Atmospheric Dynamics Feedback: Concept and Simulations

The regional climate response to radiative forcing is largely controlled by changes in the atmospheric circulation, e.g. Mediterranean drying due to a poleward expansion of the Hadley cell. However, global climate sensitivity also depends on the circulation response, an effect we call the "atmospheric dynamics feedback". Using a technique to isolate the effect of changes in atmospheric circulation on top-of-atmosphere radiation, we calculate the atmospheric dynamics feedback in a range of climate models for the first time. Globally averaged, atmospheric circulation changes are typically a positive feedback on climate change and contribute substantially to the intermodel spread in the equilibrium temperature response. Circulation changes at low latitudes are a robust negative feedback on climate change (a type of 'iris' effect) whereas high-latitude changes are a positive feedback. The effectiveness of low-latitude versus high-latitude circulation changes for influencing global mean temperature is tested using idealized forcing simulations, and the implications for understanding and constraining past and future climate changes are discussed.