The impact of AMOC weakening on the global monsoon in EC-Earth3 water hosing simulations

Abstract

Changes in Atlantic Meridional Overturning Circulation (AMOC) affect tropical precipitation through the coupling with the Hadley Circulation and cross-equatorial atmospheric heat transport. Climate model simulations project a possible weakening of the AMOC under global warming. Here, we run model experiments with EC-Earth3 where we artificially weaken the AMOC through the release of a freshwater anomaly at high latitudes. The simulated AMOC collapse of ~57% for 60 model years allows us to investigate atmospheric heat and circulation readjustment to AMOC weakening and impacts on tropical precipitation, including the global monsoon. We find that the Inter Tropical Convergence Zone (ITCZ) shifts equatorward and tropical precipitation decreases over its northern flank while it increases southward due to reduced northward oceanic heat transport. Global monsoon is also impacted by AMOC weakening: Northern/Southern Hemisphere monsoons are weaker/stronger than the control experiment, with different sensitivities according to different regions: monsoons systems in the Atlantic sector are strongly impacted by AMOC decline. We further explore interbasin anomalies in the zonal/meridional atmospheric heat transport and net energy input triggered by the AMOC decline by examining local Hadley and Walker circulation asymmetries. Given that a ~57% reduction in the AMOC strength is within the inter-model range of future projections by the end of the 21st century, our results have important implications for understanding the role of AMOC in future tropical precipitation response.