AMOC tipping risk reconsidered

The AMOC is crucial and sensitive part of the global climate system. It transports huge amounts of heat north across the equator into the northern Atlantic. It is the main reason why the Northern Hemisphere is 1 – 2 °C warmer than the Southern Hemisphere (Feulner et al. 2013) and makes Europe’s climate unusually mild for its latitude.

Due to AMOC instabilities, the northern Atlantic region has been the major hotspot of drastic climate changes in Earth’s history, as seen in data from Greenland ice cores and many other sources of paleoclimatic proxy data (Rahmstorf 2002).

The AMOC is expected to weaken strongly in response to human-caused global warming (IPCC 2021). Since Stommel (1961) and Broecker (1987) the risk of the AMOC being destabilised at a tipping point has been much discussed, especially since the emergence of a remarkable cooling patch in the subpolar gyre to the west of the British Isles (Drijfhout et al. 2012, Rahmstorf et al. 2015).

Until recently this has been considered a ‘low probability high impact risk’, to be taken seriously mainly because of the devastating impacts it would have. New research over the past years has changed this viewpoint. Neither a full AMOC shutdown nor a subpolar gyre convection collapse (also with major impacts on society) can be considered ‘low probability’ any more (e.g. Swingedouw et al. 2021, Drijfhout et al. 2025).

This talk will discuss recent scientific developments regarding the risk of AMOC instability.

 

References

Broecker, W. (1987). Unpleasant surprises in the greenhouse? Nature 328: 123.

Drijfhout, S., J. R. Angevaare, J. Mecking, R. M. van Westen and S. Rahmstorf (2025). Shutdown of northern Atlantic overturning after 2100 following deep mixing collapse in CMIP6 projections. Environmental Research Letters 20(9) doi: 10.1088/1748-9326/adfa3b.

Drijfhout, S., G. J. van Oldenborgh and A. Cimatoribus (2012). Is a Decline of AMOC Causing the Warming Hole above the North Atlantic in Observed and Modeled Warming Patterns? Journal of Climate 25(24): 8373-8379 doi: 10.1175/jcli-d-12-00490.1.

Feulner, G., S. Rahmstorf, A. Levermann and S. Volkwardt (2013). On the origin of the surface air temperature difference between the hemispheres in Earth's present-day climate. Journal of Climate 26(18): 7136-7150 doi: doi:10.1175/JCLI-D-12-00636.1

IPCC (2021). Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Geneva, IPCC. 2391 pages.

Rahmstorf, S. (2002). Ocean circulation and climate during the past 120,000 years. Nature 419(6903): 207-214 doi: 10.1038/nature01090.

Rahmstorf, S., J. E. Box, G. Feulner, M. E. Mann, A. Robinson, S. Rutherford and E. J. Schaffernicht (2015). Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation. Nature Climate Change 5(5): 475-480 doi: 10.1038/nclimate2554.

Stommel, H. (1961). Thermohaline convection with two stable regimes of flow. Tellus 13: 224-230.

Swingedouw, D., A. Bily, C. Esquerdo, L. F. Borchert, G. Sgubin, J. Mignot and M. Menary (2021). On the risk of abrupt changes in the North Atlantic subpolar gyre in CMIP6 models. Ann N Y Acad Sci 1504(1): 187-201 doi: 10.1111/nyas.14659.