Australasian Hydroclimate Response to the Collapse of the Atlantic Meridional Overturning Circulation Under Pre‐Industrial and Last Interglacial Climates

Abstract Abrupt climate change events during the last glacial period and the Last Interglacial (LIG) resulted from changes in the Atlantic Meridional Overturning Circulation (AMOC). Over the last 50 years, there is some evidence that the AMOC has weakened, and it is projected to weaken further or even collapse this century driven by the increase in atmospheric greenhouse gases. However, the impact of an AMOC weakening on Australasian hydroclimate is still unclear, particularly under a climate warmer than the pre‐industrial (PI). Using the ACCESS‐ESM1.5 model, we assess the processes impacting seasonal hydroclimate in the Australasian region in response to an AMOC shutdown under PI and the LIG climatic conditions. While the broad hydroclimate response to an AMOC shutdown is similar in both experiments, notable regional differences emerge, highlighting the influence of background climate states. During austral summer (DJF), the AMOC shutdown leads to drier conditions over the Maritime Continent between S and N and increased precipitation over northern Australia under both PI and LIG conditions. However, the precipitation increase over Australia is weaker under PI than LIG. During austral winter (JJA), mid to high southern regions of Australia and New Zealand experience drying in response to the AMOC shutdown under PI boundary conditions, while under LIG boundary conditions, only southeastern Australia and New Zealand exhibit drier conditions, with northwestern Australia displaying wetter conditions. These results underscore the complex and region‐specific responses of Australasian hydroclimate to AMOC disruptions, highlighting the importance of considering background climate states when assessing such impacts.