The worldwide collection of information about ongoing glacier changes was initiated in 1894 with the foundation of the International Glacier Commission at the 6th International Geological Congress in Zurich, Switzerland. It was hoped that long-term glacier observations would give insight into processes of climatic change such as the formation of ice ages. Since then, the goals of international glacier monitoring have evolved and multiplied. Today, the World Glacier Monitoring Service (WGMS) collects standardized observations on changes in mass, volume, area and length of glaciers with time (glacier fluctuations), as well as statistical information on the distribution of perennial surface ice in space (glacier inventories). Such glacier fluctuation and inventory data are high priority key variables in climate system monitoring; they form a basis for hydrological modelling with respect to possible effects of atmospheric warming, and provide fundamental information in glaciology, glacial geomorphology and quaternary geology. The highest information density is found for the Alps and Scandinavia, where long and uninterrupted records are available.
The tasks of the WGMS are
This work is being carried out at the Geographical Institute of the University of Zurich in collaboration with the Glaciology Section at the Laboratories of Hydraulics, Hydrology and Glaciology (VAW) of ETH Zurich under the auspices of the International Commission on Snow and Ice (ICSI), the Global Environment Monitoring System (GEMS), the Federation of Astronomical and Geophysical Data Analysis Services (FAGS) and the Division of Water Science of UNESCO. Data from WGMS flow into the World Data Center (WDC-A) for Glaciology (Boulder/Colorado) and the Global Resources Information Database (GRID) of GEMS (Geneva/Switzerland).
Collection of standardized glacier fluctuation data follows recommendations published by UNESCO in 1969 and regularly updated instructions for submission of data for the publication series Fluctations of Glaciers. The third and fourth volume of this series saw a major step towards computer-based processing of data, and in the last two volumes efforts were made to internationally collect and publish short abstracts on special events such as glacier surges, ice avanlanches, glacier floods or debris flows, drastic retreats of tidal glaciers and glacier-volcano interactions. The 1989 published World Glacier Inventory - Status 1988 is a guide to the existing statistical data base on the world-wide distribution and morphological characteristics of glaciers as documented in regional inventories (some detailed others preliminary). Publication of the biennial Glacier Mass Balance Bulletin has now been started and a systematic remote sensing of glaciers in regions of difficult access is being planned. In addition, a strategy is being developed on how to correctly interpret and periodically assess ongoing changes. The goal is to build up a modern service of global glacier monitoring with the measured information being stored in a data base system enabling easy access to scientific users.
Today, a focus of worldwide glacier monitoring concerns the early detection of climatic change. Central aspects connected with detection of climatic change caused by anthropogenic greenhouse forcing include
Observed glacier fluctuations contribute important information about all four aspects above. In fact, glacier fluctuations in cold mountain areas result from changes in the mass and energy balance at the Earth's surface. Rates and ranges of such glacier changes can be determined quantitatively over various time intervals and expressed as corresponding energy fluxes with their long-term variability. This permits direct comparison with other effects of natural and estimated anthropogenic greenhouse forcing. In addition, glacier changes are linked to changing atmospheric conditions via important filters, such as pronounced memory and enhancement functions. As a consequence, glacier changes are among the clearest signals of ongoing warming trends existing in nature. Both, glacier mass balance as the direct/undelayed signal and glacier length change as an indirect/delayed signal, must be applied in combination for worldwide glacier and climate system monitoring.
2. Glacier fluctuations
The primary goals of systematic, long-term glacier mass balance measurements which optimally combine the geodetic/photogrammetric method (repeated mapping) with direct glaciological observations (annual measurements at stakes and pits) in order to determine changes in volume/mass of entire glaciers with high temporal resolution are usually to
The annual specific balance as a regional signal can be obtained most economically using geodetic/photogrammetric volume change determinations repeated at time intervals of several years to a few decades with or without annual observations on a minimum of three strategically selected index stakes: two stakes should be monitored near the equilibrium line where the surface area is most extended and one near the glacier front to determine ablation gradients and to quantitatively interpret length changes over extended time periods as explained below. Data interpretation can be made by applying a simplified version of the linear balance model which assumes the mass balance variation at each point of the glacier to be proportional to the mass balance variation of the entire glacier. This concept builds on the experience that the spatial distribution of mass balance often remains highly similar from year to year. The third stake recommended for a minimum stake network should be installed at the glacier terminus in order to keep control on the reliability of the linear balance model and to introduce adequate corrections if necessary.
Mass balance studies for improvement of the process of understanding with respect to energy and mass fluxes at glacier surfaces require extensive stake networks to be maintained and seasonally observed at the end of both the (winter) accumulation as well as the (summer) ablation period. Even with high densities of stakes and pits, the absolute values of volume/mass change must be carefully calibrated by repeated geodetic/photogrammetric mapping, because the representativity of the monitored (stake/pit-) network with respect to the entire glacier can otherwise not easily be assessed: especially crevassed areas with their enlarged surfaces tend to escape the direct glaciological analysis. Process-orientated mass balance observations are, thus, expensive and time consuming. As a consequence, they should concentrate on characteristric effects of climatic variability. Mass balance gradients and their temporal changes under conditions of maritime/continental, tropical/polar climates etc., as well as their longterm evolution with potential climatic changes are of primary interest with respect to 2-dimensional considerations and models. The 3-dimensional dsitribution of mass balance patterns as a function of energy balance components such as snowfall, snow redistribution, solar radiation, sensible heat flux etc. are nowadays investigated with digital terrain models and corresponding calculations of solar radiation, air temperature etc. An ultimate goal of such investigations is to parametrrize unmeasured glaciers and, thus, to better describe ongoing changes at a worldwide scale.
Secular mass balances have been measured for six glaciers in the European Alps by repeated precision mapping since the late 19th century. The average annual mass loss over the entire period varies between 0.2 and 0.6 m water equivalent. The overall loss in Alpine ice thickness since the end of the Little Ice Age is measured in tens of meters. Results from continuous mass balance observations during the period 1980-1993 in North America, Eurasia and Africa are summarized in Figure 1. The average of all 35 glaciers is strongly influenced by the great number of Alpine and Scandinavian glaciers. A mean value is, therefore, also calculated using only one single (in some places averaged) value for each of the 11 mountain ranges involved. The annual signal of the mean mass balance is by far smaller than the regional variability but can be improved by cumulating mass balance values over extended periods of time. The mean specific net balance (-0.3 m water equivalent) over the entire period reflects an additional energy flux of 3 W per squaremeter - characteristic energy fluxes involved with the shrinkage of mountain glaciers roughly correspond to the estimated radiative forcing. Decadal to secural trends appear to be comparable beyound the scale of individual mountain ranges, with continentality of the climate being the main classifying factor besides individual hypsometric effects. However, detailed analyses reveal considerable spatio-temporal variability over short time periods. Results from worldwide glacier mass balance programmes thus constitute an important key for validating timedependent climate models at global to regional scales.
Fig. 1: Mean net balance (left) and cumulative mean net balance (right) continuously measured for the period 1980 to 1993 on 35 glaciers in 11 mountain ranges (from IAHS (ICSI)/UNEP/UNESCO 1994).
The remarkable signal characteristics of glacier length changes immediately appear by looking at cumulative values and different size categories (Fig. 2):
For the latter two size categories, the high-frequency (interannual) 'noise' is filtered out but the 'memory' of all major prennial ice bodies enables cumulation of effects for decades to centuries. Moreover, the secular thickness change of a few tens of meters is 'amplified' into a length change measured in hundreds to thousands of meters. The extreme clarity of this signal makes it possible to apply very simple observational methods such as, for instance, repeated tape-line readings. This, in turn, enables the cooperation of numerous non-specialists with long-term measurements at several hundreds of glacier snouts all over the world. The so-collected quantitative and qualitative observations or secular glacier retreat in mountain ranges, especially at low altitudes, leave no doubt about the fact that climate change causing glacier mass loss is, indeed, fast and a global phenomenon.
Fig. 2: Cumulative length changes since 1900 of 3 charactreristic glacier types in the Swiss Alps. Small circque glaciers such as Pizol Glacier have low basal shear stresses and directly respond to annual mass balance and snowline variability through deposition/melting of snow/firn at the glacier margin. Medium-size mountain glaciers such as Trient Glacier flow under high basal shear stresses and dynamically react to decadal mass balance variations in a delayed and strongly smoothed manner. Large valley glaciers such as Aletsch Glacier may be too long to dynamically react to decadal mass balance variations but exhibit strong signals of secular developments. Considering the whole spectrum of glacier response characteristics gives the best information on secular, decadal and annual developments.
An extensive data basis on topographic glacier parameters is being built up in regional glacier inventories (Table 1). Repetition of such glacier inventory work is planned at time intervals which are comparable to characteristic dynamic response times of mountain glaciers (a few decades). This should help with analyzing changes at regional scale and with assessing the representativity of continous measurements which can only be carried out on a few selected glaciers. In addition, glacier inventory data also serve as a statistical basis for extrapolating the results of observations or model calculations concerning individual glaciers and to simulate regional aspects of past and potential future climate change effects. This latter application requires the introduction of a parametrization scheme using the four main geometric parameters contained in detailed inventories (length; maximum and minimum altitude along the central flowline; surface area) and using correspondingly simple algorithms for deriving such parameters as overall slope, mean and maximum thickness, equilibrium line altitude, mass balance at the glacier terminus, response time etc.
| Table 1: Glazierized surface areas of the World | |||
|---|---|---|---|
| South America | 25 908 kmē | Europe | 53 967 kmē |
| Patagonian Icefields | 21 200 kmē | Iceland | 11 260 kmē |
| Argentina (north of 47.5° S) | 1 385 kmē | Svalbard | 36 612 kmē |
| Chile (north of 46 ° S) | 743 kmē | Scandinavia (with Jan Mayen) | 3 174 kmē |
| Bolivia | 566 kmē | Alps | 2 909 kmē |
| Peru | 1 780 kmē | Pyrenees/Mediterranean Mountains | 12 kmē |
| Ecuador | 120 kmē | USSR/Asia | 185 211 kmē |
| Colombia | 111 kmē | USSR | 77 223 kmē |
| Venezuela | 3 kmē | Turkey/Iran/Afghanistan | 4 000 kmē |
| North America | 276 100 kmē | Pakistan/India | 40 000 kmē |
| Mexico | 11 kmē | Nepal/Bhutan | 7 500 kmē |
| USA (with Alaska) | 75 283 kmē | China | 56 481 kmē |
| Canada | 200 806 kmē | Indonesia | 7 kmē |
| Greenland | 1 726 400 kmē | New Zealand/Subantarctic Islands | 7 860 kmē |
| Africa | 10 kmē | New Zealand | 860 kmē |
| Subantarctic Islands | 7 000 kmē | ||
| Antarctica | 13 586 310 kmē | ||
| Grand Total | 15 861 766 kmē | ||
A test study with the European Alps indicates a total Alpine glacier volume of some 130 kmģ at the mid-1970's. Total loss in Alpine surface ice mass from 1850 to the mid-1970's can be estimated at about half the original value. Most of this change took place during the second half of the 19th century and the first half of the 20th century, i.e. in times of a weak anthropogenic forcing. The short intervals of fast warming occured during this period may have been predominantly natural but could have included anthropogenic forcing effects as well. During the decade from 1980 to 1990, about 10 to 20% of the ice mass remaining in the European Alps around 1970/80 melted. Continuation of this development or even acceleration with annual mass losses of around 1 meter per year or more as anticipated from realistic IPCC scenarios for the coming century could eliminate major parts of the presently existing Alpine ice volume within decades. The striking sensitivity of glacierization in cold mountain areas with respect to trends in atmospheric warming clearly appears.
One century of systematic observations clearly reveals a general shrinking of mountain glaciers at a global scale. This general shrinking remains one of the most reliable pieces of evidence for a worldwide secular warming trend. At a secular time scale, the observed melt rates indicate energy fluxes which roughly correspond to the estimated anthropogenic greenhouse forcing. The trend was, however, most pronounced during the first half of the 20th century. After about 1950, glaciers started to grow again in several regions especially on the maritime slopes of mountain ranges where they are most sensitive to increased precipitation and where they gain mass despite rising air temperature. Since the 1980's, the general shrinking tendency of mountain glaciers has been accelerating again. At least in the Alps, glacier shrinkage now seems to be passing a high and possibly accelerating rate beyond the range of preindustrial variability.
In the last years a database system was built up to store the collected data of the Inventories (WGI) and the Fluctuations of Glaciers (FoG). The WGI database contains data describing the spatial variability of the world's glaciers. This database presently (Figure 3a) contains
Fig. 3a: Database scheme for the World Glacier Inventory data. PK = primary key and FK = foreign key.
Fig. 3b: Database scheme for the Fluctuations of Glacier data. PK = primary key and FK = foreign key.
The FoG database is based on structure of thematic data groups in order to enable a better overview: It contains
At present, the database of the FoG contains data from the last four volumes of the IAHS publication series Fluctation of Glaciers (1970-1990).
5.1 Fluctuation of Glaciers
For further information link to the WGMS home page
http://www.wgms.ch or contact
For WGMS information, see also
the IACS web site.
Prof. Dr. Wilfried Haeberli
Director WGMS
Department of Geography
Universitaet Zurich
Winterthurer Str. 190
CH-8057 ZURICH
Switzerland
FAX: ++41-1-6356848
e-mail: haeberli@geo.unizh.ch