Climate change: It is no longer possible to save the glaciers at the size they are today
Dr. Christian Sommer from the Institute of Geography at FAU was involved in the first systematic recording of measurement data tracking the dramatic retreat of glaciers
Over the last 25 years approximately 39 percent of glacier ice has disappeared: the results of the Glambie study from the European Space Organization ESA are dramatic. For the paper, Dr. Christian Sommer, Prof. Dr. Matthias Braun and Dr. Thorsten Seehaus from the Institute of Geography at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) collected satellite data from glaciers in the Alps, the South American Andes and the Arctic. The results are expected to be incorporated into the next World Climate Report.
Dr. Sommer, the glaciers in Central Europe have lost approximately 39 percent of their ice since the year 2000. Glaciers across the globe are melting increasingly rapidly, on average approximately 273 billion tons of ice are melting every year. That sounds dramatic. Were you surprised by the results of the Glambie study?
Dr. Christian Sommer: No, we knew that glaciers are melting so rapidly. The new and pioneering aspect of the study is the methods it uses and its approach of combining very different glacial measurements. The regular World Climate Reports from the United Nations are fairly well-known. In them, the Intergovernmental Panel on Climate Change reports on the retreat of the glaciers. In the past, these reports were based on results of scientific publications on the topic of glacial melt. The mean was taken of measurements from across the globe to derive a global average. However, this did not allow for any differences between the individual measuring methods to be taken into account, for example factors such as over which time period, using which method and how accurately changes were measured. For the first time, the Glambie study systematically compares a wealth of data delivered by 35 international teams of researchers. Our aim was to deliver more reliable results on a regional and a global level. In the next World Climate Report our results will probably be used to depict the status quo of glacial melt over the last two decades.
Together with your colleagues, you evaluated data from the German satellite mission TanDEM-X in order to determine the volume of glacier ice. Could you explain that in more detail?
Dr. Christian Sommer: The satellite mission TanDEM-X was launched in 2010 and is managed by the German Aerospace Center. Using radar interferometry, two satellites create a three dimensional image of the Earth, in other words a digital model of the surface height. These digital terrain models are comparable with the function in Google Maps that displays contour lines in the terrain view. The same technology is used. Using the satellite images, we can detect and compare the terrain height for each pixel. As the satellites have been repeatedly capturing images of the Earth’s surface for more than ten years now, we can observe how the surface and volume of ice in the glaciers is changing.
The United Nations has declared 2025 the International Year of Glaciers’ Preservation. What are the chances that we will be able to save the ice fields in the mountains from disappearing?
Dr. Christian Sommer: In the last 20 years, glaciers at very high altitudes such as in the Himalayas, that have until now been only slightly affected by climate change, have started to show clear signs of significant ice loss. 20 years ago there were still some mountainous areas where this was not necessarily the case. If the ice only melted a little, researchers at the time were unsure as to whether the glacier actually was changing in the long term or whether the measurements were inaccurate. For ten years now, however, we have been observing significant melting rates in all high mountain ranges across the globe. The glaciers outside the polar regions that are not melting can be counted on several hands. It is no longer possible to save the glaciers at the size they are today, even if all countries immediately refrained from emitting greenhouse gases.
According to prognoses, half of all glaciers will have disappeared by the end of the century. And that is even if we still manage to reach the 1.5 degree goal, which is extremely unlikely.
Dr. Christian Sommer: Yes, that is to be expected. The reason is that global warming means that the snow line is becoming higher and higher during summer months. At the same time, in a number of mountainous areas, including in the Alps, we are observing that there are hardly any high-altitude “retreats” that remain cool enough for snow to remain for several years without melting in summer. For example, if you go into the Austrian Alps in the height of summer, you can see that many glaciers are already melting even up to their highest points. It is to be expected that many glaciers will disappear from the relatively low mountainous areas such as the Alps, the Caucasus or the Rocky Mountains in North America. Several glaciers in the Alps have already broken into pieces or have melted entirely. One of the glaciers on the Zugspitze has already nearly disappeared altogether.
There is a clear connection between climate change and the melting of the glaciers, isn’t there? I’m asking because there are still people who doubt that, including politicians.
Dr. Christian Sommer: The melting of the ice is quite clearly the glaciers’ reaction to climate change. As long as there is a balance between the existing ice masses in the glaciers and surrounding temperatures, the ice that melts in the summer and the ice that is gained in the winter remain in equilibrium. The glacier is stable. However, this equilibrium has been disrupted for decades now due to the rising temperatures in mountainous regions.
What are the consequences?
Dr. Christian Sommer: Sea levels are rising. In the Glambie study we show that the 6542 billion tonnes of glacier ice that melted between 2000 and 2023 have already led to a rise of 18 millimeters. A second important factor is the volumes of water that flow off the glaciers in summer. That plays a major role in regions with low levels of precipitation such as the Northern Andes or parts of the Himalayas. Glaciers act like a buffer – if it only rains a little after the snow melt in spring, their meltwater still flows into the valleys in the summer. However, if the glaciers continue to shrink this leads to water shortages in the valley for agriculture and drinking water reserves start to become scarce as well. In Central Europe, the buffer effect of the glaciers is particularly important for water levels in large rivers at the height of the summer, but it is also necessary for creating renewable energy in hydro power stations that require a relatively stable flow of water all year round. Glaciers are nature’s freshwater reserves.
How do you see your role as a scientist in the debate about climate change in society?
Dr. Christian Sommer: As a scientist I investigate mountainous regions and describe physical changes to the natural landscape. I don’t want to preach. But I would urge people to open their eyes when they are out in nature. The changes in the glaciers in the Alps have even been made into a tourist attraction, with signs in certain places showing where the ice used to reach. You don’t have to be a mountaineer to witness the retreat of the glaciers.
What recommendations for action does the Glambie study give?
Dr. Christian Sommer: The results underline the importance of observing changes to the natural landscape. The various satellite missions used by the teams of researchers involved in the study are extremely costly. Some of the satellites have already been in space for many years now and are probably approaching the end of their lifespan. There must be subsequent missions and we need even better monitoring of changes to natural landscapes. At the moment, we are able to observe global warming and glacial melting at a large scale. However, in order to gain a detailed insight into climate change and glaciers, we would need improved temporal resolution. For people in regions with little rain it would be helpful to know how much the glaciers are melting year for year. Until now, we have been lacking the technical prerequisites needed to give an accurate prognosis.
A major international project
For the study (Glacier Mass Balance Intercomparison Exercise, Glambie for short) by the European Space Agency ESA a total of 35 teams consisting of approximately 450 scientists from across the globe compiled data from field measurements and from optical, radar, laser and gravimetry satellite missions. Using the data from these sources, the scientists created time series of changes in mass for all glacial regions across the globe from 2000 to 2023. The study summarized 233 estimates of regional changes to glacial mass.
Further information:
Dr. Christian Sommer
Institute of Geography
Phone: + 49 9131 85 23303
chris.sommer@fau.de