Poleward shift of subtropical highs drives Patagonian glacier mass loss.

Patagonian glaciers have been rapidly losing mass in the last two decades, but the driving processes remain poorly known. Here we use two state-of-the-art regional climate models to reconstruct long-term (1940-2023) glacier surface mass balance (SMB), i.e., the difference between precipitation accumulation, surface runoff and sublimation, at about 5 km spatial resolution, further statistically downscaled to 500 m. High-resolution SMB agrees well with in-situ observations and, combined with solid ice discharge estimates, captures recent GRACE/GRACE-FO satellite mass change. Glacier mass loss coincides with a long-term SMB decline (-0.35 Gt yr), primarily driven by enhanced surface runoff (+0.47 Gt yr) and steady precipitation. We link these trends to a poleward shift of the subtropical highs favouring warm northwesterly air advections towards Patagonia (+0.14°C dec at 850 hPa). Since the 1940s, Patagonian glaciers have lost 1350  ± 449 Gt of ice, equivalent to 3.7  ± 1.2 mm of global mean sea-level rise.