Use of GWP values in GHG inventories under the UNFCCC

Many people, including experts, have become confused with the publication of multiple Global Warming Potential (GWP) values by the IPCC.

The IPCC has published its Third Assessment Report (TAR) and Fourth Assessment Report (AR4), providing the most current and comprehensive scientific assessments of climate change. Within these reports, the global warming potentials (GWPs) of several gases have been revised twice relative to the IPCC’s Second Assessment Report (SAR) and new GWPs have been calculated for an expanded set of gases.

Since the SAR, the IPCC has applied an improved calculation of CO₂ radiative forcing and an improved CO₂ response function (presented in WMO 1999). The GWPs are drawn from WMO (1999) and the SAR, with updates for those cases where significantly different new laboratory or radiative transfer results have been published. Additionally, the atmospheric lifetimes of some gases have been recalculated.

Because the revised radiative forcing of CO₂ in the TAR is about 12 percent lower than that in the SAR, the GWPs of the other gases relative to CO₂ tend to be larger, taking into account revisions in lifetimes. In addition, the values for radiative forcing and lifetimes have been calculated for a variety of halocarbons, which were not presented in the SAR.

GWP values were again updated in the IPCC AR4, and will likely be revised again in future IPCC assessment reports.