The Radiative Forcing Index (RFI) is a measure that quantifies the additional impact of non-CO2 greenhouse gases on the atmosphere. It is a multiplier used to compare the total climate effect of emissions from aviation to the effect of CO2 alone. The RFI takes into account factors like water vapor, aerosols, and contrails, which enhance the warming impact of flights. This index helps to provide a more comprehensive understanding of aviation’s full contribution to climate change.