According to a news release from the University of Colorado at Boulder, Industrial Age soot is responsible for the mid-1800s Alps glacier retreat. Researchers believe that the study’s results may end a long-lasting scientific debate about why the Alps glaciers retreated starting in the 1860s, years before global temperatures began increasing again.

Glacier records in the central European Alps stretching back to the 1500s reveal that between 1860 and 1930 massive valley glaciers in the Alps suddenly retreated by an average of almost 0.6 mile. During that time, however, temperatures in Europe dropped by almost 1.8 degrees Fahrenheit. Scientists have had trouble making sense of the disparity between the climate and glacier records.

“Something was missing from the equation,” said lead author Thomas Painter, a snow and ice scientist at NASA’s Jet Propulsion Laboratory, in a statement.

Painter and his colleagues looked at what was taking place in Europe at the time to determine the reason for the mismatch between the climate and glacier records. During the Industrial Age, industry in Western Europe started burning coal at a feverish pace, sending large amounts of black carbon and other dark particles into the atmosphere.

When black carbon particles land on snow, they darken the surface. This melts the snow and reveals the underlying glacier to sunlight and somewhat warm air earlier in the year, resulting in more and faster melt.

To calculate how much black carbon was in the atmosphere and the snow when the Alps glaciers tarted to retreat, the researchers examined ice cores drilled from high up on several European mountain glaciers. By determining the levels of carbon particles caught in the ice core layers and factoring in modern observations of the dispersion of pollutants in the Alps, they could approximate how much black carbon collected on glacial surfaces at lower elevations, where levels of black carbon are usually the highest.

The researchers then conducted computer models of glacier behavior, beginning with documented weather conditions and adding the effect of lower-elevation black carbon. By adding this effect, the simulated glacier mass loss and timing finally matched up with the historic record of glacial retreat, in spite of the cool temperatures of the time.

“This study uncovers some likely human fingerprints on our changing environment,” said Waleed Abdalati, Director of the Cooperative Institute for Research in Environmental Sciences at the UC-Boulder. “It’s a reminder that the actions we take have far-reaching impacts on the environment in which we live.”

“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,” added co-author Georg Kaser of University of Innsbruck.

The study’s findings are discussed in greater detail in the journal Proceedings of the National Academy of Sciences.

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