[LINK] Likelihood on an AMOC shutdown

[Antony Barry]

This link summarises a paper which warns of an AMOC shutdown over a multi-decadal timescale. https://www.brief.news/climate-change/2025/10/26/atlantic-current-faces-collapse?categories=AI&categories=Climate+change&date=2025-10-27&utm_source=daily-brief&utm_medium=email&source=%2Femail&uid=clncfg0vj001es610d6r44diy&eid=A02kiG0hwH

I got Perplexity AI to do its own summary (below) of the original paper for comparison.
	
Summary of the paper “Shutdown of northern Atlantic overturning after 2100 following deep mixing collapse in CMIP6 projections”:
This study examines the long-term projections from recent CMIP6 climate models, focusing on the Atlantic Meridional Overturning Circulation (AMOC). The authors find that, especially under high greenhouse gas emission scenarios (SSP585), all extended model runs predict a drastic weakening and eventual shutdown of the northern AMOC after the year 2100. This shutdown is often preceded by a collapse of deep ocean mixing in the Labrador, Irminger, and Nordic Seas—primarily due to reduced northward salt transport and increased surface warming—triggering a “tipping point” after which recovery would take centuries (if at all). Even some intermediate (SSP245) and low-emission (SSP126) scenarios show this effect in several models.

Major findings and implications:
AMOC Shutdown Mechanism: The shutdown is linked to a dramatic loss of deep convection and mixing in the North Atlantic, leading to a shallower, weaker overturning cell. The process is driven mainly by reduced salinity from less northward salt transport and is triggered by surface warming.
Climate Impacts: This results in drastically decreased northward heat transport and much reduced ocean heat release north of 45°N, potentially causing strong surface cooling in the subpolar North Atlantic and northwestern Europe—unless overwhelmed by greenhouse-gas-induced global warming.
Timescale: The transition unfolds over several decades to a century, so it does not meet the IPCC definition of “abrupt” collapse, but represents a terminal, long-term shift.
Early Signs: Observations already show a declining trend in deep mixing across the key regions, though internal variability is still dominant.
Model Uncertainty: Models may underestimate risk due to neglecting Greenland meltwater, biases, and insufficient resolution of ocean eddies and mixing.
Risk Assessment: The risk of a northern AMOC shutdown is higher than assumed in past IPCC assessments, even in some lower-emission scenarios.
Conclusion: The study concludes that the potential for a major, long-term weakening or shutdown of the northern AMOC is significant under continued climate change, highlighting a climate tipping point with widespread implications for Europe and the global climate system. The results suggest that IPCC risk assessments may need to be revised upward.
https://iopscience.iop.org/article/10.1088/1748-9326/adfa3b
Antony Barry
antonybbarry at gmail.com