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Abstract The difference between North Atlantic subpolar gyre sea surface temperatures (SPG SSTs) and hemispheric‐ or global‐scale surface temperatures has been utilized as an index of centennial‐timescale changes in Atlantic Meridional Overturning Circulation (AMOC) strength. Here, using Community Earth System Model ensembles, we show that surface temperature‐based indices (STIs) proposed to date largely reflect global‐scale temperature trends and thus do not reflect dynamical relationships with AMOC. More broadly, we find that relationships between STIs, SPG SSTs, and AMOC strength differ greatly in significance and magnitude over different time periods because they are dependent upon the nature of external forcing. In the twentieth century, characterized by offsetting greenhouse gas and aerosol forcing, the relationship between SSTs and AMOC strength varies widely and changes sign across a 20‐member ensemble. We conclude that STIs and SPG SSTs are poor predictors of centennial‐timescale AMOC strength variations.
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Slowed Response of Atlantic Meridional Overturning Circulation Not a Robust Signal of Collapse
Abstract Using an idealized model of the Atlantic meridional overturning circulation (AMOC), we test whether changes in the statistical properties of an AMOC time series can reveal Critical Slowing Down (CSD) and serve as early warnings of an upcoming critical transition. We calculate CSD indicators for simulations across varying parameter regimes, investigating the system's steady‐state dynamical structure and its evolution under gradual climate forcing. We find that the modeled AMOC features bistability for relatively weak gyre salinity exchange, but no bistability when the gyres are sufficiently strong. However, CSD indicators consistently warn of a collapse across the gyre strength parameter space, even when no bifurcations occur, thus raising false alarms. We argue that CSD should be applied cautiously in systems where the dynamical structure and physical response to forcing are not fully known (such as the AMOC), specifically where it is not a priori clear whether the system is in a multistable regime.
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- PAR ID:
- 10576514
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 52
- Issue:
- 2
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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