Ozone radiative feedback in global warming simulations with CO2 and non-CO2 forcing

Abstract

It has been found that ozone radiative feedback acts to reduce the climate sensitivity in global warming simulations including interactive atmospheric chemistry, if the radiative forcing origins from CO2 increase. The effect can be traced to a negative feedback from stratospheric ozone changes and it is amplified by a reduced positive feedback from stratospheric water vapor. These findings cannot be simply transferred to simulations in which the warming is driven by a non-CO2 radiative forcing. Using a perturbation of surface NOx and CO emissions as an example, it can be demonstrated that a tropospheric ozone feedback may have significant impacts on physical feedbacks. These interactions can act to an extent that the effect of a negative ozone feedback can be reversed by changes in other feedbacks, thus increasing the climate sensitivity instead of reducing it. We also address some conceptual issues showing up as chemical feedbacks are added to set of physical feedbacks in simulation with interactive chemistry.