A study by the University of Milan shows the blackening of the glaciers in Stelvio National Park from the 1980s to the present day. A change driven by the accumulation of debris and pollution.
The glaciers of Stelvio National Park are getting increasingly "black" and therefore increasingly vulnerable to climate change. This is the finding of a group of researchers from the department of environmental science and policy at the University of Milan, who have for the first time analysed 40 years of data from Landsat satellites.
The research, published in Global and Planetary Change, focused on the Ortles-Cevedale mountain group and was coordinated by researcher Davide Fugazza, who examined the data using an algorithm that, working from satellite imagery, made it possible to obtain the albedo value, that is, the reflectivity of the surface.
Albedo is in fact a fundamental property of a glacier's surface, as it indicates the capacity to reflect solar radiation. A light surface, such as fresh snow, has a particularly high albedo value and therefore reflects the majority of incoming solar radiation. A dark surface, such as rock, has a much lower albedo value and therefore only a minimal fraction of solar radiation is reflected. A lower albedo thus implies greater absorption of solar radiation by the ice and increased melting, with significant consequences for the health of the glacier.
By analysing the Landsat image archive from the early 1980s to the present day, the researchers discovered that the majority of the glaciers studied have undergone a significant decrease in albedo. In other words, a blackening of the glacier.
Among the main causes of this phenomenon is the increase in debris coming from the rocky walls surrounding the glacier — debris that falls onto the ice as a result of rising temperatures. As well as destabilising slopes, rising temperatures also cause the early melting of snow that fell in winter and greater exposure of the ice during summer.
A significant contribution to the blackening also comes from dust transported through the atmosphere, both of natural origin (such as desert dust) and of anthropogenic origin (for example, fine particulate matter from diesel engine combustion, or dust produced by industrial activities in the Po Valley, or indeed from wildfires).
"This is the first study in which the extent of blackening is assessed on glaciers of the Alpine arc over such a long time period," comments Fugazza. "Knowing the intensity of this phenomenon makes it possible to estimate ice melt more accurately, assess the effects of blackening on glacier retreat, and develop predictive models to obtain indications of the sensitivity of glaciers to climate change."
The Forni Glacier, the largest in the Ortles-Cevedale, is among the Alpine arc's "critically ill" glaciers, where, as Fugazza explains to Il Fatto Quotidiano, a 30 per cent loss of glaciated surface was recorded between 1960 and 2015. In just over fifty years, in other words, 137 square kilometres of permanent snow and ice have melted — an area essentially equivalent to the extent of Lake Como.