On top of the world’s highest mountains, glaciers act as “water towers” by storing fresh water. Meltwater from glaciers and snow supplies water for drinking, irrigation, hydropower and ecosystems to entire regions. Glaciers retreat when the ice mass that formed many years ago melts faster than snow can replace. Due to global warming, the world’s glaciers are melting at double the speed they had in the past two decades. Between 2000 and 2019, glaciers lost 267 gigatons of ice per year, roughly equivalent to the mass of 46,500 Great Pyramids of Giza. In a warming world, we are projected to lose around 50 per cent of glaciers (excluding Greenland and Antarctica) by 2100, even if global warming can be limited to 1.5°C.
Mountain glacier melting
As a glacier begins to retreat, its ice gradually melts and increases the amount of water flowing to the river basin. With more meltwater, the risk of flooding downstream increases. In some cases, this can lead to “glacial lake outburst floods”, in which a natural dam fails and suddenly releases meltwater with devastating consequences. Eventually, the glacier experiences its highest amount of melting and produces the maximum volume of water runoff, known as “peak water”. After this point, freshwater availability will steadily decline. Peak water has already been passed or is expected to occur within the next 10 years in basins dominated by small glaciers like those in Central Europe, western Canada or South America. Even the glaciers on the highest peaks, such as those in the high mountains of Asia, are predicted to reach peak water around the middle of this century. As such, the 90,000+ glaciers of the Himalayas, Karakorum and Hindu Kush mountains are at risk, and so are the nearly 870 million people that rely on them.
gigatons of ice lost from glaciers between 2000 and 2019
world's glaciers projected to be lost by 2100
people at risk of negative effects due to glacier retreat
Meltwater is often used to compensate for the lack of rain during dry seasons. As glaciers shrink, this potential is diminished, meaning that mountain communities and their downstream counterparts will have to radically shift how they manage water resources. In the Andes, where peak water has already passed for many glaciers, communities are grappling with the impacts of unreliable water sources from both the glaciers and climate change-induced difference in rainfall. For example, the Quelccaya glacier in Peru was once the world’s largest tropical ice cap, but it has shrunk by 31 per cent in the last 30 years, contributing to periodic water scarcity in the dry season and widespread impacts. Villagers living at the foot of the Quelccaya glacier, for instance, lost up to one third of their alpacas during a drought in 2021. The loss of glaciers is also a loss of iconic features in many mountain areas that has several tangible and intangible negative consequences for livelihoods, economies and heritage.
Glacier retreat is a call for action to take urgent measures to reduce greenhouse gas emissions. These glaciers are natural wonders and are essential for the survival and well-being of many communities who will have to adapt to a warmer and more unpredictable climate with direct consequences for their livelihoods and their access to water.
Tipping point: When glaciers retreat, long-term ice storage melts and is gradually released as meltwater. Initially, the volume of water released increases until a maximum is reached, known as peak water. After this tipping point, glacier meltwater volume decreases as the glacier continues to shrink with effects on freshwater availability for humans and other species.
Shared Root Causes
Human-induced greenhouse gas emissionsShared with Uninsurable future, Unbearable heat, Accelerating extinctions
Continued anthropogenic greenhouse gas emissions increase global temperatures, accelerating unfavourable conditions for physical, natural and human systems
Lack of informationShared with Uninsurable future, Groundwater depletion, Accelerating extinctions
Insufficient or inaccurate data and models to estimate the true extent of the risk species, water systems or human settlements are facing
Cultural heritage lossShared with Space debris, Accelerating extinctions
Loss or damage to physical or intangible attributes that provide cultural meaning, knowledge and belonging
Glacier retreat will change ecosystems in ways that threaten various species and increase the risk of extinctions