Glacier Equilibrium‐Line Altitude Change Across Alaska and Adjacent Canada Indicates a Cold, Dry Little Ice Age and Weaker Aleutian Low

As Arctic warming accelerates, understanding hydroclimate shifts is key to projecting glacier melt and sea‐level rise. We assess the climatic signature of the Little Ice Age (LIA; ∼1250 to 1900) by quantifying changes in equilibrium‐line altitude (ΔELA) for 215 Alaskan glaciers from the LIA maximum to present (2016–2024), using remote sensing and geographic information system methods. ELAs have risen by 170 ± 8 m, equivalent to 1.6 ± 0.3°C summer warming (assuming constant precipitation) or 248 ± 89 mm w.e. annual precipitation increase (assuming 2.3°C warming). The latter is ∼4X the precipitation change observed since 1950. Glacier morphology and topographic setting explain 32% of ΔELA variance, likely reflecting differing sensitivities to climatic shifts and elevation‐dependent warming. Spatially interpolated ΔELA residuals are most strongly correlated to winter precipitation ( r  = −0.67). Results suggest the LIA was characterized by (a) colder, drier conditions and (b) a weak, westward‐displaced Aleutian Low that has since strengthened and shifted eastward. Plain Language Summary Glaciers respond sensitively to changes in climate, particularly to shifts in temperature and precipitation. In this study, we measured how much the altitude of the glacier equilibrium line (the boundary between snow accumulation and melt) has changed since the Little Ice Age (LIA), a cool period from year ∼1250–1900. Across 215 glaciers in Alaska, the equilibrium line has risen by an average of ∼170 m. This change is roughly equivalent to ∼1.6°C of summer warming or an increase of ∼250 mm in annual precipitation. Factors such as glacier orientation, slope, and topographic setting (elevation), explain about one‐third of the variation in how much equilibrium lines have shifted, likely reflecting differences in glacier sensitivity to climate changes and stronger warming at higher elevations. After accounting for these effects, the remaining changes correlate more strongly with climate variables, particularly with winter precipitation. Overall, the magnitude and spatial pattern of equilibrium line shifts across Alaska indicate (a) climate during the LIA was colder and drier than today, consistent with a positive coupling between temperature and precipitation over the past several centuries, and (b) a weaker, westward‐shifted Aleutian Low pressure system during the LIA, which has since strengthened and migrated eastward. Key Points Alaskan glacier equilibrium lines have risen at least ∼170 m since the Little Ice Age (LIA) maximum, with the largest shifts in the southeast Glacier morphology and setting explain ∼32 % of equilibrium‐line variance reflecting differing sensitivities and elevation‐dependent warming The LIA was overall cooler and drier; regional precipitation shifts are consistent with a weaker, westward Aleutian Low