Response of the General Circulation of the Atmosphere to Global Warming

We will discuss the possible response of the large-scale atmospheric structure to a warmer climate, using results from comprehensive models submitted to the CMIP5 archive, results from idealized models, and simpler physical arguments. We try to identify what changes are likely to be robust and what the underlying mechanisms might be. Overall, the results suggest that changes that involve the 'dynamics' are less robust (in a sense that will be explained) than results that follow directly from thermodynamic and/or radiative effects.

In particular, analytic arguments and numerical calculations that suggest that under global warming the height of the tropopause will increase in both the transient response and final equilibrium state, and an increase is clearly found in all the comprehensive models in CMIP5 Upper stratosphere cooling can also be explained by an analytic argument.

Many models show an expansion and weakening of the Hadley Cell, and a poleward shift of the midlatitude jets. However, the intermodal scatter is large and there is no single compelling argument that explains the results. Although the dynamical changes associated with the circulation appear less robust we cannot conclude they are unknowable or unpredictable.