Pliocene subtropical hydroclimate linked to monsoon dynamics

Abstract:

Simulations of future climate project drying of the global subtropics in response to climate change. However, paleoclimatic evidence from past warm intervals, including the mid-Pliocene, or mid-Piacenzian warm period between 3.3 and 3.0 Million years ago, suggest more mesic subtropics in response to higher greenhouse gases. Previous efforts to explain past mesic subtropical conditions have focused on the role of the zonal mean Hadley circulation. Here, we synthesize proxy records and PlioMIP2 model simulations and show that mesic subtropical conditions across North Africa and Eurasia are the result of a poleward expansion of monsoon circulations. Detailed analyses of climate model simulations suggest that this zonally asymmetric monsoon expansion is driven by land surface and ice sheet feedbacks that alter surface albedo and temperatures. These results represent a new explanation for mesic subtropical conditions in the Pliocene, and emphasizes the role of zonally asymmetric adjustments of the hydrological cycle in past warm climates.