Calving is a critical factor in the dynamics of marine-terminating glaciers, yet its long-term behavior remains poorly understood. Existing models calibrate calving parameters with decadal observational periods and assume they remain constant, effectively overlooking shifts in external drivers like ice mélange. We investigate calving evolution from 1981 to 2021 using a centennial reconstruction of Kangerlussuaq Glacier and identify significant calving regime changes. We show that a shift in the calving parameterization precedes corresponding changes in ice mélange, identified using Landsat data, by four years. This suggests that, while mélange may have a strong impact on calving rates on seasonal timescales, this effect does not persist over multi-decadal timescales. Long-term projections that account for variations in calving parameterization indicate that Kangerlussuaq Glacier will continue to retreat in most scenarios, with ice mass losses ranging from 220 to 1090 Gt, equivalent to 0.61 to 3.01 mm of global sea level rise.