CO2 Equivalent (CO2e)

CO2 equivalent is the common unit that adds up a mix of greenhouse gases by weighting each by its global warming potential, so methane, nitrous oxide, and CO2 can be compared and summed. It is the unit of every shipping carbon metric: the GFI is gCO2e per megajoule on a well-to-wake basis, and the EU MRV and IMO DCS report fleet emissions in tonnes of CO2e. The choice of GWP horizon (usually 100 years) changes how heavily short-lived methane counts.