Resolving short-term meteorological variability amplifies projected glacier loss and sea-level rise.

Global glacier models typically rely on temperature-index mass balance calculations forced with aggregated meteorological data, limiting their ability to resolve short-term variability. Here, we develop a daily-resolution version of the Global Glacier Evolution Model (GloGEM), which we apply globally and compare against the monthly configuration. Our results show that the daily model more closely reproduces mass balance observations and provides a more detailed representation of glacier runoff. Accounting for short-term meteorological variability leads to systematically greater projected mass loss, with up to 25% greater loss in Svalbard. These differences arise from extreme melt days, precipitation-phase transitions, and surface-type feedbacks not fully represented at monthly resolution. Globally, the daily model yields ice volume losses of 26 ± 10% under low-emission and 47 ± 17% under high-emission scenarios over 2025-2100 (ensemble mean ± 1 StD), resulting in an additional 5-10% mass loss (20-33 mm of global mean sea-level rise) relative to the monthly implementation. Resolving high-frequency forcing, or accounting for its effects through parameterisations, is therefore essential for robust glacier projections, while its omission may systematically underestimate future glacier loss.