Impacts of AMOC Collapse on Monsoon Rainfall: A Multi-Model Comparison

A collapse of the Atlantic Meridional Overturning Circulation (AMOC) would have substantial impacts on global precipitation patterns, especially in the vulnerable tropical monsoon regions. We assess these impacts in experiments that apply the same freshwater hosing to four state-of-the-art climate models with bistable AMOC. As opposed to previous results, we find that the spatial and seasonal patterns of precipitation change are remarkably consistent across models. We focus on the South American Monsoon (SAM), the West African Monsoon (WAM), the Indian Summer Monsoon (ISM) and the East Asian Summer Monsoon (EASM). Models consistently suggest substantial disruptions for WAM, ISM, and EASM with shorter wet and longer dry seasons (-29.07%, -18.76%, and -3.78% ensemble mean annual rainfall change, respectively). Models also agree on changes for the SAM, suggesting rainfall increases overall, in contrast to previous studies. These are more pronounced in the southern Amazon (+43.79%), accompanied by decreasing dry-season length. Consistently across models, our results suggest a robust and major rearranging of all tropical monsoon systems in response to an AMOC collapse. The Atlantic Meridional Overturning Circulation (AMOC) is a key element of the Earth's climate system, transporting large amounts of heat and salt northward in the upper layers of the Atlantic Ocean. Although its likelihood remains highly uncertain, a collapse of the AMOC in response to anthropogenic climate change would have catastrophic ecological and societal consequences. This is especially true in the vulnerable monsoon regions of the tropics. Yet, the precise effects of an AMOC collapse on the tropical monsoon systems remain unclear. We take advantage of a climate model intercomparison project, and provide a detailed and systematic analysis of the seasonal impacts of an AMOC collapse on the major tropical monsoon systems. We find remarkable, previously unseen, agreement between four independent state-of-the-art climate models. Consistently across models, our results suggest major rearranging of all tropical monsoon systems in response to an AMOC collapse. A collapse of the Atlantic Meridional Overturning Circulation (AMOC) would cause a major rearrangement of all tropical monsoon systems Four state-of-the-art climate models show remarkable agreement on the effects of an AMOC collapse Revealed impacts persist for at least 100 years, and so are irreversible over at least a human lifetime