How much ice is stored in the world’s glaciers? And where exactly is it located? A new study led by Ca’ Foscari University of Venice, in collaboration with the Institute of Polar Sciences of the National Research Council of Italy (CNR-ISP), provides an updated global map of glacier ice volume.

The study ¹ introduces IceBoost v2.0, a machine-learning model developed by Niccolò Maffezzoli, physicist and researcher at Ca’ Foscari University of Venice and affiliated with CNR-ISP. IceBoost v2.0 was trained on more than 7 million ice-thickness measurements collected from glaciers across the globe. The model combines these observations with 26 physical and geometrical variables (including topographic slope and curvature, ice velocity, and temperature) to reconstruct on a point-by-point basis the ice thickness, and thus the volume, of every glacier included in the Randolph Glacier Inventory (RGI), the world’s most up-to-date global glacier inventory, excluding the polar ice sheets.

An interactive web-app allows users to explore the data from Maffezzoli’s model for every glacier worldwide.

According to the new estimates, the world’s glaciers contain approximately 150,000 cubic kilometres of ice, equivalent to 32.3 centimetres of global mean sea-level rise if they were to melt completely (excluding Antarctica and Greenland). While this figure is consistent with previous global estimates, IceBoost v2.0 provides a far more realistic estimation of each glacier’s distribution, matching field observations up to 40% more accurately.

One of the most striking examples is the Geikie Plateau in eastern Greenland, where the glacier is up to 2 kilometres thick. In this area, IceBoost v2.0 estimates nearly twice as much ice as previously reported. “The distribution of glacier ice thickness is a fundamental variable for glaciological and climate models,” explains Niccolò Maffezzoli. “To predict how glaciers will evolve by 2100 and quantify their contribution to sea-level rise, we first need the most detailed possible picture of their current state. Researchers involved in the Glacier Model Intercomparison Project (GlacierMIP4), who are producing the next generation of glacier simulations to inform the IPCC’s assessments of glacier evolution through to 2100, will use IceBoost v2.0 as their sole representation of present-day situation.”

The new dataset also provides valuable guidance for future field campaigns and scientific investments. In fact, IceBoost v2.0 maps identify regions where model estimates are most reliable, as well as areas where additional observations are most urgently needed, including the Himalaya and the Karakoram ranges, and the major Patagonian ice fields. The research also has significant implications for freshwater management. Glaciers sustain rivers, ecosystems, agriculture, and local communities, supporting the livelihoods of around 1.9 billion people worldwide. Better estimates of glacier thickness and ice volume make it possible to produce more reliable projections of future freshwater availability, particularly in increasingly arid and desertifying regions such as parts of South America.

“Glaciers are highly complex systems. Although the governing physics is well understood, many of the parameters involved in the equations remain unknown, poorly constrained or  extremely difficult to measure,” Maffezzoli concludes. “Machine-learning models offer an alternative approach: they learn directly from data, generating predictions without imposing a predefined physical description. When sufficient data is available, this approach often proves highly effective. The future lies in hybrid models, where physical modelling and learning from experimental measurements work together to produce even more accurate estimates. We must move quickly: glaciers at mid-latitudes, including those in the Alps, are expected to disappear within the next few decades.”

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Arctic terrestrial permafrost ecosystems store around 1,300 gigatonnes of carbon from organic sources, such as from the remains of plants. Sediments in oceans and river deltas contain a further 400 gigatonnes. Global warming, however, is taking its toll on this natural freezer: temperatures in the Arctic are rising faster than anywhere else on our planet, with the result that permafrost in the region is thawing rapidly. The carbon stored here can then enter the Arctic Ocean via rivers and eroding coastlines. “Consequently, up to 0.02 gigatonnes are entering the sea each year, and according to forecasts, this outflow could rise by 70 to 150 per cent by the year 2100,” says Dr Manuel Ruben, lead author of the study from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). “However, how much of this is released back into the atmosphere as a greenhouse gas and how much is stored in the seabed has, until now, been largely unknown.” Yet, this knowledge is essential for assessing the climate impact of thawing permafrost.

To get to the bottom of this unknown, the researchers retrieved and analysed sediment cores taken at various intervals off the coast of the Canadian island of Herschel Island ¹. The cores contain deposits spanning around 50 years. Analysis of the sediments revealed something surprising: “Although the sea here carries away huge quantities of organic carbon from the coast, surprisingly little of it ends up in the ocean’s active carbon cycle,” says Manuel Ruben. “Microorganisms convert around ten per cent of the organic carbon from the sediments into gases, which rise into the water and can then enter our atmosphere.” The major share, however, is stored in the seabed.

In conducting their analysis, the researchers first examined the composition of the sediment cores in detail and also investigated how rapidly permafrost deposits accumulate on the seabed. To this end, they measured how much inorganic dissolved carbon accumulates in tiny cavities within the sediment layers – known as pore water. This provides an indication of how much CO₂ microorganisms have ‘exhaled’ after ‘digesting’ the organic carbon. The isotopic composition of the pore water provides insights into which organic material from which source has been broken down. ”Carbon isotopes represent our atomic indicators that can identify the food source of the microorganisms,” says Prof. Gesine Mollenhauer, a geochemist at the AWI and co-spokesperson for the ‘The Ocean Floor – Earth’s Unexplored Interface’ cluster of Excellence. “The ¹³C isotope, for example, tells us whether they have consumed carbon from land or from the sea. By way of the ¹⁴C isotope, we were able to determine whether the single-celled organisms preferred old organic carbon from permafrost or fresh organic carbon from algae remains.”

One explanation for this lies in the eating habits of these tiny organisms: “The sediment is home to ‘gourmet’ bacteria that apparently prefer fresh carbon stemming from, for example, more recent algal remains over the ‘old’ carbon from permafrost deposits,” explains Gesine Mollenhauer. This suggests that the organic carbon entering the sea from land contributes less to the amount of greenhouse gases in the atmosphere than originally feared. “However, we do need further research here. This is because some of the organic carbon from the permafrost may already have been broken down before it reaches the seabed.”

In addition to the impact of land-ocean carbon transport on atmospheric greenhouse gas levels, further effects are possible. For instance, this transport influences the biogeochemistry of coastal waters, which also play an important role in providing food for the local population. This is because the sediments alter the amount of sunlight available: on the one hand, the freshly broken-off fragments cloud the coastal ocean, while on the other hand, the organic carbon they contain discolours the water as it dissolves into it. Single-celled organisms such as algae, however, need light to convert this into biomass and oxygen. This primary production, in turn, forms the foundation for marine life such as fish, crustaceans and seals. The researchers aim to investigate these complex interrelationships, among other things, as part of the international ‘Arctic Pulse’ campaign planned for 2027. Through coordinated measurement campaigns aboard the Polarstern research icebreaker, using the AWI’s research aircraft and on land, they will investigate how rapid environmental change is altering ecosystems in the Arctic.

“Our study shows, more precisely than ever before, how much carbon is safely stored in the seabed – and just how much of the decomposed material actually originates from the old permafrost,” says Manuel Ruben. “This provides an important foundation for climate models that can predict the consequences of permafrost thawing for the global climate.”

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