Stratospheric ozone causes a negative feedback in CO2-driven climate change simulations

Ozone has been considered mainly as a contributor to climate change in terms of radiative forcing. However, it is also providing a radiative feedback when climate change is induced by, for example, a radiative forcing from CO2 increase. Interactively coupled chemistry-climate models can be used to identify and quantify this feedback. In a set of simulations forced by CO2 increase of different strength we find a negative ozone radiative feedback, which reduces the climate sensitivity compared to a model system where the ozone distribution is prescribed. Stratospheric ozone is more important than tropospheric ozone for this chemical feedback. The feedback mechanisms mainly works through intensification of the Brewer-Dobson circulation as sea surface temperature increases. The stratospheric water vapour feedback is modified by interaction with the ozone feedback, becoming less positive than in simulations with fixed ozone. Hence, a negative ozone feedback and a reduced water vapour feedback overlap constructively in CO2-driven simulations with interactive ozone, giving a global sea surface temperature response that is 4 to 10% smaller than in a corresponding simulation without interactive chemistry.