Mountain glaciers are sensible indicators of climate change, reacting particularly to changes in summer temperatures and winter precipitation. Therefore the oscillation of mountain glaciers provides information on climate changes at times and in regions with sparse instrumental climate observations.
The importance of glacier studies for climatology is best illustrated by the work of Penck and Brückner (1909), which led to the acceptance of the existence of ice ages and triggered research on the related climate change.: In the early 20th century they demonstrated the interrelation of glaciers and climate by proving that erratic blocks in the Alpine foreland had been transported there by glaciers during the ice ages. Modern glacier monitoring is based on records of glacier mass changes (i.e. mass balance), length changes (i.e. fluctuation) of glaciers and the compilation of glacier areas and surface elevation in glacier inventories.
On a global scale, mountain glaciers have generally retreated since the Little Ice Age maximum, which occurred about 1850 in the Alps (Vaughan et al., 2013). At regional or local level and for shorter time scales, glaciers react individually (Kuhn et al., 1985) based on their specific topography and local effects of global climate change.
In Tyrol, South Tyrol and Veneto, the time series of glaciological parameters are among the longest world-wide. The first measurements within these three regions date back to the year 1601 (Nicolussi, 1990). The systematic measurements of length changes in the project area began in 1881 in the Austro-Hungarian Empire by some of the Austrian Alpine Clubs and later, starting from 1919, similar studies were made by Italian state agencies. Nowadays the length variation of glaciers is monitored for 10 % of the glaciers. Starting around 1950, mass balance today is measured for 1 % of the glaciers in the project area. Within the project area mountain glaciers cover 411,57 km².
For the interpretation of the glaciological data it is important to know where glaciers exist and how they respond to weather and climate. Glaciers can exist where winter snow does not melt during summer for several decades (Cuffey and Paterson, 2010). This is the case at high altitudes with reduced incoming direct solar radiation, as well as a result of high snow accumulation due to precipitation, wind or avalanches. Winter snow, with a density varying from 100 kg/m³ to 400 kg/m³ becomes firn (density varying from 400 kg/m³ to 830 kg/m³), and after several decades, glacier ice (918 kg/m³). Snow, ice and firn flow down to the valley with the force of gravity.
The area of a glacier which gains mass in the winter season (October to September) is called accumulation zone. In contrast, the glacier loses mass over the year in the ablation zone. The balance of the mass gains or losses in the accumulation and ablation zone is called mass balance. A negative balance means the glacier is losing mass. If the mass balance is negative for a couple of years, glacier length and area decrease. After a year of positive mass balance, the glacier gains mass. As a consequence flow velocity increases and the glacier advances. An advancing glacier tongue pushes debris and boulders along. After a glacier retreat, these moraines mark a glacier maximum, which can be mapped and dated by radiocarbon and surface exposure methods.
Cuffey K M, Paterson W (2010): The physics of glaciers, Elsevier.
Kuhn M, Markl G, Kaser G, Nickus U, Obleitner F, Schneider H (1985): Fluctuations of climate and mass balance: different responses of two adjacent glaciers. Zeitschrift für Gletscherkunde und Glazialgeologie 21, 409–416.
Nicolussi K (1990): Bilddokumente zur Geschichte des Vernagtferners im 17. Jahrhundert. Zeitschrift für Gletscherkunde und Glazialgeologie 26 (2): 97-119.
Penck A, Brückner E (1909): Die Alpen im Eiszeitalter. Taunitz, Leipzig.
Vaughan DG, Comiso JC, Allison I, Carrasco J, Kaser G, Kwok R, Mote P, Murray T, Paul F, Ren J, Rignot E, Solomina O, Steffen K, Zhang T (2013): Observations: Cryosphere. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, Hrsg. Stocker TF, Qin D, Plattner GK, Tignor M, Allen SK, Boschung J, Nauels A, Xia Y, Bex V, Midgley PM. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.