Focus on Cryosphere Loss.

 

Cryospheric decline compounds the existing pressures on water resources. The world, in multiple locations, has already lost over 30% of its glacier mass since 1970, and several low-latitude mountain ranges risk losing functional glaciers entirely within decades, eliminating long-standing natural savings accounts that once buffered seasonal water shortages. Snowpack and permafrost degradation add further uncertainty to water availability and storage in highlatitude and high-altitude systems. In glacier-fed basins across Asia, the Andes, and other mountain regions, communities are already experiencing a transition from “peak water”— a period of temporarily increased melt and runoff—to declining flows, with implications for hydropower, irrigation, and ecological integrity. Mountain glaciers and seasonal snowpacks function as the “water towers of the world,” storing cool-season precipitation and releasing it as meltwater during dry and warm periods. The downstream water supply for around 1.5–2 billion people is at least partly dependent on these high mountain water towers, particularly in basins such as the Indus, Ganges–Brahmaputra, Amu Darya, Yangtze, Yellow, and several Andean rivers30,31. As warming progresses, many of these systems first experience a peak water, followed by a long-term decline in dry-season flows once glacier volume is substantially reduced. For irrigated agriculture and hydropower in already stressed basins, this means that historical assumptions about reliable late-summer water supplies are no longer valid. This creates major operational and water allocation challenges as the existing infrastructure and institutions have been designed to fit the historical conditions that no longer exist. Cryosphere loss also alters the frequency and character of extreme events. In deglaciating mountain regions, the formation and growth of glacial lake outburst floods, which can produce destructive flash floods downstream impacting human settlements, assets, and infrastructure. At the same time, reduced snow cover and permafrost degradation can destabilize slopes, increasing landslide risk and sediment loads in rivers. These evolving hazards complicate flood management, infrastructure planning, and disaster risk reduction, particularly where dams, roads, and settlements were designed for historical cryosphericconditions. The cryosphere represents a form of underappreciated but essential natural capital that is being irreversibly liquidated. Once glaciers have lost most of their mass and seasonal snowpacks have shrunk or shifted upslope, there is no realistic pathway to restore their buffering function within human time frames. This means that societies downstream of the world’s major mountain ranges must rapidly adapt to a future with more variable and, in many cases, lower and more erratic dry-season flows—even if annual average precipitation does not decline. The liquidation of this frozen savings account thus interacts with groundwater depletion and surface-water overallocation to lock many basins into a permanent worsening water deficit state.

 

Paired satellite images (from Sentinel-2 true-color) showing the disappearance of glaciers in the Aru Range, Western Tibetan Plateau, China, between 2017 (top) and 2025 (bottom), primarily driven by climate change and warmer temperatures.

 Projected changes in the likelihood of future floods and droughts under climate change. Values reflect the increased frequency of future events relative to the historical period (1971–2000) as a percentage. Estimates are based on a multi-model ensemble comparing future conditions (2071–2100) to historical baselines, with projections derived under high-emissions scenarios (RCP8.5 for floods and SSP5–8.5 for droughts).