauffement Global). CO2 = 1 by convention. Current reference values are from the IPCC’s 6th report (AR6, 2021), recommended by GHG Protocol, CDP, SBTi and ESRS: fossil CH4 = 29.8 and biogenic CH4 = 27.2 over 100 years, N2O = 273, SF6 = 25,200. Over 20 years, CH4 rises to 82.5: the choice of time horizon radically changes the weight of short-lived gases. GWP converts all GHGs into CO2 equivalent (CO2e), the common unit of all carbon accounting. Updated with every IPCC report: an inventory calculated under AR5 (CH4 = 28) is not directly comparable to an AR6 inventory.
Key figures
- 29.8100-year GWP of fossil methane according to IPCC AR6 (82.5 over 20 years)
- 273100-year GWP of nitrous oxide (N2O), stable over both time horizons (IPCC AR6)
- 25,200100-year GWP of SF6, the most warming gas in standard inventories (GHG Protocol table, August 2024)
Questions and answers
What is the difference between 100-year and 20-year GWP?
The time horizon changes the relative weight of short-lived gases. Fossil methane has 29.8 times the weight of CO2 over 100 years, but 82.5 times over 20 years (IPCC AR6). Regulatory reporting (BEGES, CSRD) uses the 100-year horizon; the 20-year horizon mainly helps inform rapid methane reduction strategies.
Should AR5 or AR6 values be used for a carbon inventory?
AR6. GHG Protocol, CDP, SBTi and ESRS recommend values from the IPCC’s 6th report (2021). Historical data calculated under AR5 must be recalculated or flagged when comparing years, because methane values differ (28 under AR5, 29.8 under AR6 for fossil CH4).