Using an analytical convective quasi-equilibrium (QE), first-baroclinic mode framework, we relate changes in the circulation to changes in tropopause height and in the zonal tropospheric temperature gradient (ZTG). In this framework, a robust increase in tropopause height strengthens zonally asymmetric circulations as climate warms. Circulation strength also increases with the ZTG, but the ZTG can either weaken or strengthen with a global warming, depending on surface properties. A simple QE closure that relates the ZTG to near-surface thermal properties is used to express stationary circulation changes with global warming in terms of surface boundary conditions and radiative-convective properties of the tropical atmosphere.
We demonstrate the relevance of this mechanism in an idealized moist GCM integrated over a wide range of climates, as well as in a large ensemble of comprehensive climate simulations of a 21st century global warming scenario. Our first-baroclinic mode theory provides a novel and dynamically based understanding of stationary circulation sensitivity to climate change, complementing existing energetic constraints of the tropical circulation.