Radiative forcings and global warming potentials of 39 greenhouse gases

The radiative forcings and global warming potentials for 39 greenhouse gases are evaluated using narrowband and broadband radiative transfer models. Unlike many previous studies, latitudinal and seasonal variations are considered explicitly, using distributions of major greenhouse gases from a combination of chemical-transport model results and Upper Atmosphere Research Satellite (UARS) measurements and cloud statistics from the International Satellite Cloud Climatology Project. The gases examined include CO2, CH4, N2O, plus a number of chlorofluorocarbons, hydrochlorofluorocarbons, hydrofluorocarbons, hydrochlorocarbons, bromocarbons, iodocarbons, and perfluorocarbons (PFCs). The model calculations are performed on a 5 degrees latitude grid from 82.5 degrees S to 82.5 degrees N. The radiative forcings determined by the model are then used to derive global warming potential for each of the compounds, which are compared with prior analyses. In addition, the latitudinal and seasonal dependence of radiative forcing since preindustrial time is calculated. The vertical profiles of the gases are found to be important in determining the radiative forcings; the use of height-independent vertical distributions of greenhouse gases, as used in many previous studies, produce errors of several percent in estimated radiative forcings for gases studied here; the errors for the short-lived compounds are relatively higher. Errors in evaluated radiative forcings caused by neglecting both the seasonal and the latitudinal distributions of greenhouse gases and atmospheres are generally smaller than those due to height-independent vertical distributions. Our total radiative forcing due to increase ill major greenhouse gas concentrations for the period 1765-1992 is 2.32 Wm(-2), only 2% higher than other recent estimates; however, the differences for individual gases are as large as 23%.