Inhomogeneous radiative forcing of homogeneous greenhouse gas

Abstract:

Radiative forcing of a homogeneous greenhouse gas can be very inhomogeneous because the forcing is dependent on other atmospheric and surface variables. In the case of doubling CO₂, the forcing values can vary geographically from negative to positive values, with the range being a few times the magnitude of the global mean forcing. The factors that cause the forcing to vary are investigated here. The temperature change across the atmospheric column (temperature lapse rate) is found to be the factor that explains most clear-sky forcing variation (R²>0.9), while cloud radiative forcing is an especially good predictor of the difference between clear-sky and all-sky forcing (R²>0.99). A linear regression model is constructed for estimating CO₂ forcing from geophysical variables and is tested using independent data. The inhomogeneity of CO₂ forcing has important implications for climate change. The effects of forcing distribution on planetary scale energy transport, circulation (Walker Cell) adjustment, and precipitation will be discussed and compared to the effects of the overall and individual feedbacks.