Showing papers by "Wilfried Haeberli published in 2008"

Spatial variability of glacier elevation changes in the Swiss Alps obtained from two digital elevation models

Abstract: [1] Massive glacier thinning in the Alps during the past 20 years is documented by direct mass balance measurements on nine regularly observed glaciers. How representative this limited sample of glaciers is for the entire Alps, however, remained uncertain. The near-global digital terrain model from the SRTM enables a closer analysis of this question, which is of fundamental importance to assess overall glacier volume change. Here we present elevation changes from 1985 to 1999 for about 1050 glaciers in the Swiss Alps. The analysis reveals extreme thickness losses (>80 m) for flat/low-lying glacier tongues and a strong overall surface lowering. The mean cumulative mass balance of the nine glaciers with direct measurements (−10.8 m w.e.) agrees well with the mean change of the entire region from DEM differencing (−11 m w.e.) and can thus be considered to be representative. Mean thickness change of individual glaciers is correlated with their size, elevation, and exposure to solar irradiation. This implies that mass losses of large glaciers can be underestimated when they are directly inferred from values measured at much smaller glaciers.

A sensitivity study of factors influencing warm/thin permafrost in the Swiss Alps

Abstract: Alpine permafrost distribution is controlled by a great number of climatic, topographic and soil-specific factors, including snow cover, which plays a major role. In this study, a one-dimensional finite-element numerical model was developed to analyze the influence of individual snow-specific and climatic factors on the ground thermal regime. The results indicate that the most important factor is snow depth. Snow depths below the threshold value of 0.6 m lack sufficient insulation to prevent low atmospheric temperatures from cooling the soil. The date of first winter snow insulation and variations in mean annual air temperature (MAAT) are also shown to be important. Delays in early-winter snow insulation and in summer snow disappearance are shown to be of approximately equal significance to the ground thermal conditions. Numerical modelling also indicates that the duration of effective thermal resistance of snow cover governs the slope of the linear dependency between MAAT and mean annual ground surface temperatures (MAGST). Consequently, the most direct effect of a long-term rise in air temperatures on ground temperatures is predicted under a thin snow cover with early snowmelt in spring and/or where a large change in the date of total snowmelt occurs, in response to atmospheric warming.

Observations and considerations on destabilizing active rock glaciers in the European Alps

Abstract: In many high mountain regions, warming of perennially frozen ground in both coarse debris and rock walls has a major influence on slope stability. In this context, indications of destabilizing active rock glaciers, such as high horizontal velocities (up to 4 ma-1), front advance rates of up to 4 ma-1, and development of crevasse-like cracks (up to 14 m deep), have been documented and monitored in the Alps for a few years. Beside the limited knowledge of rock glacier dynamics, our principle hypothesis is that the primary factors controlling the development of cracks and the destabilization of rock glacier tongues are the rheological properties of warming ice. In addition, we postulate that hydrological effects of unfrozen water within the active layer, the permafrost body, or at its base may contribute to the initiation of the slide-like mass wasting.

Historical and Holocene glacier–climate variations: General concepts and overview

Abstract: This special issue provides an overview of recent research activities concerning past to recent changes in the timing of glacier changes and their linkages to climate. The contributions are based on presentations from two “glacier–climate–cryosphere” sessions co-organized by the EU-funded GLOCHAMORE project (Global Change in Mountain Regions), PAGES (Past Global Changes) and the WGMS (World Glacier Monitoring Service) at the Open Science Conference on “Global Change inMountain Regions” organized by the MRI (Mountain Research Initiative) and held in Perth Scotland, Oct. 2–6, 2005. Covering a wide range of glacier-related topics, the conference sessions and this issue link studies and observations on the Late Quaternary to present in an attempt to bring together scientists and research results, which relate to the increasingly important issue of climate change. Results are presented from throughout the world, underscoring the important role that glacier-related research plays in assessing past and recent variations of the cryosphere and the climate system. Evidence from directly measured observations essentially covering the past century and the rapid and accelerating ongoing changes are collected and assessed by the WGMS. PAGES, on the other hand, maintains its focus on the

Climate, glaciers and permafrost in the Swiss Alps 2050: scenarios, consequences and recommendations

Abstract: Climate scenarios for the time horizon of 2050 in the Swiss Alps as simulated by using high-resolution ensemble modeling indicate most likely changes in temperature /precipitation by + 2°C / + 10% in winter and + 3°C / - 20% in summer. Such a development would lead to the vanishing of about 75% of the existing glacier surface and deep warming of permafrost in mountain peaks. Corresponding impacts would mainly concern rather dramatic changes in landscape appearance, slope stability and the water cycle. The formation of lakes in the forefields of retreating or even collapsing glaciers together with the decreasing stability of rock walls leads to an increasing probability of major rock falls impacting onto water bodies and triggering dangerous flood waves. A special recommendation was therefore provided to systematically assess the safety of natural, artificial and newly forming lakes in the Alps.

WGMS (2008): global glacier changes: facts and figures

Abstract: Changes in glaciers and ice caps provide some of the clearest evidence of climate change, and as such they constitute key variables for early detection strategies in global climate-related observations. These changes have impacts on global sea level fluctuations, the regional to local natural hazard situation, as well as on societies dependent on glacier meltwater. Internationally coordinated collection and publication of standardised information about ongoing glacier changes was initiated back in 1894. The compiled data sets on the global distribution and changes in glaciers and ice caps provide the backbone of the numerous scientific publications on the latest findings about surface ice on land. Since the very beginning, the compiled data has been published by the World Glacier Monitoring Service and its predecessor organisations. However, the corresponding data tables, formats and meta-data are mainly of use to specialists. It is in order to fill the gaps in access to glacier data and related background information that this publication aims to provide an illustrated global view of the available data sets related to glaciers and ice caps, their distribution around the globe, and the changes that have occurred since the maximum extents of the so-called Little Ice Age (LIA). International glacier monitoring has produced a range of unprecedented data compilations including some 36 000 length change observations and roughly 3 400 mass balance measurements for approximately 1 800 and 230 glaciers, respectively. The observation series are drawn from around the globe; however, there is a strong bias towards the Northern Hemisphere and Europe. A first attempt to compile a world glacier inventory was made in the 1970s based mainly on aerial photographs and maps. It has resulted to date in a detailed inventory of more than 100 000 glaciers covering an area of about 240 000 km2 and in preliminary estimates, for the remaining ice cover of some 445 000 km2 for the second half of the 20th century. This inventory task continues through the present day, based mainly on satellite images. The moraines formed towards the end of the Little Ice Age, between the 17th and the second half of the 19th century, are prominent features of the landscape, and mark Holocene glacier maximum extents in many mountain ranges around the globe. From these positions, glaciers worldwide have been shrinking significantly, with strong glacier retreats in the 1940s, stable or growing conditions around the 1920s and 1970s, and again increasing rates of ice loss since the mid 1980s. However, on a time scale of decades, glaciers in various mountain ranges have shown intermittent re-advances. When looking at individual fluctuation series, one finds a high rate of variability and sometimes widely contrasting behaviour of neighbouring ice bodies. In the current scenarios of climate change, the ongoing trend of worldwide and rapid, if not accelerating, glacier shrinkage on the century time scale is most likely of a non-periodic nature, and may lead to the deglaciation of large parts of many mountain ranges in the coming decades. Such rapid environmental changes require that the international glacier monitoring efforts make use of the swiftly developing new technologies, such as remote sensing and geo-informatics, and relate them to the more traditional field observations, in order to better face the challenges of the 21st century.

Alpine-wide distributed glacier mass balance modelling: a tool for assessing future glacier change?

Abstract: Distributed glacier mass balance models enable the calculation of the mass balance for each point of a glacier surface from meteorological input data. In view of the observed enhanced down-wasting of Alpine glaciers in recent years, such models become increasingly valuable for assessment of ongoing and future glacier change. However, their potential for large-area application by using gridded input data sets has not been fully exploited yet. In this contribution we describe the major components of distributed glacier mass balance models and apply a model that is based on the calculation of the energy balance to a larger test site (Mischabel region) in Switzerland.We thereby force the model with gridded data sets from annual precipitation, satellite-derived albedo and daily potential solar radiation as well as climatic means of meteorological variables. While the latter can easily be tuned to agree with observed mass balance distributions of specific glaciers, other nearby glaciers get unrealistically high positive or negative balances in the same simulation. Besides a variable sensitivity of individual glaciers, this hints to processes acting on a local scale, that are not yet considered in the model (e.g. snow redistribution by wind). However, the model is well suited for sensitivity studies with the included variables, and the mass balance sensitivities obtained agree well with results from previous studies (e.g. we calculate a 125 m rise of the equilibrium line altitude (ELA) for a 1 °C temperature increase). Once the local processes have been included successfully, we see a large potential of forcing such models with future climate data as computed by regional climate models. The resulting changes in mass balance or ELA on a glacier-specific basis may then be used as an input for further impact models which calculate future discharge or water resources.

Comparison of exposure ages and spectral properties of rock surfaces in steep, high alpine rock walls of Aiguille du Midi, France

Abstract: Among various factors, permafrost and frost-thaw cycles play an important role for the stability of steep rock slopes in high alpine regions. Climate change in general and local temperature and precipitation trends in particular are likely to influence permafrost and, consequently, also the stability of rock walls. As stress relief following deglaciation can be excluded at Aguille du Midi (France), rockfall activity is mainly related to changes in permafrost and frost-thaw cycles. To put modern observations of possible climate-induced rockfalls into perspective, information on past rockfall activity is required. In this study, we investigated a combination of surface exposure dating and spectrometry to derive a correlation between rock surface ages and their spectral properties in homogenous lithology. The surface ages found varied from less than 2,000 years to around 40,000 years, and showed a clear correlation with reflectance behavior in the range 380–580 nm. These results may be a first step towards the possible generation of spatial data fields of age distribution in steep rock walls. This may provide deeper insights into spatial and temporal rock-wall development of permafrost in high alpine permafrost environments.

Integrated glacier monitoring strategies: comments on a recent correspondence

Abstract: 1. Mass balance measured at individual points can indeed provide more direct information than values which are interand extrapolated for entire glaciers. The interest in corresponding point information is growing in connection with distributed massand energy-balance modelling. We also fully agree that seasonal mass-balance determinations are of high value with respect to process understanding and numerical model development. The point made in our paper, however, concerns (1) the relation of point measurements to the mass balance of entire glaciers, (2) the need for regular calibration of the resulting glacier mass-balance values using independent measurements such as repeated geodetic/photogrammetric surveys and (3) the comparability with other components of the described integrated monitoring strategy (area/volume/length change and inventory data). The problem with lacking or infrequent calibration becomes obvious in the case of Silvretta glacier, Swiss Alps: recent remapping revealed (cf. Huss and others, 2008a) that the mass-balance values reported for this glacier during the past 25 years have been far too positive and must now be corrected by a value (several decimeters w.e. a) which roughly corresponds to characteristic loss rates of mountain glaciers during the 20th century.