Haeberli & Hoelzle 1995 Application of inventory data for estimating characteristics...

Référence bibliographique complète

HAEBERLI W., HOELZLE M. Application of inventory data for estimating characteristics of and regional climate-change effects on mountain glaciers: a pilot study with the European Alps. Annals of Glaciology, 1995, Vol. 21, p. 206-212.

Abstract: A parameterization scheme using simple algorithms for unmeasured glaciers is being applied to glacier inventory data to estimate the basic glaciological characteristics of the inventoried ice bodies and simulate potential climate change effects on mountain glaciers. For past and potential climate scenarios, glacier changes for assumed mass balance changes are calculated as step functions between steady-state conditions for time intervals that approximately correspond to the characteristic dynamic response time (a few decades) of the glaciers. In order to test the procedure, a pilot study was carried out in the European Alps where detailed glacier inventories had been compiled around the mid-1970s. Total glacier volume in the Alps is estimated at about 130 km3 for the mid-1970s; strongly negative mass balances are likely to have caused a loss of about 10-20% of this total volume during the decade 1980-1990. Backward calculation of glacier-length changes using a mean annual mass balance of 0.25 m w.e. a-1 since the end of the Little Ice Age around 1850 AD gives considerable scatter but satisfactory overall results as compared with long-term observations. The total loss of Alpine surface ice mass since 1850 can be estimated at about half of the original value. An acceleration of this development, with annual mass losses of about 1 m a-1 or more as anticipated by the IPCC scenario A for the coming century, could eliminate major part of the presently existing Alpine ice volume within decades.

Organismes / Contact

Laboratory of Hydraulics, Hydrology and Glaciology, Federal Institute of Technology (ETH), CH-8092 Zürich, Switzerland.
World Glacier Monitoring Service (GEMS/UNEP, IHP/UNESCO, FAGS/ICSU, ICSI/IAHS).

(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

Massif / Secteur

Site(s) d'étude

Période(s) d'observation

(1) - Modifications des paramètres atmosphériques

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

(2) - Effets du changement climatique sur le milieu naturel

The total surface area of all 5050 inventoried surface ice bodies is 2909 km2 (Haeberli et al., 1989). The surface area of the 1763 glaciers larger than 0.2 km2 is 2533 km2 (88%). The total volume of these glaciers is calculated as 126 km3, that of the others as 2.6 km3. Total glacier volume in the Alps is estimated at about 130 km3 for the mid-1970s.

The most part of the Alpine glaciers are not strictly temperate but rather polythermal. Most glaciers (88%) have mean annual air temperatures at the equilibrium line between -2°C and -6°C, indicating transitional climatic conditions. The sample of presently existing Alpine glaciers is dominated by small and steep glaciers with average thicknesses of a few tens of metres. They react through (vertical) surface altitude changes rather than pronounced (horizontal) advance/retreat. Calculated surface velocities in the ablation areas of the small mountain glaciers are typically a few tens of metres.

The decade 1980-90, with a mean annual mass balance of -0.65 m w.e. as measured on 8 glaciers in the Alps (Caréser, Gries, Hintereis, Kesselwand, Saint Sorlin, Sarennes, Silvretta, Sonnblick; Haeberli & Müller, 1988; Haeberli & Hoelzle, 1993; Haeberli, 1994), may have brought about a loss in surface ice volume of nearly 20 km3 or about 10-20% of the total volume existing around 1970.

Correcting the mass balance forcing for each of the 13 glaciers to fit the measured length change gives an average mass balance of 0.33 +/- 0.09 m a-1 average mass loss. If the 1850-1970 period is treated as one single retreat period without consideration of the 35 years of stationary glaciers (1890-1925), the above calculated value reduces to 0.2-0.3 m w.e. a-1. The energy required for melting this amount of ice is 2-3 W m-2. Such values roughly correspond to the observed long term trend of atmospheric warming. It is assumed that in the 1970s at least 35% of the glacierized surface area existing around 1850 has disappeared. The corresponding volume change is estimated at 45-50%.

In such a scenario (-0.9 m a-1 during a time interval of 50 years), 441 small glaciers representing 25% of the glaciers larger than 0.2 km2 existing in the mid-1970s would disappear. In comparison with conditions in the mid-1970s, about 1/3 of the surface area and more than 1/2 the ice volume would be lost.

Sensibilité du milieu à des paramètres climatiques

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

The basis for the parameterization scheme (cf. Hoelzle, 1994) consists of measured inventory data on the total length, maximum/minimum altitude and surface area of the investigated glaciers. From these basic parameters, mean altitude, vertical extent and average surface slope are derived as a first step. Ice thickness in the ablation area is derived too and maximum thickness is determined as estimated from known ice thickness measurements on various Alpine glaciers (Müller et al., 1976). Mean altitude is taken as an approximation for equilibrium-line altitude (ELA) and the mass balance at the glacier tongue is computed. Different velocities are also calculated.

Glacier-length changes (cf. Paterson, 1981; Haeberli, 1994) for given disturbances in mass balance are calculated with respect to the characteristic dynamic response time from Johannesson et al. (1989). Near surface thermal regime (10 m temperature) is defined from empirical relations between mean annual air, firn and ice temperatures (Haeberli & Alean, 1985).

The data for the European Alps, containing a total 5050 perennial surface ice bodies, were compiled for the mid-1970s. Only 1763 of these (35%) are larger than 0.2 km2 with complete information available about surface area, total length and maximum and minimum altitude. The parameterization scheme is applied to this part of the sample.

A first experiment was run to simulate maximum glacier extent around 1850 AD in order to check the proposed scheme (compared to observations on 13 glaciers) and then to simulate changes that have happened since. The results show that the different sensitivities of long-term glacier length as a response of uniform mass balance forcing can be quite well reproduce and that the chosen mass balance forcing (-0.25 m a-1) appears to underestimate slightly the real evolution.

In a second step, calculations were made with a mass balance forcing of -0.9 m a-1 during a time interval of 50 years and starting from the conditions of the mid-1970s. This could more or less correspond to the consequences of the IPCC scenario A till 2025.

(3) - Effets du changement climatique sur l'aléa

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

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

(2) - Effets du changement climatique sur le milieu naturel
Reconstitutions
Observations	The total surface area of all 5050 inventoried surface ice bodies is 2909 km2 (Haeberli et al., 1989). The surface area of the 1763 glaciers larger than 0.2 km2 is 2533 km2 (88%). The total volume of these glaciers is calculated as 126 km3, that of the others as 2.6 km3. Total glacier volume in the Alps is estimated at about 130 km3 for the mid-1970s. The most part of the Alpine glaciers are not strictly temperate but rather polythermal. Most glaciers (88%) have mean annual air temperatures at the equilibrium line between -2°C and -6°C, indicating transitional climatic conditions. The sample of presently existing Alpine glaciers is dominated by small and steep glaciers with average thicknesses of a few tens of metres. They react through (vertical) surface altitude changes rather than pronounced (horizontal) advance/retreat. Calculated surface velocities in the ablation areas of the small mountain glaciers are typically a few tens of metres.
Modélisations	The decade 1980-90, with a mean annual mass balance of -0.65 m w.e. as measured on 8 glaciers in the Alps (Caréser, Gries, Hintereis, Kesselwand, Saint Sorlin, Sarennes, Silvretta, Sonnblick; Haeberli & Müller, 1988; Haeberli & Hoelzle, 1993; Haeberli, 1994), may have brought about a loss in surface ice volume of nearly 20 km3 or about 10-20% of the total volume existing around 1970. Correcting the mass balance forcing for each of the 13 glaciers to fit the measured length change gives an average mass balance of 0.33 +/- 0.09 m a-1 average mass loss. If the 1850-1970 period is treated as one single retreat period without consideration of the 35 years of stationary glaciers (1890-1925), the above calculated value reduces to 0.2-0.3 m w.e. a-1. The energy required for melting this amount of ice is 2-3 W m-2. Such values roughly correspond to the observed long term trend of atmospheric warming. It is assumed that in the 1970s at least 35% of the glacierized surface area existing around 1850 has disappeared. The corresponding volume change is estimated at 45-50%. In such a scenario (-0.9 m a-1 during a time interval of 50 years), 441 small glaciers representing 25% of the glaciers larger than 0.2 km2 existing in the mid-1970s would disappear. In comparison with conditions in the mid-1970s, about 1/3 of the surface area and more than 1/2 the ice volume would be lost.
Hypothèses

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

Pays / Zone	Massif / Secteur	Site(s) d'étude	Exposition	Altitude	Période(s) d'observation
Europe	Alps				1850-2020