New evidence from Italy (Adamello Group, Lombardy) for analysing the ongoing decline of Alpine glaciers

Glaciers worldwide are showing overwhelming evidence of the impact of climatic change. In the Alpine region the warming experienced since the early 1980s, while synchronous with warming at the global scale, is of a far greater amplitude and exceeds 1 °C, which represents roughly a three-fold amplification of the global climate signal. To evaluate the magnitude of climate change impacts, recent data covering large and representative areas are needed. This paper is aimed at contributing to describe the recent evolution of Alpine glaciers by analysing surface area changes in a representative subset of data (34 glaciers located in the Adamello Group, Lombardy, Italy). Four surface area records, for the years 1983, 1991, 1999 and 2003, were analysed. The 1983, 1999 and 2003 surface area records were compiled by the authors by combining aerial photo analysis, Differential Global Positioning System (DGPS) surveys of glaciers and Geographic Information System (GIS) data processing. The analysis led to a quantification of surface reduction: c. 19% from 1983 to 2003 for glaciers in the Adamello group. Small glaciers proved to contribute strongly to total area loss: in 2003, 31 glaciers (c. 91% of the total number) were smaller than 1 km2, covering 2.28 km2 (c. 10% of the total area), but accounted for 39% of the total loss in area (losing 2.05 km2 from 1983 to 2003). The rate of area change accelerated in the later period, with surface reduction between 1999 and 2003 amounting to c. 5.5% (with respect to the 1999 total glacier coverage), equal to a mean area loss of c. 0.34 km 2 /year; the mean yearly loss over the previous period (1991-1999) was found equal to 0.23 km2/year. This acceleration coincided with a clear local warming and a small local decrease in snow cover depth and duration which resulted strongly related to North Atlantic Oscillation (NAO) winter variability.