Scientists have long debated why glaciers in the central European Alps began retreating during the 1860s, decades before global temperatures began their most recent rise. In the present study, a US-led research team analysed the black carbon content of ice cores drilled from high up several European mountain glaciers. Using modern observations of the distribution of pollutants in the Alps, they were then able to estimate how much black carbon was deposited on glacial surfaces at lower elevations, where levels of black carbon tend to be highest.

From the 1850s, rapid industrialisation saw increasing combustion of coal, which caused the release of black carbon into the atmosphere. As this soot settled onto the snow, it darkened the surface, increasing the rate of snow melt and exposing the underlying glacier ice to sunlight and relatively warm air earlier in the year.

Starting with recorded weather conditions, the team ran computer models of glacier behaviour. When they added the impact of the lower-elevation black carbon they had extrapolated from the ice cores, they found that the model results for both the timing and mass loss from the glaciers were consistent with the historical record of glacial retreat.

‘We must now look closer at other regions on Earth, such as the Himalaya, to study the present-day impacts of black carbon on glaciers,’ said one of the study’s co-authors Georg Kaser of the University of Innsbruck.

This story was published in the October 2013 edition of Geographical Magazine