PlioMIP models shed light on key Southern Hemisphere processes

One of the most remarkable features of the mid-Pliocene climate is the polar amplified warming, which occurred at a higher magnitude in the Northern than that in Southern Hemisphere. In this study, we use the PlioMIP models, including phases one and two, to investigate how the differing rates of warming between Hemispheres affect the Southern Hemisphere climate. Through energetic constraints for the position of the Inter-Tropical Convergence Zone (ITCZ), we find that there is a consistent northward shift of the ITCZ in the mid-Pliocene, which is accompanied by intensified low-level wind circulation in the tropical and subtropical Southern Hemisphere. We show that these changes in the atmospheric circulation drive weakened South American Monsoon and South Atlantic and Pacific Convergence Zones. Additionally, we find that the mean state changes create unfavorable conditions to the development of the main tropical modes of SST variability in the Pacific and Atlantic oceans. More precisely, a northward ITCZ shift and intensified southeasterly trades winds in the equatorial Pacific reduce the probability of occurrence of extreme El-Niño events in the eastern Pacific. In the Atlantic Ocean, the ITCZ shift weakens the northeasterly trades along the African coast reducing the activity of the Atlantic Meridional Mode. Thus, the PlioMIP simulations allowed us to identify key mechanisms for important climate features under a warmer scenario.