We assess the effective radiative forcing due to ozone-depleting
substances using models participating in the Aerosols and Chemistry
Model Intercomparison Project (AerChemMIP). A large inter-model spread
in this globally averaged quantity necessitates an “emergent
constraint” approach whereby we link the radiative forcing to the
amount of ozone depletion simulated during 1979-2000, excluding two
volcanically perturbed periods. During this period ozone-depleting
substances were increasing, and several merged satellite-based
climatologies document the ensuing decline of total-column ozone. We use
these analyses to come up with effective radiative forcing magnitudes.
For all of these satellite climatologies we find an effective radiative
forcing outside or on the edge of the previously published “likely”
range given by the 5th Assessment Report of IPCC, implying an offsetting
effect of ozone depletion and/or other atmospheric feedbacks of -0.4 to
-0.25 Wm-2, which is in absolute terms is larger than the previous best
estimate of -0.15 Wm-2.