Multi-model evidence of future tropical Atlantic precipitation change modulated by AMOC decline

Abstract: Projections from global climate models reveal a significant inter-model spread in future rainfall changes in the tropical Atlantic by the end of the 21st century, including alterations to the Intertropical Convergence Zone (ITCZ) and monsoonal regions. While existing studies have identified various sources of uncertainty, our research uncovers a prominent role played by the decline of the Atlantic Meridional Overturning Circulation (AMOC) for the inter-model spread. Firstly we examine 30 climate model simulations (using the ssp5-8.5 scenario) from the CMIP6 archive and show that models that present a more substantial AMOC decline exhibit an equatorward shift of the ascending branch of the Atlantic regional Hadley circulation, resulting in a southward displacement of the ITCZ. Conversely, models characterized by a smaller AMOC decline do not indicate any ITCZ displacement. Secondly, we use targeted experiments (using the abrupt 4xCO2 experiment) to specifically isolate the effects of a weakened AMOC from the changes in precipitation that would occur if, under continuous global warming, the AMOC did not weaken. Our results demonstrate that net precipitation anomalies in the abrupt 4xCO2 experiments are displaced southwards compared to the simulation with fixed AMOC strength, corroborating our previous findings. Our study has implications for understanding the mechanisms driving future changes in tropical Atlantic precipitation, and underscores the central role played by the AMOC in future climate change.