Radiation change in w/m2 at the top of the troposphere due to a forcing agent. Increase of snow in polar regions produces a negative radiative forcing. A doubling of co2 concentrations produces a positive radiative forcing: positive radiative forcing produces a warming response, negative radiative forcing produces a cooling response. The ipcc has undertaken a comprehensive assessment of the globally averaged radiative forcing associated with all forcing agents that might have affected earth"s energy balance since 1750. Co2 produces the largest positive radiative forcing (1. 68 w/m2) Ch4 produces the second largest radiative forcing (~1 w/m2) The total positive radiative forcing of greenhouse gases is ~3w/m2. Radiative forcing associated with chemical pollutants: these pollutants spend a relatively short time in the atmosphere, compare their net effect on global radiative forcing with those of well mixed greenhouse gases. Aerosols increase more sites for water vapor condensation.