Wetter subtropics in a warmer world: Contrasting past and future hydrological cycles

Significance The subsiding flow of the atmospheric Hadley circulation controls dry conditions over vast subtropical bands where the main arid regions of the globe reside. In the context of future changes in the atmospheric hydrological cycle, understanding precipitation changes in the subtropics is of particular importance given the scarcity of water resources in these locations. A major puzzle arises when contrasting the drier conditions in the subtropics predicted by climate models under global warming scenarios against the wetter conditions seen in reconstructions of past warm climates, including the warm, ∼400 ppm CO 2 , Pliocene. Our modeling results address this puzzle and highlight the importance of correctly predicting how the meridional temperature gradient between the tropics and the subtropics will change with global warming.