Fluctuations des bilans de masse des glaciers des Alpes françaises depuis le debut du 20^e siècle au regard des variations climatiques

Influence of climate change on French glaciers mass balance over the 20th century

Laboratoire de Glaciologie et de Géophysique de l'Environnement du CNRS, associé à l'Université Joseph Fourier, 54 rue Molière, BP 96, 38402 Saint Martin d'Hères Cedex, France

Abstract

The relationships between mass balance and meteorological data were used to reconstruct the mass balances of six glaciers back to 1907 using old maps and photogrammetric measurements. Sensitivity analysis shows that a 25 to 30% increase in precipitation would compensate a 1^o C temperature rise for the mass balances of glaciers. From these results, the 20^th Century may be divided into four periods: two steady state periods, 1907-1941 and 1954-1981, during which the mass of glaciers remained almost constant, and two deficit periods, 1942-1953 and 1982-1999, marked by a sharp reduction in glacier mass. Regarding mean ablation at 2800 m asl, a 22 Wm^-2 increase in energy balance is required to explain the ablation difference between the two most recent periods, 1954-1981 and 1982-1999. According to the energy balance analysis, the increase in air temperature explains more than 60% of this ablation rise.