Significance Mass loss from the Greenland Ice Sheet is expected to be a major contributor to 21st Century sea-level rise, but projections retain substantial uncertainty due to the challenges of modeling the retreat of the tidewater outlet glaciers that drain from the ice sheet into the ocean. Despite the complexity of these glacier–fjord systems, we find that over a 20-y period much of the observed tidewater glacier retreat can be explained as a predictable response to combined atmospheric and oceanic warming, bringing us closer to incorporating these effects into the ice sheet models used to predict sea-level rise.