Recent glacier changes in the Alps observed by satellite: Consequences for future monitoring strategies

The new satellite-derived Swiss glacier inventory revealed that mean glacier area loss per decade from 1985 to 1998/99 has accelerated by a factor of seven compared to the period 1850–1973. Moreover, the satellite data display much evidence that down-wasting (i.e. stationary thinning) has become a major source of glacier mass loss, an observation that is confirmed by in situ mass balance measurements. Many of the observed changes (growing rock outcrops, tongue separation, formation of pro-glacial lakes, albedo lowering, collapse structures) are related to positive feedbacks which accelerate further glacier disintegration once they are initiated. As such, it is unlikely that the recent trend of glacier wastage will stop (or reverse) in the near future. In view of the rapid non-uniform geometry changes, special challenges emerged for the recently established tiered glacier monitoring strategy within the framework of the Global Climate/Terrestrial Observing System (GCOS/GTOS). The challenges include: (1) loss of mass balance series due to disintegrating glaciers, (2) problematic extrapolation of index stake measurements from a calibration period under different climate conditions, (3) critical evaluation of measured length changes, (4) establishment of an operational glacier inventorying strategy using satellite data and (5) the calculation of new topographic parameters after glacier split up that can be compared to previous parameters.