Accelerated mass loss of glaciers across Alaska since the Little Ice Age

Abstract Alaskan glaciers presently dominate contributions to global glacier mass loss and are projected to do so throughout the 21 st Century. Here we assess centennial-scale evolution and mass loss of 5289 Little Ice Age (LIA) glaciers by mapping geomorphological evidence of glacier extent and by reconstructing ablation area ice surfaces. We find that Alaskan glaciers have experienced extensive fragmentation and have lost at least 19 ± 2.8% total area since the local LIA maximum (year 1810) to year 2008. Individual glaciers had a median area loss of 32 ± 4.7%. Our ice surface reconstruction for LIA glacier ablation areas leads to a total volume loss estimate of at least 3345 ± 836 km 3 , equating to a mass loss of at least 2844 ± 711 Gt and a sea level equivalent of 8 ± 2 mm. Glacier mass balance since the LIA to 2008 was − 0.09 ± 0.02 m w.e. yr − 1 , which, compared with − 0.67 ± 0.13 m w.e. yr − 1 between 2000 and 2019, suggests a 7.4 ± 2.0 times acceleration across Alaska. Three quarters of Alaskan mountain regions shifted from near equilibrium mass balance between the LIA and 2008 (c. − 0.01 m w.e. yr − 1 ) to substantial mass loss (more negative than − 0.7 m w.e. yr − 1 ) between 2000 and 2019. Our Glacier Bay LIA icefield reconstruction evidences the greatest fragmentation, area, volume and mass loss of any known single LIA glacier globally. Our mapping, glacier reconstructions and mass loss findings will serve glacier evolution modelling, inform proglacial systems analysis, and support ecosystem services management especially within protected areas.