New evidence of glacier darkening in the Ortles-Cevedale group from Landsat observations

摘要

Glacier darkening, or the decrease in glacier albedo over time, has been reported for glaciers in several parts of the world. In this study, we use data from the Landsat archive spanning back to 1984 to investigate the long-term evolution of surface albedo in the ablation area of 15 selected glaciers in the Ortles-Cevedale group, Central Italian Alps, and determine rates and magnitude of darkening. We calculate albedo trends using all available images acquired between 1984 and 2011, by filtering for cloud and snow cover. To confirm that the trends are robust, we perform tests on three pseudo-invariant calibration sites located outside glaciers, ruling out an influence of sensor degradation or varying solar geometry. All 15 investigated glaciers show a decrease in the albedo, which is significant at the 95% (99%) confidence level for 14 (12) glaciers. Albedo trends range between - 0.001 y(-1) and - 0.006 y(-1), with an average of - 0.003 y(-1).We compare our results with previous research in the study area to evaluate the effects of increasing supraglacial debris and climate change on the decrease in albedo; the first appears particularly important for some glaciers and we hypothesize glacier darkening might be caused by a combination of these two factors.