Loris Compagno

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Compagno

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Loris

ORCID

0000-0002-5422-7281

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Publications 1 - 9 of 9

Twenty-first century global glacier evolution under CMIP6 scenarios and the role of glacier-specific observations
Zekollari, Harry; Huss, Matthias; Schuster, Lilian; et al. (2024)
The Cryosphere
Projecting the global evolution of glaciers is crucial to quantify future sea-level rise and changes in glacier-fed rivers. Recent intercomparison efforts have shown that a large part of the uncertainties in the projected glacier evolution is driven by the glacier model itself and by the data used for initial conditions and calibration. Here, we quantify the effect that mass balance observations, one of the most crucial data sources used in glacier modelling, have on glacier projections. For this, we model the 21st century global glacier evolution under Coupled Model Intercomparison Phase 6 project (CMIP6) climate scenarios with the Global Glacier Evolution Model (GloGEM) calibrated to match glacier-specific mass balance observations, as opposed to relying on regional mass balance observations. We find that the differences in modelled 21st century glacier changes can be large at the scale of individual glaciers (up to several tens of percent), but tend to average out at regional to global scales (a few percent at most). Our study thus indicates that the added value of relying on glacier-specific observations is at the subregional and local scale, which will increasingly allow projecting the glacier-specific evolution and local impacts for every individual glacier on Earth. To increase the ensemble of models that project global glacier evolution under CMIP6 scenarios, simulations are also performed with the Open Global Glacier Model (OGGM). We project the 2015–2100 global glacier loss to vary between 25 ± 15 % (GloGEM) and 29 ± 14 % (OGGM) under SSP1-2.6 to 46 ± 26 % and 54 ± 29 % under SSP5-8.5 (ensemble median, with 95 % confidence interval; calibration with glacier-specific observations). Despite some differences at the regional scale and a slightly more pronounced sensitivity to changing climatic conditions, our results agree well with the recent projections by Rounce et al. (2023), thereby projecting, for any emission scenario, a higher 21st century mass loss than the current community estimate from the second phase of the Glacier Model Intercomparison Project (GlacierMIP2).
Modelling supraglacial debris-cover evolution from the single glacier to the regional scale: an application to High Mountain Asia
Compagno, Loris; Huss, Matthias; Miles, Evan S.; et al. (2021)
The Cryosphere Discussions
Currently, about 12–13 % of High Mountain Asia's glacier area is debris-covered, altering its surface mass balance. However, in regional-scale modelling approaches, debris-covered glaciers are typically treated as clean-ice glaciers, leading to a potential bias when modelling their future evolution. Here, we present a new approach for modelling debris area and thickness evolution, applicable from single glaciers to the global scale. We implement the module into the Global Glacier Evolution Model (GloGEMflow), a combined mass-balance ice-flow model. The module is initialized with both glacier-specific observations of the debris’ spatial distribution and estimates of debris thickness, accounts for the fact that debris can either enhance or reduce surface melt depending on thickness, and enables representing the spatio-temporal evolution of debris extent and thickness. We calibrate and evaluate the module on a select subset of glaciers, and apply the model using different climate scenarios to project the future evolution of all glaciers in High Mountain Asia until 2100. Compared to 2020, total glacier volume is expected to decrease by between 35 ± 15 % and 80 ±11 %, which is in line with projections in the literature. Depending on the scenario, the mean debris-cover fraction is expected to increase, while mean debris thickness is modelled to show only minor changes, albeit large local thickening is expected. To isolate the influence of explicitly accounting for supraglacial debris-cover, we re-compute glacier evolution without the debris-cover module. We show that glacier geometry, area, volume and flow velocity evolve differently, especially at the level of individual glaciers. This highlights the importance of accounting for debris-cover and its spatio-temporal evolution when projecting future glacier changes.
Future growth and decline of high mountain Asia's ice-dammed lakes and associated risk
Compagno, Loris; Huss, Matthias; Zekollari, Harry; et al. (2022)
Communications Earth & Environment
Glaciers around the world are shrinking rapidly and will continue to do so in the next decades. Anticipating the consequences resulting from such glacier changes is key to design and implement adequate mitigation measures. Here, we focus on the future evolution of potential ice-dammed and supraglacial lakes in High Mountain Asia, as such lakes are responsible for the majority of glacier lake outburst floods in the region. We identify 11,129 potential lakes at present, with a total maximum volume of 2070 million m3. We find a strong correlation between large modelled lakes and historical outburst floods. By accounting for the evolution of glaciers under different climate change mitigation measures, we project that the number of potential ice-dammed lakes could increase by between 15 and 18% until 2080, with a concomitant 45–55% increase in their volume. Our findings thus suggest that a temporary increase of glacier lake outburst floods is to be expected in the coming decades.
Modelling supraglacial debris-cover evolution from the single-glacier to the regional scale: an application to High Mountain Asia
Compagno, Loris; Huss, Matthias; Miles, Evan Stewart; et al. (2022)
The Cryosphere
Currently, about 12 %–13 % of High Mountain Asia’s glacier area is debris-covered, which alters its surface mass balance. However, in regional-scale modelling approaches, debris-covered glaciers are typically treated as clean-ice glaciers, leading to a bias when modelling their future evolution. Here, we present a new approach for modelling debris area and thickness evolution, applicable from single glaciers to the global scale. We derive a parameterization and implement it as a module into the Global Glacier Evolution Model (GloGEMflow), a combined mass-balance ice-flow model. The module is initialized with both glacier-specific observations of the debris' spatial distribution and estimates of debris thickness. These data sets account for the fact that debris can either enhance or reduce surface melt depending on thickness. Our model approach also enables representing the spatiotemporal evolution of debris extent and thickness. We calibrate and evaluate the module on a selected subset of glaciers and apply GloGEMflow using different climate scenarios to project the future evolution of all glaciers in High Mountain Asia until 2100. Explicitly accounting for debris cover has only a minor effect on the projected mass loss, which is in line with previous projections. Despite this small effect, we argue that the improved process representation is of added value when aiming at capturing intra-glacier scales, i.e. spatial mass-balance distribution. Depending on the climate scenario, the mean debris-cover fraction is expected to increase, while mean debris thickness is projected to show only minor changes, although large local thickening is expected. To isolate the influence of explicitly accounting for supraglacial debris cover, we re-compute glacier evolution without the debris-cover module. We show that glacier geometry, area, volume, and flow velocity evolve differently, especially at the level of individual glaciers. This highlights the importance of accounting for debris cover and its spatiotemporal evolution when projecting future glacier changes.
Brief communication: Do 1.0, 1.5, or 2.0 °C matter for the future evolution of Alpine glaciers?
Compagno, Loris; Eggs, Sarah; Huss, Matthias; et al. (2021)
The Cryosphere
With the Paris Agreement, the urgency of limiting ongoing anthropogenic climate change has been recognised. More recent discussions have focused on the difference of limiting the increase in global average temperatures below 1.0, 1.5, or 2.0 ∘C compared to preindustrial levels. Here, we assess the impacts that such different scenarios would have on both the future evolution of glaciers in the European Alps and the water resources they provide. Our results show that even half-degree differences in global temperature targets have important implications for the changes predicted until 2100, and that – for the most optimistic scenarios – glaciers might start to partially recover, owing to possibly decreasing temperatures after the end of the 21st century.
Process-based modelling for regional- to global- scale future impacts of glacier changes
Compagno, Loris (2022)
As a direct consequence of climate change, glaciers worldwide are rapidly losing mass. This trend is projected to continue in the future, with consequences for sea level, natural hazards, water availability, and tourism. Quantifying the future evolution of glaciers under different climate scenarios by using process-based glacier evolution models is the key to anticipate glacier-related impacts, to undertake appropriate and prompt mitigation measures, and to anticipate future adaptations. In this thesis, the global glacier evolution model GloGEMflow is further developed and evaluated to simulate the evolution of glaciers at regional to global scales. An important focus is on the impacts of changing glaciers, which includes studies on potential hazardous ice-dammed lakes, glacier runoff contribution to streamflow, and the potential of changing glaciers for hydropower generation. The first chapter addresses the sensitivity of different climate forcing products on the modelled glacier evolution. To do so, we initialize GloGEMflow with three distinct climate datasets in the past (E-OBS, ERA-I, ERA-5), while the future climate is prescribed by using output from various regional and global-scale climate models. The analysis is performed for Scandinavian and Icelandic glaciers, for which the evolution is modelled from 2000 to 2100. We find that the projected evolution is only slightly (between 5 and 7 %) impacted by the choice of utilized climate data, which we attribute to our model calibration strategy that relies on observed glacier-specific mass balances. In the second part of the thesis, a new approach for modelling the evolution of supraglacial glacier debris cover both in space (including thickness) and time is developed and is integrated in GloGEMflow. Debris cover is known to strongly affect the mass balance of glaciers, and this is particularly true in High Mountain Asia, where glaciers deliver water to more than one billion people. The newly developed debris-cover module is initialized with both glacier-specific observations on the debris’ spatial distribution and estimates of debris thickness. Our results suggest that explicitly accounting for debris cover has only a minor effect of between 1 and 3% difference on the projected regional volume change by 2100 compared to not accounting for explicitly debris cover. Despite this, we argue that the improved process representation has a strong added value when aiming at capturing the spatial mass balance distribution within a glacier, and that the effect is not negligible when considering differences between individual glaciers. The third part of the thesis focuses on the future evolution of potential ice-dammed and supraglacial lakes in High Mountain Asia. In this region, such lakes are responsible for the majority of glacier lake outburst floods, regularly causing fatalities and economic damage. We find a strong correlation between large modelled lakes and historical outburst floods. By accounting for the evolution of glaciers under different climate scenarios, we project the future evolution of glacier-dammed lakes throughout the 21st century. The results show that the increase in the number and volume of ice-dammed lakes by 2080 could be between 15 and 18% and 45 to 55 %, respectively. This suggest a potential concomitant increase in glacial lake outburst floods. From 2080, ice-dammed lakes’ volume and numbers decrease as a consequence of the loss in glacier area that dominates the signal. In the fourth part, we study the effect that limiting the increase in global average temperatures to 1.0, 1.5, or 2.0 C compared to pre-industrial levels has on the future glacier evolution. This exercise is focused on the European Alps, sheds light on the urgency of limiting anthropogenic climate change from a glaciological perspective, and highlights the consequences from a water resources perspective. The results indicate that every half-degree difference in global temperature has strong implications for the future evolution of glaciers and their runoff in the European Alps. By 2100, Alpine glaciers are projected to lose 44 21% (+1.0 C), 68 12 % (+1.5 C), and 81 8% (+2.0 C) of their 2020 ice volume. The analysis also includes some projections of glaciers that go beyond the typically-used 2100 time horizon. More specifically, we show that under low-emission scenarios, a stabilization and possible re-advance of glaciers is possible throughout the 22nd and 23rd century in the European Alps. Finally, we analyze the water storage and hydropower potential of mountain areas projected to become ice-free during the course of the 21st century. Thus, we perform a first-order suitability assessment of constructing a dam in front of each glacier on Earth, taking into account environmental, technical and economic factors. Globally, we estimate a maximal, theoretical total storage and hydropower potential of 875 260km3 and 1,355 515TWha-1, respectively. These results indicate that deglaciating basins could provide an important contribution to national energy supplies in a number of countries, which would be particularly relevant in High Mountain Asia.
Process-Based Modelling for Regional- to Global- Scale Future Impacts of Glacier Changes
Compagno, Loris (2022)
VAW-Mitteilungen
Glacier preservation doubled by limiting warming to 1.5°C versus 2.7°C
Zekollari, Harry; Schuster, Lilian; Maussion, Fabien; et al. (2025)
Science
Glaciers adapt slowly to changing climatic conditions, with long-term implications for sea-level rise and water supply. Using eight glacier models, we simulated global glacier evolution over multicentennial timescales, allowing glaciers to equilibrate with climate under various constant global temperature scenarios. We estimate that glaciers globally will lose 39 (range, 15 to 55)% of their mass relative to 2020, corresponding to a global mean sea-level rise of 113 (range, 43 to 204) mm even if temperatures stabilized at present-day conditions. Under the +1.5°C Paris Agreement goal, more than twice as much global glacier mass remains at equilibration (53% versus 24%) compared with the warming level resulting from current policies (+2.7°C by 2100 above preindustrial). Our findings stress the need for stringent mitigation policies to ensure the long-term preservation of glaciers.
Global glacier change in the 21st century: Every increase in temperature matters
Rounce, David R.; Hock, Regine; Maussion, Fabien; et al. (2023)
Science
Glacier mass loss affects sea level rise, water resources, and natural hazards. We present global glacier projections, excluding the ice sheets, for shared socioeconomic pathways calibrated with data for each glacier. Glaciers are projected to lose 26 ± 6% (+1.5°C) to 41 ± 11% (+4°C) of their mass by 2100, relative to 2015, for global temperature change scenarios. This corresponds to 90 ± 26 to 154 ± 44 millimeters sea level equivalent and will cause 49 ± 9 to 83 ± 7% of glaciers to disappear. Mass loss is linearly related to temperature increase and thus reductions in temperature increase reduce mass loss. Based on climate pledges from the Conference of the Parties (COP26), global mean temperature is projected to increase by +2.7°C, which would lead to a sea level contribution of 115 ± 40 millimeters and cause widespread deglaciation in most mid-latitude regions by 2100.

Publications 1 - 9 of 9

Loris Compagno

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