GWP

Global Warming Potential expresses the climate impact of a greenhouse gas relative to CO2 over a fixed horizon, normally 100 years (GWP100). Marine fuel accounting uses the IPCC Fifth Assessment Report values: methane at 28 and nitrous oxide at 265, adopted in the IMO LCA Guidelines (MEPC.391(81)) and FuelEU Maritime. These factors convert methane slip and N2O into CO2-equivalent, which is why LNG and ammonia carry climate penalties that a pure tank-to-wake CO2 count would miss. The choice of GWP100 over GWP20 materially changes methane’s weighting in policy debate.