Extremely Warm European Summers predicted more accurately by considering Sub-Decadal North Atlantic Ocean Heat Accumulation

In the past decades European summers were marked by extreme heat, marking the most severe warm seasons of temperature records. In particular, in 2003, 2018, and 2022, Europe experienced unprecedented extreme temperatures with temperature anomalies exceeding 2.5 standard deviations. The prolonged heat affected human health, agriculture, economy, and our whole ecosystem, highlighting the need for reliable climate predictions. By using the Max-Planck-Institute Earth System Model, we demonstrate that these extreme summers could have been predicted at least three years in advance by taking into account the preceding sub-decadal variations of heat content in the North Atlantic Ocean. By using a subset of ensemble members that can explicitly include the heat accumulation in the North Atlantic, the prediction skill of physical states, i.e. temperature could be improved, but also user-specific quantities in the agricultural sector, such as growing degree days, for both, Europe-wide and smaller scales for certain regions and specific growing degree day thresholds for crop harvests. These findings underscore the value of incorporating sub-decadal oceanic processes into user-relevant climate prediction methodologies. We demonstrate that the agricultural sector particularly benefits from improved predictions for growing degree days which allow for timely adaption and preparation against extreme heat.