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Basal hydrology of the Greenland Ice Sheet (GIS) influences its dynamics andmass balance through basal lubrication and ice–bed decoupling or efficientwater removal and ice–bed coupling. Variations in subglacial water pressurethrough the seasonal evolution of the subglacial hydrological system helpcontrol ice velocity. Near the ice sheet margin, large basal conduits aremelted by the viscous heat dissipation (VHD) from surface runoff routed tothe bed. These conduits may lead to efficient drainage systems that lowersubglacial water pressure, increase basal effective stress, and reduce icevelocity. In this study we quantify the energy available for VHDhistorically at present and under future climate scenarios. At present,345 km<sup>3</sup> of annual runoff delivers 66 GW to the base of the ice sheetper year. These values are already ∼ 50 % more than the historical1960–1999 value of 46 GW. By 2100 under IPCC AR5 RCP8.5 (RCP4.5) scenarios, 1278 (524) km<sup>3</sup> of runoff may deliver 310 (110) GW to the ice sheet base. Hence, the ice sheet may experience a 5-to-7-fold increase in VHD in the near future which will enhance opening of subglacial conduits near the margin and will warm basal ice in the interior. The other significant basalheat source is geothermal heat flux (GHF), which has an estimated value of 36GW within the present-day VHD area. With increasing surface meltwaterpenetration to the bed the basal heat budget in the active basal hydrologyzone of the GIS will be increasingly dominated by VHD and relatively lesssensitive to GHF, which may result in spatial changes in the ice flow fieldand in its seasonal variability

The past, present, and future viscous heat dissipation available for Greenland subglacial conduit formation