Obtain the GHG Protocol Global Warming Potential Values document (version 2.0, August 2024) from ghgprotocol.org; it provides the authoritative AR6 GWP100 table for inventory use.
For methane from fossil fuel fugitive sources (oil and gas systems, coal mining, carbide or ethylene production), apply the Methane - fossil GWP100 value of 29.8.
For all other methane sources — combustion emissions, landfill, livestock, wastewater, and rice cultivation — apply the Methane - non-fossil GWP100 value of 27.0.
Record both the GWP source (IPCC AR6) and the time horizon (100-year) in your inventory documentation; many reporting programs require this disclosure.
Do not apply the fossil GWP (29.8) to combustion sources; combustion CO2 is already reported separately, so using the fossil value would double-count the oxidation-to-CO2 effect.
Known gotchas
The GHG Protocol August 2024 document separates methane into fossil (29.8) and non-fossil (27.0), not a single value; using a single figure for all methane sources is no longer correct under AR6 guidance.
The non-fossil AR6 GWP100 is 27.0, not 27.9; 27.9 is an intermediate calculation in the IPCC methodology and is not the reported inventory value in the GHG Protocol table.
If a reporting program still mandates AR5 values, the AR5 non-fossil GWP100 is 28 and the AR5 fossil GWP100 is 30; do not mix AR5 and AR6 values within the same inventory.
Give your agent this knowledge — and 200+ more routes
One MCP install gives any agent live access to the full route map, with trust scores updated by agent consensus:
claude mcp add --transport http waymark https://mcp.waymark.network/mcp