Radiative Forcing and Global Warming Potentials of CH₄ and N₂O

As the main long-lived greenhouse gases, CH₄ and N₂O are included in the Kyoto Protocol, and countries are required to limit the rapid increase in their emissions since the Industrial Revolution. In this work, a radiative transfer model with a high resolution of 998 bands is used to calculate the instantaneous radiative efficiencies, stratospheric- adjusted radiative efficiencies, and lifetime-adjusted radiative efficiencies of CH₄ and N₂O for clear and cloudy skies, as well as their global warming potentials (GWPs) and global temperature potentials (GTPs). Simple fitting formulas for calculating the adjusted radiative forcing due to CH₄ and N₂O are given on the basis of the model results in this work. It is shown that the radiative efficiencies of CH₄ and N₂O for cloudy skies are 4.142×10^-4 W m^-2 ppb^-1 (1ppb=10^-9) and 3.125×10^-3 W m^-2 ppb^-1 after stratospheric adjustment, and 3.732×10^-4 W m^-2 ppb^-1 and 2.987×10^-3 W m^-2 ppb^-1, respectively, after lifetime adjustment, which are highly consistent with those of the IPCC (2007). Moreover, the 100-year GWPs of CH₄ and N₂O are 16 and 266, respectively, and their corresponding 100-year GTPs are 18 and 268 for sustained emissions, and 0.24 and 233 for pulse emissions. These results indicate that CH₄ and N₂O will still play a critical role in future global warming, second only to CO₂.