Sea level fears as Greenland darkens

[nitpicker]

http://www.bbc.com/news/science-environment-40686984

Sea level fears as Greenland darkens

David Shukman
Science editor

24 July 2017

From the section Science & Environment

Scientists are "very worried" that the melting of the Greenland ice sheet could accelerate and raise sea levels more than expected. They say warmer conditions are encouraging algae to grow and darken the surface. Dark ice absorbs more solar radiation than clean white ice so warms up and melts more rapidly.
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Algae were first observed on the Greenland ice sheet more than a century ago but until recently its potential impact was ignored. Only in the last few years have researchers started to explore how the microscopically small plants could affect future melting. A five-year UK research project known as Black and Bloom is under way to investigate the different species of algae and how they might spread, and then to use this knowledge to improve computer projections of future sea level rise.

The possibility of biologically inspired melting was not included in the estimates for sea level rise published by the UN's climate panel, the IPCC, in its latest report in 2013. That study said the worst-case scenario was a rise of 98cm by the end of the century.

One concern now is that rising temperatures will allow algae to flourish not only on the slopes of the narrow margins of the ice-sheet but also on the flat areas in the far larger interior where melting could happen on a much bigger scale.
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When we flew by helicopter onto the ice sheet, the rolling landscape seemed surprisingly grey - my first impression was that it looked dirty. Much of the surface was covered with what looked like patches of soot and it was pockmarked with countless holes at the bottom of which were pitch-black layers of a mix of algae, bacteria and minerals known as cryoconite.
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Over the last 20 years, Greenland has been losing more ice than it gains through snowfall in winter - a change in a natural balance that normally keeps the ice-sheet stable. And one of the project scientists, Dr Andrew Tedstone, a glaciologist and also of Bristol University, said that over much of the same period, images from the MODIS satellite showed a darkening trend with the years of greatest dark producing most meltwater.
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Earlier research had found that the ice sheet is covered with a range of contaminants carried on the winds including dust and soot from as far away as Canadian prairie fires and the industrial heartlands of China, America and Europe. But studies over the past five years have shown that the majority of the dark material may be biological with different kinds of algae turning the ice black, brown, green and even mauve.
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The final phase of the Black and Bloom project involves weaving the new factor of biological darkening into climate models to come up with revised estimates for future sea level rise.
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Meanwhile, another factor that may be driving the melting has been identified by an Austrian member of the team, Stefan Hofer, a PhD student at Bristol. In a paper recently published in Science Advances, he analysed satellite imagery and found that over the past 20 years there has been a 15% decrease in cloud cover over Greenland in the summer months. "It was definitely a 'wow' moment," he told me.
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