A weakened AMOC warms winters and drives summer multidecadal variability over Europe

The Atlantic Meridional Overturning Circulation (AMOC) is a key regulator of global climate and has been a subject of major scientific interest. Observational studies have raised concerns about its ongoing weakening and potential collapse this century. While climate models generally show an overall cooling over Europe as a result of this weakening, confirmation based on observations is lacking due to difficulties in assessing causality in data. Here, we overcome this problem by constructing causality maps and tracking AMOC’s impact over Europe in observations. First, the causal link between AMOC and its SST fingerprint is established. Then, decomposing the SST fingerprint of AMOC into a decreasing centennial trend and a multidecadal oscillation (AMO), we find the trend impacts only winter and AMO only summer. In winter, the weakening warms north-central Europe and increases northern precipitation, with no overall cooling being observed nor expected. In summer, AMO induces multidecadal oscillations in temperature and precipitation. These quantitative results can be an observational benchmark for future model simulations, inform policy making, and national security.