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Just one of 38 positive feedbacks
Greenland
Ice Is Turning Black, and That’s Not the Bad News
7
November, 2014
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.”
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.
