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Abstract Paleoclimate records indicate substantial decreases in precipitation associated with the South Asian monsoon in response to Atlantic meridional overturning circulation (AMOC) perturbations, yet the underlying mechanisms remain poorly understood. In this study, we investigate the impacts of a collapsed AMOC on the South Asian monsoon using a suite of North Atlantic freshwater hosing simulations conducted with the NCAR Community Earth System Model, version 1 (CESM1), global climate model under preindustrial conditions. Our results show that a weakened AMOC leads to reduced monsoon rainfall and a southward shift of the Southern Hemisphere branch of the intertropical convergence zone (ITCZ). We also see a substantial increase in precipitation over the Indochina Peninsula, driven by enhanced winds across the Bay of Bengal. We show that these responses cannot be explained by global energy budget arguments and instead propose a local dynamical mechanism in which enhanced winds over the Bay of Bengal increase orographic precipitation across the Indochina Peninsula. These findings have important implications for both projections of future AMOC weakening or collapse under continued anthropogenic warming and for interpreting paleoclimate records of past monsoon variability. Significance StatementThis study explores how the South Asian monsoon responds to a collapse of the Atlantic meridional overturning circulation (AMOC), a large-scale ocean circulation system in the climate system. This is important because climate models project that the AMOC will weaken due to increased anthropogenic warming. While much work has been done on how tropical precipitation changes at global scales, fewer studies have focused on local basins or monsoon systems. We find that the South Asian monsoon weakens in response to an AMOC collapse. However, we also show that the current leading framework of energy budget theory cannot fully explain the regional changes around the Indian Ocean. In particular, there is an increase in precipitation over the Bay of Bengal and the Indochina Peninsula which is driven by local dynamics rather than global energy shifts. These findings highlight the need for region-specific analysis and may help guide future research, including the interpretation of past climate records in this region.
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This content will become publicly available on March 1, 2027
Multi‐Stability of the Present‐Day Atlantic Meridional Overturning Circulation
ABSTRACT The Atlantic Meridional Overturning Circulation (AMOC) plays a key role in the climate system, especially in the global meridional heat transport. Historical reconstructions indicate that the AMOC has weakened by about 15% since the mid‐20th century. Paleoclimate records, ocean theory, as well as a hierarchy of climate models suggest that the AMOC is a tipping element, sensitive to changes in buoyancy fluxes at the air‐sea interface, and could transition into a substantially weaker or fully collapsed state. Such a transition would have significant climate impacts on decadal to centennial timescales, potentially exceeding societal adaptability. Assessing the probability of such a transition, particularly before 2100, requires evaluating whether a collapsed AMOC state is possible under current forcing conditions. While conceptual and intermediate‐complexity models have long identified collapsed states, comprehensive global climate models have only recently done so. Based on integrating model diagnostics with observations and current AMOC theory this review article critically evaluates the current arguments for and against the evidence of a multi‐stable AMOC regime. We conclude that the evidence base in favor of such a regime has broadened over the last years and that the present‐day AMOC is in such a regime. This article is categorized under:Paleoclimates and Current Trends > Modern Climate ChangePaleoclimates and Current Trends > Earth System BehaviorClimate Models and Modeling > Knowledge Generation with Models
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- Award ID(s):
- 2421170
- PAR ID:
- 10676878
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- https://doi.org/10.1002/wcc.70049
- Date Published:
- Journal Name:
- WIREs Climate Change
- Volume:
- 17
- Issue:
- 2
- ISSN:
- 1757-7780
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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