It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Wednesday, February 19, 2025
Melting glaciers accelerate sea level rise and put drinking water supply at risk
Last decade, the loss of ice in the more populated regions, such as Europe, increased at ever-faster rates
All relatively small glaciers combined (because those of Antarctica and Greenland are not included) lost approximately 5% of their volume between 2000 and 2023. This amounts to a loss of 273 billion tonnes of ice, which is more than double that of the Antarctica Ice Sheet. In Central Europe, think of the Alps, even 39% of the ice mass was lost.
Intensifying loss Unsurprisingly, the amount of meltwater coming down varies per year. But the pattern that is becoming visible the researchers call shocking. Between 2012 and 2023, much more ice was lost (36% more meltwater) compared to the decade before.
It is not only about rising sea levels, says Bert Wouters. “We will directly notice the melting of these glaciers. Because they are located where many people live, it will affect drinking water supplies, in particular in South America and Asia. And the risk of flooding after the melt season also poses a danger.”
Combining global melt data Bert Wouters is Associate Professor of Geoscience and Remote Sensing at TU Delft and ensured that the data from many studies together produced a solid estimate. “From the accessible glaciers, we have lots of field measurements. From all those other glaciers, we have data from satellites. The methods and thus the meltwater estimates were often varying. It was a big challenge to make it scientifically unified.”
The team of researchers, part of the Glacier Mass Balance Intercomparison Exercise (Glambie), succeeded. This resulted in an annual time series of glacier mass changes for all glacier regions globally from 2000 to 2023.
Community estimate of global glacier mass changes from 2000 to 2023
Article Publication Date
20-Feb-2025
Global retreat of glaciers has strongly accelerated
International researchers with the participation of Graz University of Technology present a global assessment of ice loss since the beginning of the millennium. In a global comparison, the glaciers in the Alps and Pyrenees are melting the fastest.
There are currently around 275,000 glaciers worldwide, in which huge quantities of fresh water are stored. But this reservoir is increasingly shrinking. Since the turn of the millennium, glaciers around the world – i.e. ice masses on land excluding the Greenland and Antarctic ice sheets – have lost around 273 billion tonnes of ice per year. This corresponds to about five and a half times the volume of Lake Constance. Overall, the world’s glaciers have lost around five per cent of their total volume since the year 2000. This is the conclusion reached by an international research team of which Tobias Bolch from the Institute of Geodesy at Graz University of Technology (TU Graz) is a member. The team published the corresponding, comprehensive study today in the scientific journal Nature. It is striking that ice loss has accelerated significantly in recent years. In the second half of the period under investigation (2012 to 2023), it was 36 per cent higher than in the period from 2000 to 2011.
For their study, the researchers collected, homogenised and evaluated glacier data from different sources, including field measurements directly on glaciers as well as radar, laser and gravimetric data from numerous satellite missions. “We compiled 233 estimates of regional glacier mass changes from about 450 data contributors organised in 35 research teams,” explains Michael Zemp, who led the study. Tobias Bolch adds: “The data from ESA Earth observation satellites, as well as from other international space organisations, is particularly important for our research. By analysing this data – measurements of elevation changes are particularly valuable here – we were able to determine the condition of glaciers worldwide.” The result is a unique time series of annual glacier mass changes in the years from 2000 to 2023 for all glacier regions of the world. Due to the large amount of precise data, this study is much more reliable than previous studies of global glacier changes, which were based on less accurate or incomplete data.
18 millimetres sea level rise
The loss of ice from the glaciers since 2000 has led to a rise in sea level of 18 millimetres. This makes the melting of glaciers the second strongest driver of sea level rise after ocean warming, well ahead of the mass loss of the Greenland and Antarctic ice sheets.
Strong regional differences
However, not all glacier regions are affected to the same extent. While the glaciers of the Antarctic and sub-Antarctic islands have only lost 1.5 per cent of their mass, they have shrunk the most in the Alps and the Pyrenees, at around 39 per cent. “Due to their low altitude, they are particularly affected by the higher temperatures,” explains Tobias Bolch. “Additionally, the Alpine and Pyrenean glaciers are comparatively small, which is also a disadvantage. Glaciers generally have a cooling effect on the microclimate of their surroundings. However, this effect is only weakl for small glaciers, which is another reason why the glaciers in the Alps and Pyrenees are shrinking the most.”
Declining meltwater supply in Alpine streams
Valuable freshwater supplies are being lost with the ice from the glaciers. Paradoxically, this is not yet noticeable in many of the world’s glacier-fed rivers; the water volumes from glacier melt have actually increased in most cases. However, these outflows will peak in the future and then decline steadily. “In the European Alps, we have already exceeded this peak discharge. Hence our glaciers will supply the rivers with less and less water,” says Tobias Bolch. “This is becoming a problem especially during longer dry periods. Glacier tributaries are then particularly important as continuous water suppliers. This stabilising effect is increasingly being lost.”
The study on the development of glaciers was carried out as part of the ESA-supported research initiative “Glacier Mass Balance Intercomparison Exercise (GlaMBIE)”. GlaMBIE is coordinated by the World Glacier Monitoring Service (WGMS) hosted at the University of Zurich in collaboration with the University of Edinburgh and the company Earthwave.
Publication: Community estimate of global glacier mass changes from 2000 to 2023
Authors: The GlaMBIE Team (Michael Zemp, Livia Jakob, Inés Dussaillant, Samuel U. Nussbaumer, Noel Gourmelen, Sophie Dubber, Geruo A, Sahra Abdullah, Liss Marie Andreassen, Etienne Berthier, Atanu Bhattacharya, Alejandro Blazquez,, Laura F. Boehm Vock, Tobias Bolch, Jason Box, Matthias H. Braun, Fanny Brun, Eric Cicero, William Colgan, Nicolas Eckert, Daniel Farinotti, Caitlyn Florentine, Dana Floricioiu, Alex Gardner, Christopher Harig, Javed Hassan, Romain Hugonnet, Matthias Huss, Tómas Jóhannesson, Chia-Chun Angela Liang, Chang-Qing Ke, Shfaqat Abbas Khan, Owen King, Marin Kneib, Lukas Krieger, Fabien Maussion, Enrico Mattea, Robert McNabb, Brian Menounos, Evan Miles, Geir Moholdt, Johan Nilsson, Finnur Pálsson, Julia Pfeffer, Livia Piermattei, Stephen Plummer, Andreas Richter, Ingo Sasgen, Lilian Schuster, Thorsten Seehaus, Xiaoyi Shen, Christian Sommer, Tyler Sutterley, Désirée Treichler, Isabella Velicogna, Bert Wouters, Harry Zekollari, Whyjay Zheng)
This image, recorded by the Sentinel-2 satellite on 6 October 2017, shows the melting Scott (left), Sheridan (middle), and Childs (right) glaciers feeding lakes and rivers in their forefields.
Separate from the continental ice sheets in Greenland and Antarctica, glaciers covered an area of 705,221 km2 and contained 121,728 billion tons of ice globally in 2000. Since then, glaciers have lost about 5% of their ice globally, and regionally between 2% on the Antarctic and Subantarctic Islands and 39% in Central Europe. Annually, glaciers lost 273 billion tons – 273,000,000,000,000 kg – of ice, with an increase of 36% from the first (2000−2011) to the second (2012−2023) half of the period. Glacier mass loss is about 18% larger than the loss from the Greenland Ice Sheet and more than twice that from the Antarctic Ice Sheet.
Worldwide research community effort
For the new study, an international research team under the coordination of the World Glacier Monitoring Service (WGMS), hosted at the University of Zurich (UZH) in Switzerland, carried out the so-called Glacier Mass Balance Intercomparison Exercise (GlaMBIE). The research community collected, homogenized, combined, and analyzed glacier mass changes from different field and satellite observation methods. The team then compared and combined the results from the different methods into an annual time series of glacier mass changes for all glacier regions in the world from 2000 to 2023.
The researchers compiled 233 estimates of regional glacier mass changes from about 450 data contributors organized in 35 research teams. “By combining the advantages of the different observation methods, GlaMBIE provides not only new insights into regional trends and year-to-year variability. We could also identify differences among observation methods, which is an opportunity to better understand and improve future estimates,” says Michael Zemp, UZH professor at the Department of Geography, who led the study.
Sinking regional freshwater resources, rising global sea levels
From 2000 to 2023, the global glacier mass loss totals 6,542 billion tons. This loss contributed 18 mm to global sea-level rise at an annual rate of 273 billion tons or 0.75 millimeters yearly. With this, glaciers are currently the second-largest contributor to global sea-level rise, after the warming of the ocean and before the contributions from the Greenland Ice Sheet, changes in land water storage, and the Antarctic Ice Sheet.
In addition, glacier melt results in the loss of regional freshwater resources. “To put this in perspective, the 273 billion tonnes of ice lost in one single year amounts to what the entire global population consumes in 30 years, assuming three litres per person and day,” states Zemp.
“Glaciers are vital freshwater resources, especially for local communities in Central Asia and Central Andes, where glaciers dominate runoff during warm and dry seasons”, says UZH glaciologist Inés Dussaillant, who was involved in the GlaMBIE analyses. “But when it comes to sea-level rise, the Arctic and Antarctic regions with their much larger glacier areas are the key players. Almost one quarter of the glacier contribution to sea-level rise originates from Alaska,” she adds.
Limiting negative effects through climate protection
The present study marks an important milestone for the International Year of Glaciers’ Preservation in 2025 and the Decade of Action for Cryospheric Sciences (2025−2034) declared by the United Nations. GlaMBIE provides a new observational baseline for future studies, allowing improved projections of freshwater resources and sea-level rise.
“Our observations and recent modelling studies indicate that glacier mass loss will continue and possibly accelerate until the end of this century”, says UZH glaciologist and GlaMBIE project manager Samuel Nussbaumer. “This underpins Intergovernmental Panel on Climate Change’s call for urgent and concrete actions to reduce greenhouse gas emissions and associated warming to limit the impact of glacier wastage on local geohazards, regional freshwater availability, and global sea-level rise”, he concludes.
A fleet of satellites has been used to monitor glaciers worldwide using optical, radar, laser and gravity measurements. From top: CryoSat, Terra, ICESat, and the twin GRACE spacecraft, above a map of elevation change for the Vatnajökull ice cap on Iceland.
Credit
ESA, NASA, and Planetary Visions
This image, recorded by the Sentinel-2 satellite on 12 September 2017, shows the blue glaciers on the reddish-brown Franz Josef Land archipelago north of the 80th parallel in the Arctic Ocean (black). The glaciers (blue) are covered with little or no snow (white), indicating a significant mass loss.
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