Scientists at NASA and the Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder have uncovered strong evidence that soot sent into the air by a rapidly industrializing Europe during the mid-1800s caused the abrupt retreat of mountain glaciers in the European Alps.
Thomas Painter, a snow and ice scientist at NASA's Jet Propulsion Laboratory in California, is the lead author of the study, published this week in the Proceedings of the National Academy of Sciences.
Painter said the findings might help resolve a longstanding scientific debate about why the Alps glaciers started retreating in the 1860s, decades before global temperatures started rising again.
“Something was missing from the equation,” Painter said.
The scientists studied the “powerful economic and atmospheric transformation spurred by industrialization” and determined that a massive increase in the amount of coal being burnt increased the amount of black carbon and other dark particles in the atmosphere.
“When black carbon particles settle on snow, they darken the surface,” a statement from CIRES explained.
“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.”
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.
By measuring the levels of carbon particles trapped in the ice core layers and taking into consideration modern observations of the distribution of pollutants in the Alps, they could estimate how much black carbon was deposited on glacial surfaces at lower elevations, where levels of black carbon tend to be highest.
The team then ran computer models of glacier behavior, starting with recorded weather conditions and adding the impact of lower-elevation black carbon. By including this impact, the simulated glacier mass loss and timing were finally consistent with the historic record of glacial retreat, despite the cool temperatures of the time.
CIRES director Waleed Abdalati, a co-author of the study, said this research was a reminder of the impact of human actions.
“This study uncovers some likely human fingerprints on our changing environment,” Abdalati said.
"It’s a reminder that the actions we take have far-reaching impacts on the environment in which we live."
The study calls for research to be conducted in other regions, such as the Himalayas, to study the present-day impacts of black carbon on glaciers, particularly with increased industrialization and coal-burning in Asia.
