(CN) — Researchers found significant melting at the bottom of the Greenland ice sheet that can be attributed to dam-like conditions that are not traditionally included in sea rise predictions.
An international team of scientists led by the University of Cambridge spearheaded the study, which was published Monday in the journal Proceedings of the Natural Academy of Sciences. They found that the thousands of meltwater lakes and streams formed on the surface of the ice sheet over the course of the summer drain through cracks in the glacier, cascading down shafts known as moulins.
Poul Christoffersen, professor of glaciology and co-author of the study, likened the effect to that of a dam. The falling water in a dam creates kinetic energy that goes through a turbine to generate electricity. With the ice sheet, the meltwater falls from a substantially higher height than that of even the largest dams. Nurek Dam in Tajikistan, the tallest dam in the world, is 984 feet tall. The moulins from the top of the Greenland ice sheet can descend more than 4,900 feet. Instead of generating electricity, the falling meltwater generates heat.
“We are transferring huge quantities of meltwater from the surface down to the icy base, which is a substantially lower elevation. That energy has got to go into something,” Christoffersen explained. “Because it can’t flow very efficiently at the base of the ice sheet, the ice sheet lifts up and the water just becomes sort of a turbulent sheet. That creates friction in the water and all the energy simply goes into warming up the water, and the water therefore starts to melt the ice sheet from the bottom up.”
According to a statement accompanying the research, the findings indicate that “the power produced by the falling water during peak melt periods was comparable to the power produced by the Three Gorges Dam in China, the world’s largest hydroelectric power station.”
When the melt area reaches its greatest extent in the summer, “the Greenland ice sheet produces more hydropower than the world’s ten largest hydroelectric power stations combined,” the statement said.
Christoffersen said the study’s results were “unprecedented.”
“It’s quite phenomenal to have a sub-glacial setting melt at the rate we report,” he said, explaining many previous studies focused on small glaciers where the moulins did not have the height to result in the level of melting seen at the Greenland ice sheet. Christoffersen said two independent methods of observation confirmed the melting.
The Greenland ice sheet is now the largest single contributor to global sea level rise. Christoffersen noted that the melting of the ice from warming temperatures explains “roughly half of the total amount of ice that’s lost.” The other half stems from the ice and icebergs that are discharged.
“Scientists have long been wondering what the link between these two factors is,” Christoffersen said, adding that the research could help scientists examine how meltwater flowing to the bottom of the ice sheet lubricates and affects the ice sheet’s flow.
The base of the ice sheet is ordinarily isolated from exposure to the atmosphere for hundreds of thousands, even millions of years. Christoffersen said the research shows how the base of the ice sheet is increasingly affected by meltwater from the surface, and thus more exposed to the effects of climate change. The melting of the ice sheet’s base has not been typically included in predictions of sea level rise.
Christoffersen said this may not significantly change sea level rise itself, but the melting of the ice sheet’s base over time could have a considerable effect on how much ice breaks off from the ice sheet or how quickly glaciers move.
“What we’ve seen in Greenland is astounding,” Christoffersen said. He noted that some years, sea levels rise a millimeter from Greenland ice melt alone, a significant departure from a few decades ago when the ice sheet made no contribution to sea level rise. He added that the melting base threatens the ice sheet’s stability. “The question is how fast and for how long are these changes in Greenland going to be? When is one millimeter per year going to be two millimeters per year from one ice sheet alone?”
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