Abstract. Changes in surface albedo represent one of the main forcing agents that can counteract, to some extent, the positive forcing from increasing greenhouse gas concentrations. Here, we quantify the changes in ocean surface albedo from ship wakes and provide an estimate of radiative forcing over the global oceans. Our analysis is based on airborne radiation measurements over the Pacific Ocean near the California coast, where we determined that a ship wake increases reflected sunlight by more than 100% in some cases. Based on registered ships of 100 000 gross tonnage (GT), and assuming a global distribution of 30 000 ships, we estimated the global radiative forcing of ship wakes to be −0.003 Wm⁻², which is comparable to the forcing of aircraft contrails, but not anticipated in the Intergovernmental Panel on Climate Change (IPCC) 2007 assessment report. From these results, we conclude that the climate impacts associated with ships will become more significant with growing ship traffic.