Understanding AMOC stability: The North Atlantic Hosing Model Intercomparison Project

The Atlantic meridional overturning circulation (AMOC) is an important part of our climate system. The AMOC is predicted to weaken under climate change; however, theories suggest that it may have a tipping point beyond which recovery is difficult, hence showing quasi-irreversibility (hysteresis). Although hysteresis has been seen in simple models, it has been difficult to demonstrate in comprehensive global climate models. Here, we outline a set of experiments designed to explore AMOC hysteresis and sensitivity to additional freshwater input as part of the North Atlantic Hosing Model Intercomparison Project (NAHosMIP). These experiments include adding additional freshwater (hosing) for a fixed length of time to examine the rate and mechanisms of AMOC weakening and whether the AMOC subsequently recovers once hosing stops. Initial results are shown from eight climate models participating in the Sixth Coupled Model Intercomparison Project (CMIP6). The AMOC weakens in all models as a result of the freshening, but once the freshening ceases, the AMOC recovers in half of the models, and in the other half it stays in a weakened state. The difference in model behaviour cannot be explained by the ocean model resolution or type nor by details of subgrid-scale parameterisations. Likewise, it cannot be explained by previously proposed properties of the mean climate state such as the strength of the salinity advection feedback. Instead, the AMOC recovery is determined by the climate state reached when hosing stops, with those experiments where the AMOC is weakest not experiencing a recovery.

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Related Links	Related Dataset #1 : CCCma CanESM5 model output prepared for CMIP6 CMIP abrupt-4xCO2 Related Dataset #2 : CCCma CanESM5 model output prepared for CMIP6 CMIP historical Related Dataset #3 : CCCma CanESM5 model output prepared for CMIP6 CMIP piControl Related Dataset #4 : EC-Earth-Consortium EC-Earth3 model output prepared for CMIP6 CMIP abrupt-4xCO2 Related Dataset #5 : EC-Earth-Consortium EC-Earth3 model output prepared for CMIP6 CMIP historical Related Dataset #6 : EC-Earth-Consortium EC-Earth3 model output prepared for CMIP6 CMIP piControl Related Dataset #7 : IPSL IPSL-CM6A-LR model output prepared for CMIP6 CMIP abrupt-4xCO2 Related Dataset #8 : IPSL IPSL-CM6A-LR model output prepared for CMIP6 CMIP historical Related Dataset #9 : IPSL IPSL-CM6A-LR model output prepared for CMIP6 CMIP piControl Related Dataset #10 : MOHC HadGEM3-GC31-LL model output prepared for CMIP6 CMIP abrupt-4xCO2 Related Dataset #11 : MOHC HadGEM3-GC31-MM model output prepared for CMIP6 CMIP abrupt-4xCO2 Related Dataset #12 : MOHC HadGEM3-GC31-LL model output prepared for CMIP6 CMIP historical Related Dataset #13 : MOHC HadGEM3-GC31-MM model output prepared for CMIP6 CMIP historical Related Dataset #14 : MOHC HadGEM3-GC31-LL model output prepared for CMIP6 CMIP piControl Related Dataset #15 : MOHC HadGEM3-GC31-MM model output prepared for CMIP6 CMIP piControl Related Dataset #16 : MPI-M MPI-ESM1.2-HR model output prepared for CMIP6 CMIP abrupt-4xCO2 Related Dataset #17 : MPI-M MPI-ESM1.2-LR model output prepared for CMIP6 CMIP abrupt-4xCO2 Related Dataset #18 : MPI-M MPI-ESM1.2-HR model output prepared for CMIP6 CMIP historical Related Dataset #19 : MPI-M MPI-ESM1.2-HR model output prepared for CMIP6 CMIP piControl Related Dataset #20 : NCAR CESM2 model output prepared for CMIP6 CMIP abrupt-4xCO2 Related Dataset #21 : NCAR CESM2 model output prepared for CMIP6 CMIP historical Related Dataset #22 : NCAR CESM2 model output prepared for CMIP6 CMIP piControl Related Dataset #23 : NAHosMIP experimental protocol Related Dataset #24 : NAHosMIP data
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Author	Jackson, L. C. Alastrué de Asenjo, E. Bellomo, K. Danabasoglu, Gokhan Haak, H. Hu, Aixue Jungclaus, J. Lee, W. Meccia, V. L. Saenko, O. Shao, A. Swingedouw, D.
Publisher	UCAR/NCAR - Library
Publication Date	2023-04-06T00:00:00
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Topic Category	geoscientificInformation
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Metadata Date	2025-07-11T15:52:48.564344
Metadata Record Identifier	edu.ucar.opensky::articles:26238
Metadata Language	eng; USA
Suggested Citation	Jackson, L. C., Alastrué de Asenjo, E., Bellomo, K., Danabasoglu, Gokhan, Haak, H., Hu, Aixue, Jungclaus, J., Lee, W., Meccia, V. L., Saenko, O., Shao, A., Swingedouw, D.. (2023). Understanding AMOC stability: The North Atlantic Hosing Model Intercomparison Project. UCAR/NCAR - Library. https://n2t.org/ark:/85065/d78g8qnp. Accessed 17 August 2025.

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Understanding AMOC stability: The North Atlantic Hosing Model Intercomparison Project

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