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Greenland Meltwater May Be Major Contributor to Sea Level Rise

Jan 13, 2015 12:32 PM EST

The massive Greenland Ice Sheet, the second largest ice sheet in the world, has long been considered a threat to global sea level rise, and now new research finds that its network of meltwater rivers and streams may be a major contributor to these rising waters.

In the past, scientists have focused their attention mostly on the ice sheet's lakes - bodies of water that quickly drain - and the massive slabs of ice that break off from Greenland and slide into the ocean, later to become icebergs.

Until now, little attention has been paid to the rivers and streams flowing on top of the ice sheet. But researchers show that this ill-considered factor plays a bigger role than previously realized, most likely responsible for the same, if not more, sea level rise than the other two sources combined.

When snow and ice thaw during the summertime, these waterways form a complex drainage system that captures virtually all surface runoff from the ice sheet, and can release this water in a matter of just two days.

"It's the world's biggest water park, with magnificent and beautiful - but deadly - rushing blue rivers cutting canyons into the ice," lead study author Laurence C. Smith, from the University of California, Los Angeles (UCLA), said in a press release.

Using a helicopter, satellite imagery, buoys fitted with GPS technology, and a drone boat specially designed for the project, UCLA researchers were able to map the river network and calculate the rivers' flow rates during the summer of 2012. It just so happens that during this time, the Greenland Ice Sheet experienced a massive and extremely unusual melt only seen once before in the last 700 years.

"It was a real preview of just how quickly that ice sheet can melt and the meltwater can escape," Smith explained.

Through their data they found that the surface of the ice sheet is somewhat like Swiss cheese - all 523 actively flowing streams across a 2,000-square-mile area drained into moulins, or sink holes, which then carried meltwater under the ice and into the ocean. Meanwhile, a modest "sponge" effect was occurring below the surface, where the ice sheet drained at a rate of 55,000-61,000 cubic feet per second - that's more than double the average flow of the Colorado River.

Missing Meltwater

However, there is a mysterious discrepancy in their results, where some of the draining water can't be accounted for, and researchers are still trying to figure out where this missing meltwater ends up.

"The model automatically assumes that the meltwater is going directly to the ocean," said co-author Marco Tedesco. "Some can get retained under the ice. More research is definitely needed."

Still, what does end up in the ocean is needless to say concerning. Just looking at the Isortoq River alone - one of at least 100 large terrestrial rivers linking the melting Greenland Ice Sheet to the world's oceans - meltwater is draining at an astonishing average flow rate of 23,000 to 46,000 feet per second.

It has been known for some time that if the Greenland Ice Sheet melts completely it could raise global sea levels by a staggering 20 feet in the face of climate change. But these new findings, published in the journal Proceedings of the National Academy of Sciences, add more worry to the equation. They also show scientists that existing climate models may need to be modified to better determine how rising seas may impact coastal communities and the environment in the future.

"If we can get better estimates, then we can have better projections for the extent and the impact of global warming," Tedesco added. "Greenland is really the big player for sea level rise in the future, so improving climate models is extremely crucial."

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