Thousands of New Meltwater Rivers from on Greenland Ice Sheet

New rivers are appearing on the surface of the Greenland ice sheet as it loses its ability to absorb meltwater, a new study has found. 

Thousands of new rivers of meltwater are forming on Greenland's ice sheet far inland and dumping gigatonnes of water into the ocean. That could boost sea levels faster than expected, a new study suggests.

The massive ice sheet covering much of Greenland is on average 1.5 to 2 kilometres thick and contains enough ice to raise world sea levels by about six metres if it all melted. That process could take thousands of years to complete, but has been accelerating due to climate change.

Scientists previously thought that melting process might be slowed down by a porous layer on the surface of the ice called firn, which is partway between ice and snow.

Climate models expected the firn layer to absorb up to 30 to 40 per cent of any meltwater that travels across the ice sheet, allowing it to refreeze instead of pouring into the ocean.

But a new international study has found that during 2012, an unusual amount of melting caused the top of the firn to freeze into solid ice. That meant it could no longer absorb the meltwater, which instead formed thousands of new rivers snaking across the surface of the ice sheet to the ocean.

"That hadn't been seen before," said William Colgan, a researcher at York University in Toronto who co-authored the new study.

"That was a very powerful visual, to see just how dramatically the firn had changed — to see no rivers one year, and the next year rivers extending an additional 20, maybe even 30 kilometres inland."

The rivers could be several metres wide and many appeared farther inland than had ever been seen before.

The Intergovernmental Panel on Climate Change's predictions of sea level rise are based on models that assume the firn would fill up gradually over the course of a century, reducing the amount of meltwater that Greenland pours into the oceans.

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