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Glaciers are the ambassadors of climate change. Their worldwide decline has serious impacts on natural hazards, the water cycle, and sea level rise. The monitoring of glaciers documents the increasingly rapid melting, which has culminated in a suite of extreme years—for example, 2023 in North America and the European Alps. Numerical simulations of future glacier change, supported by a large basis of observational data, allow us to understand the enormous changes ahead and prepare us for a world without glaciers. Technical approaches to reduce glacier melting have been developed and are applicable locally—for example, in connection with tourist activities—but they clearly fail at the larger scale. [ABSTRACT FROM AUTHOR]

Glacier mass balance reconstructions provide a means of placing relatively short observational records into a longer-term context. Here, we use multiple proxies from Pinus cembra trees from God da Tamangur, combining tree ring anatomy and stable isotope chronologies to reconstruct seasonal glacier mass balance (i.e., winter, summer, and annual mass balance) for the nearby Silvretta Glacier over the last 2 centuries. The combination of tree ring width, radial diameter of earlywood cell lumina, and latewood radial cell wall thickness provides a highly significant reconstruction for summer mass balance, whereas for the winter mass balance, the correlation was less significant but still robust when radial cell lumina were combined with δ18O records. A combination of the reconstructed winter and summer mass balances allows the quantification of the annual mass balance of the Silvretta Glacier for which in situ measurements date back to 1919. Our reconstruction indicates a substantial increase in glacier mass during the first half of the 19th century and an abrupt termination of this phase after the end of the Little Ice Age. Since the 1860s, negative glacier mass balances have been dominant and mass losses accelerate as anthropogenic warming picks up in the Alps. [ABSTRACT FROM AUTHOR]

Glacier mass-balance reconstructions provide a means of placing relatively short observational records into a longer-term context. Here, we use multiple proxies from Pinus cembra trees from God da Tamangur combining tree-ring anatomy and stable isotope chronologies to reconstruct seasonal glacier mass balance (i.e. winter, summer and annual mass balance) for the nearby Silvrettagletscher over the last two centuries. The combination of tree-ring width, radial cell wall thickness and δ13C isotope records provide a highly significant reconstruction for summer mass balance, whereas, for winter mass balance, the correlation was less significant but still robust when radial cell lumen was combined with δ18O and δ13C records. Combination of the reconstructed winter and summer mass balances allows quantification of the annual mass balance of Silvrettagletscher, for which in-situ measurements date back to 1919. Our reconstruction indicates a substantial increase in glacier mass during the first half of the 19th century and an abrupt termination of this phase after the end of the Little Ice Age. Since the 1860s, negative glacier mass balances have been dominant and mass losses accelerate as anthropogenic warming picks up in the Alps. This abrupt termination of the Little Ice Age cannot be found if the mass balance reconstruction is obtained from the gridded temperature and precipitation fields (1 × 1 km) available for Switzerland since 1763. [ABSTRACT FROM AUTHOR]

In order to assess future glacier evolution and meltwater runoff, accurate knowledge on the volume and the ice thickness distribution of glaciers is crucial. However, in situ observations of glacier thickness are sparse in many regions worldwide due to the difficulty of undertaking field surveys. This lack of in situ measurements can be partially overcome by remote-sensing information. Multi-temporal and contemporaneous data on glacier extent and surface elevation provide past information on ice thickness for retreating glaciers in the newly deglacierized regions. However, these observations are concentrated near the glacier snouts, which is disadvantageous because it is known to introduce biases in ice thickness reconstruction approaches. Here, we show a strategy to overcome this generic limitation of so-called retreat thickness observations by applying an empirical relationship between the ice viscosity at locations with in situ observations and observations from digital elevation model (DEM) differencing at the glacier margins. Various datasets from the European Alps are combined to model the ice thickness distribution of Alpine glaciers for two time steps (1970 and 2003) based on the observed thickness in regions uncovered from ice during the study period. Our results show that the average ice thickness would be substantially underestimated (∼ 40 %) when relying solely on thickness observations from previously glacierized areas. Thus, a transferable topography-based viscosity scaling is developed to correct the modelled ice thickness distribution. It is shown that the presented approach is able to reproduce region-wide glacier volumes, although larger uncertainties remain at a local scale, and thus might represent a powerful tool for application in regions with sparse observations. [ABSTRACT FROM AUTHOR]

Spatio-temporal reconstruction of winter glacier mass balance is important for assessing long-term impacts of climate change. However, high-altitude regions significantly lack reliable observations, which is limiting the calibration of glaciological and hydrological models. Reanalysis products provide estimates of snow precipitation also for remote high-mountain regions, but this data come with inherent uncertainty, and assessing their biases is difficult given the low quantity and quality of available (long-term) in situ observations. In this study, we aim at improving knowledge on the spatio-temporal variations in winter glacier mass balance by exploring the combination of data from reanalyses and direct snow accumulation observations on glaciers using machine learning. We use the winter mass balance data of 95 glaciers distributed over the European Alps, western Canada, Central Asia and Scandinavia and compare them with the total precipitation from the ERA5 and the MERRA-2 reanalysis products during the snow accumulation seasons from 1981 until 2019. We develop and apply a machine learning model to adjust the precipitation from the reanalysis products along the elevation profile of the glaciers and consequently to reconstruct the winter mass balance in both space (for glaciers without observational data) and time (filling observational data gaps). The employed machine learning model is a gradient boosting regressor (GBR), which combines several meteorological variables from the reanalyses (e.g. air temperature, relative humidity) with topographical parameters. These GBR-derived estimates are evaluated against the winter mass balance data using (i) independent glaciers (site-independent GBR) and (ii) independent accumulation seasons (season-independent GBR). Both approaches resulted in reduced biases and increased correlation between the precipitation of the original reanalyses and the winter mass balance data of the glaciers. Generally, the GBR models have also shown a good representation of the spatial (vertical elevation intervals) and temporal (years) variability of the winter mass balance on individual glaciers. [ABSTRACT FROM AUTHOR]

Ongoing climate change and associated glacier retreat is causing rapid environmental change, including shifts in high-alpine landscapes. Glacier lakes, which can form in topographical depressions left behind by glacier retreat, are prominent features within such landscapes. Whilst model-based estimates for the number and area of future glacier lakes exist for various mountain regions across the world, the exact morphology and temporal evolution remain largely unassessed. Here, we leverage a recently released, measurement-based estimate for the subglacial topography of all glaciers in the Swiss Alps to provide an estimate about the number, size, time of emergence, and sediment infill of future glacier lakes. The topographical information is based on 2450 km of measured ice thickness profiles, whilst the temporal evolution of glaciers is obtained from a glacier evolution model forced with an ensemble of climate projections. We estimate that up to 683 potential lakes with an area >5000 m 2 and a depth >5 m could emerge across the Swiss Alps if glaciers were to disappear completely, with the potential to hold a total water volume of up to 1.16 [1.05, 1.32] km 3 (numbers and 95 % confidence interval). For a middle-of-the-road climate scenario, we estimate that about 10 % (0.12 [0.04, 0.18] km 3) and 48 % (0.56 [0.26, 0.67] km 3) of this volume could be realized by 2050 and 2100, respectively. In a first-order assessment, we also estimate that ca. 45 % of the newly emerging glacier lakes (260 out of 570) will be transient features, i.e. will disappear again before the end of the century owing to refilling with sediments released by glacial erosion and proglacial sediment transport. [ABSTRACT FROM AUTHOR]

Glacier monitoring in Switzerland has resulted in some of the longest and most complete data series globally. Mass balance observations at individual locations, starting in the 19th century, are the backbone of the monitoring as they represent the raw and original glaciological data demonstrating the response of snow accumulation and snow/ice melt to changes in climate forcing. So far, however, the variety of sources of historic measurements has not been systematically processed and documented. Here, we present a new complete and extensive point glacier mass balance dataset for the Swiss Alps that provides attributes for data quality and corresponding uncertainties. Original sources were digitized or re-assessed to validate or to correct existing entries and to identify metadata. The sources of data are highly diverse and stem from almost 140 years of records, originating from handwritten field notes, unpublished project documents, various digital sources, published reports, and meta-knowledge of the observers. The project resulted in data series with metadata for 63 individual Swiss glaciers, including more than 60 000 point observations of mass balance. Data were systematically analysed and homogenized, e.g. by supplementing partly missing information based on correlations inferred from direct measurements. A system to estimate uncertainty in all individual observations was developed indicating that annual point balance is measured with a typical error of 0.07 m water equivalent (w.e.), while the average error in winter snow measurements is 0.20 m w.e. Our dataset permits further investigating the climate change impacts on Swiss glaciers. Results show an absence of long-term trends in snow accumulation over glaciers while melt rates have substantially increased over the last 3 decades. The complete dataset is available at DOI 10.18750/massbalance.point.2021.r2021 (GLAMOS, 2021). [ABSTRACT FROM AUTHOR]

With ongoing climate change water availability in the source regions of alpine streams are at stake. In particular, dry mountain regions which currently rely on glacial meltwater will need to adapt. Since rock glaciers are more resilient to climate change and occur in nearly all high‐mountain catchments around the globe with some form of glacierization, it is of interest to investigate their contribution to runoff under different climate scenarios. Three well‐monitored rock glacier sites in the Swiss Alps (Murtèl, Ritigraben, and Schafberg) have been investigated under the climate change scenarios corresponding to low, medium and high greenhouse gas emissions to determine how their runoff contribution is affected. By the end of the 21st century, runoff from permafrost melting could account for 5–12% (12.0% for Murtèl, 7.0% for Ritigraben, and 5.0% for Schafberg) of monthly catchment runoff at maximum in an average year, and up to 50% in extreme years. For the low‐emission scenario, little change in the runoff contribution from rock glaciers is found, while the medium‐emission scenario shows increased variability and a shift in the seasonal runoff peak to earlier in the year. The high‐emission scenario indicates a further increase in the variability of the permafrost runoff contribution and also the development of a secondary seasonal peak in autumn, most prominently in the late century. [ABSTRACT FROM AUTHOR]

Accurate knowledge of the ice thickness distribution and glacier bed topography is essential for predicting dynamic glacier changes and the future developments of downstream hydrology, which are impacting the energy sector, tourism industry and natural hazard management. Using AIR-ETH, a new helicopter-borne ground-penetrating radar (GPR) platform, we measured the ice thickness of all large and most medium-sized glaciers in the Swiss Alps during the years 2016–20. Most of these had either never or only partially been surveyed before. With this new dataset, 251 glaciers – making up 81% of the glacierized area – are now covered by GPR surveys. For obtaining a comprehensive estimate of the overall glacier ice volume, ice thickness distribution and glacier bed topography, we combined this large amount of data with two independent modeling algorithms. This resulted in new maps of the glacier bed topography with unprecedented accuracy. The total glacier volume in the Swiss Alps was determined to be 58.7 ± 2.5 km3 in the year 2016. By projecting these results based on mass-balance data, we estimated a total ice volume of 52.9 ± 2.7 km3 for the year 2020. Data and modeling results are accessible in the form of the SwissGlacierThickness-R2020 data package. [ABSTRACT FROM AUTHOR]

Glacier mass-balance observations at seasonal resolution have been performed since 1914 at two sites on Claridenfirn, Switzerland. The measurements are the longest uninterrupted records of glacier mass balance worldwide. Here, we provide a complete re-analysis of the 106-year series (1914–2020), focusing on both point and glacier-wide mass balance. The approaches to evaluate and homogenize the direct observations are described in detail. Based on conservative assumptions, average uncertainties of $\pm$ 0.25 m w.e. are estimated for glacier-wide mass balances at the annual scale. It is demonstrated that long-term variations in mass balance are clearly driven by melting, whereas decadal changes in accumulation are uncorrelated with mass balance and can only be relevant in short periods. Mass change of Claridenfirn is impacted by dry calving at a frontal ice cliff. Considerations of ice volume flux at a cross-profile reveal long-term variations in frontal ice loss accounting for $\sim$ 9% of total annual ablation on average. The effect of changes in frontal ablation mostly explains $\lt$ 10% of the mass-balance difference relative to the period 1960–1990, but accounts for $\sim$ 20% in 2010–2020. Glacier mass changes are discussed in the context of observations throughout the European Alps indicating that Claridenfirn is regionally representative. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Glaciers in the European Alps rapidly lose mass to adapt to changes in climate conditions. Here, we investigate the relationship and lag between climate forcing and geometric glacier response with a regional glacier evolution model accounting for ice dynamics. The volume loss occurring as a result of the glacier‐climate imbalance increased over the early 21st century, from about 35% in 2001 to 44% in 2010. This committed loss reduced to ~40% by 2018, indicating that temperature increase was outweighing glacier retreat in the early 2000s but that the fast retreat effectively somewhat diminished glacier imbalances. We analyze the lag in glacier response for each individual glacier and find mean response times of 50 ± 28 years. Our findings indicate that the response time is primarily controlled by glacier slope and secondarily by elevation range and mass balance gradient, rather than by glacier size. Plain Language Summary: Glaciers are out of balance with present‐day climatic conditions. By using a state‐of‐the‐art computer model that can simulate the evolution of many glaciers, we show that the imbalance between glaciers in the European Alps and climatic conditions grew during the early 21st century. Although this imbalance has recently decreased, glaciers are still expected to lose an important part of their mass, even if temperatures were to be stabilized at present‐day levels. This is an expression of glaciers adapting to present‐day climatic conditions. Our simulations suggest that the glacier response is strongly dependent on the surface steepness rather than on glacier size, as commonly reported. Key Points: Climate warming outpaced glacier retreat in the European Alps until 2010, increasing the imbalance between glacier geometry and climateAfter 2010, the imbalance between glacier geometry and climate decreased, but a committed volume loss of ~40% is still projectedFirst regional glacier response time inventory accounting for ice flow, hinting at the crucial role of the glacier slope, as opposed to size [ABSTRACT FROM AUTHOR]

We model the future evolution of the largest glacier of the European Alps – Great Aletsch Glacier, Switzerland – during the 21st century. For that purpose we use a detailed three-dimensional model, which combines full Stokes ice dynamics and surface mass balance forced with the most recent climate projections (CH2018), as well as with climate data of the last decades. As a result, all CH2018 climate scenarios yield a major glacier retreat: Results range from a loss of 60% of today's ice volume by 2100 for a moderate CO2 emission scenario (RCP2.6) being in line with the Paris agreement to an almost complete wastage of the ice for the most extreme emission scenario (RCP8.5). Our model results also provide evidence that half of the mass loss is already committed under the climate conditions of the last decade. [ABSTRACT FROM AUTHOR]

Glaciers in the European Alps play an important role in the hydrological cycle, act as a source for hydroelectricity and have a large touristic importance. The future evolution of these glaciers is driven by surface mass balance and ice flow processes, of which the latter is to date not included explicitly in regional glacier projections for the Alps. Here, we model the future evolution of glaciers in the European Alps with GloGEMflow, an extended version of the Global Glacier Evolution Model (GloGEM), in which both surface mass balance and ice flow are explicitly accounted for. The mass balance model is calibrated with glacier-specific geodetic mass balances and forced with high-resolution regional climate model (RCM) simulations from the EURO-CORDEX ensemble. The evolution of the total glacier volume in the coming decades is relatively similar under the various representative concentrations pathways (RCP2.6, 4.5 and 8.5), with volume losses of about 47 %–52 % in 2050 with respect to 2017. We find that under RCP2.6, the ice loss in the second part of the 21st century is relatively limited and that about one-third (36.8 % ± 11.1 %, multi-model mean ±1σ) of the present-day (2017) ice volume will still be present in 2100. Under a strong warming (RCP8.5) the future evolution of the glaciers is dictated by a substantial increase in surface melt, and glaciers are projected to largely disappear by 2100 (94.4±4.4 % volume loss vs. 2017). For a given RCP, differences in future changes are mainly determined by the driving global climate model (GCM), rather than by the RCM, and these differences are larger than those arising from various model parameters (e.g. flow parameters and cross-section parameterisation). We find that under a limited warming, the inclusion of ice dynamics reduces the projected mass loss and that this effect increases with the glacier elevation range, implying that the inclusion of ice dynamics is likely to be important for global glacier evolution projections. [ABSTRACT FROM AUTHOR]

The European Alps, the cradle of pioneering glacial studies, are one of the regions where geological markers of past glaciations are most abundant and well-studied. Such conditions make the region ideal for testing numerical glacier models based on simplified ice flow physics against field-based reconstructions and vice versa. Here, we use the Parallel Ice Sheet Model (PISM) to model the entire last glacial cycle (120-0 ka) in the Alps, using horizontal resolutions of 2 and 1 km. Climate forcing is derived using two sources: present-day climate data from WorldClim and the ERA-Interim reanalysis; time-dependent temperature offsets from multiple palaeo-climate proxies. Among the latter, only the European Project for Ice Coring in Antarctica (EPICA) ice core record yields glaciation during marine oxygen isotope stages 4 (69-62 ka) and 2 (34-18 ka). This is spatially and temporally consistent with the geological reconstructions, while the other records used result in excessive early glacial cycle ice cover and a late Last Glacial Maximum. Despite the low variability of this Antarcticbased climate forcing, our simulation depicts a highly dynamic ice sheet, showing that Alpine glaciers may have advanced many times over the foreland during the last glacial cycle. Ice flow patterns during peak glaciation are largely governed by subglacial topography but include occasional transfluences through the mountain passes. Modelled maximum ice surface is on average 861m higher than observed trimline elevations in the upper Rhône Valley, yet our simulation predicts little erosion at high elevation due to cold-based ice. Finally, despite the uniform climate forcing, differences in glacier catchment hypsometry produce a timetransgressive Last Glacial Maximum advance, with some glaciers reaching their modelled maximum extent as early as 27 ka and others as late as 21 ka. [ABSTRACT FROM AUTHOR]

In this study we present 19 new or re-analysed series of glacier-wide seasonal mass balance for the Swiss Alps based on direct measurements. The records partly start around 1920 and continue until today. Previously unpublished and unevaluated observations of point winter and annual balance are compiled from various sources and archives. These highly valuable datasets have not yet been consistently evaluated and were thus unavailable to the scientific community. Using distributed modelling for spatial interpolation and extrapolation and homogenization of the point measurements, we infer continuous series of area-averaged mass balance. The results are validated against independent decadal ice volume changes from photogrammetric surveys. Six of the new seasonal series cover 60 years and more and add a substantial amount of information on the variations of regional glacier mass change. This will strengthen the worldwide collection of glacier monitoring data, especially for the data-sparse period before the 1980s. We compare our results to existing long-term series and present an updated assessment of mass-balance variability and glacier sensitivity throughout the European Alps. [ABSTRACT FROM AUTHOR]

In view of the rapid and accelerating glacier retreat observed in the European Alps during the last decades, the repeated creation of glacier inventories is important to understand the spatio-temporal variability of glacier changes and to support modeling studies. This article presents the latest glacier inventory for the entire Swiss Alps (SGI2010) derived by manual digitization from high-resolution (25 cm) aerial orthophotographs acquired between 2008 and 2011. Its accuracy is assessed by comparing the extents of clean, snow-and/or debris-covered glaciers derived from multiple digitization by several experts. The potential of more precise mapping of debris-covered glaciers is pointed out through the combination of aerial orthophotos with Differential Synthetic Aperture Radar Interferometry (DInSAR) techniques. In order to investigate the accuracy of glacier outlines obtained from medium-resolution satellite remote sensing imagery, a Landsat derived 2003 inventory is directly compared to all glaciers of the eastern Swiss Alps mapped with 2003 aerial orthoimagery. For the Swiss Alps, the total glacierized area mapped for 2010 is 944.3 ±24.1 km2. Resulting area changes are -362.6 km2 (-27.7%, or -0.75% a-1) between 1973 and 2010. It is shown that satellite remote sensing techniques using medium-resolution source data misclassified more than 25% in area of very small glaciers (<0.5 km2). Therefore, use of high-resolution satellite or airborne imagery for future inventory creation in areas dominated by very small glaciers is recommended. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the mass balance and ice volume change in glaciers in European Alps from 1900 to 2011. The study performs mass balance extrapolation on data obtained from world glacier monitoring services (WGMS) and field data and modeling for glaciers in France, Austria, and Italy. Result shows that European Alps have mean glacier mass balance of -0.31 ± 0.04 meter w.e. -1 in 1900-2011.

The article discusses a study which provided an analysis of the interactions between seismic activity, surface motion, and subglacial water drainage in the steep part of the temperate Triftgletscher during summer 2008. Triftgletscher is situated between the Gadmer and Hasli valleys in the Bernese Alps in Switzerland. The technique applied to evaluate surface motion and hourly runoff is described and the related results are presented. The impact of runoff changes on surface motion on a timescale of several days is observed.

We discuss potential transitions of six climatic subsystems with large-scale impact on Europe, sometimes denoted as tipping elements. These are the ice sheets on Greenland and West Antarctica, the Atlantic thermohaline circulation, Arctic sea ice, Alpine glaciers and northern hemisphere stratospheric ozone. Each system is represented by co-authors actively publishing in the corresponding field. For each subsystem we summarize the mechanism of a potential transition in a warmer climate along with its impact on Europe and assess the likelihood for such a transition based on published scientific literature. As a summary, the 'tipping' potential for each system is provided as a function of global mean temperature increase which required some subjective interpretation of scientific facts by the authors and should be considered as a snapshot of our current understanding. [ABSTRACT FROM AUTHOR]

The article addresses the future evolution and glacier retreat of Grosser Aletschgletscher, Switzerland, the largest glacier in the European Alps, in a changing climate using a three-dimensional (3D) combined surface mass-balance and glacier dynamics model. The inaccurate description of basal sliding explains the disagreements in the glacier terminus retreat along the central flowline. The median climatic evolution reveals a 90 percent decrease in glacier ice volume by the end of 2100 and potential complete disintegration. The researchers also observed the significant impact of the retarding effect of supraglacial debris on future glacier evolution on the rate of glacier terminus retreat.

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The article provides information on aspects related to tackling of water stress in Alps and distribution of water resources. Topics discussed include analysis of water-related problems and socio-economic structure, participation of scenario development, and measurement of infrastructure through inter-communal.

The artificial reduction of glacier melt is gaining increased attention due to accelerated ice wastage with atmospheric warming. In Switzerland, active coverage of glaciers using geotextiles is performed at currently nine sites and since up to 15 years. The measures represent an efficient method to locally safeguard the operability of ski slopes or other touristic attractions. Here, we present an assessment of the evolution of geotextile-covered areas and the correspondingly avoided ice melt across the Swiss Alps. Presently, about 0.18 km2, or 0.02% of the total Swiss glacier area, is covered by geotextiles, with a doubling of the covered area since 2012. Up to 350,000 m3 of ice melt per year have been mitigated by this technique. We estimate the overall costs of active glacier melt reduction, and compute the price of 1 m3 of saved glacier ice, a number relevant for planning such measures. Average costs over the last decade range from 0.6 to 7.9 CHF m−3 yr−1 depending on the type of installation and its location on the glacier. These relatively high costs are an indication for the considerable economic value attributed to glacier ice. We also show that artificial melt reduction is not scalable. Whilst local interventions can be efficient and profitable, a hypothetical application to the larger scale shows that saving Alpine glaciers by technological solutions is neither achievable nor affordable. • Active glacier melt reduction in Switzerland using geotextiles is applied at nine sites • Artificial mitigation of ice melt is locally efficient but not scalable • Investments for avoiding the melting of 1 cubic metre of ice range from 0.6 to 8 CHF per year [ABSTRACT FROM AUTHOR]

Glaciers in the European Alps play an important role for the runoff regime of mountainous drainage catchments, act as a source for hydroelectricity and have a large touristic importance. To date, studies on the future evolution of these ice masses typically rely on parameterizations, in which ice dynamics are not explicitly accounted for. So far, only few studies have explicitly coupled ice flow and surface mass balance processes, and these have focused on individual glaciers, rather than on the regional scale.Here, we model the future evolution of glaciers in the European Alps with GloGEMflow, an extended version of the Global Glacier Evolution Model (GloGEM), accounting for both surface mass balance and ice flow. Glaciers are identified through the outlines from the Randolph Glacier Inventory, and an inversion approach is utilized to estimate the initial glacier thickness. For model calibration and evaluation, we rely on an extensive dataset, including amongst others in-situ and geodetic mass balance measurements, glacier length changes, and surface velocity measurements. This allows for a novel, glacier-specific initiliaztion and calibration procedure. The climatic data for the historical period is drawn from the ENSEMBLES daily gridded observational dataset (E-OBS), while for future climatic conditions we rely on EURO-CORDEX Regional Climate Model simulations.The evolution of the total glacier volume in the coming decades is relatively similar under various representative concentrations pathways (RCPs), and about half of the present-day (2017) ice volume is lost by 2050. We find that under RCP2.6, the ice loss in the second part of the 21st century is relatively limited and that about one-third of the present-day ice volume will still present in 2100. Under a strong warming scenario (RCP8.5) the future evolution of the glaciers is determined by a substantial increase in surface melt, and glaciers are projected to largely disappear by 2100 (>90% volume and area loss vs. 2017). For a given RCP, differences in future changes are mainly determined by the driving global climate model, rather than the RCM that is coupled to it, and these differences are larger than those linked to various model parameters. We find that including ice dynamics reduces the projected mass loss under a limited warming, and that this effect increases with the glacier elevation range. Our results suggest that including ice dynamics will be important for future global glacier evolution simulations. [ABSTRACT FROM AUTHOR]

Great Aletschgletscher is the largest glacier of the European Alps. With a length of more than20 km and ice thicknesses of up to 800 m it covers an area of 80 km2. Located in theUNESCO world heritage, Aletschgletscher is one of the most important touristic natureattractions in Switzerland, but also its meltwaters have a considerable relevance for thehydrological cycle. Although the future retreat of Great Aletschgletscher has already beeninvestigated by several studies, the most recent climate scenarios, downscaled for theSwiss Alps (CH2018), permit an update and significant refinement of previousassessments. Here, we present results of a detailed three-dimensional model, combining surface massbalance and glacier dynamics, that has previously been applied and thoroughly validated forAletschgletscher. Ice flow is described with the full Stokes equations, and the glacier surfaceevolution is obtained by solving a transport equation for the volume of fluid. Daily surfacemelt and accumulation rates are calculated using a temperature-index model driven with localmeteorological data for the past. For the period 2019-2100, we rely on 68 individual climatescenarios downscaled within the CH2018 project. The scenarios refer to different GCM-RCMcombinations and have been forced with three CO2-emission pathways (RepresentativeConcentration Pathways RCP2.6, RCP4.5, and RCP8.5). In addition, we also performequilibrium experiments with repeating climate conditions of the last decades to isolatethe impact of the warming observed in recent years from the one expected in thefuture. In line with previous studies, we find a median ice volume reduction of roughly 75% by2100 compared to today for RCP4.5. The spread of the individual GCM-RCM chains is,however, considerable (–62% to –95% volume change). A complete disintegration of the14 km long glacier tongue below Konkordiaplatz is expected under this scenario, with severalremaining ice bodies only above 3000 m.a.s.l. Even for the moderate emission scenarioRCP2.6, consistent with the Paris agreement, a major retreat of Aletschgletscher is found(60% and 36% reduction in volume and area, respectively). For the extreme RCP8.5 scenario,an almost complete wastage of Aletschgletscher is indicated with just tiny remnants of ice inthe highest regions. When applying the meteorological conditions of the last 10 years(2008-2018), Aletschgletscher is found to lose almost half of its present volume and retreatby more than 10 km. This demonstrates the considerable inertia of the largest glacier of theAlps, and illustrates the important mass loss already committed with present climate. [ABSTRACT FROM AUTHOR]

Mass balance observations at seasonal resolution are performed at two measurement sitessince 1914 on Claridenfirn, Switzerland. The series is known as the worldwide longestuninterrupted measurements of glacier mass balance. Here, provide a complete re-analysis of the 104-year series of both point and glacier-widemass balance. We include a detailed description of the approaches to evaluate andhomogenize the direct observations, and perform a comprehensive estimation of theuncertainties. Particular attention is payed to losses due to ice avalanches from an ice cliff atthe glacier terminus, i.e. an ablation process different from melting, which complicates thedetermination of glacier-wide mass balance. Long-term variations in mass balancecomponents at the point-scale are interpreted in relation to ongoing changes inmeteorological forcing. Multi-decadal glacier-wide mass balances are discussed in the context of comparableobservations throughout the European Alps. Based on conservative assumptions, an overallaverage random uncertainty in annual glacier-wide mass balance of ±0.25 m w.e. a−1, and of±0.10 m w.e. a−1 at the decadal scale is found. Significant trends in melt and mass balanceare observed since the 1980s with a 38% increase in melting compared to 1961-1990 overthe last decade. Long-term variability in snow accumulation at the elevation of2700-2900 m a.s.l. is small except for a sharp decrease in the first years of the 21st century. [ABSTRACT FROM AUTHOR]

Glaciers in the Alps reached their last maximum extent at the end of the Little Ice Age (around 1850). The cause of the preceding advance and the following retreat is still debatable. Different studies attributed this evolution to temperature, winter precipitation, volcanic radiative cooling, or black carbon deposition on snow.We developed a simple model for yearly glacier volume changes. The model includes air temperature, precipitation, tropospheric and stratospheric aerosols, and black carbon concentration in snow. The effect of these forcings is implemented using mass balance sensitivities, which are partly derived from literature. For temperature and precipitation, different reconstructions were considered. The tropospheric and stratospheric aerosols are model-based. For black carbon, we used ice core measurements from Colle Gnifetti, which is located at the border between Switzerland and Italy. We conducted a great number of simulations between 1700 and 2000, in which we explored the uncertainty range of the sensitivities as well as of the forcings. The model was applied to a number of glaciers in the Swiss Alps, and simulated volume changes were compared with available geodetic mass balances. With our approach, we are able to attribute the simulated changes in glacier volume to the aforementioned forcings. Our results indicate that tropospheric and stratospheric aerosols could be crucial for explaining the rapid glacier advance in the first half of the 19th century and the subsequent retreat. However, the substantial glacier mass loss over the last 150 years is primarily driven by changes in air temperature. [ABSTRACT FROM AUTHOR]

Ice-marginal moraines are widely used as indicators of palaeoclimate in mountainous regions, yet the genetic processes of their formation remain incompletely understood. Here, we present new data on the geomorphology and sedimentology of annually formed moraine ridges in the foreland of Gornergletscher, Switzerland, with the aim of reconstructing the processes of their formation, assessing their preservation potential over longer time scales, and evaluating the climatic significance of these terrestrial archives. A specific focus is set on moraine ridges that formed between 2007 and 2019, a period when the glacier front was subject to pronounced retreat and thinning. Four dominant mechanisms of moraine formation could be identified to be operating across the foreland: (I) freeze-on of submarginal sediments to the advancing glacier sole; (II) the formation of ice-cored moraines controlled by the emergence of englacial debris bands on the glacier surface; (III) efficient bulldozing and deformation of pre-existing fluvial or lacustrine sediments by the advancing glacier; and (IV) inefficient bulldozing of these deposits with the incorporation of dead ice into moraine bodies. The spatial distribution of these processes in the foreland depends on a set of climatological, topographical, and glaciological boundary conditions, the most important of which appears to be the slope of the ice margin. The largest and most well-defined moraines can be genetically linked to efficient bulldozing operating along a sufficiently steep glacier front. These moraines frequently form parts of longer, continuous chains and can be used to calculate frontal retreat rates of the glacier through time. Comparing this record of ice retreat with climatic data reveals a statistically significant correlation to annual air temperature anomalies, which is especially strong for the period between 2005 and 2017. Longer series of annual moraines may therefore provide important information about the climatic drivers that govern glacier retreat. However, dead ice is often found to be incorporated into moraine bodies along the present, thin ice margin. Upon melt-out of the ice, the morphologies and internal structures of these moraines are strongly altered, thus limiting their preservation potential over longer timescales. In such a scenario, the morphological record remaining in a deglaciated landscape may be incomplete or entirely lacking. Therefore, we conclude that great care must be taken when interpreting moraine sequences in a palaeoclimatic context. • At Gornergletscher, minor moraines are formed by an annually advancing glacier lobe. • Thinning of the glacier in recent years has affected moraine-forming processes. • Moraines formed at a thin ice margin have a strongly limited preservation potential. • In the last decades, frontal retreat is increasingly coupled to summer temperatures. [ABSTRACT FROM AUTHOR]