Un service d’observation des glaciers des alpes françaises « glacioclim-alpes », pour quoi faire ?

Abstract

Glaciers act as very good climate indicators, and the relationship they develop with climate can be exploited at 2 levels. First of all, changes in meteorological conditions are directly recorded in glacier mass balance changes (in the form of either winter precipitation or summer ablation). Therefore, from separately measuring these two terms, climatic trends can be inferred and corresponding results are all the better as mass balance series are spanning longer periods. These mass balance changes then later express under the form of fluctuations in glacier length and thickness and/or ice surface velocities. Measuring these changes is another means of inferring climate change, although the relationship is much more complex because of a time-lagging non-linear response due to complicated processes such as ice rheology or basal gliding which only a deterministic ice-flow model can capture. Due to this specificity and complexity of the dynamical response of glaciers, using these glacier changes for climate reconstructions will also require as long as possible measurement series. It is therefore in this context of a better understanding of climate through glacier change that the glacier survey network was initiated. Three main types of measurements are undertaken ; (i) mass balance measurements with both winter accumulation and summer ablation, (ii) glacier dynamical response to mass balance change in the form of thickness and length changes as well as surface velocity measurements and last (iii) measurements of local meteorology with the help of Automatic Weather Stations. This paper describes the structure and the context in which the survey network was initiated as well as all the ensuing measurements. Some scientific applications are then presented as the results of these observations like the significant changes in surface mass balance connected to the strong changes in radiative and turbulent heat fluxes at the surface of glaciers over the last decades, or the better understanding of ice dynamics from direct inspection of glacier dynamical changes or from using these latter changes for tuning, validating and exploiting the results of an ice flow model.