Using a state-of-the-art general circulation model, we examine the recovery of Arctic sea ice from prescribed ice-free summer conditions in simulations of 21st century climate. We find that after such perturbations, Arctic summer sea-ice extent returns to the original unperturbed extent within 1–3 years. The excess oceanic heat that had built during the ice-free summer is returned rapidly to the atmosphere during the following autumn and winter. The excess heat then leaves the Arctic partly through increased longwave emission at the top of the atmosphere and partly through reduced atmospheric heat advection from lower latitudes. Oceanic heat transport does not contribute significantly to the loss of the excess heat. Our results suggest that anomalous loss of Arctic sea ice during a certain single summer is reversible. Hence, hysteretic threshold behavior is unlikely to occur during the decline of Arctic summer sea-ice cover in the 21st century.