Water flowing beneath the ice plays a much more complex role in the melting of Greenland's glaciers than they previously imagined, scientists have revealed.
Researchers previously thought that meltwater simply lubricated ice against the bedrock, speeding the flow of glaciers out to sea.
Now, new studies have revealed that the effect of meltwater on acceleration and ice loss - through fast-moving outlet glaciers that connect the inland ice sheet to the ocean - is much more complex.
This is because a kind of plumbing system evolves over time at the base of the ice, expanding and shrinking with the volume of meltwater.
Researchers are now developing new low-cost technologies to track the flow of glaciers and get a glimpse of what lies beneath the ice.
As ice melts, water trickles down into the glacier through crevices large and small, and eventually forms vast rivers and lakes under the ice, according to Ian Howat, assistant professor of earth sciences at Ohio State University.
Researchers once thought that this sub-glacial water was to blame for sudden speed-ups of outlet glaciers along the Greenland coasts.
"We've come to realize that sub-glacial meltwater is not responsible for the big accelerations that we've seen for the last ten years," Howat said. "Changes in the glacial fronts, where the ice meets the ocean, are the real key," he added.
"That doesn't mean that meltwater is not important. It plays a role along these glacial fronts - it's just a very complex role, one that makes it hard for us to predict the future," he said.
Howat and his colleagues have determined that friction between the glacial walls and the fjords that surround them is probably what holds outlet glaciers in place, and sudden increases in ocean water temperature cause the outlet glaciers to speed up.
The research has implications for ice loss elsewhere in the world - including Antarctica - and could ultimately lead to better estimates of future sea level rise due to climate change.