Glacier Retreat and Climate Change
The World Glacier Monitoring Service (WGMS), based at the University of Zurich, has maintained the most comprehensive global record of glacier mass change since 1894. The data it publishes leaves little room for ambiguity: the world's mountain glaciers have been losing mass at an accelerating rate since the middle of the twentieth century, with the pace of loss roughly doubling between the period 1980-2000 and the period 2000-2020.
The WGMS record and what it shows
The WGMS Fluctuations of Glaciers database aggregates observations from hundreds of reference glaciers across every glaciated region on earth. The key summary statistic is specific mass balance, measured in metres of water equivalent per year. The global mean mass balance across all WGMS reference glaciers has been negative in every year since 1980 with one or two minor exceptions. The cumulative mass loss since 1950 is equivalent to a column of ice roughly 30 to 35 metres thick across the entire glaciated surface area.
The 2023 WGMS State of the Global Cryosphere update reported one of the most negative years on record globally. Glaciers in the Alps, the Caucasus, Scandinavia, and the western United States all recorded exceptional losses. Swiss glaciers alone lost approximately 4% of their total remaining volume in the single year of 2022, the worst on record for the Alps.
Sea level contribution
Mountain glaciers and ice caps outside Greenland and Antarctica contribute approximately 0.7 mm per year to global mean sea level rise, according to estimates synthesised by the IPCC Sixth Assessment Report (2021). This figure is smaller than the contribution from thermal expansion of ocean water and the combined contribution from the two ice sheets, but it is highly significant because mountain glacier melt is faster, more certain, and will continue even if warming stabilises, as glaciers that are no longer in equilibrium with current temperatures continue adjusting for decades after the forcing changes.
If warming reaches 2 degrees C above the pre-industrial baseline, WGMS projections suggest that 40 to 50 percent of present glacier volume outside the ice sheets will be lost by 2100. At 1.5 degrees C, the figure falls to 25 to 30 percent. The difference between the two scenarios — approximately 30 mm of sea level rise — is a significant portion of the low-end projections for total sea level rise this century.
Alpine retreat: the Aletsch example
The Great Aletsch Glacier in the Swiss canton of Valais is the largest glacier in the Alps, covering approximately 82 km2 with a length of about 23 km. The WGMS record shows that the Aletsch tongue has retreated approximately 3.5 km since 1900, of which roughly 1.5 km has occurred since 1970. The terminal moraine systems deposited during the Little Ice Age maximum around 1850 now stand several hundred metres above the current ice surface in some sections, documenting how dramatically the ice volume, not just the length, has changed.
The Massa bridge near Blatten, once at river level beside the glacier margin, now looks up at bare rock walls that the ice formerly filled. The Swiss Glacier Monitoring Network projects that the Aletsch will lose the majority of its length by 2100 under a middle warming scenario, with the upper plateau retaining significant ice volume much longer.
Andean water supply and the Peruvian crisis
The glaciers of the Peruvian Andes, concentrated in the Cordillera Blanca and Cordillera Vilcanota ranges, serve as the primary dry-season water source for millions of people in the Rio Santa and Mantaro river basins. During Peru's dry season from May through September, meltwater from the Cordillera Blanca glaciers represents a large fraction of streamflow in the Santa River, supplying irrigation, hydroelectric generation, and municipal water to Huaraz, Trujillo, and the coastal lowlands.
The Peruvian glaciers have lost more than 50% of their surface area since the 1970s according to Peru's National Water Authority (ANA), with the rate of loss increasing substantially after 2000. The consequence is a hydrological paradox: as glaciers retreat, peak runoff initially increases as the ice melts faster, temporarily improving water availability; but as the glaciers diminish below a critical size, dry-season flow drops sharply because there is simply less ice to melt. Many Andean glaciers have passed through this peak water phase, and hydrologists project serious dry-season water shortages in the coming decades.
Himalayan asymmetry
The Himalayan and Karakoram ranges present the most complex regional picture in global glaciology. The majority of Himalayan glaciers are retreating at rates broadly consistent with other mountain regions, but a significant subset — primarily in the Karakoram range straddling Pakistan and China — have been stable or even slightly advancing since the 1980s. This phenomenon, referred to as the Karakoram Anomaly, is attributed to regional circulation patterns that have increased winter snowfall in the Karakoram while temperatures have risen less sharply than in adjacent ranges.
The Gangotri Glacier in Uttarakhand, the primary source of the Ganges River, has retreated approximately 22 km since 1780, with the rate of retreat around 22 metres per year in recent decades according to ISRO and the Geological Survey of India. Khumbu Glacier in Nepal, the approach route to Everest, has thinned markedly on its lower tongue and the Khumbu Icefall has become more unstable, influencing route conditions on the mountain. Glaciologists broadly project that the Hindu Kush- Himalaya region will lose one-third to two-thirds of its glacier volume by 2100 depending on the emissions pathway.
Greenland mass balance
The Greenland Ice Sheet is a separate system from the mountain glaciers discussed above, but its tidewater outlet glaciers are monitored by WGMS in partnership with the National Snow and Ice Data Center. The ice sheet has been losing mass at accelerating rates since the 1990s, contributing approximately 0.8 mm per year to sea level in the most recent decade — more than mountain glaciers worldwide combined. Jakobshavn Glacier, Greenland's fastest-flowing outlet, briefly slowed and even slightly advanced around 2013 to 2016 due to incursion of cooler Atlantic waters into the fjord, before resuming accelerated retreat. This event illustrates how ocean temperature, not just atmospheric warming, is a first-order control on tidewater glacier dynamics.
The 1.5 degree threshold
The Paris Agreement's 1.5-degree target has become a benchmark in glaciological projections. Glacier models suggest that limiting warming to 1.5 degrees C preserves roughly 70 percent of current mountain glacier volume globally by 2100, while a 3-degree pathway reduces that to approximately 50 percent — including the near-total loss of glaciers in ranges such as the European Alps, the tropical Andes, and the mountains of Central Asia. Some losses are already locked in due to the thermal inertia of the climate system. A glacier that existed in 1850 and exists today has already committed to significant further retreat regardless of emissions changes made now; the question is whether the remnants survive into the twenty-second century.
See the affected glaciers on the map
Every glacier mentioned in this article is mapped on the interactive map. The map draws from OpenStreetMap glacier data and is updated as mapping coverage improves. Use it to compare the current extent of retreating glaciers against the descriptions above.