Global estimates of glacier equilibrium-line altitude ratios for enhanced paleoclimate reconstructions

Abstract Glacial landforms record valuable information about past climates, but quantitative reconstructions depend on robust estimates of glacier characteristics, particularly the equilibrium-line altitude. Traditional approaches rely on global mean or median values of equilibrium-line altitude ratios (Accumulation Area Ratio, Toe-to-Headwall Altitude Ratio, and Area-Altitude Balance Ratio) to calculate equilibrium-line altitude. However, these ratios vary across glacier types and climatic regimes, meaning that use of a single value can introduce substantial errors. Here we present empirically-constrained global estimates of equilibrium-line altitude ratios for approximately 215,000 glaciers derived from numerical modeling. We find that the Accumulation Area Ratio provides the most reliable approximation of the equilibrium-line altitude, particularly when adjusted for glacier type. Explicitly accounting for climatic setting, glacier size, slope and aspect when selecting equilibrium-line altitude ratios further improves accuracy of past climate reconstructions. Our work provides insights into global glacier characteristics and establishes a stronger basis for reconstructing past climates.