Michael Zemp

Six decades of glacier mass-balance observations: a review of the worldwide monitoring network

Abstract Glacier mass balance is the direct and undelayed response to atmospheric conditions and hence is among the essential variables required for climate system monitoring. It has been recognized as the largest non-steric contributor to the present rise in sea level. Six decades of annual mass-balance data have been compiled and made easily available by the World Glacier Monitoring Service and its predecessor organizations. In total, there have been 3480 annual mass-balance measurements reported from 228 glaciers around the globe. However, the present dataset is strongly biased towards the Northern Hemisphere and Europe and there are only 30 ‘reference’ glaciers that have uninterrupted series going back to 1976. The available data from the six decades indicate a strong ice loss as early as the 1940s and 1950s followed by a moderate mass loss until the end of the 1970s and a subsequent acceleration that has lasted until now, culminating in a mean overall ice loss of over 20mw.e. for the period 1946–2006. In view of the discrepancy between the relevance of glacier mass-balance data and the shortcomings of the available dataset it is strongly recommended to: (1) continue the long-term measurements; (2) resume interrupted long-term data series; (3) replace vanishing glaciers by early-starting replacement observations; (4) extend the monitoring network to strategically important regions; (5) validate, calibrate and accordingly flag field measurements with geodetic methods; and (6) make systematic use of remote sensing and geo-informatics for assessment of the representativeness of the available data series for their entire mountain range and for the extrapolation to regions without in situ observations; and (7) make all these data and related meta-information available.

Integrated monitoring of mountain glaciers as key indicators of global climate change: the European Alps

Abstract The internationally recommended multi-level strategy for monitoring mountain glaciers is illustrated using the example of the European Alps, where especially dense information has been available through historical times. This strategy combines in situ measurements (mass balance, length change) with remote sensing (inventories) and numerical modelling. It helps to bridge the gap between detailed local process-oriented studies and global coverage. Since the 1980s, mass balances have become increasingly negative, with values close to –1mw.e. a–1 during the first 5 years of the 21st century. The hot, dry summer of 2003 alone caused a record mean loss of 2.45 mw.e., roughly 50% above the previous record loss in 1998, more than three times the average between 1980 and 2000 and an order of magnitude more than characteristic long-term averages since the end of the Little Ice Age and other extended periods of glacier shrinkage during the past 2000 years. It can be estimated that glaciers in the European Alps lost about half their total volume (roughly 0.5% a–1) between 1850 and around 1975, another 25% (or 1%a–1) of the remaining amount between 1975 and 2000, and an additional 10–15% (or 2–3% a–1) in the first 5 years of this century.

The Concept of Essential Climate Variables in Support of Climate Research, Applications, and Policy

Climate research, monitoring, prediction, and related services rely on accurate observations of the atmosphere, land, and ocean, adequately sampled globally and over sufficiently long time periods. The Global Climate Observing System, set up under the auspices of United Nations organizations and the International Council for Science to help ensure the availability of systematic observations of climate, developed the concept of essential climate variables (ECVs). ECV data records are intended to provide reliable, traceable, observation-based evidence for a range of applications, including monitoring, mitigating, adapting to, and attributing climate changes, as well as the empirical basis required to understand past, current, and possible future climate variability. The ECV concept has been broadly adopted worldwide as the guiding basis for observing climate, including by the United Nations Framework Convention on Climate Change (UNFCCC), WMO, and space agencies operating Earth observation satellites. This ...

Towards remote monitoring of sub-seasonal glacier mass balance

Abstract This study presents a method that allows continuous monitoring of mass balance for remote or inaccessible glaciers, based on repeated oblique photography. Hourly to daily pictures from two automatic cameras overlooking two large valley glaciers in the Swiss Alps are available for eight ablation seasons (2004–11) in total. We determine the fraction of snow-covered glacier surface from orthorectified and georeferenced images and combine this information with simple accumulation and melt modelling using meteorological data. By applying this approach, the evolution of glacier-wide mass balance throughout the ablation period can be directly calculated, based on terrestrial remote-sensing data. Validation against independent in situ mass-balance observations indicates good agreement. Our methodology has considerable potential for the remote determination of mountain glacier mass balance at high temporal resolution and could be applied using both repeated terrestrial and air-/spaceborne observations.

Mass Balance Re-analysis of Findelengletscher, Switzerland; Benefits of Extensive Snow Accumulation Measurements

A re-analysis is presented here of a 10-year mass balance series at Findelengletscher, a temperate mountain glacier in Switzerland. Calculating glacier-wide mass balance from the set of glaciological point balance observations using conventional approaches, such as the profile or contour method, resulted in significant deviations from the reference value given by the geodetic mass change over a five-year period. This is attributed to the sparsity of observations at high elevations and to the inability of the evaluation schemes to adequately estimate accumulation in unmeasured areas. However, measurements of winter mass balance were available for large parts of the study period from snow probings and density pits. Complementary surveys by helicopter-borne ground-penetrating radar (GPR) were conducted in three consecutive years. The complete set of seasonal observations was assimilated using a distributed mass balance model. This model-based extrapolation revealed a substantial mass loss at Findelengletscher of -0.43m w.e. a^-1 between 2004 and 2014, while the loss was less pronounced for its former tributary, Adlergletscher (-0.30m w.e. a^-1). For both glaciers, the resulting time series were within the uncertainty bounds of the geodetic mass change. We show that the model benefited strongly from the ability to integrate seasonal observations. If no winter mass balance measurements were available and snow cover was represented by a linear precipitation gradient, the geodetic mass balance was not matched. If winter balance measurements by snow probings and snow density pits were taken into account, the model performance was substantially improved but still showed a significant bias relative to the geodetic mass change. Thus the excellent agreement of the model-based extrapolation with the geodetic mass change was owed to an adequate representation of winter accumulation distribution by means of extensive GPR measurements.

Introduction: Global glacier monitoring— a long-term task integrating in situ observations and remote sensing

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.

Evaluating Volumetric Glacier Change Methods Using Airborne Laser Scanning Data

Abstract Assessments of geodetic volume change are widely used in glaciology and have a long tradition dating back to the nineteenth century. Over time, the geodetic method and corresponding data storage have been developed further, but the resulting methodological heterogeneity can lead to errors that are difficult to separate from other survey uncertainties. In this study we used high‐resolution airborne laser scanning data from the indelengletscher in the wiss lps to evaluate state‐of‐the‐art volumetric glacier change methods. For the first time we have been able to simulate errors arising from different geodetic methods and spatial resolutions. The evaluation showed that, although the digital elevation models were perfectly co‐registered, systematic and random method‐ and scale‐dependent errors still occurred. These errors have an impact on the resulting volume changes at lower spatial resolutions and may lead to exponentially larger uncertainties. Volume changes from contour methods provided reasonably accurate results, while volumetric change assessments from central profile lines were especially prone to biases at any scale.

13.10 Glacial Responses to Climate Change

The response of glaciers to atmospheric warming has become a key issue in scientific as well as public and even political discussions about human impacts on the climate system. The predominant tendency of continued worldwide glacier shrinkage may indeed constitute one of the clearest indications in nature of rapid climate change at a global scale. More than a century of systematic and internationally coordinated observations provide quantitative documentation of this development and a basis for model developments in view of possible future scenarios. Mountain ranges at lower latitudes have lost large percentages of their glacier areas and volumes since the end of the Little Ice Age. Many of them may even become largely to even completely de-glaciated already during the coming decades. Such changes have the potential to profoundly affect environmental conditions in and around cold mountain chains. Sea-level rise, changing seasonality in water supply, and local formation of new lakes reflect changes in the water cycle at global, continental, and regional to local scales. They are accompanied by rather marked changes in landscape appearance, slope stability, erosion/sedimentation, and hazard conditions. The monitoring of glaciers itself faces difficult challenges of vanishing glaciers with long-term mass-balance observations. Modern techniques of spatial modeling increasingly help with integrated analysis of observed phenomena and early anticipation of possible developments.

Integrated glacier monitoring strategies: comments on a recent correspondence

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.

Toward an imminent extinction of Colombian glaciers

ABSTRACT This study documents the current state of glacier coverage in the Colombian Andes, the glacier shrinkage over the twentieth century and discusses indication of their disappearance in the coming decades. Satellite images have been used to update the glacier inventory of Colombia reflecting an overall glacier extent of about 42.4 ± 0.71 km2 in 2016 distributed in four glacierized mountain ranges. Combining these data with older inventories, we show that the current extent is 36% less than in the mid-1990s, 62% less than in the mid-twentieth century and almost 90% less than the Little Ice Age maximum extent. Focusing on Nevado Santa Isabel (Los Nevados National Park), aerial photographs from 1987 and 2005 combined with a terrestrial LiDAR survey show that the mass loss of the former ice cap, which is nowadays parceled into several small glaciers, was about −2.5 m w.e. yr−1 during the last three decades. Radar measurements performed on one of the remnant glaciers, La Conejeras glacier, show that the ice thickness is limited (about 22 m in average in 2014) and that with such a mass loss rate, the glacier should disappear in the coming years. Considering their imbalance with the current climate conditions, their limited altitudinal extent and reduced accumulation areas, and in view of temperature increase expected in future climate scenarios, most of the Colombian glaciers will likely disappear in the coming decades. Only the largest ones located on the highest summits will probably persist until the second half of the twenty-first century although very reduced.