GWP and IPCC AR version for methane?

[Carranza55]

We are currently using USEEIO data (via Cornerstone) to calculate Scope 3 GHG emissions and require confirmation of the underlying Global Warming Potential (GWP) values for our assurance and disclosure records.

In the characterization matrix (Table C), we observed a methane GWP value of 27.9. We would like to confirm the following:

IPCC Assessment Report: Does the current USEEIO/Cornerstone model default to AR6 for its 100-year GWP values?

Methane Characterization: We noted the 27.9 value aligns with the IPCC AR6 value for methane excluding indirect oxidation effects (as opposed to the fossil-source value of 29.8 or non-fossil value of 27.0). Could you confirm if this is the case, and if this "direct-only" value is applied across all industry sectors regardless of methane source (fossil vs. biogenic)?

[WesIngwersen]

Hi @Carranza55 thank you for your question. Yes, that methane GWP of 27.9 is applied universally (across all sectors), because our nomenclature (FEDEFL) and approach does not currently distinguish fossil and biogenic methane sources.

We welcome more input on how this aligns with reporting guidance as we are open to considering changes.