Europe’s latest summer heatwaves have produced some highly visible energy disruptions. Nuclear reactors have reduced output as rivers became too warm or too shallow for cooling. Drought has constrained hydropower, and low water levels have disrupted fuel transport on the Rhine. None of these effects is unprecedented. More significant is their potential to occur concurrently, while extreme temperatures simultaneously increase electricity demand. The question now is which risks could materially alter assumptions about Europe’s future energy systems?