Réf. Haeberli & Beniston 1998 - A

Référence bibliographique complète
HAEBERLI, W. BENISTON, M.,1998, Climate change and its impacts on glaciers and permafrost in the Alps. Ambio, vol 27, p 258-265.

Mots-clés
Permafrost reaction to climate change, glaciers, revegetation of exposed slopes

Organismes / Contacts
Physical Geography Department, University of Zürich ;
Department of Geography, University of Fribourg ; haeberli@geo.uniz.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
Temperature, precipitations, sunshine duration, air pressure Permafrosts Mass movements Slope instability, debris flows

Pays / Zone
Massif / Secteur
Site(s) d'étude
Exposition
Altitude
Période(s) d'observation
Europe European Alps Eight sites for the temperature evolution   From Zürich (569 m) to Säentis (2500 m) 1900 to 1990 for the temperature observations

(1) - Modifications des paramètres atmosphériques
Reconstitutions
 
Observations

Climate change in the Alps has been characterized by increase of minimum temperatures of about 2°C, a more modest increase in maximum temperatures, little trend in the precipitations data, and a general decrease of sunshine duration.

Air pressure data exhibit a number of decadal-scale fluctuations, with the appearance of unusual behavior in the 1980s: pressure reached annual average values far higher than at any other time in the century.

There is a switch in the gradient of temperature anomaly. For warm winters, the higher the elevation, the stronger the positive anomaly; the reverse is true for cold winters.

Modélisations
 
Hypohesis
In a double-CO2 concentration scenarios, there will be higher winter temperature and more marked increase in summer temperatures (temperatures should increase more at high elevation sites than at low elevation sites). Precipitation is also higher and more intense in winter, but much reduced in summer.

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

 


(2) - Impacts du changement climatique sur le milieu naturel
Reconstitutions
 
Observations

Since 1850, the european alpine glaciers have lost about 30 to 40% in glacierized surface area and around 50% in ice volume. During the decade 1980-1990, glacier mass losses further increased by more than 50% with espect to the secular average for the 20th century.

The extent of Alpine ice is probably more reduced today than ever before during the past 5000 years.

Climate change impacts on permafrost is much less known than the impacts on glaciers.

Measurement in the first 60m of the ground show a more or less stable surface temperature between 1950 and 1980. As a consequence of the exceptional 1980s warming, the annual rate of thaw settlement due to melting ground ice in Alpine permafrost may have more than doubled since the 1970s and tends to reach the decimeter range. Boreholes observations also indicate that permafrost temperatures are now rising at high rate but can be drastically influenced by snow cover conditions in early wintertimes.

Modélisations
 
Hypothèses

Mountain permafrost is supposed to react to climate change in the form of: ice melt at the permafrost table with or without change in active layer thickness (direct response with a year timescale); disturbance of temperature profiles within the permafrost (delayed response with a decade to centuries timescale); and displacement of the permafrost base (final response with a centuries to millenia timescale).

The situation of the Alpine ice appear to be evolving at a high and possibly accelerating rate towards or even beyond the "warm" limit of natural variability during the upper Holocene (maximum natural glacier retreat for the last 10 000 years).

Under an anticipated warming of 4°C, there would be an upward shift of the equilibirum line by some 200 to 300 m and yearly thickness loss of 1 to 2 m for temperate and alpine glaciers.

Lower limit of permafrost occurence in the Alps could rise by several hundred meters in a scenario of accelerate warming. This tendecy could be counterbalance by a reduction of isolation due to a decrease in snow cover.

The slow vegetation of deglaciated areas would lead to increase sediments load in the corresponding rivers and could lead to accelerate sedimentation in lakes and artificial reservoirs at high altitude. Revegetation of terrain following deglaciation is slow under high-mountain climatic conditions, and, therefore leave deglaciated morainic deposits unprotected against erosion for extended time (from decade to centuries).


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

(3) - Impacts du changement climatique sur l'aléa
Reconstitutions
 
Observations
 
Modélisations
 
Hypothèses
On slopes steeper than 25-30°, stability problems can develop in freshly exposed or thawin non consolidated sediments. Debris flows of various magnitude may result under such conditions, especially during heavy precipitation events.

Permafrost degradation in fissured rock walls is likelyto have long-term impacts on frost weathering and rockfall activity by reducing the strength and increasing the permeability at depth of meters to ten of meters.

Formation and disappearance of ice-damned lakes, generaly accompany marked change in glacier extent, and steep hanging glaciers, which are partially or entirely frozen to their beds could become less stable.

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

(4) - Remarques générales

 


(5) - Syntèses et préconisations
Empirical knowledge would have to be replaced increasingly by improved process understanding, especially concerning runoff formation and slope stability.