Soot may have more of an effect on climate than we realized. It turns out that black carbon sent into the air by a rapidly industrializing Europe likely caused the abrupt retreat of mountain glaciers in the European Alps. The findings reveal the answer to a long-standing mystery surrounding the disappearance of this ice.

In the 1860s, the Alps glaciers retreated. This was decades before global temperatures started rising again. In fact, glacier records in the central European Alps dating back to the 1500s show that between 1860 and 1930, loosely defined as the end of the Little Ice Age in Europe, large valley glaciers in the alps retreated about .6 miles. This occurred at a time when weather in Europe cooled by nearly 1.8 degrees.

In order to find out exactly why glaciers retreated during this cool period, the researchers turned to history. In the years following the 1850s, Europe was in the midst of a powerful economic and atmospheric transformation. Industrialization spewed soot into the air as coal was burned in earnest. This black carbon settled in the form of particles on snow. Dark-colored in nature, these particles absorb heat, melting the snow and exposing the underlying glacier to sunlight and relatively warm air.

In order to investigate this phenomenon a bit further, the scientists decided to determine exactly how much black carbon was in the atmosphere and the snow when the Alps glaciers began to retreat. Using ice cores, they found exactly how much black carbon was deposited on glacial surfaces at lower elevations. They then ran computer models of glacier behavior.

In the end, the researchers found that glacial retreat was consistent with the timing and impact of lower-elevation black carbon. This revealed that the soot from industrialization was the cause for this retreat, despite cooler global temperatures.

"This study uncovers some likely human fingerprints on our changing environment," said Waleed Abdalati, one of the researchers, in a news release. "It's a reminder that the actions we take have far-reaching impacts on the environment in which we live."

The findings are published in the journal Proceedings of the National Academy of Sciences.