Analysis of radiative feedbacks in model simulations including interactive chemisty

Including interactive atmospheric chemistry in climate change simulations may have a significant impact on the climate sensitivity. In CO2-driven simulations the climate sensitivity has been found to be reduced. The reason is a negative feedback from stratospheric ozone (absent from models without chemistry), which is amplified by reducing the positive feedback of stratospheric water vapor. A complete feedback analysis reveals that other physical feedbacks, in particular the cloud radiative feedback, are also modified by the presence of chemical interactions. This feature may be more pronounced in climate change simulations driven by non-CO2 radiative forcings. In such cases the change of conventional (physical) radiative feedbacks could even overcompensate the direct feedback effect from changes of interactive chemical tracers. It will also be emphasized that further methodological developments to radiative feedback analysis are called for, in order to interpret the feedbacks arising in chemistry-climate models in a proper cause and effect sense.