Climate Change: Glacier Mass Balance

February 14, 2020

Among the most dramatic evidence that Earth's climate is warming is the dwindling and disappearance of mountain glaciers around the world. Based on preliminary data, 2018 is likely to be the 30th year in a row of mass loss of mountain glaciers worldwide. According to the State of the Climate in 2018,

The cumulative mass balance from 1980 to 2018 is −21.7 m, the equivalent of cutting a 24-m [79-foot] thick slice off the top of the average glacier.

Explore this interactive graph: Click and drag either axis to view different parts of the graph. To squeeze or stretch the graph in either direction, hold your Shift key down, then click and drag. The graph shows cumulative mass loss in "meters of water equivalent," which is the depth of the meltwater spread out over the glacier's surface area.  Data* are from the World Glacier Monitoring Service, and provided by Mauri Pelto.

Glaciers that exist today are remnants of the last ice age. Thick sheets of ice advanced and retreated across most continents several times before withdrawing to the polar regions about 10,000 years ago. Continent-scale ice sheets still cover Greenland and Antarctica, while smaller ice caps and glaciers retreated to the world's high latitudes and mountains. 

Photo comparison of Alaska's Pedersen Glacier in 1917 and 2005

Pedersen Glacier, at Aialik Bay in Alaska’s Kenai Mountains, in 1917 (left) and 2005 (right). In the early 20th century, the glacier met the water and calved icebergs into a marginal lake near the bay. By 2005, the glacier had retreated, leaving behind sediment allowed the lake to be transformed into a small grassland. Photos courtesy of Louis H. Pedersen (1917) and Bruce F. Molina (2005), obtained from the Glacier Photograph Collection, Boulder, Colorado USA: National Snow and Ice Data Center/World Data Center for Glaciology. Large images: 1917 | 2005

Originally, scientists began studying glaciers only for the clues they offered about Earth’s climate during past ice ages. Today, they are also trying to understand how quickly human-caused climate change will cause them to disappear altogether. 

Measuring glacier change

Glaciers gain mass through snowfall and lose mass through melting and sublimation (when water evaporates directly from solid ice). Glaciers that terminate in a lake or the ocean also lose mass through iceberg calving. 

To see if a glacier is growing or shrinking, glaciologists check the condition of snow and ice at several locations on the glacier at the end of the melt season. The scientists check snow levels against stakes they’ve inserted in the glacier, dig snow pits in the surface to examine the sequence of seasonal layers, and insert long poles into the glacier to probe characteristics of the snow and ice.

Photo of Alaska’s Lemon Creek Glacier in September 2014

Alaska’s Lemon Creek Glacier in September 2014. Virtually no snow covered the glacier, which exposes the terminus to the Sun and accelerates glacier retreat. This glacier must keep at least 62% of its snow cover to keep from losing mass. Photo by Chris McNeil, via Mauri Pelto.

Generally, the difference in thickness of snow from the previous measurement indicates the glacier’s mass balance—whether the glacier has grown or shrunk.

Change over time

Scientists have described more than one hundred thousand glaciers in the World Glacier Inventory, but only a small fraction of these have been consistently monitored for long enough to measure climate-related changes in their size or mass. Scientists refer to this collection of about 40 glaciers as "reference" glaciers.

Photos documenting the disintegration of Italy’s Careser Glacier between 1933 (top) and 2012 (bottom). Careser is one of ~40 climate reference glaciers in the World Glacier Monitoring Service's inventory. Photos courtesy of Luca Carturan, University of Padova.

In the 2018 State of the Climate report (edited by NOAA NCEI scientists and published by the American Meteorological Society), scientists reported that in 2017 (the most recent year with complete data), the 42 reference glaciers tracked by the World Glacier Monitoring Service lost an amount of ice equivalent to 921 millimeters (3 feet) of water, while the full network of 142 glaciers lost 951 millimeters (3.1 feet). 

Water equivalent is the amount of liquid water that would result if a given amount of ice or snow melted and spread out over the surface of a glacier.

Preliminary data for 2018 suggest that reference glaciers loss an amount of ice equivalent to 1,247 millimeters (4 feet) of water. If the final tally is close to this number, 2018 will surpass 2003 as the year with the greatest annual ice losses from mountain glaciers worldwide. Cumulative ice loss between 1980 and 2018 is −21.7 meters of water equivalent, the equivalent of cutting a 24-m (79-foot) thick slice off the top of the each glacier.

The pace of glacier loss has accelerated from -228 millimeters (9 inches) per year in the 1980s, to -443 millimeters (17 inches) per year in the 1990s, to -676 millimeters (2.2 feet) per year in the 2000s, to -921 millimeters (3 feet) per year for 2010-2018. Today, many glaciologists are concerned with predicting when various glaciers will disappear altogether.  In many parts of the world—including the western United States, South America, China, and India—glaciers are frozen reservoirs that provide a reliable water supply each summer to hundreds of millions of people and the natural ecosystems on which they depend.


Pelto, M., WGMS Network. (2018). Alpine glaciers [in State of the Climate in 2017]. Bulletin of the American Meteorological Society, 99(8), S23–S25.

Zemp, M., Roer, I., Kääb, A., Hoelzle, M., Paul, F., and Haeberli, W. 2008. Global Glacier Changes: facts and figures. World Glacier Monitoring Service, UNEP, 88 p. ISBN:978-92-807-2898-9. Accessed August 29, 2011.

World Glacier Monitoring Service Glacier Mass Balance Bulletin Accessed August 29, 2011.

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