Réf. Hoelzle & al. 2003 - A

Référence bibliographique complète
HOELZLE, M., HAEBERLI, W., DISCHL, M., PESCHKE, W. Secular glacier mass balances derived from cumulative glacier length changes. Global and Planetary Change, 2003, Vol. 36, 295-306.

Abstract : Glacier mass changes are considered to represent natural key variables with respect to strategies for early detection of enhanced greenhouse effects on climate. The main problem, however, with interpreting worldwide glacier mass balance evolution concerns the question of representativity. One important key to deal with such uncertainties and to assess the spatio­temporal representativity of the few available measurements is the long-term change in cumulative glacier length. The mean specific mass balance determined from glacier length change data since 1900 shows considerable regional variability but centers around a mean value of about - 0.25 m/year water equivalent.

Mots-clés
Glacier fluctuations, glacier length changes, glacier mass changes, climate change

Organismes / Contact
Department of Geography, Glaciology and Geomorphodynamics Group, University of Zurich, Winterthurerstr. 190, CH- 8057 Zurich, Switzerland
Laboratory of Hydraulics, Hydrology and Glaciology, Federal Institute of Technology, Gloriastr. 37/39, CH-8092 Zurich, Switzerland

(1) - Paramètre(s) atmosphérique(s) modifié(s)
(2) - Elément(s) du milieu impacté(s)
(3) - Type(s) d'aléa impacté(s)
(3) - Sous-type(s) d'aléa
  Glaciers    

Pays / Zone
Massif / Secteur
Site(s) d'étude
Exposition
Altitude
Période(s) d'observation
World - Swiss         20th century

(1) - Modifications des paramètres atmosphériques
Reconstitutions
 
Observations
 
Modélisations
 
Hypothèses
 

Informations complémentaires (données utilisées, méthode, scénarios, etc.)

 


(2) - Effets du changement climatique sur le milieu naturel
Reconstitutions
 
Observations
The results [of several studies] all confirm the order of magnitude (a few decimeters per year) characterizing worldwide annual ice thickness loss during recent decades. Glacier retreat in the 20th century is [clearly] a worldwide phenomenon.

Large glaciers have suffered from the largest absolute length change measured since 1894. Long glaciers (>10 km) retreated continuously or remained stationary except in western Iceland. Glaciers in the size category of 2 to 10 km show clear decadal reactions. Advance periods in the 1970-1980s could not only be observed in the European Alps, but also in the Pamir-Alai, Tien-Shan, Olympic, and Coast Mountains. Advance tendencies continued into the 1990s for glaciers near the Norwegian West Coast and in Iceland. This development in the North Atlantic appears to parallel a similar development in the New Zealand Alps and forms a strong contrast to the European Alps, Rocky Mountains, Coast Mountains, and Cordillera Central where general retreat in the 1980-1990s is pronounced.

Consideration of the cumulative length change curves in more detail reveals distinct differences between evolutions in various mountain ranges at decadal time. The worldwide glacier signal of climate change seems to be more or less homogenous at multi-decadal to secular time scales only.

Average mass losses of long and flat glaciers [in Switzerland] have exceeded those of smaller glaciers: typical values center around - 0.25 m/year for larger glaciers and around - 0.11 m/year for the smaller ones. The main reason for large/flat glaciers to have higher mass losses may probably be that the larger thickness limits long-term ice losses to a lesser degree than in small glaciers where the bed is reached relatively soon. This result confirms that—other factors being equal—length and slope exert a predominant influence not only on flow dynamics but also on overall mass losses of glaciers—an interesting feedback between mass balance and flow dynamics over decadal to secular time scales.

The results of the parameterization for glaciers wolrwide confirm the trend observed in the sample from the Swiss Alps for smaller glaciers to have lost mass at a slower rate than larger ones.

On average of the world­wide sample, larger glaciers have lost around -0.25 m/year, a value which is identical to the value calculated for the larger Swiss glaciers.

The reconstructed rates of secular mass losses strongly differ between humid-maritime-type glaciers such as those of western Scandinavia and dry-continental type glaciers in the Altai area, for instance. The sensitivity with respect to secular trends in global warming of maritime-type glaciers is much higher than the one of continental-type glaciers.
Modélisations
 
Hypothèses
Future changes [mass loss] will affect firstly the maritime ones and then, with a certain delay, the continental ones, which are mostly of polythermal or cold stage.

Sensibilité du milieu à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)
Mass balance
Intercomparison is based on 68 glaciers from the Swiss glacier network and 90 selected glaciers worldwide. Swiss glaciers with their overall length and mean slope were subdivided into five classes as follows :
• Class 1 (long and flat valley glaciers, sample: 4 glaciers): glaciers longer than 10 km with a mean slope of < 15j; glaciers in this class reveal constant retreat since the beginning of the measurements.
• Class 2  (intermediate valley and mountain gla­ciers, sample: 11 glaciers): glaciers with a length between 5 and 10 km and a mean slope between 10° and 25°; such glaciers show strong fluctuations with large amplitudes and up to three advance and retreat periods since 1880.
• Class 3 (steep mountain glaciers, sample:19 glaciers): glaciers with a length between 1 and 5 km and a mean slope ranging from 15° to 25°; these glaciers show moderate fluctuations and amplitudes but exhibit quite large variability and strongly individual reaction.
• Class 4 (flat mountain glaciers, sample:14 glaciers): glaciers with a length between 1 and 10 km and a mean slope < 15°; glaciers of this type underwent weak fluctuations with small amplitudes but a clear overall retreat.
• Class 5: (extremely small and extremely steep glaciers, sample: 20 glaciers): glaciers shorter than 1 km with a mean slope larger than 15° or with a length between 1 and 5 km and a mean slope larger than 25°; glaciers at the extremes of size and slope show a pronounced high-frequency variability with moderate to large amplitude.


Direct measurement of mean mass balance (vs calculated from glacier length change for time intervals >= the response time of the glaciers) :
- Rhone glacier ( 1881-1987) : -0.25 m/yr (-0.28 m/yr)
- Gries glacier (1962-1996): -0.27 m/yr (-0.22 m/yr)
- Silvretta glacier (1960-1996): - 0.05 m/yr (- 0.02 m/yr)
- Grosser Aletsch glacier (1920-1996): -0.22 m/yr (- 0.22 m/yr)

(3) - Effets du changement climatique sur l'aléa
Reconstitutions
 
Observations
 
Modélisations
 
Hypothèses
 

Paramètre de l'aléa
Sensibilité du paramètres de l'aléa à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)
 
 

(4) - Remarques générales

The study presented here clearly shows that for direct intercomparisons of cumulative glacier length changes, shorter time scales and high temporal meas­urements are necessary. Especially, to derive the annual (very small glaciers) or decadal (medium-sized glaciers) fluctuations, such measurements have to be done. The high temporal measurements in the Alps and in Scandinavia are good examples. New technologies like satellites offer new possibilities to derive in the future long-term length changes, espe­cially for deriving secular trends in mean mass balances. The concept of Jo´ hannesson et al. (1989a,b) presents the possibility to roughly estimate secular mass balance changes by using length change measure­ments. This means that length change measurements are, for the future, one of the most important key variables in global glacier monitoring strategies. The secular mass loss is a worldwide phenomenon in the period since 1850. Future changes will affect firstly the maritime ones and then, with a certain delay, the continental ones, which are mostly of polythermal or cold stage.


(5) - Syntèses et préconisations
In addition to mass balance, this study shows that length observations of a representative subset of the world glaciers are and will be, in the future, a very valuable key factor, among others, for assessing climate change effects at regional or worldwide scale (Haeberli, 1998). In the strategy of the Global Terrestrial Network for Glaciers (GTNet-G) within the Global Climate Observing System (GCOS)/Global Terrestrial Observing System (GTOS), long-term observations of glacier length change data at a mini­mum of about 10 sites within each mountain range are attributed highest priority. These glaciers should be selected according to size and dynamic response from the existing set of sites where glacier length is monitored. At this level, spatial representativeness is very important. Today, approximately 800 glaciers where only length is measured are compatible with Tier 4 of the GTNet-G-strat egy. Because access is infrequent, they can be located wherever necessary to ensure representativeness.

Référence citées (extraits) :

Haeberli, W., 1994. Accelerated glacier and permafrost changes in the Alps. In: Beniston, M. (Ed.), Mountain Environments in Changing Climates. Routledge, London, pp. 91 – 107.

Haeberli, W., 1998. Historical evolution and operational aspects of worldwide glacier monitoring. In: Haeberli, W., Hoelzle, M., Suter, S. (Eds.), Into the Second Century of Worldwide Glacier Monitoring: Prospects and Strategies. Studies and Reports in Hydrology. UNESCO, Paris, pp. 35 – 51.

Haeberli, W., Frauenfelder, R., Hoelzle, M., Maisch, M., 1999. On rates and acceleration trends of global glacier mass changes. Geografisk Annaler 81A, 585 – 591.

Haeberli, W., Cihlar, J., Barry, R., 2000. Glacier monitoring within the global climate observing system—a contribution to the Fritz Muüller Memorial. Annals of Glaciology 31, 241 – 246.

Johannesson, T., Raymond, C., Waddington, E., 1989a. A simple method for determining the response time of glaciers. In: Oerlemans, J.(Ed.), Glacier Fluctuations and Climatic Change. Kluwer Academic Publishing, Dordrecht, pp. 343 – 352.

Johannesson, T., Raymond, C., Waddington, E., 1989b. Time-scale for adjustment of glaciers to changes in mass balance. Journal of Glaciology 35 (121), 355 – 369.

Kuhn, M., 1980. Climate and glaciers. IAHS 131, 3– 20.

Maisch, M., Wipf, A., Denneler, B., Battaglia, J., Benz, C., 1999. Die Gletscher der Schweizer Alpen: Gletscherhochstand 1850 — aktuelle Vergletscherung — Gletscherschwundszenarien. Schlussbericht NFP 31. vdf Hochschulverlag. Zürich.

Nye, J.F., 1960. The response of glaciers and ice-sheets to seasonal and climatic changes. Proceedings of the Royal Society. Series A 256, 559 – 584.

Oerlemans, J., 1988. Simulation of historic glacier variations with a simple climatic-glacier model. Journal of Glaciology 34 (118), 333 – 341.

Oerlemans, J., 1997. A flowline model for Nigardsbreen, Norway: projection of future glacier length based on dynamic calibration with the historic record. Annals of Glaciology 24, 382 – 389.

Oerlemans, J., 1998. Modelling glacier fluctuations. In: Haeberli, W., Hoelzle, M., Suter, S. (Eds.), Into the Second Century of Worldwide Glacier Monitoring: Prospects and Strategies. Studies and Reports in Hydrology. UNESCO, Paris, pp. 85 – 96.

Oerlemans, J., Anderson, B., Hubbard, A., Huybrechts, P., Jo´ han­nesson, T., Knap, W.H., Schmeits, M., Stroeven, A.P., van der Wal, R.S.W., Wallinga, J., Zuo, Z., 1998. Modelling the response of glaciers to climate warming. Climate Dynamics 14, 267 – 274.

Paterson, W.S.B., 1981. The Physics of Glaciers, 2nd ed. Pergamon, Oxford. New York, Tokyo.

WMO, 1997. GCOS/GTOS plan for terrestrial climate-related observation. World Meteorological Organization, Geneva.

Zuo, Z., Oerlemans, J., 1997b. Numerical modelling of the historic front variation and the future behavior of the Pasterze glacier, Austria. Annals of Glaciology 24, 234 – 241.