Warm ocean water melts the floating extensions of the Antarctic Ice Sheet called ice shelves. While melting of ice shelves does not contribute to sea-level rise because they are already floating, the thinning of the ice shelves that this causes reduces their ability to hold back the flow of the grounded glaciers behind them. This causes faster ice flow to the ocean and sea-level rise. Recent ocean measurements around Antarctica have shown that the ocean temperature near West Antarctica varies by a few degrees over years or decades, which may be unrelated to ocean temperature changes associated with climate change.  However, modeling studies of how much Antarctic glaciers will contribute to sea-level rise have largely ignored these short-term fluctuations.  We ran an ice sheet model of Thwaites Glacier, one of the largest glaciers in the region, that includes these short-term fluctuations in ocean temperature dozens of times to investigate if they affect how quickly the glacier retreats.  The model simulations that included the fluctuations always retreated more slowly than a run that ignored them.  Depending on the strength and frequency of the fluctuations, the delay in glacier retreat and sea-level rise was up to 10%. This delay occurs primarily because the ocean temperatures near Thwaites Glacier are already relatively warm for Antarctic conditions, and it is easier for temperature fluctuations to bring colder water to the ice shelf than it is to bring warmer water.  Our results show that short term fluctuations due to climate variability can matter to glaciers in Antarctica, and that ice sheet and climate models need to take them into account when projecting future sea-level rise.