Radiative forcings and global warming potentials of 39 greenhouse gases

The radiative forcings and global warming potentials for 39 greenhouse gase s are evaluated using narrowband and broadband radiative transfer models. U nlike many previous studies, latitudinal and seasonal variations are consid ered explicitly, using distributions of major greenhouse gases from a combi nation of chemical-transport model results and Upper Atmosphere Research Sa tellite (UARS) measurements and cloud statistics from the International Sat ellite Cloud Climatology Project. The gases examined include CO2, CH4, N2O, plus a number of chlorofluorocarbons, hydrochlorofluorocarbons, hydrofluor ocarbons, hydrochlorocarbons, bromocarbons, iodocarbons, and perfluorocarbo ns (PFCs). The model calculations are performed on a 5 degrees latitude gri d 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 t he compounds, which are compared with prior analyses. In addition, the lati tudinal and seasonal dependence of radiative forcing since preindustrial ti me is calculated. The vertical profiles of the gases are found to be import ant in determining the radiative forcings; the use of height-independent ve rtical distributions of greenhouse gases, as used in many previous studies, produce errors of several percent in estimated radiative forcings for gase s studied here; the errors for the short-lived compounds are relatively hig her. Errors in evaluated radiative forcings caused by neglecting both the s easonal and the latitudinal distributions of greenhouse gases and atmospher es are generally smaller than those due to height-independent vertical dist ributions. 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%.