Accelerating glacier volume loss on Juneau Icefield driven by hypsometry and melt-accelerating feedbacks.

Globally, glaciers and icefields contribute significantly to sea level rise. Here we show that ice loss from Juneau Icefield, a plateau icefield in Alaska, accelerated after 2005 AD. Rates of area shrinkage were 5 times faster from 2015-2019 than from 1979-1990. Glacier volume loss remained fairly consistent (0.65-1.01 km 3 a -1 ) from 1770-1979 AD, rising to 3.08-3.72 km 3 a -1 from 1979-2010, and then doubling after 2010 AD, reaching 5.91 ± 0.80 km 3 a -1 (2010-2020). Thinning has become pervasive across the icefield plateau since 2005, accompanied by glacier recession and fragmentation. Rising equilibrium line altitudes and increasing ablation across the plateau has driven a series of hypsometrically controlled melt-accelerating feedbacks and resulted in the observed acceleration in mass loss. As glacier thinning on the plateau continues, a mass balance-elevation feedback is likely to inhibit future glacier regrowth, potentially pushing glaciers beyond a dynamic tipping point.