image: Glacier mass balance at the 1°geographic grid for the periods 1975–2000 (a) and for 2000–2013 (b), respectively. Changes in glacier mass balance at the geographic grid (c) and mountain scales (d), respectively
Credit: ©Science China Press，Yushan Zhou, Wenfeng Chen
The research team, including Associate Professor Yushan Zhou from Central South University, Professors Xin Li and Donghai Zheng, and Dr. Yingzheng Wang from the Institute of Tibetan Plateau Research of the Chinese Academy of Sciences, together with other collaborators, used historical satellite imagery to trace glacier changes across High Mountain Asia over nearly four decades. Their findings reveal that glacier mass loss has accelerated significantly since 2000, but not all glaciers have followed the same pattern.
Often called the "Asian Water Tower," High Mountain Asia is home to one of the largest concentrations of glaciers outside the polar regions. These glaciers provide vital freshwater resources for approximately 250 million people living downstream. As the climate warms, understanding how these glaciers have changed over time has become increasingly important. Yet most large-scale satellite-based assessments have focused on the period since 2000, leaving an important gap in scientists' understanding of earlier glacier changes.
To look further into the past, the researchers turned to historical satellite photographs taken in the 1970s. Much like a time capsule, these images preserve a detailed record of mountain landscapes from decades ago. By combining them with more recent digital elevation models, the team reconstructed glacier mass changes from 1975 to 2013, extending the regional observation record back by approximately 25 years.
The results revealed a striking shift. Between 1975 and 2000, glaciers across High Mountain Asia lost an average of approximately 12.8 billion cubic meters of water equivalent per year. During 2000–2013, this figure rose to 19.7 billion cubic meters per year, representing a 54% increase in the rate of glacier mass loss. However, the changes were far from uniform. Glaciers in the western Himalayas and southeastern Tibetan Plateau experienced particularly rapid losses, while some glaciers in the western Kunlun Mountains and surrounding regions showed slower losses or even slight gains. The researchers also found that during 2000–2013, the so-called "Karakoram anomaly," a phenomenon in which some glaciers have remained relatively stable or gained mass despite widespread losses elsewhere, may not be confined to the traditionally recognized Pamir–Karakoram–western Kunlun region, but instead exhibit a circum-Tarim Basin distribution pattern.
Why have glaciers in different parts of the same region behaved so differently? The researchers found that temperature and precipitation play different roles across High Mountain Asia. In areas influenced by the summer monsoon, changes in temperature and snowfall are particularly important. In regions dominated by westerly winds, changes in rainfall are more closely associated with glacier mass balance. These differences help explain why neighboring mountain ranges can experience contrasting glacier changes.
By bringing historical satellite observations into the present, the study offers a clearer picture of how High Mountain Asia's glaciers have evolved over nearly four decades. The findings provide an important reference for understanding future glacier changes and their potential impacts on water resources and glacier-related hazards, while demonstrating the lasting scientific value of historical satellite imagery.