It isn’t just happening in Greenland. It’s happening in the Himalayas, in western North America, in the Arctic circle. For the past few decades, glaciers and ice sheets in these locations are turning black, darkening from soot and other pollutants. Sure, it’s an aesthetic problem, but black ice leads to a much larger and more dangerous problem: Sea level rise.
In the Tibetan Himalayas, dung and wood are used to fuel cooking stoves. Over time, the soot produced by these fires has drifted on the wind and settled on the surrounding glaciers – glaciers that feed the Yangtze, Yellow, Mekong and Ganges rivers and sustain two billion people. A 2009 study from the Proceedings of the National Academy of Sciences suggests that this soot, coupled with global warming trends, is playing a key role in melting the Himalayan glaciers.
This is because the soot decreases snow’s “albedo,” its ability to reflect solar energy back into space. White snow, ice and clouds can reflect a portion of the sun’s rays and remain cool, even when they cover large areas. Darker areas, however, even small ones, absorb the sun’s heat much more easily. Thus, as snow darkens, it melts much more easily.
The effect of soot on Himalayan glaciers is the same observed on Greenland’s ice sheets. Utilizing remote sensing data, a report published in Nature Geoscience earlier this year “indicates that the springtime darkening [of the Greenland ice sheet] since 2009 stems from a widespread increase in the amount of light-absorbing impurities in snow, as well as in the atmosphere.”
The soot that’s blackening the ice comes from multiple sources: pollen and dust, industrial and automotive exhaust, and forest fires. In early October, Jason Box from the Geological Survey of Denmark and Greenland reported that there had been more forest fires in the northern hemisphere this year than any year in the last decade.
America, for example, is experiencing drier conditions and longer fire seasons, which has resulted in bigger, costlier wildfires along its west coast. Fires have been so severe that the state exhausted its larger-than-average $209 million fire-fighting budget in the first three months of the fiscal year.
Recently, Box used drones to survey Greenland’s darkening ice. The damage can be glimpsed in the video below.
“The Arctic is warming up twice as fast as the Subarctic, and we think it may be due to the dark ice that absorbs the sun’s rays rather than reflecting them as white ice would,” Box told ScienceNordic. “Therefore, it is important that we get a better understanding of the significance of the dark ice.”
As the temperature rises, microbes are finding it easier to survive in the Arctic. Algae is beginning to thrive in Greenland, which further minimizes the area’s albedo and accelerates the melting process.
“The microbes are currently getting more space to live and grow,” says Box’s colleague, Marek Stibal. “Moreover, they are not dependent on being brought by the wind, and it makes their contribution even more significant.”
Black ice and snow is very likely a contributing factor to the “unprecedented rate” of volume loss in the Greenland ice sheet observed by the European Space Agency’s CryoSatellite. As global ice sheets continue to blacken, they will melt even faster, potentially leading to more advanced sea level rise by the end of this century than previously predicted.