A new physically based approach for calculating glacier ice thickness distribution and volume is presented and applied to all glaciers and ice caps worldwide. Combining glacier outlines of the ...globally complete Randolph Glacier Inventory with terrain elevation models (Shuttle Radar Topography Mission/Advanced Spaceborne Thermal Emission and Reflection Radiometer), we use a simple dynamic model to obtain spatially distributed thickness of individual glaciers by inverting their surface topography. Results are validated against a comprehensive set of thickness observations for 300 glaciers from most glacierized regions of the world. For all mountain glaciers and ice caps outside of the Antarctic and Greenland ice sheets we find a total ice volume of 170 × 103 ± 21 × 103 km3, or 0.43 ± 0.06 m of potential sea level rise.
Key Points
First ice volume assessment of all individual glaciers around the globe
Novel methodology to estimate glacier ice thickness distribution
Potential sea level rise of 170,000 glaciers and ice caps worldwide is 0.43 m
The use of Unmanned Aerial Vehicles (UAV) for photogrammetric surveying has recently gained enormous popularity. Images taken from UAVs are used for generating Digital Surface Models (DSMs) and ...orthorectified images. In the glaciological context, these can serve for quantifying ice volume change or glacier motion. This study focuses on the accuracy of UAV-derived DSMs. In particular, we analyze the influence of the number and disposition of Ground Control Points (GCPs) needed for georeferencing the derived products. A total of 1321 different DSMs were generated from eight surveys distributed on three glaciers in the Swiss Alps during winter, summer and autumn. The vertical and horizontal accuracy was assessed by cross-validation with thousands of validation points measured with a Global Positioning System. Our results show that the accuracy increases asymptotically with increasing number of GCPs until a certain density of GCPs is reached. We call this the optimal GCP density. The results indicate that DSMs built with this optimal GCP density have a vertical (horizontal) accuracy ranging between 0.10 and 0.25 m (0.03 and 0.09 m) across all datasets. In addition, the impact of the GCP distribution on the DSM accuracy was investigated. The local accuracy of a DSM decreases when increasing the distance to the closest GCP, typically at a rate of 0.09 m per 100-m distance. The impact of the glacier's surface texture (ice or snow) was also addressed. The results show that besides cases with a surface covered by fresh snow, the surface texture does not significantly influence the DSM accuracy.
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 climate
After 2010, the imbalance between glacier geometry and climate decreased, but a committed volume loss of ~40% is still projected
First regional glacier response time inventory accounting for ice flow, hinting at the crucial role of the glacier slope, as opposed to size
Due to climate change, worldwide glaciers are rapidly declining. The trend will continue into the future, with consequences for sea level, water availability and tourism. Here, we assess the future ...evolution of all glaciers in Scandinavia and Iceland until 2100 using the coupled surface mass-balance ice-flow model GloGEMflow. The model is initialised with three distinct past climate data products (E-OBS, ERA-I, ERA-5), while future climate is prescribed by both global and regional climate models (GCMs and RCMs), in order to analyze their impact on glacier evolution. By 2100, we project Scandinavian glaciers to lose between 67 ± 18% and 90 ± 7% of their present-day (2018) volume under a low (RCP2.6) and a high (RCP8.5) emission scenario, respectively. Over the same period, losses for Icelandic glaciers are projected to be between 43 ± 11% (RCP2.6) and 85 ± 7% (RCP8.5). The projected evolution is only little impacted by both the choice of climate data products used in the past and the spatial resolution of the future climate projections, with differences in the ice volume remaining by 2100 of 7 and 5%, respectively. This small sensitivity is attributed to our model calibration strategy that relies on observed glacier-specific mass balances and thus compensates for differences between climate forcing products.
We have reviewed about 100 studies on past changes in climate, snow cover, glaciers and runoff in Central Asian headwater catchments, which have been published in the past 20years. We included ...studies published by Central Asian researchers in Russian language, which are usually not easily accessible to international researchers.
Most studies agreed on general warming trends in Central Asia with acceleration since the 1970s, but varied with regard to seasonal changes and the magnitude of the warming. Most studies also confirmed that glaciers in the Tien Shan and the Pamir continue to retreat and to shrink, though only little is known about mass and volume changes. Only few studies investigated changes in seasonal snow cover, and they suggested a decrease in maximum snow depth and a reduction in snow cover duration. The studies on runoff trends in the high mountain areas of Central Asia indicated a complex response of catchments to changes in climate. It appears that catchments with a higher fraction of glacierized area showed mainly increasing runoff trends in the past, while river basins with less or no glacierization exhibited large variations in the observed runoff changes.
We conclude that our knowledge is still incomplete in particular with regard to the magnitude and the spatio-temporal patterns of changes in the water cycle of Central Asian headwater catchments. The limitations in our knowledge are due to (1) the scarcity of reliable and appropriate data sets especially for the glacio-nival zone; (2) methodological limitations of trend analysis; (3) the heterogeneity in both spatial and temporal extent of the available analyses, hampering the synthesis to a regional picture; and (4) the insufficiently understood interactions between changes in highly-variable climate parameters, the cryosphere, and the hydrological response of individual headwater catchments.
Finally, there is a need for sound attribution studies linking the observed hydrological changes in individual catchments to particular processes triggered by climatic and cryospheric changes. This research gap needs urgently to be closed as projections of future hydrological changes are of vital importance for water management in Central Asia.
•We provide a comprehensive review of more than 100 studies and data sets.•We discuss the underlying data sets, the methods, and the related uncertainties.•Knowledge on the magnitude and the spatio-temporal pattern of change is incomplete.•Major research gaps concern changes in seasonal snow cover and river runoff.•There is a need for detailed change attribution studies.
The potential exploitation of areas becoming ice-free in response to ongoing climate change has rarely been addressed, although it could be of interest from the water management perspective. Here we ...present an estimate for the potential of mitigating projected changes in seasonal water availability from melting glaciers by managing runoff through reservoirs. For the European Alps we estimate that by the end of the century, such a strategy could offset up to 65% of the expected summer-runoff changes from presently glacierized surfaces. A first-order approach suggests that the retention volume potentially available in the areas becoming deglacierized is in excess of the volume required for achieving the maximal possible mitigation by more than one order of magnitude. Obviously, however, such a strategy cannot compensate for the reduction in annual runoff caused by glacier ice depletion. Our estimates indicate that by 2070-2099, 0.73 0.67 km3 a−1 of this non-renewable component of the water cycle could be missing in Alpine water supplies.
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
Accurate estimations of ice thickness and volume are indispensable for ice flow modelling, hydrological forecasts and sea-level rise projections. We present a new ice thickness estimation ...model based on a mass-conserving forward model and a Bayesian inversion scheme. The forward model calculates flux in an elevation-band flow-line model, and translates this into ice thickness and surface ice speed using a shallow ice formulation. Both ice thickness and speed are then extrapolated to the map plane. The model assimilates observations of ice thickness and speed using a Bayesian scheme implemented with a Markov chain Monte Carlo method, which calculates estimates of ice thickness and their error. We illustrate the model's capabilities by applying it to a mountain glacier, validate the model using 733 glaciers from four regions with ice thickness measurements, and demonstrate that the model can be used for large-scale studies by fitting it to over 30 000 glaciers from five regions. The results show that the model performs best when a few thickness observations are available; that the proposed scheme by which parameter-knowledge from a set of glaciers is transferred to others works but has room for improvements; and that the inferred regional ice volumes are consistent with recent estimates.
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