Depth of Convection and the Weakening of Tropical Circulation in Global Warming

Anthropogenic forcings, such as greenhouse gases and aerosols, are starting to show their influence on the climate, as evidenced by a global warming trend observed in the past century. The weakening of tropical circulation, a consequence of global warming, has also been found in observations and in twenty-first-century climate model simulations. It is a common belief that this weakening of tropical circulation is associated with the fact that global-mean precipitation increases more slowly than water vapor. Here, a new mechanism is proposed for this robust change, which is determined by atmospheric stability associated with the depth of convection. Convection tends to extend higher in a warmer climate because of an uplifting of the tropopause. The higher the convection, the more stable the atmosphere. This leads to a weakening of tropical circulation.