Climate change induced by equatorial superrotation

Understanding the potential reorganizations of the large-scale atmospheric circulation in the tropics is important in the context of anthropogenic climate change and from a theoretical point of view, but also because they might be connected with warm climates of the past. A particularly spectacular, albeit hypothetical, example of such a reorganization is the case of equatorial superrotation, characterized by strong westerly winds at the equator. While potential dynamical processes underlying a transition to equatorial superrotation have been studied to some extent, the question of how the circulation changes would be coupled to the broader climate features has not yet been addressed. In this work, we adopt this perspective and investigate the consequences of such a circulation change on Earth's surface climate and hydrological cycle.

Using general circulation model (GCM) simulations in an aquaplanet setup with an imposed equatorial torque to force superrotation in the atmosphere, we observe large changes in the surface temperature and precipitation distribution. The results show an important global surface warming, comparable to a doubling of the CO₂ concentration, which affects in particular regions outside of the tropics, such as the mid-latitudes. In addition, the meridional structure of the precipitation profile becomes flatter; the tropics become drier and the subtropics wetter. These changes are strongly linked to the effect of the circulation changes on the meridional transport of energy and moisture. We analyze these changes and the associated radiative budget changes using a forcing/feedback framework.

Overall, this study demonstrates that equatorial superrotation can have a significant impact on the surface climate, independently of any external radiative forcing. This provides further evidence that such major changes in the large scale circulation might be relevant for warm climates of the Earth, in the past or in the future.