Anyone who has ever built a sandcastle on the beach knows how quickly seawater in the sand can undermine the castle. A new study by the British Antarctic Survey concludes that warmer seawater could act in a similar way on the underside of layers of ice on the Earth’s surface, causing them to melt faster than previously thought.
That means computer models used to predict Antarctic ice melt may underestimate the extent to which the vast range of warming water beneath the ice is contributing to the melting, according to the study published Tuesday in the journal Nature Geoscience.
The faster melting of the ice sheets could lead to even greater flooding sooner than expected in coastal communities on the US East Coast, where flood days are already more frequent on the coasts and coastal rivers.
The study is at least the second in five weeks to report that warmer ocean water may be helping ice in glaciers and ice sheets melt faster than previously thought. Scientists are working to improve these important models used in planning for sea level rise.
Relatively warmer seawater can penetrate well beyond the so-called “grounding zone,” where near-surface ice meets the sea and floating ice shelves, and seep between the underlying land and the ice sheet, the new study says. And that could have “dramatic consequences” and contribute to sea level rise.
“We have identified the possibility of a new tipping point in the melting of the Antarctic ice sheet,” said lead author Alex Bradley, an ice dynamics researcher on the study. “This means that our predictions of sea level rise may be significantly underestimated.”
“Ice sheets are very sensitive to melting in their grounding zone,” Bradley said. “We found that melting in the grounding zone exhibits a ‘tipping point-like’ behavior, where a very small change in ocean temperature can cause a very large increase in melting in the grounding zone, which in turn would cause a very large change in the flow of the overlying ice.”
The study follows an independent study published in May that found “severe melting” of Antarctica’s Thwaites Glacier, commonly referred to as the “Doomsday Glacier.” That study, published in the Proceedings of the National Academy of Sciences, reported visible evidence of warm ocean water being pumped beneath the glacier.
The land-based ice sheets in Antarctica and Greenland are gradually sliding toward the ocean, creating a boundary at the edge of the sea where melting can occur. Scientists report that melting along these zones is a major factor in sea level rise worldwide.
Water seeping beneath an ice sheet opens up new cavities, and those cavities let more water in, which in turn causes even larger areas of ice to melt, according to the British Antarctic Survey. Small increases in water temperature can speed up this process, but computer models from the Intergovernmental Panel on Climate Change and others don’t take that into account, the authors found.
“There’s physics missing here that isn’t included in our ice sheet models. They’re not able to simulate the melting beneath the surface ice that we think is happening,” Bradley said. “We’re now working on incorporating that into our models.”
Lead author of the study published in May, Eric Rignot, a glaciologist at the University of California, Irvine, told USA TODAY that much more seawater is flowing into the glacier than previously thought, making the glacier “more sensitive to ocean warming and more likely to break apart as the ocean gets warmer.”
On Tuesday, Rignot said the study’s results provided “additional incentives to study this part of the glacier system more closely,” including the importance of tides, which exacerbate the problem.
“These and other studies indicate a greater sensitivity of glaciers to warm water and mean that sea level rise in the coming century will be much greater than expected, possibly up to twice as high,” Rignot said.
Contributor: Doyle Rice, USA TODAY