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Observations of glacier mass changes are key to understanding the response of glaciers to climate change and related impacts, such as regional runoff, ecosystem changes, and global sea level rise. Spaceborne optical and radar sensors make it possible to quantify glacier elevation changes, and thus multi-annual mass changes, on a regional and global scale. However, estimates from a growing number of studies show a wide range of results with differences often beyond uncertainty bounds. Here, we present the outcome of a community-based inter-comparison experiment using spaceborne optical stereo (ASTER) and synthetic aperture radar interferometry (TanDEM-X) data to estimate elevation changes for defined glaciers and target periods that pose different assessment challenges. Using provided or self-processed digital elevation models (DEMs) for five test sites, 12 research groups provided a total of 97 spaceborne elevation-change datasets using various processing approaches. Validation with airborne data showed that using an ensemble estimate is promising to reduce random errors from different instruments and processing methods but still requires a more comprehensive investigation and correction of systematic errors. We found that scene selection, DEM processing, and co-registration have the biggest impact on the results. Other processing steps, such as treating spatial data voids, differences in survey periods, or radar penetration, can still be important for individual cases. Future research should focus on testing different implementations of individual processing steps (e.g. co-registration) and addressing issues related to temporal corrections, radar penetration, glacier area changes, and density conversion. Finally, there is a clear need for our community to develop best practices, use open, reproducible software, and assess overall uncertainty to enhance inter-comparison and empower physical process insights across glacier elevation-change studies. [ABSTRACT FROM AUTHOR]

Observations of glacier mass changes are key to understanding the response of glaciers to climate change and related impacts, such as regional runoff, ecosystem changes, and global sea-level rise. Spaceborne optical and radar sensors make it possible to quantify glacier elevation changes, and thus multi-annual mass changes, on a regional and global scale. However, estimates from a growing number of studies show a wide range of results with differences often beyond uncertainty bounds. Here, we present the outcome of a community-based inter-comparison experiment using spaceborne optical stereo (ASTER) and synthetic aperture radar interferometry (TanDEM-X) data to estimate elevation changes for defined glaciers and target periods that pose different assessment challenges. Using provided or self-processed digital elevation models (DEMs) for five test sites, 12 research groups provided a total of 97 spaceborne elevation-change datasets using various processing strategies. Validation with airborne data showed that using an ensemble estimate is promising to reduce random errors from different instruments and processing methods, but still requires a more comprehensive investigation and correction of systematic errors. We found that scene selection, DEM processing, and co-registration have the biggest impact on the results. Other processing steps, such as treating spatial data voids, differences in survey periods, or radar penetration, can still be important for individual cases. Future research should focus on testing different implementations of individual processing steps (e.g. co-registration) and addressing issues related to temporal corrections, radar penetration, glacier area changes, and density conversion. Finally, there is a clear need for our community to develop best practices, use open, reproducible software, and assess overall uncertainty in order to enhance inter-comparison and empower physical process insights across glacier elevation-change studies. [ABSTRACT FROM AUTHOR]

Some of the highest specific mass change rates in Antarctica are reported for the Antarctic Peninsula. However, the existing estimates for the northern Antarctic Peninsula (<70 ∘ S) are either spatially limited or are affected by considerable uncertainties. The complex topography, frequent cloud cover, limitations in ice thickness information, boundary effects, and uncertain glacial–isostatic adjustment estimates affect the ice sheet mass change estimates using altimetry, gravimetry, or the input-output method. Within this study, the first assessment of the geodetic mass balance throughout the ice sheet of the northern Antarctic Peninsula is carried out employing bi-static synthetic aperture radar (SAR) data from the TanDEM-X satellite mission. Repeat coverages from the austral winters of 2013 and 2017 are employed. Overall, coverage of 96.4 % of the study area by surface elevation change measurements and a total mass budget of -24.1±2.8 Gt a -1 are revealed. The spatial distribution of the surface elevation and mass changes points out that the former ice shelf tributary glaciers of the Prince Gustav Channel, Larsen A and B, and Wordie ice shelves are the hotspots of ice loss in the study area and highlights the long-lasting dynamic glacier adjustments after the ice shelf break-up events. The highest mass change rate is revealed for the Airy–Seller–Fleming glacier system at -4.9±0.6 Gt a -1 , and the highest average surface elevation change rate of -2.30±0.03 m a -1 is observed at Drygalski Glacier. The comparison of the ice mass budget with anomalies in the climatic mass balance indicates, that for wide parts of the southern section of the study area, the mass changes can be partly attributed to changes in the climatic mass balance. However, imbalanced high ice discharge drives the overall ice loss. The previously reported connection between mid-ocean warming along the southern section of the west coast and increased frontal glacier recession does not repeat in the pattern of the observed glacier mass losses, excluding in Wordie Bay. The obtained results provide information on ice surface elevation and mass changes for the entire northern Antarctic Peninsula on unprecedented spatially detailed scales and with high precision and will be beneficial for subsequent analysis and modeling. [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]

Glaciers in the Russian High Arctic have been subject to extensive atmospheric warming due to global climate change, yet their contribution to sea level rise has been relatively small over the past decades. Here we show surface elevation change measurements and geodetic mass balances of 93 % of all glacierized areas of Novaya Zemlya, Severnaya Zemlya, and Franz Josef Land using interferometric synthetic aperture radar measurements taken between 2010 and 2017. We calculate an overall mass loss rate of -22±6 Gt a -1 , corresponding to a sea level rise contribution of 0.06±0.02 mm a -1. Compared to measurements prior to 2010, mass loss of glaciers on the Russian archipelagos has doubled in recent years. [ABSTRACT FROM AUTHOR]

Mountain glaciers are known to be strongly affected by global climate change. Here we compute temporally consistent changes in glacier area, surface elevation and ice mass over the entire European Alps between 2000 and 2014. We apply remote sensing techniques on an extensive database of optical and radar imagery covering 93% of the total Alpine glacier volume. Our results reveal rapid glacier retreat across the Alps (−39 km² a−1) with regionally variable ice thickness changes (−0.5 to −0.9 m a−1). The strongest downwasting is observed in the Swiss Glarus and Lepontine Alps with specific mass change rates up to −1.03 m.w.e. a−1. For the entire Alps a mass loss of 1.3 ± 0.2 Gt a−1 (2000–2014) is estimated. Compared to previous studies, our estimated mass changes are similar for the central Alps, but less negative for the lower mountain ranges. These observations provide important information for future research on various socio-economic impacts like water resource management, risk assessments and tourism. Glaciers in the European Alps are strongly affected by global warming, yet there is no methodologically consistent alpine-wide analysis on glacier changes. Here the authors show significant glacier retreat and an ice mass loss of 1.3 ± 0.2 Gt a−1, derived from contemporaneous measurements of glacier areas and elevations. [ABSTRACT FROM AUTHOR]

Climate change has led to a significant shrinkage of glaciers in the Tropical Andes during the last decades. Recent multi-temporal quantifications of ice mass loss at mountain range to regional scale are missing. However, this is fundamental information for future water resource planning and glacier change projections. In this study, we measure temporally consistent glacier area changes and geodetic mass balances throughout the Bolivian Cordillera Real and Tres Cruces based on multi-sensor remote-sensing data. By analyzing multi-spectral satellite images and interferometric SAR data, a glacier recession of 81 ± 18 km2 (29%; 5.1 ± 1.1 km2 a−1), a geodetic mass balance of −403 ± 78 kg m−2 a−1 and a total ice mass loss of 1.8 ± 0.5 Gt is derived for 2000–2016. In the period 2013–2016, ice mass loss was 21% above the average rate. A retreat rate of 15 ± 5 km2 a−1 and a mass budget of −487 ± 349 kg m−2 a−1 are found in this more recent period. These higher change rates can be attributed to the strong El Niño event in 2015/16. The analyses of individual glacier changes and topographic variables confirmed the dependency of the mass budget and glacier recession on glacier aspect and median elevation. [ABSTRACT FROM AUTHOR]

Glaciers in tropical regions are very sensitive to climatic variations and thus strongly affected by climate change. The majority of the tropical glaciers worldwide are located in the Peruvian Andes, which have shown significant ice loss in the last century. Here, we present the first multi-temporal, region-wide survey of geodetic mass balances and glacier area fluctuations throughout Peru covering the period 2000–2016. Glacier extents are derived from Landsat imagery by performing automatic glacier delineation based on a combination of the NDSI and band ratio method and final manual inspection and correction. The mapping of debris-covered glacier extents is supported by synthetic aperture radar (SAR) coherence information. A total glacier area loss of -548.5±65.7 km 2 (-29 %, -34.3 km 2 a -1) is obtained for the study period. Using interferometric satellite SAR acquisitions, bi-temporal geodetic mass balances are derived. An average specific mass balance of -296±41 kg m -2 a -1 is found throughout Peru for the period 2000–2016. However, there are strong regional and temporal differences in the mass budgets ranging from 45±97 to -752±452 kg m -2 a -1. The ice loss increased towards the end of the observation period. Between 2013 and 2016, a retreat of the glacierized area of -203.8±65.7 km 2 (-16 %, -101.9 km 2 a -1) is mapped and the average mass budget amounts to -660±178 kg m -2 a -1. The glacier changes revealed can be attributed to changes in the climatic settings in the study region, derived from ERA-Interim reanalysis data and the Oceanic Nino Index. The intense El Niño activities in 2015/16 are most likely the trigger for the increased change rates in the time interval 2013–2016. Our observations provide fundamental information on the current dramatic glacier changes for local authorities and for the calibration and validation of glacier change projections. [ABSTRACT FROM AUTHOR]

Analysis of a recent surge of Morsnevbreen, Svalbard, is used to test predictions of the enthalpy balance theory of surging. High-resolution time series of velocities, ice thickness and crevasse distribution allow key elements of the enthalpy (internal energy) budget to be quantified for different stages of the surge cycle. During quiescence (1936–1990), velocities were very low, and geothermal heat slowly built-up enthalpy at the bed. Measurable mass transfer and frictional heating began in 1990–2010, then positive frictional heating-velocity feedbacks caused gradual acceleration from 2010 to 2015. Rapid acceleration occurred in summer 2016, when extensive crevassing and positive air temperatures allowed significant surface to bed drainage. The surge front reached the terminus in October 2016, coincident with a drop in velocities. Ice plumes in the fjord are interpreted as discharge of large volumes of supercooled water from the bed. Surge termination was prolonged, however, indicating persistence of an inefficient drainage system. The observations closely match predictions of the theory, particularly build-up of enthalpy from geothermal and frictional heat, and surface meltwater, and the concomitant changes in ice-surface elevation and velocity. Additional characteristics of the surge reflect spatial processes not represented in the model, but can be explained with respect to enthalpy gradients. [ABSTRACT FROM AUTHOR]

Although the glaciers in the Antarctic periphery currently modestly contribute to sea level rise, their contribution is projected to increase substantially until the end of the 21st century. The South Shetland Islands (SSI), located to the north of the Antarctic Peninsula, are lacking a geodetic mass balance calculation for the entire archipelago. We estimated its geodetic mass balance over a 3–4-year period within 2013–2017. Our estimation is based on remotely sensed multispectral and interferometric SAR data covering 96% of the glacierized areas of the islands considered in our study and 73% of the total glacierized area of the SSI archipelago (Elephant, Clarence, and Smith Islands were excluded due to data limitations). Our results show a close to balance, slightly negative average specific mass balance for the whole area of −0.106 ± 0.007 m w.e. a−1, representing a mass change of −238 ± 12 Mt a−1. These results are consistent with a wider scale geodetic mass balance estimation and with glaciological mass balance measurements at SSI locations for the same study period. They are also consistent with the cooling trend observed in the region between 1998 and the mid-2010s. [ABSTRACT FROM AUTHOR]

Glaciers worldwide undergo drastic changes in adaption to changing climatic conditions.Accelerated retreat and surface lowering have been reported by numerous studiesfrom various glaciated regions. A detailed knowledge about their status is of broadpublic interest, as glaciers are essential fresh water resources in semi-arid and aridregions and drivers of sea level change. The aim of this study is to provide a statusinformation in respect to the mass change of mountain glaciers between 60˚ Nand 56˚ S. Our glacier specific dataset covers a time range between 2000 and2011-2015. We derive digital elevation models (DEM) from TanDEM-X (TerraSAR-Add-on for Digital Elevation Measurements), a SAR bi-static satellite radarmission operated by the German Aerospace Center DLR and EADS. We primarily usescenes from the years 2011 -2013 acquired during the first global DEM phase of themission. These DEMs are co-registered and compared to DEMs of the Shuttle RadarTopography Mission (SRTM) acquired in February 2000. we compute surface elevationchange and calculate geodetic mass balance on the glaciated areas outside the polarregions. Our results show a total glacier mass change rate of -19.43±0.60 Gt a−1 for the SouthAmerican continent over the observation period. This loss is predominantly driven bythe large Patagonian icefields and its outlet glaciers. Regarding Tierra del Fuegoand tropical South America our results show less distinct glacier depletion thanpreviously conducted studies. For the High Mountain Asia covering the Himalaya,Nyainqentangla, Hindu Kush and Karakoram ranges our preliminary results reveal a masschange rate of -9.7±0.79 Gt a−1. This value is lower than previously publishedworks. To complete the global perspective, more than 3000 TanDEM-X datasets are currentlypassing through our elaborated processing chain to derive elevation change data also for theremaining regions (North American Continent, New Zealand and the missing regions ofAsia). The approach will result in an unprecedented, nearly worldwide consistent elevationchange database for individual glaciers. It will help understand the fate of terrestrial icebodies on different geographic scales and support modelling activities as a fundamentalcal/val dataset. We recommend regular acquisitions of TanDEM-X imagery over glaciatedground to update this baseline data. The technology and developed methods constitute highlyefficient tools for large-scale monitoring in particular in regions of pervasive cloud cover. [ABSTRACT FROM AUTHOR]

Tropical glaciers are very sensitive to climatic changes and therefore strongly affected by global warming. Nearly all glaciers in the tropics are located in the Peruvian and Bolivian Andes, where significant glacier recession was reported since in the last century. Previous studies regarding ice mass loss and glacier retreat focus on specific mountain ranges or individual glaciers and consider different observation periods. In this study, we carried out the first multi-temporal, region wide analysis of geodetic glacier mass balances and area changes throughout Peru and Bolivia, by means of multi-sensor remote sensing, for the study period 2000-2016. A total glacier area loss of -29% (-37 km² a-1) is derived by automatic glacier mapping using Landsat imagery. Geodetic mass balances are derived from interferometric SAR acquisitions. An average specific mass balance of -395±55 kg m-2 a-1 is computed for the period 2000-2016. A strong regional and temporal variability in the mass balances ranging between 68±102 kg m-2 a-1 to -990±476 kg m-2 a-1 is found. For the period 2013-2016, increased glacier recession of -117 km² a-1 and a more negative mass budget of -753±178 kg m-2 a-1 is discovered. The observed glaciological changes can be correlated with changes in the climatic conditions and the strong El Niño event in 2015/16 is most likely the reason for the high ice loss rates in the period 2013-2016. Run off from the glaciated areas is a important water resource for large regions in Peru and Bolivia and our measurements provide crucial information for water resource management and glacier change projections. [ABSTRACT FROM AUTHOR]