Observational constraints imply limited future Atlantic meridional overturning circulation weakening
Abstract
The degree to which the Atlantic meridional overturning circulation (AMOC) weakens over the twenty-first century varies widely across climate models, with some predicting substantial weakening. Here we show that this uncertainty can be greatly reduced by using a thermal-wind expression that relates the AMOC strength to the meridional density difference and the overturning depth in the Atlantic. This expression captures the intermodel spread in AMOC weakening, with most of the spread arising from overturning depth changes. The overturning depth also establishes a crucial link between the present-day and future AMOC strength. Climate models with a stronger and deeper present-day overturning tend to predict larger weakening and shoaling under warming because the present-day North Atlantic is less stratified, allowing for a deeper penetration of surface buoyancy flux changes, larger density changes at depth and, consequently, larger AMOC weakening. By incorporating observational constraints, we conclude that the AMOC will experience limited weakening of about 3–6 Sv (about 18–43%) by the end of this century, regardless of emissions scenario. These results indicate that the uncertainty in twenty-first-century AMOC weakening and the propensity to predict substantial AMOC weakening can be attributed primarily to climate model biases in accurately simulating the present-day ocean stratification.
Copyright and License
© 2025 Springer Nature Limited.
Acknowledgement
This work was supported by the National Science Foundation (NSF) Graduate Research Fellowship Program under NSF Award DGE1745301 (D.B.B.), the Cooperative Institute for Climate, Ocean, and Ecosystem Studies (CICOES) under NOAA Cooperative Agreement NA20OAR4320271, Contribution No. 2025-1450 (D.B.B.), the David and Lucile Packard Foundation and NSF Award OCE-1756956 (A.F.T.), Schmidt Sciences, LLC (T.S. and L.Z.), and NSF Awards OCE-1850900 and AGS-1752796 (K.C.A.).
Data Availability
We thank the climate modelling groups for producing and making available their model output, which is accessible on the Earth System Grid Federation (ESGF) Portal (https://esgf-node.llnl.gov/search/cmip6/).
Code Availability
The code needed to calculate the overturning depth scale is available on Zenodo at https://doi.org/10.5281/zenodo.15103083 (ref. 53).
Additional details
- National Science Foundation
- DGE-1745301
- National Oceanic and Atmospheric Administration
- NA20OAR4320271
- David and Lucile Packard Foundation
- National Science Foundation
- OCE-1756956
- Schmidt Sciences, LLC
- National Science Foundation
- OCE-1850900
- National Science Foundation
- AGS-1752796
- Accepted
-
2025-04-25
- Available
-
2025-05-29Published
- Caltech groups
- Division of Geological and Planetary Sciences (GPS)
- Publication Status
- Published