Drier tropical and subtropical Southern Hemisphere in the mid-Pliocene Warm Period
Gabriel M. Pontes, Ilana Wainer, Andréa S. Taschetto, Alex Sen Gupta, Ayako Abe‐Ouchi, Esther C. Brady, Wing‐Le Chan, Deepak Chandan, Camille Contoux, Ran Feng, Stephen J. Hunter, Yoichi Kame, Gerrit Lohmann, Bette L. Otto‐Bliesner, W. R. Peltier, Christian Stepanek, Julia C. Tindall, Ning Tan, Qiong Zhang, Zhongshi Zhang
Abstract
Thermodynamic arguments imply that global mean rainfall increases in a warmer atmosphere; however, dynamical effects may result in more significant diversity of regional precipitation change. Here we investigate rainfall changes in the mid-Pliocene Warm Period (~ 3 Ma), a time when temperatures were 2-3ºC warmer than the pre-industrial era, using output from the Pliocene Model Intercomparison Projects phases 1 and 2 and sensitivity climate model experiments. In the Mid-Pliocene simulations, the higher rates of warming in the northern hemisphere create an interhemispheric temperature gradient that enhances the southward cross-equatorial energy flux by up to 48%. This intensified energy flux reorganizes the atmospheric circulation leading to a northward shift of the Inter-Tropical Convergence Zone and a weakened and poleward displaced Southern Hemisphere Subtropical Convergences Zones. These changes result in drier-than-normal Southern Hemisphere tropics and subtropics. The evaluation of the mid-Pliocene adds a constraint to possible future warmer scenarios associated with differing rates of warming between hemispheres.