Historically unprecedented global glacier decline in the early 21st century

Observations show that glaciers around the world are in retreat and losing mass. Internationally coordinated for over a century, glacier monitoring activities provide an unprecedented dataset of glacier observations from ground, air and space. Glacier studies generally select specific parts of these datasets to obtain optimal assessments of the mass-balance data relating to the impact that glaciers exercise on global sea-level fluctuations or on regional runoff. In this study we provide an overview and analysis of the main observational datasets compiled by the World Glacier Monitoring Service (WGMS). The dataset on glacier front variations (⇠42 000 since 1600) delivers clear evidence that centennial glacier retreat is a global phenomenon. Intermittent readvance periods at regional and decadal scale are normally restricted to a subsample of glaciers and have not come close to achieving the maximum positions of the Little Ice Age (or Holocene). Glaciological and geodetic observations (⇠5200 since 1850) show that the rates of early 21st-century mass loss are without precedent on a global scale, at least for the time period observed and probably also for recorded history, as indicated also in reconstructions from written and illustrated documents. This strong imbalance implies that glaciers in many regions will very likely suffer further ice loss, even if climate remains stable

Gletscherbeobachtung und globale Trends

Gletscher sind ein wichtiges Element der Kryosphäre und in den Hochgebirgen der Erde weit verbreitet. Ihr Beitrag zum Meeresspiegelanstieg sowie ihre Bedeutung als Klimazeiger, Wasserspeicher und -spender, sind allgemein bekannt. Sie werden seit über 100 Jahren systematisch vermessen und erlauben uns damit, das heutige Klima im Kontext der Vergangenheit zu sehen. Die lokalen Beobachtungen im Feld werden zunehmend mit Fernerkundungsdaten ergänzt, welche eine regionale Perspektive bieten und ganze Gebirgsräume abdecken. Das erlaubt eine sehr viel genauere Hochrechnung ihrer Änderungen. Die Beobachtungen zeigen, dass die Gletscher weltweit in rasantem Tempo schmelzen, sich der Abfluss verändert und sie massiv zum Meeresspiegelanstieg beitragen. Zudem verändert sich das Potenzial für Naturgefahren. In Zukunft wird die Vermessung der Gletscher immer schwieriger, da sie vielerorts zerfallen oder sich in Schuttfelder verwandeln. Glacier monitoring and global trends: Glaciers are important elements of the cryosphere that can be found in many high mountain regions on Earth. Their contribution to sea-level rise as well as their importance as a climate indicator, water reserve and resource are well known. They are systematically observed for more than 100 years and allow us to interpret current climatic conditions in the context of the past. The local observations in the field are increasingly complemented by remote sensing based data, which provide a regional perspective by covering entire mountain ranges. This allows for a much better extrapolation of their changes. The observations show that glaciers are melting at a rapid pace worldwide, with changes in runoff and a massive contribution to sea-level rise. In addition, the potential for natural hazards is also changing. In the future, it will be more and more difficult to measure glaciers, as they will disintegrate in many places or turn into scree

Exploring uncertainty in glacier mass balance modelling with Monte Carlo simulation

By means of Monte Carlo simulations we calculated uncertainty in modelled cumulative mass balance over 400 days at one particular point on the tongue of Morteratsch Glacier, Switzerland, using a glacier energy balance model of intermediate complexity. Before uncertainty assessment, the model was tuned to observed mass balance for the investigated time period and its robustness was tested by comparing observed and modelled mass balance over 11 years, yielding very small deviations. Both systematic and random uncertainties are assigned to twelve input parameters and their respective values estimated from the literature or from available meteorological data sets. The calculated overall uncertainty in the model output is dominated by systematic errors and amounts to 0.7 m w.e. or approximately 10% of total melt over the investigated time span. In order to provide a first order estimate on variability in uncertainty depending on the quality of input data, we conducted a further experiment, calculating overall uncertainty for different levels of uncertainty in measured global radiation and air temperature. Our results show that the output of a well calibrated model is subject to considerable uncertainties, in particular when applied for extrapolation in time and space where systematic errors are likely to be an important issue

The new remote-sensing-derived Swiss glacier inventory: I. Methods

A new Swiss glacier inventory is to be compiled from satellite data for the year 2000. The study presented here describes two major tasks: (1) an accuracy assessment of different methods for glacier classification with Landsat Thematic Mapper (TM) data and a digital elevation model (DEM); (2) the geographical information system (GIS)-based methods for automatic extraction of individual glaciers from classified satellite data and the computation of three-dimensional glacier parameters (such as minimum, maximum and median elevation or slope and orientation) by fusion with a DEM. First results obtained by these methods are presented in Part II of this paper (Kääb and others, 2002). Thresholding of a ratio image from TM4 and TM5 reveals the best-suited glacier map. The computation of glacier parameters in a GIS environment is efficient and suitable for worldwide application. The methods developed contribute to the U.S. Geological Survey-led Global Land Ice Measurements from Space (GLIMS) project which is currently compiling a global inventory of land ice masses within the framework of global glacier monitoring (Haeberli and others, 2000)

The Swiss Glaciers 2007/08 and 2008/09

ISSN:1424-2222ISSN:1423-282

A new glacier inventory on southern Baffin Island, Canada, from ASTER data: I. Applied methods, challenges and solutions

The quantitative assessment of glacier changes as well as improved modeling of climatechange impacts on glaciers requires digital vector outlines of individual glacier entities. Unfortunately, such a glacier inventory is still lacking in many remote but extensively glacierized regions such as the Canadian Arctic. Multispectral satellite data in combination with digital elevation models (DEMs) are particularly useful for creating detailed glacier inventory data including topographic information for each entity. In this study, we extracted glacier outlines and a DEM using two adjacent Terra ASTER scenes acquired in August 2000 for a remote region on southern Baffin Island, Canada. Additionally, Little Ice Age (LIA) extents were digitized from trimlines and moraines visible on the ASTER scenes, and Landsat MSS and TM scenes from the years 1975 and 1990 were used to assess changes in glacier length and area. Because automated delineation of glaciers is based on a band in the shortwave infrared, we have developed a new semi-automated glacier-mapping approach for the MSS sensor. Wrongly classified debris-covered glaciers, water bodies and attached snowfields were corrected manually for both ASTER and MSS. Glacier drainage divides were manually digitized by combining visual interpretation with DEM information. In this first paper, we describe the applied methods for glacier mapping and the glaciological challenges encountered (e.g. data voids, snow cover, ice caps, tributaries), while the second paper reports the data analyses and the derived changes