Glaciers in western North America experience exceptional transient snowline rise over satellite era

Abstract We analyze changes in the maximum annual transient snowline elevation (M A TSL) of glaciers for two regions in western North America from 1984 to 2024 using five satellite remote sensing datasets. M A TSL reached its highest elevations in 2019 (155 m above the long-term average) for Alaska (Region 1) and in 2023 (148 m) for Western Canada and USA (Region 2). The rate of M A TSL rise accelerated fourfold, increasing from 2.1 ± 0.8 m a −1 in 1984–2010 ( r 2 = 0.1, p < 0.01) to 8.9 ± 1.7 m a −1 in 2010–2024 ( r 2 = 0.5, p < 0.01). In 2019, 91 glaciers exceeded the 95th percentile M A TSL elevation, a threshold indicative of complete loss of the accumulation area, in Region 1. In Region 2, 149 glaciers exceeded this threshold in 2023. Year-to-year variability in M A TSL was strongly influenced by mean summer air temperature with sensitivities of +46 m °C −1 ( r 2 = 0.54) and +23 m °C −1 ( r 2 = 0.30) for Regions 1 and 2, respectively. Mean spring snow water equivalent also played an important role with sensitivities of −351 mm w.e. −1 ( r 2 = 0.48) and −155 mm w.e. −1 ( r 2 = 0.37), respectively. Per-glacier analysis revealed that south-facing slopes experienced the largest M A TSL increases. Terrain attributes, including slope, aspect, hypsometry, and elevation, enhanced M A TSL prediction models compared to those using only climate variables. The pronounced rise in M A TSL underscores a critical glacier melt feedback mechanism, warranting further investigation. This study highlights the utility of automated M A TSL time-series mapping for regional-scale analyses and identifies key limitations and opportunities for future research.