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.
Currently the Greenland ice sheet is adding up to 1mm a year to the rise in the global average level of the oceans.
It is the largest mass of ice in the northern hemisphere covering an area about seven times the size of the United Kingdom and reaching up to 3km (2 miles) in thickness.
This means that the average sea level would rise around the world by about seven metres, more than 20ft, if it all melted.
That is why Greenland, though remote, is a focus of research which has direct relevance to major coastal cities as far apart as Miami, London and Shanghai and low-lying areas in Bangladesh and parts of Britain. . . .
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. . . .
White snow reflects up to 90% of solar radiation while dark patches of algae will only reflect about 35% or even as little as 1% in the blackest spots.
When we flew by helicopter onto the ice sheet, the rolling landscape seemed surprisingly grey - my first impression was that it looked dirty. . . .
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. . . .
we know that they're very dark and we know that that's accelerating melt but that's not something that's built into any of our climate projections - and that's something that needs to change."
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. . .
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:
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