Temperature reconstruction from the length fluctuations of small glaciers in the eastern Alps (northeastern Italy)

In this study, a linear model computing the air temperature fluctuations from the measured glacier snout fluctuations has been applied, for the first time, to three small glaciers in the western Tauern Alps (eastern Alps) in the period 1929-2011. The considered glaciers, with areas between 0.2 and (Formula presented.), are characterized by relevant time variations of their morphology, length and slope. The model requires the knowledge of two parameters: the glacier climate sensitivity (Formula presented.) and the glacier response time (Formula presented.), both depending on the glacier morphological characteristics and on the precipitation. Applied to the glaciers assuming (Formula presented.) and (Formula presented.) as in the original formulation, it underestimates the temperature increase of (Formula presented.) derived over the whole period from the in situ data. Given the characteristics of these small glaciers, these parameters have been recalibrated by means of a non-linear least-square regression using an independent set of glaciers. Their mean value is of about 210 m/K and 3.8 years respectively. With the recalibrated values of the new glacier climate sensitivity (Formula presented.) and response time (Formula presented.), the temperature fluctuations derived by the model reproduce well those obtained from the observed temperatures computed over the hydrological year, with linear correlations between 0.8 and 0.9. The increase of the modeled mean temperature over the whole period fits in with that derived from observed temperature. Considering that the length fluctuations of these small glaciers affect significantly their slope and length, we tested the impact in the model of a time dependent formulation of (Formula presented.) and (Formula presented.): the results indicate slight improvements both in the values of the correlation between the reconstructed and the observed temperature fluctuations and in the global temperature increase. Given the above value of climate sensitivity, the large retreat of the small alpine glaciers threatens their survival within a few decades, but the morphological changes in progress may counteract the glacier disappearance.