We identify subdecadal variations in European summer temperatures in coupled and uncoupled century-long reanalyses. Spectral analyses reveal significant peaks at 5-10 years in the midtwentieth century. The subdecadal variations show substantial amplitudes of~1-1.5°C, associated with extremely warm summers during their positive phases. We use forced ocean model experiments and show that the European summer temperature variations are associated with the subdecadal coupled North Atlantic climate system. A positive winter NAO-like forcing is associated with changes in the ocean circulation and mass and heat convergence occurring 1-2 years prior to European summer temperature rise. Ocean heat content and sea surface temperature increase in the subtropical North Atlantic. The atmospheric response is barotropic and induces wave activity fluxes toward the European continent, modulation of the jet positions, and blocking frequency. The atmospheric response establishes a pathway connecting the subdecadal coupled North Atlantic climate system to European summer temperature.