Réf. Haeberli & al. 2007 - A

Référence bibliographique complète
HAEBERLI W., HOELZLE M., PAUL F., ZEMP M. Integrated monitoring of mountain glaciers as key indicators of global climate change: the European Alps. Annals of Glaciology, 2007, Vol. 46, p. 150-160.

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 -1 m w.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 m w.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.

Mots-clés
Glaciers, climate change, Alps, monitoring, evolution.

Organismes / Contact
Glaciology and Geomorphodynamics Group, Department of Geography, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland.
haeberli@geo.unizh.ch

(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
Europe Alps       1850-2005

(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
For the time since the end of the Little Ice Age around 1850, mass-balance reconstructions provide long-term mass-balance averages of -0.25 to -0.3 m w.e. a-1, i.e. three to four times less than the most recently observed values.

A straightforward continuity consideration was applied to longer-term cumulative length changes of Grosser Aletschgletscher, Switzerland, (Haeberli and Holzhauser, 2003) which was reconstructed in detail from historical documents, moraine dating and fossil trees for the past 3500 years (Holzhauser et al., 2005). Over the past two millennia, characteristic century to half-century mass-balance averages (mean +/- 0.3 and maximum +/- 0.5 m w.e. a-1) are comparable to the loss rates since the Little Ice Age and they were far below those observed since 1981. In fact, the mass losses observed since the mid-1980s (about 0.75 m w.e. a-1) exceed the maximum, and even double the maximum, characteristic long-term loss rates during the past two millennia.
Observations
Uninterrupted in situ measurements since 1967 of mass balance at nine Alpine glaciers (Saint-Sorlin and Sarennes, France; Gries and Silvretta, Switzerland; Careser, Italy; Hintereis, Kesselwand, Vernagt and Sonnblick, Austria) are available. Near-equilibrium conditions until 1981 were followed by very strong and continued if not accelerating mass loss (0.7 m w.e. a-1; trend of increase in mass loss 0.03-0.04 m w.e. a-2). During the first 5 years of the 21st century, mean annual mass losses have been close to 1 m w.e. a-1. The hot, dry summer of 2003 alone caused a record mean loss of 2.45 m w.e., roughly 50% above the previous record loss in 1998. Continued non-zero balances indicate ongoing climate forcing (assuming feedbacks from albedo, elevation change, debris cover or dry/wet calving do not affect mass balance for the considered glaciers), and increasing deviations from zero balances reflect accelerating change.

Observed and reconstructed mass losses are therefore also a function of glacier size (Hoelzle et al., 2003), with large glaciers reducing their thickness more rapidly than small ones. Morphological phenomena of downwasting (flat longitudinal and concave transversal surface profiles, abundant debris cover, collapse holes above subglacial drainage channels, lake formation) have now become visible on many glacier tongues. With continued thickness losses of 1 m w.e. a-1 or even more, the glaciers with longterm mass-balance time series may disappear within a few decades from now.
Modélisations
Best estimates for total volumes and volume changes (cf. Haeberli et al., 2004; Paul et al., 2004; Zemp et al., 2006) show that glaciers in the European Alps lost about half their total volume (roughly 0.5% a-1) between 1850 and around 1975, another 25% (1% a-1) of the remaining amount between 1975 and 2000, and an additional 10-15% (2-3% a-1) in the first 5 years of this century. The latter estimate is obtained from the mean value of the mass-balance observations at nine Alpine glaciers in combination with the new satellite-derived glacier areas from 1998/99 (Paul, 2004) and a simple model of calculating total glacier volume from mean thickness (Maisch et al., 2000).
Hypothèses
The increasingly fast mass and “vertical” thickness loss clearly points to an accelerating trend in climatic forcing. The corresponding additional energy flux calculated as the latent heat of the disappearing ice (around 10 Wm-2 as an average of the past 5 years) is about twice the estimated present-day radiative forcing alone (several Wm-2; Wild et al.2005) and most probably relates to important feedback mechanisms.

Sensibilité du milieu à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)
   

(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 following illustrates various methods of assessing past, current and future glacier mass changes by combining field data and/or remote sensing information with numerical modeling:

• Air temperature predominates in the temporal variability of the energy balance (e.g. Braithwaite, 2006; Braithwaite and Raper, 2007) and causes mass balances to be spatially correlated over large regions (spanning several hundred kilometres: Letréguilly and Reynaud, 1990; Cogley and Adams, 1998), an effect which is most likely due to combined influences from sensible-heat and longwave radiation (Ohmura, 2001);

• Patterns of long-term precipitation have a strong influence on glacier variability in space (mass turnover, englacial temperatures, relation to periglacial permafrost, mass-balance sensitivity: e.g. Oerlemans, 2001; Haeberli and Burn, 2002; Braithwaite, 2006) but change rather weakly in time (over decadal to centennial periods) and hence appear to have only secondary effects with respect to recent glacier fluctuations (e.g. Oerlemans, 2005; Schöner and Böhm, 2007);

• Dynamic response times for complete adjustment to equilibrium conditions are slope-dependent, for the simple reason that they depend on ice thickness divided by the balance at the terminus (Johannesson et al., 1989) and the balance at the terminus (in steady-state condition) tends towards zero with slope decreasing towards zero (Haeberli and Hoelzle, 1995); characteristic values are on the order of decades for typical (relatively thin and steep) mountain glaciers but may reach centuries for large (thick), flat glaciers;

• Geometric changes over such time intervals are primarily governed by mass conservation (Greuell, 1992; Boudreaux and Raymond, 1997; Hoelzle et al., 2003) rather than by specific aspects of glacier flow;

• Albedo and mass-balance/altitude feedbacks can have strong impacts (Paul et al., 2005; Raymond and Neumann, 2005) and may even cause self-reinforcing “runaway effects” (downwasting rather than retreat of glaciers where “vertical” thickness loss is faster than the capacity of a glacier to “horizontally” retreat); increasing debris cover, on the other hand, tends to decouple glaciers from atmospheric influences and can markedly slow down ice melting and strongly retard tongue retreat (Smiraglia et al., 2000).

(5) - Syntèses et préconisations
 

Références citées :

Boudreaux, A. and C. Raymond. 1997. Geometry response of glaciers to changes in spatial pattern of mass balance. Ann. Glaciol., 25 , 407–411.

Braithwaite, R. 2006. Measuring and modelling the mass balance of glaciers for global change. In Knight, P.G., ed. Glacier science and environmental change . Oxford, etc., Blackwell Publishing, 418–423.

Braithwaite, R.J. and S.C.B. Raper. 2007. Glaciological conditions in seven contrasting regions estimated with the degree-day model. Ann. Glaciol., 46 (see paper in this volume).

Cogley, J.G. and W.P. Adams. 1998. Mass balance of glaciers other than the ice sheets. J. Glaciol., 44 (147), 315–325.

Greuell, W. 1992. Hintereisferner, Austria: mass-balance reconstruction and numerical modelling of the historical length variations. J. Glaciol., 38 (129), 233–244.

Haeberli, W. and M. Hoelzle. 1995. Application of inventory data for estimating characteristics of and regional climate-change effects on mountain glaciers: a pilot study with the European Alps. Ann. Glaciol., 21 , 206–212. [Fiche Biblio]

Haeberli, W. and C. Burn. 2002. Natural hazards in forests: glacier and permafrost effects as related to climate change. In Sidle, R.C., ed. Environmental change and geomorphic hazards in forests . Wallingford, Oxon., CABI Publishing, 167–202.

Haeberli, W. and H. Holzhauser. 2003. Alpine glacier mass changes during the past two millennia. PAGES News, 11 (1), 13–15.

Haeberli, W. and 7 others . 2004. Effects of the extreme summer 2003 on glaciers and permafrost in the Alps – first impressions and estimations. Geophys. Res. Abstr. 6, 03063. (1607-7962/gra/ EGU04-A-03063.)

Hoelzle, M.,W. Haeberli, M. Dischl andW. Peschke. 2003. Secular glacier mass balances derived from cumulative glacier length changes. Global Planet. Change, 36 (4), 295–306. [Fiche Biblio]

Holzhauser, H., M. Magny and H.J. Zumbuhl. 2005. Glacier and lake-level variations in west-central Europe over the last 3500 years. Holocene, 15 (6), 789–801.

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

Letréguilly, A. and L. Reynaud. 1990. Space and time distribution of glacier mass-balance in the Northern Hemisphere. Arct. Alp. Res., 22 (1), 43–50.

Maisch, M., A. Wipf, B. Denneler, J. Battaglia and C. Benz. 2000. Die Gletscher der Schweizer Alpen: Gletscherschwund 1850, Aktuelle Vergletscherung, Gletscherschwund-Szenarien 21. Jahrhundert. Zürich, vdf Hochschulverlag AG ETH Zürich. (Schlussbericht NFP 31.)

Oerlemans, J. 2001. Glaciers and climate change. Lisse, etc., A.A. Balkema.

Oerlemans, J. 2005. Extracting a climate signal from 169 glacier records. Science, 308 (5722), 675–677.

Ohmura, A. 2001. Physical basis for the temperature-based meltindex method. J. Appl. Meteorol., 40 (4), 753–761.

Paul, F., A. Kääb, M. Maisch, T. Kellenberger and W. Haeberli. 2004. Rapid disintegration of Alpine glaciers observed with satellite data. Geophys. Res. Lett., 31 (L21), L21402. (10.1029/2004GL020816.)

Paul, F. 2004. The new Swiss glacier inventory 2000: application of remote sensing and GIS. (PhD thesis, University of Zürich.) [Fiche Biblio]

Paul, F., H. Machguth and A. Kääb. 2005. On the impact of glacier albedo under conditions of extreme glacier melt: the summer of 2003 in the Alps. EARSeL eProc., 4 (2), 139–149.

Raymond, C.F. and T.A. Neumann. 2005. Retreat of Glaciar Tyndall, Patagonia, over the last half-century. J. Glaciol., 51 (173), 239–247.

Schöner, W. and R. Böhm. 2007. A statistical mass-balance model for reconstruction of LIA ice mass for glaciers in the European Alps. Ann. Glaciol., 46 (see paper in this volume).

Smiraglia, C., G. Diolaiuti, D. Casati and M.P. Kirkbride. 2000. Recent areal and altimetric variations of Miage Glacier (Monte Bianco massif, Italian Alps). IAHS Publ. 264 (Symposium at Seattle 2000 – Debris-Covered Glaciers ), 227–233.

Wild, M. and 9 others . 2005. From dimming to brightening: decadal changes in solar radiation at Earth's surface. Science, 308 (5723), 847–850.

Zemp, M., W. Haeberli, M. Hoelzle and F. Paul. 2006. Alpine glaciers to disappear within decades? Geophys. Res. Lett., 33 (L13), L13504. (10.1029/2006GL026319.) [Fiche Biblio]