Réf. Harris & al 2003 - A

Référence bibliographique complète
HARRIS, C., VONDER MÜHLL, D., ISAKEN, K., HAEBERLI, W., SOLLID, J.L., KING, L., HOLMLUND, P., DRAMIS, F., GUGLIELMIN, M., PALACIOS D., Warming permafrost in European mountains.Global and Planetary Change, 2003, 39, 215 –225.

Abstract: Here [the authors] present the first systematic measurements of European mountain permafrost temperatures from a latitudinal transect of six boreholes extending from the Alps, through Scandinavia to Svalbard. Boreholes were drilled in bedrock to depths of at least 100 m between May 1998 and September 2000. Geothermal profiles provide evidence for regional-scale secular warming, since all are nonlinear, with near-surface warm-side temperature deviations from the deeper thermal gradient. Topographic effects lead to variability between Alpine sites. First approximation estimates, based on curvature within the borehole thermal profiles, indicate a maximum ground surface warming of + 1 °C in Svalbard, considered to relate to thermal changes in the last 100 years. In addition, a 15-year time series of thermal data from the 58-m-deep Murtèl–Corvatsch permafrost borehole in Switzerland, drilled in creeping frozen ice-rich rock debris, shows an overall warming trend, but with high-amplitude interannual fluctuations that reflect early winter snow cover more strongly than air temperatures. Thus interpretation of the deeper borehole thermal histories must clearly take account of the potential effects of changing snow cover in addition to atmospheric temperatures.

Mots-clés
Permafrost, global warming, borehole temperatures, European mountains

Organismes / Contacts
Department of Earth Sciences, Cardiff University, P.O. Box 914, Cardiff CF10 3YE, UK
University of Basel, Petergraben 35/3, CH-4051 Basel, Switzerland
Norwegian Meteorological Institute, P.O. Box 43 Blindern, N-0313 Oslo, Norway
Department of Geography, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich
Department of Physical Geography, University of Oslo, P.O. Box 1042, Blindern, N-0316 Oslo
Geographical Institute, Justus Liebig University, Senckenbergstrasse 1, Giessen D35390, Germany
Department of Physical Geography, Stockholm University, S-10591 Stockholm, Sweden
Department of Geological Sciences, Third University of Rome, Largo San Leonardo Murialdo, 1-00146 Rome
Geological Survey of Lombardy, Milan, Italy
Departmento de AGR y Geografia Física, Universidad Complutense, Madrid 28040, Spain

(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 Snow cover, Permafrost    

Pays / Zone
Massif / Secteur
Site(s) d'étude
Exposition
Altitude
Période(s) d'observation
Switzerland Engadin Murtèl–Corvatsch   2670m (borehole site) 1987-1994

(1) - Modifications des paramètres atmosphériques
Reconstitutions
 
Observations
Meteorological stations such as St. Bernhard 2472 m (Switzerland) [Boehm et al., 2001] and Silandro at 720 m (Valtelina, Italy) indicate significant increases in 20th century atmospheric temperatures at high elevations within the Alps.
Modélisations
 
Hypothèses
 

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

(2) - Effets du changement climatique sur le milieu naturel
Reconstitutions
 
Observations
The PACE mountain permafrost borehole network offers the prospect of long-term monitoring as part of the Global Terrestrial Network for Permafrost (GTN-P) of the Global Climate Observing System (GCOS).

The first data sets presented show thermal gradients consistent with 20th century surface warming. Relief and aspect lead to greater variability between the Swiss and Italian Alpine boreholes than between those in Scandinavia and Svalbard. Observed warm-side deviation of ground temperatures at both 20 and 40 m is greater in the polar latitude Svalbard borehole than the more southerly boreholes in the network, suggesting greater warming at higher latitudes, as predicted by Global Climate Models (Houghton et al., 1996). First approximations of surface warming range from 0.5 °C at Stockhorn, Switzerland and Juvvasshøe, Norway to 1.0 °C at Janssonhaugen in Svalbard. A 15-year record of permafrost temperatures from the 58 m deep Murtèl–Corvatsch in Switzerland shows a warming trend, but with large amplitude interannual variations that reflect early winter snow thickness and duration rather than mean air temperatures. The significance of snow cover to the thermal regime of the upper permafrost boundary must therefore be carefully considered in interpreting future thermal inversion modelling of the permafrost geothermal profiles.

The longest continuous series of temperature measurements within European mountain permafrost is from the 58 m deep borehole at Murtèl–Corvatsch (Engadin, Switzerland) which was drilled in 1987 through slowly creeping ice-rich debris (Vonder Mühll et al., 1998; Haeberli et al., 1988; Vonder Mühll, 2001). Rapid warming of the uppermost 25 m of permafrost was observed between 1987 and 1994. The mean annual ground surface temperature is estimated to have increased from -3.3 °C (1988) to -2.3 °C (1994). However, low snowfall in December and January in the winter of 1994–1995, followed by moderate snow fall in 1995–1996 caused intense cooling of the ground and permafrost temperatures returned to values similar to those in 1987. Early winter snow was thin in 1998–1999 and winter ground temperatures remained low in 1999, 2000 and 2001. Mean permafrost temperature at a depth of 11 m rose and fell by 1.0 °C and at 20 m by 0.4 °C during the 15-year observation period, the dominant variable being snow cover rather than mean atmospheric temperatures. Thus, interpretation of inversion modelling based on the PACE borehole profiles must take account of the complex relationship between the ground surface and atmospheric temperatures, particularly the strong modulating affect of snow conditions. Overall, permafrost warming during the 15 years of observation at Murtèl–Corvatsch was about 0.6 °C at 11.6 m (within the depth range of strong seasonal temperature variability) and 0.2 °C at 20 m (below the depth of seasonal variation), indicating continued if not accelerated warming in recent years.
Modélisations
 
Hypothèses
 

Sensibilité du milieu à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)
Permafrost has been identified as one of six cryospheric indicators of global climate change within the monitoring framework of the WMO Global Climate Observing System (GCOS) (Cihlar et al., 1997; Burgess et al., 2000; Harris et al., 2001a,b). Permafrost reacts sensitively to changes in atmospheric temperature (e.g. Anisimov and Nelson, 1996 [...]).

Permafrost temperature profiles show near-surface warm-side deviation from linear, with thermal gradients increasing with depth. [...] Borehole thermal gradients may be influenced by four major factors; regional geothermal heat flux, variation in lithology with depth, ground surface topography (governing the shape of the local upper thermal boundary), and past changes in ground surface temperatures.[...] In the Alps, the high relief results in heat flow less than the Swiss average of 85 mW/m² (Bodmer and Rybach, 1984). Bedrock lithology influences thermal diffusivity, but in all PACE boreholes, little variation in lithology was observed during drilling. Three-dimensional modelling of the temperature field is necessary to assess the influence of topography. However, initial data suggest that at the PACE permafrost borehole sites, the final factor, past changes in ground surface temperature, is highly significant with respect to depth-related changes in the thermal gradient.
During drilling, boreholes were flushed with chilled compressed air, and no liquids were used. [...] Standardized instrumentation procedures included installation of 30 individually calibrated thermistors with absolute accuracy better than ± 0.05 °C, at increasing downhole depth intervals (Harris et al., 2001b). Boreholes were lined with plastic tubing to allow periodic recalibration of thermistors. No fluid such as oil was introduced inside the borehole liner. Data are recorded every 6 h in the uppermost 5 m, and every 24 h at greater depths. [...] At all sites permafrost thickness exceeded expectations on the basis of atmospheric temperatures. In all cases, the depth of penetration of the seasonal thermal signal was around 20 m.

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

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

(4) - Remarques générales

Initial measurements of geothermal profiles from series of six recently drilled boreholes in the high-elevation mountain permafrost zone of Europe are reported in this paper. All boreholes were drilled by the EU-funded Permafrost and Climate in Europe (PACE) Project (Harris et al., 2001a,b) between May 1998 and September 2000. The PACE boreholes discussed here include the Schilthorn and Stockhorn Mountains (Switzerland), Stelvio Pass (Italy) Juvvasshøe, Jotunheimen (Norway), Tarfalaryggen (Sweden) and Janssonhaugen (Svalbard).

Inversion modelling offers the potential for estimating the evolution of former changes in surface temperature from observed geothermal profiles [see references in the study] and since heat advection by groundwater flow can be excluded in ice-bearing permafrost, inversion modelling is particularly appropriate. However, in the European mountains, topographic influences on the upper thermal boundary must be considered, and at lower latitudes the significance of aspect may be considerable, so that three-dimensional analysis of the geothermal fields is a critical component of inversion modelling. This analysis is currently in progress, and results are not yet available. It is important to stress, therefore, that the current paper presents only a first approximation of likely surface warming at the PACE borehole sites interpreted from the observed near-surface geothermal profiles.


(5) - Syntèses et préconisations
 

Références citées :

Anisimov, O.A., Nelson, F.E., 1996. Permafrost distribution in the Northern Hemisphere under scenarios of climate change. Global and Planetary Change 14, 59 –72.

Bodmer, Ph., Rybach, L., 1984. Geothermal map of Switzerland (heat flow density). Commission Suisse de Géophysique. Materiaux pour la géologie de la Suisse, vol. 22. Kümmerli and Frey, Bern, p. 47.

Boehm, R., Auer, R.I., Brunetti, M., Maugeri, M., Nanni, T., Scoehner, W., 2001. Regional temperature variability in the European Alps 1760 –1998 from homogenised instrumental time series. International Journal of Climatology 21, 1779 –1801.

Burgess, M.M., Smith, S.L., Brown, J., Romanovsky, V., Hinkel, K., 2000. Global Terrestrial Network for Permafrost (GTNet-P): permafrost monitoring contributing to global climate observations. Geological Survey of Canada, Current Research, 1 –8 (2000-E14).

Cihlar, J., Barry, T.G., Ortega Gil, E., Haeberli, W., Kuma, K., Landwehr, J.M., Norse, D., Running, S., Scholes, R., Solomon, A.M., Zhao, S., 1997. GCOS/GTOS plan for terrestrial climate-related observation. GCOS 32, version 2.0, WMO/TD-796, UN¬EP/DEIA/TR, 97-7.

Haeberli, W., Huder, J., Keusen, H.-R., Pica, J., Röthlisberger, H., 1988. Core drilling through rock–glacier permafrost. Proceedings of the Fifth International Conference on Permafrost. Tapir, Trondheim, pp. 937 –942.

Harris, C., Davies, M.C.R., Etzelmüller, B., 2001a. The assessment of potential geotechnical hazards associated with mountain permafrost in a warming global climate. Permafrost and Periglacial Processes 12, 145 –156. [Fiche Biblio]

Harris, C., Haeberli, W., Vonder Mühll, D., King, L., 2001b. Permafrost monitoring in the high mountains of Europe: the PACE Project in its global context. Permafrost and Periglacial Pro-cesses 12, 3 –11.

Houghton, J.T., Meira Filho, L.G., Callander, B.A., Harris, N., Kattenberg, A., Maskell, K., 1996. Climate Change 1995: the Science of Climate Change, Intergovernmental Panel on Climate Change (IPCC). Cambridge Univ. Press, Cambridge. 572 pp.

Vonder Mühll, D., 2001. Thermal variations of mountain permafrost: an example of measurements since 1987 in the Swiss Alps. In: Visconti, G., Beniston, M., Iannorelli, E.D., Barba, D. (Eds.), Global Change in Protected Areas. Kluwer Academic Publishing, Dordrecht, pp. 83 –95.

Vonder Mühll, D., Stucki, T., Haeberli, W., 1998. Borehole temperatures in alpine permafrost: a ten year series. In: Lewkowicz, A.G., Allard, M. (Eds.), Proceedings of the Seventh International Conference on Permafrost. Collection Nordicana, vol. 57. Université Laval, Quebec, pp. 1089 –1095.