New Heights in Glacier-Climate Research: Initial Insights From the Highest Weather Stations on Earth

Weather observations from the Hindu Kush-Himalaya are extremely rare, with high-altitude glacier-accumulation zones almost completely unmonitored. This lack of basic data challenges our understanding of contemporary processes that affect glacier mass balance, undermining projections of future freshwater availability for hundreds of millions of people living downstream. Here we introduce a frontier measurement network, installed during the 2019 National Geographic and Rolex Perpetual Extreme Expedition to Everest, designed to address this critical knowledge gap. We describe the deployment of five automatic weather stations (AWSs), including three above the regional equilibrium line altitude, and the first ever AWS above 8,000m. The utility of these data for glacier-climate research is then demonstrated through application of an energy balance model to data from Everest's South Col (7,945m). We show that, despite maximum daily mean temperatures of -10°C, melt is not uncommon, with an average of 5.2 mm w.e d^-1 predicted for a bare-ice surface. We observe the melting to be driven by exceptionally high fluxes of incident shortwave radiation, occasionally reaching values typical for the top of the Earth's atmosphere (~1,360 W m^-2). Similarly intense solar radiation is observed at Everest's Western Cwm (at Camp II, 6,400 m). Combined with modelled sublimation rates of 0.45 mm d^-1, we estimate annual ablation from the South Col to be up to 2,000 mm w.e. We conclude that such losses would be undetected using temperature-index modelling approaches, and highlight the potential significance this has for understanding the sensitivity of regional glacier mass balances to climate warming.