Robust Increases in Midlatitude Static Stability in Simulations of Global Warming

We examine changes in the static stability of the midlatitude troposphere in simulations of global warming using 21 coupled climate models in the AR4 archive. The dry static stability within the midlatitudes exhibits a robust increase in the simulations, with upper tropospheric warming outpacing the lower troposphere by approximately 2 K. The increase in stability is especially evident in the summer season, and is more prominent in the Southern Hemisphere than in the Northern. The moist static stability is largely unchanged, on the other hand, showing that moist convection plays a dominant role in determining the temperature structure of the midlatitudes. We compare bulk measures of the stability with changes in meridional gradients for each individual model simulation, and find that moist theories work well in predicting the stability with the primary exception of the Northern Hemisphere summer, where enhanced surface warming over land reduces the increase in stability.