Southern Alps equilibrium line altitudes: four decades of observations show coherent glacier–climate responses and a rising snowline trend

Abstract An end of summer snowline (EOSS) photographic dataset for Aotearoa New Zealand contains over four decades equilibrium line altitude (ELA) observations more than 50 index glaciers. This provides an opportunity to create a climatological ELA reference series that has several applications. Our work screened out EOSS sites had low temporal coverage and also removed limited when the official survey did not take place. Snowline data from 41 glaciers in were retained included normalised master spans 1977–2020. Application regionally representative monthly seasonally resolved climate response function analyses showed consistently strong relationships with austral warm-season temperatures land-based stations west Southern Alps central Tasman Sea. There is trend towards higher regional snowlines since 1990s been steepening recent decades. If contemporary decadal trends are maintained, average elevation will be displaced at least 200 m normal by 2025–2034 decade. More frequent extremely high expected drive extreme cumulative mass-balance losses reduce glacierised area Zealand.