The Subpolar Gyre as Ocean–Atmosphere Bridge Between AMOC Variability and European Summer Temperature Extremes

Previous studies indicate that cooling in the Subpolar North Atlantic (SPNA), known as the “Cold Blob,” may influence European summer heat extremes. However, how internally generated ocean–atmosphere variability and anthropogenic forcing jointly shape this relationship remains poorly understood. Here, we use the 50-member Max Planck Institute Grand Ensemble (MPI-GE) under the SSP2–4.5 scenario to assess how SPNA sea surface temperature (SST) anomalies affect the likelihood of exceptionally persistent European heatwaves.

We analyze ensemble-member differences in Atlantic Meridional Overturning Circulation (AMOC)–driven heat transport, SPNA SST evolution, and associated atmospheric circulation over Europe. We find that declining AMOC heat transport enhances ocean heat divergence in the subpolar gyre, promoting SPNA surface cooling and the emergence of the Cold Blob, although the magnitude and persistence of this cooling vary strongly across ensemble members. Persistent European heatwaves are favored primarily when subpolar cooling coexists with subtropical warming, strengthening the inter-gyre SST gradient and promoting stationary large-scale pressure systems over Europe. In mid-century projections, the relationship between cold SST anomalies and heatwaves is highly sensitive to the evolving oceanic background state.

Overall, our results demonstrate that internal coupled ocean–atmosphere variability strongly modulates near-term European summer heatwave risk under climate change and identify SPNA SSTs as a promising source of seasonal-to-multiyear predictability.