Surface mass balance modelling of the Juneau Icefield highlights the potential for rapid ice loss by the mid-21st century

Plateau icefields are large stores of freshwater, preconditioned to enhanced mass loss due to their gently sloping a ccumulation areas. Accurate modelling of their mass balance is therefore crucial for sea-level rise projections. Here, we use the COupled Snowpackand Ice surface energy and mass-balance model in PYthon (COSIPY) to simulate historical and future mass balance of the Juneau Icefield, Alaska – a high elevation (>1200 m) plateau icefield. We force the model with dynamically downscaled climate simulations, for both pa st and future (RCP 8.5) conditions. The icefield’s mass balance decrea sed from a mean of -0.22 ± 0.38 m w.e. a -1 (1981 to 2019) to -1.52 ± 0.27 m w.e. a -1 (2031 to 2060), with many glaciers shifting from positive to negative mass balances at the start of the 21st century. This mass loss is a ttributed to projected rising air tempera tures and reduced snowfa ll, causing the equilibrium line altitude to rise and triggering a lbedo and melt-elevation feedbacks. These processes exacerbate melt, potentially leading to increased glacier disconnections at icefalls.