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Retreating glaciers and thawing permafrost are causing local- to regional-scale hazards that threaten lives and livelihoods, infrastructure, sustainable resource development, and national security. Permafrost hazards are gradually impacting people across the Arctic, while glacier/permafrost hazard cascades are abrupt, more localized, and most life threatening. Broad-scale hazard identification and assessment across the Arctic are needed to better inform stakeholder decision making.

Andreas Kääb Nicht alle Gebirgsgletscher der Erde fließen gemächlich, mit typischen Geschwindigkeiten von wenigen Metern bis hunderten von Metern pro Jahr. Einzelne Gletscher können instabil werden und sich vorübergehend viel schneller bewegen. Sogenannte »galoppierende« Gletscher, meist mit dem englischen Fachbegriff »surges« bezeichnet, fließen über Zeiträume von Monaten bis zu wenigen Jahren mit bis zu mehreren Kilometern pro Jahr und stoßen dabei oft auch über mehrere Kilometer vor. Bei einer weiteren Art von Gletscherinstabilität, Eislawinen, bricht von steilen Gletscherpartien Eis ab und erzeugt Lawinen, ähnlich Schneelawinen. Eine dritte seltene Art von Gletscherinstabilitäten, die erst vor kurzem erkannt wurde, kombiniert die großen Volumina von »surges« mit den hohen Geschwindigkeiten von Eislawinen. Bei diesen Gletscherlawinen rutschen große Teile flacher Gebirgsgletscher, mit einem Volumen von bis zu 100 Millionen Kubikmeter und mehr, plötzlich ab und rasen mit Geschwindigkeiten bis zu 300 km/h zu Tale. Die Klimaerwärmung verändert wo, wie häufig und wie große Gletscherinstabilitäten in den Hochgebirgen und den Polarregionen der Erde geschehen können. Allerdings sind die Wechselwirkungen diese Ereignisse mit dem Klima (z.B. Anstieg der Lufttemperaturen, Veränderung des Niederschlags) sehr komplex. Je nach lokalen Gegebenheiten können die Gefahren aus diesen Prozessen zu- oder abnehmen. When glaciers slide down: Not all mountain glaciers on Earth flow slowly, with typical speeds of a few meters to hundreds of meters per year. Individual glaciers can become unstable and temporarily move much faster. So-called surging glaciers flow over periods of months to a few years at up to several kilometres per year, and often advance over several kilometres. In another type of glacier instability, ice avalanches, ice breaks off from steep glacier areas and creates avalanches, similar to snow avalanches. A third, though rare type of glacier instability, which was only recently recognized, combines the large volumes of glacier surges with the high speeds of ice avalanches. In these glacier detachments, large parts of flat mountain glaciers, up to 100 million cubic meters and more, suddenly slide off and race down a valley at speeds of up to 300 km / h. Global warming is changing where, how often and how large glacier instabilities can occur in the high mountains and Polar Regions of the world. Changes in ice avalanches, glacier surges, and glacier detachments, however, are associated in a complex way with an increase in air temperatures. Depending on local conditions, the hazards from these processes can increase or decrease.

Raw data of "Subglacial permafrost dynamics and erosion inside subglacial channels driven by surface events in Svalbard" published in The Cryosphere. This data comprises temperature data from subglacial drainage systems of two glacier on Svalbard. Given are dates with time and temperatures in °C. The following temperatures are measured: Air temperatures inside drainage systems (called air), ice temperatures and sediment temperatures. Detailed descriptions of the measurements can be found in: https://doi.org/10.5194/tc-2020-124

The PlanetScope constellation consists of ∼150 optical cubesats that are evenly distributed like strings of pearls on two orbital planes, scanning the Earth's land surface once per day with an approximate spatial image resolution of 3 m. Subsequent cubesats on each of the orbital planes image the Earth surface with a nominal time lag of approximately 90 s between them, which produces near-simultaneous image pairs over the across-track overlaps of the cubesat swaths. We exploit this short time lag between subsequent Planet cubesat images to track river ice floes on northern rivers as indicators of water surface velocities. The method is demonstrated for a 60 km long reach of the Amur River in Siberia, and a 200 km long reach of the Yukon River in Alaska. The accuracy of the estimated horizontal surface velocities is of the order of ±0.01 m s−1. The application of our approach is complicated by cloud cover and low sun angles at high latitudes during the periods where rivers typically carry ice floes, and by the fact that the near-simultaneous swath overlaps, by design, do not cover the complete Earth surface. Still, the approach enables direct remote sensing of river surface velocities for numerous cold-region rivers at a number of locations and occasionally several times per year – which is much more frequent and over much larger areas than currently feasible. We find that freeze-up conditions seem to offer ice floes that are generally more suitable for tracking, and over longer time periods, compared with typical ice break-up conditions. The coverage of river velocities obtained could be particularly useful in combination with satellite measurements of river area, and river surface height and slope.

Permafrost is an Essential Climate Variable (ECV) within the Global Climate Observing System (GCOS), which is characterized by subsurface temperatures and the depth of the seasonal thaw layer. Complementing ground-based monitoring networks, the Permafrost CCI project funded by the European Space Agency (ESA) 2018-2021 will establish Earth Observation (EO) based products for the permafrost ECV spanning the last two decades. Since ground temperature and thaw depth cannot be directly observed from space-borne sensors, we will ingest a variety of satellite and reanalysis data in a ground thermal model, which allows to quantitatively characterize the changing permafrost systems in Arctic and High-Mountain areas. As recently demonstrated for the Lena River Delta in Northern Siberia, the algorithm uses remotely sensed data sets of Land Surface Temperature (LST), Snow Water Equivalent (SWE) and landcover to drive the transient permafrost model CryoGrid 2, which yields ground temperature at various depths, in addition to thaw depth. For the circumpolar CCI product, we aim for a spatial resolution of 1km, and ensemble runs will be performed for each pixel to represent the subgrid variability of snow and land cover. The performance of the transient algorithm crucially depends on the correct representation of ground properties, in particular ice and organic contents. Therefore, the project will compile a new subsurface stratigraphy product which also holds great potential for improving Earth System Model results in permafrost environments. We present simulation runs for various permafrost regions and characterize the accuracy and ability to reproduce trends against ground-based data. Finally, we evaluate the feasibility of future “permafrost reanalysis” products, exploiting the information content of various satellite products to deliver the best possible estimate for the permafrost thermal state over a range of spatial scales.

The cryosphere is defined by the presence of frozen water in its many forms: glaciers, ice caps, ice sheets, snow, permafrost, and river and lake ice. In the extended Hindu Kush Himalaya (HKH) region, including the Pamirs, Tien Shan and Alatua, the cryosphere is a key freshwater resource, playing a vital and significant role in local and regional hydrology and ecology. Industry, agriculture, and hydroelectric power generation rely on timely and sufficient delivery of water in major river systems; changes in the cryospheric system may thus pose challenges for disaster risk reduction in the extended HKH region.

Satellite measurements of coseismic displacements are typically based on synthetic aperture radar (SAR) interferometry or amplitude tracking, or based on optical data such as from Landsat, Sentinel-2, SPOT, ASTER, very high-resolution satellites, or air photos. Here, we evaluate a new class of optical satellite images for this purpose – data from cubesats. More specific, we investigate the PlanetScope cubesat constellation for horizontal surface displacements by the 14 November 2016 Mw 7.8 Kaikoura, New Zealand, earthquake. Single PlanetScope scenes are 2–4 m-resolution visible and near-infrared frame images of approximately 20–30 km × 9–15 km in size, acquired in continuous sequence along an orbit of approximately 375–475 km height. From single scenes or mosaics from before and after the earthquake, we observe surface displacements of up to almost 10 m and estimate matching accuracies from PlanetScope data between ±0.25 and ±0.7 pixels (∼ ±0.75 to ±2.0 m), depending on time interval and image product type. Thereby, the most optimistic accuracy estimate of ±0.25 pixels might actually be typical for the final, sun-synchronous, and near-polar-orbit PlanetScope constellation when unrectified data are used for matching. This accuracy, the daily revisit anticipated for the PlanetScope constellation for the entire land surface of Earth, and a number of other features, together offer new possibilities for investigating coseismic and other Earth surface displacements and managing related hazards and disasters, and complement existing SAR and optical methods. For comparison and for a better regional overview we also match the coseismic displacements by the 2016 Kaikoura earthquake using Landsat 8 and Sentinel-2 data.

This book focuses on the complexities of glaciers as documented via satellite observations. The complexities drive much scientific interest in the subject. The essence—that the world’s glaciers and ice caps exhibit overwhelming retreat—is also developed by this book. In this introductory chapter, we aim at providing the reader with background information to better understand the integration of the glacier-mapping initiative known as Global Land Ice Measurements from Space (GLIMS, http://www.glims.org ) within the framework of internationally coordinated glacier-monitoring activities. The chapter begins with general definitions of perennial ice on land and its global coverage, followed by a section on the relation between glaciers and climate. Brief overviews on the specific history of internationally coordinated glacier monitoring and the global monitoring strategy for glaciers and ice caps are followed by a summary of available data. We introduce the potential and challenges of satellite remote sensing for glacier monitoring in the 21st century and emphasize the importance of integrative change assessments. Lastly, we provide a synopsis of the book structure as well as some concluding remarks on worldwide glacier monitoring.

We review the use of spaceborne imagery and digital elevation models (DEMs) to evaluate glacier thinning and retreat in the Canadian Cordillera, an area that includes the provinces of British Columbia (BC), Alberta, and Yukon Territory. Glaciers in Alberta and British Columbia lost 11.1 ± 3.8 % of their area over the period 1985–2005, which represents an approximate annual shrinkage rate of 0.55 %. For the period 1985–1999 the average thinning rate of sampled glaciers was 0.78 ± 0.19 m/year water equivalent (w.e.), which equates to an annual volume loss of 22.48 ± 5.53 km3. Mean annual ice loss in the Yukon between 1977 and 2007 was 5.5 ± 1.7 km3/year, while the average mass balance for Yukon glaciers over this period was −0.45 ± 0.09 m/year. We also summarize changes in glacier extents and surface elevation from 1965 to 2005, and include examples of surging glaciers in the Yukon and glacier hazards in British Columbia.

This chapter presents an overview of some of the changes recently observed on glaciated areas in the tropical Andes of South America. Tropical glaciers are exceptional indicators of shifts in tropical climate, and the Andes are home to almost 99 % of the world’s tropical ice cover (Kaser et al. 1996). Many of the glaciated cordilleras in the northern Andes are mere remnants of what existed 50 years ago. Here we present a history of deglaciation of the Quelccaya Ice Cap in Peru, the largest body of ice in the tropics, which has lost approximately 30 % of its total area in the last 35 years; the Cordillera Blanca, a glaciated range in Peru, which has lost over 20 % of its area in the same period; glaciers in Colombia that have lost between 20–50 % or more of their area in the last few decades; Tres Cruces, a glaciated area in Bolivia, which has lost over half of its area; and one glacier in Venezuela that has lost over 90 % of its area. These changes are quite representative of overall glacier retreat throughout the tropical Andes.

Multispectral satellite data represent the primary data source for spaceborne glacier mapping and monitoring, and remote-sensing studies have generated significant results regarding global glacier observations and understandings. In this chapter we provide an overview of the use of multispectral data and the methods typically applied in glacier studies. Besides multispectral techniques based on the visible and near-infrared section and the shortwave infrared section of the spectrum, we also briefly discuss methods for analyzing thermal and radar data, with special emphasis on the mapping of debris-covered glacier ice. A further focus is on spectral change detection techniques applied to multitemporal data, with special attention to a novel image-differencing technique. Then we provide an overview of satellite image-based measurement of glacier flow. Finally, we offer a suggestion for a new combination of glacier observations to be made by both multispectral and radar/microwave remote-sensing sensors.

The Earth’s topography results from dynamic interactions involving climate, tectonics, and surface processes. In this chapter our main interest is in describing and illustrating how satellite-derived DEMs (and other DEMs) can be used to derive information about glacier dynamical changes. Along with other data that document changes in glacier area, these approaches can provide useful measurements of, or constraints on glacier volume balance and—with a little more uncertainty related to the density of lost or gained volume—mass balance. Topics covered include: basics on DEM generation using stereo image data (whether airborne or spaceborne), the use of ground control points and available software packages, postprocessing, and DEM dataset fusion; DEM uncertainties and errors, including random errors and biases; various glacier applications including derivation of relevant geomorphometric parameters and modeling of topographic controls on radiation fields; and the important matters of glacier mapping, elevation change, and mass balance assessment. Altimetric data are increasingly important in glacier studies, yet challenges remain with availability of high-quality data, the current lack of standardization for methods for requiring, processing, and representing digital elevation data, and the identification and quantification of DEM error and uncertainty.