Analysis of Alpine glacier length change records with a macroscopic glacier model

The length change record of 91 glaciers in the Swiss Alps was analyzed with a novel macroscopic glacier model (LV-model). Based on a history of equilibrium line variations, synthetic length change data were calculated. From the LV-models matching best the measured length changes, characteristic parameters were obtained. The volume time scale thus determined ranges from 5 to 170 years for glaciers of different slope and length. The analysis shows that the observed glacier length changes cannot be reproduced with an equilibrium line variation based on temperature and precipitation alone. The equilibrium line has to be lowered by 100 to 200 meters during several phases of the Little Ice Age (in the time span 1650 to 1850) to obtain observed glacier responses. Such an effect might be attributable to either higher winter precipitation in the Alps, or to radiation forcing.