The total average energy per unit time radiated by Earth is equal to the average energy flux j times the surface area 4&pi;R, where R is Earths radius. On the other hand, the average energy flux absorbed from sunlight is the solar constant S times Earths cross section of  &pi;R, times the fraction absorbed by Earth, which is one minus Earths albedo a'.
The average energy per unit time radiated out is equal to the average energy per unit time absorbed from sunlight, so:
giving:
Based on the value of 3.1 W/m^2 obtained above in the section on the one layer model, the radiative forcing due to CO relative to the average radiated flux is therefore:
An exact calculation using the MODTRAN model, over all wavelengths and including methane and ozone greenhouse gasses, as shown in the plot above, gives, for tropical latitudes, an outgoing flux  298.645 W/m for current CO levels and  295.286 W/m after CO doubling, i.e. a radiative forcing of 1.1%, under clear sky conditions, as well as a ground temperature of 299.7 K (26.6 Celsius). The radiative forcing is largely similar in different latitudes and under different weather conditions.