Changes in Equilibrium-Line Altitude and Implications for Glacier Evolution in the Asian High Mountains in the 21st Century

Abstract

In the context of global warming, glaciers in the Asian High Mountains (AHMs) are shrinking at an accelerating rate. Projecting their future change is helpful for understanding the hydrological and climatic effects related to glacier retreat. Here, we projected glacier change in the AHMs from 1979 to 2100 under shared socioeconomic pathway (SSP) scenarios from the perspective of temperature, equilibrium-line altitude (ELA), and accumulation area. The annual mean temperature in the AHMs increased by 1.26 ℃ from 1979 to 2014, corresponding to an increase of 210 m in the mean ELA and a decrease of 1.7 × 104 km2 in the glacier accumulation area. Under the SSP2-4.5 (SSP5-8.5) scenario, the annual mean temperature in the AHMs would increase by 2.84 ℃ (3.38 ℃) in 2040–2060 relative to that in 1850–1900, leading to the mean ELA reaching an elevation of 5661 m (5777 m). The accumulation area in the AHMs decreased by 46.3% from 1995 to 2014 and was projected to decrease by 60.1% in 2040–2060. Moreover, the annual mean temperature in the AHMs was projected to increase by 3.76 ℃ (6.44 ℃) in 2080-2100 relative to that in 1850-1900, corresponding to the ELA reaching an elevation of 5821 m (6245 m) and the accumulation area decreasing to 1.8 × 104 km2 (0.5 × 104 km2). These data suggest that the conditions for glacier development will disappear in most of the AHMs, except for extreme high-altitude regions in the Tianshan, Pamir, and Himalaya Mountains. Under the SSP2-4.5 (SSP5-8.5) scenario, when the global mean temperature increases 1.5 ℃ (2 ℃) above pre-industrial levels, the annual mean temperature will increase by 2.12 ℃ (2.86 ℃) and the accumulation area will decrease by 15% (48%) in the AHMs compared with that in 1995–2015. Therefore, a 1.5 ℃ increase in global warming would keep 40% more of the glacial accumulation area (1.5 × 104 km2) in the AHMs compared to a 2 ℃ increase in global warming.