How High Is Too High? Freezing Level Height as an Essential Indicator of Glacier-Climate Regime Shifts

Abstract

Tropical glaciers are rapidly retreating under anthropogenic global warming, posing significant hydrological, ecological, and socio-environmental risks. In this commentary, I show that the freezing level height (FLH) is a robust, yet underutilized, indicator of glacier regime change in the tropical Andes. Building on recent work by Turner et al. (2025, https://doi.org/10.1029/2024jd042963), I argue that the strong association between FLH and glaciers' equilibrium line altitude (ELA) offers a simplified and simultaneously physically meaningful tool to anticipate glacier responses to atmospheric warming. Turner et al. (2025, https://doi.org/10.1029/2024jd042963) used FLH data from reanalysis and Coupled Model Intercomparison Project version model output to project 21st century ELA trajectories under two shared socioeconomic pathways (SSP2-4.5 and SSP5-8.5), predicting a nearly unabated rise in the ELA across studied regions, regardless of the emission scenario. While some observational constraints remain, the findings are applicable to most existing tropical glacier regimes. Importantly, rising FLH reflects a transition from humidity- to temperature-driven mass balance, activating a cascade of positive feedbacks that accelerate ice loss. By reformulating an energy balance equation to express snowfall as a compensatory term, I demonstrate how the FLH can help identify resilient glacier landscapes, thereby informing conservation and adaptation priorities.