WASHINGTON, Sept. 2 (Xinhua) -- U.S. researchers said Monday they have uncovered "strong evidence" that soot, or black carbon, sent into the air by a rapidly industrializing Europe, likely caused the abrupt retreat of Alps mountain glaciers.
The findings, published in the U.S. journal Proceedings of the National Academy of Sciences, may help resolve the scientific debate about why the Alps glaciers retreated beginning in the 1860s, decades before global temperatures started rising again.
Central European Alps glacier records 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 abruptly retreated by an average of nearly 1 kilometer.
Yet weather in Europe cooled by about 1 degree Celsius during that time. Scientists have long been puzzled as to why the mismatch between the climate and glacier records occurred.
Now, researchers from the U.S. space agency NASA and the University of Colorado Boulder believed that black carbon is to blame.
"In the decades following the 1850s, Europe was undergoing a powerful economic and atmospheric transformation spurred by industrialization. Residents, transportation, and perhaps most importantly, industry in Western Europe began burning coal in earnest, spewing huge quantities of black carbon and other dark particles into the atmosphere," the researchers said in a statement.
"When black carbon particles settle on snow, they darken the surface. This melts the snow and exposes the underlying glacier ice to sunlight and relatively warm air earlier in the year, allowing more and faster melt," they said.
To determine how much black carbon was in the atmosphere and the snow when the Alps glaciers began to retreat, the researchers studied ice cores drilled from high up on several European mountain glaciers.
The team then ran computer models of glacier behavior, starting with recorded weather conditions and adding the impact of black carbon. By including this impact, the simulated glacier mass loss and timing finally "were consistent" with the historic record of glacial retreat, despite the cool temperatures of the time, they said.
"This study uncovers some likely human fingerprints on our changing environment," co-author Waleed Abdalati, director of the Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder said. "It's a reminder that the actions we take have far-reaching impacts on the environment in which we live."
The researchers said it's time to look closer at other regions on Earth, such as the Himalaya, to study the present-day impacts of black carbon on glaciers.