Examining the temporal variability of the mass balance of Everest’s glaciers over the last six decades

Abstract:

Regional studies of glacier surface elevation change have recently revealed pervasive ice loss from glaciers across the Himalaya in recent decades. Such studies have shown substantial spatial variability in ice loss due to regional climate variability and the growth of large populations of glacial lakes. Whilst these studies have yielded important information about the state of the cryosphere in the Himalaya, their temporal resolution remains coarse, and little is therefore known about glacier mass fluctuations at sub-decadal intervals over extended time periods. In this work, we generated a geodetic time series spanning nearly sixty years which covers the glaciers around Mount Everest at decadal time intervals. We measured consistently increasing glacier mass loss rates since the 1960s (-0.23 ± 0.12 m w.e.a^-1 from 1962-1969 Vs -0.44 ± 0.11 m w.e.a^-1 from 2009-2018), a four decade long phase of elevated ice loss from lake-terminating glaciers in the region, and anomalous surge behaviour of a glacier in the east of our study region. Using data derived from a high-altitude Lidar survey, we show that glacier thinning has occurred up to an altitude of ~5700 m in the Khumbu icefall. Several large glaciers store ice above 5600 m in the Everest region, which may soon be susceptible to melt. The temporally detailed measurements of mass loss we present will be vital in the calibration and validation of physically based glacier models designed to predict the behaviour of glaciers in the Himalaya in coming decades under different warming scenarios.