Impacts of Ocean Circulation Changes on Regional Climate Variability
DOI:
https://doi.org/10.5281/zenodo.22816105Keywords:
Atlantic Meridional Overturning Circulation, AMOC weakening, ocean-atmosphere coupling, North Atlantic warming hole, CMIP6, SSP5-8.5, European climate variability, Southern Ocean overturningAbstract
The Atlantic Meridional Overturning Circulation (AMOC) transports heat northward through the Atlantic basin and
exerts a first-order control on North Atlantic and European climate, yet how the magnitude of projected AMOC
decline translates into regional temperature and precipitation variability across individual climate models remains
incompletely quantified. Here we analysed AMOC strength at 26.5 degrees North for 24 CMIP6 models under the
SSP5-8.5 high-emission scenario, comparing historical (1985-2014) and end-of-century (2071-2100) simulation
periods, evaluated each model's historical AMOC transport against the RAPID-MOCHA observational array before
pooling the ensemble, and related each model's projected AMOC decline to its projected regional winter
temperature and precipitation response over northwestern Europe, the British Isles, Scandinavia and the Iberian
Peninsula. The ensemble-mean historical AMOC transport was 18.4 Sverdrups, moderately biased high relative to
the RAPID-MOCHA reference mean of 17.0 Sverdrups, and the ensemble projected a mean AMOC decline of 34
percent by 2071-2100 (from 18.4 to 12.1 Sverdrups), with substantial inter-model spread (interquartile range 24 to
43 percent) but no model simulating a full circulation collapse within the twenty-first century. Projected AMOC
decline was significantly correlated across models with suppressed winter warming over the subpolar North Atlantic
(r = -0.61, p < 0.01) and with reduced winter warming over northwestern Europe and the British Isles relative to the
global-mean warming signal, while Iberian Peninsula winter temperature response showed little relationship to
AMOC decline magnitude. Models retaining active historical Labrador Sea deep convection projected significantly
larger AMOC decline (39 percent) and a more pronounced subpolar cooling signature than models with historically
weak or absent Labrador Sea convection (27 percent decline), identifying deep-convection representation as a
specific, evaluable source of inter-model projection spread. These results indicate that the magnitude of projected
AMOC weakening is a quantitatively meaningful predictor of regional winter climate response over northwestern
Europe specifically, and that narrowing uncertainty in regional temperature projections for this region is tractable
through targeted evaluation of model deep-convection representation in the Labrador Sea.
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