Afternoon Must-Read: John Timmer: Glaciers Draining Antarctic Basin Destabilized, Big Sea Level Rise All But Certain

John Timmer: Glaciers draining Antarctic basin destabilized, big sea level rise all but certain: “Researchers at UC Irvine and the Jet Propulsion Laboratory have announced results…

…indicating that glaciers across a large area of West Antarctica have been destabilized…. These glaciers are all that stand between the ocean and a massive basin of ice that sits below sea level…. Even in the short term, the new findings should increase our estimates for sea level rise by the end of the century, the scientists suggest. But the ongoing process of retreat and destabilization will mean that the area will contribute to rising oceans for centuries…. The glaciers… drain into the Amundsen Sea. On the coastal side, the ends of the glacier are actually floating on ocean water. Closer to the coast, there’s what’s called a “grounding line,” where the weight of the ice above sea level pushes the bottom of the glacier down against the sea bed. From there on, back to the interior of Antarctica, all of the ice is directly in contact with the Earth. That’s a rather significant fact, given that, just behind a range of coastal hills, all of the ice is sitting in a huge basin that’s significantly below sea level. In total, the basin contains enough ice to raise sea levels approximately four meters….

The grounding line… keep[s] the sea back from the base of the deeper basin. Once ocean waters start infiltrating the base of a glacier, the glacier melts, flows faster, and thins. This lessens the weight holding the glacier down, ultimately causing it to float, which hastens its break up. Since the entire basin is below sea level (in some areas by over a kilometer), water entering the basin via any of the glaciers could destabilize the entire thing….

The study tracks a number of glaciers that all drain into the region: Pine Island, Thwaites, Haynes, and Smith/Kohler…. The Pine Island Glacier came ungrounded in the second half of the past decade, retreating up to 31km in the process… all the glaciers in the area are in retreat…. The speakers at the press conference agreed that the new data shows that the recently released IPCC estimates for sea level rise are out of date…. The real problem, however, comes later. Glaciers can establish new grounding lines if there’s a feature in the terrain, such as a hill that rises above sea level, that provides a new anchoring point. The authors see none….

Modeling… work focuses on the Thwaites glacier, which appears to be the most stable…. The authors simulated the behavior of Thwaites using a number of different melting rates…. Every single one of these situations saw the Thwaites retreat into the deep basin within the next 1,000 years. In the higher melt scenarios—the ones most reflective of current conditions—this typically took only a few centuries…. There appeared to be a tipping point. In every simulation that saw an extensive retreat, rates of melting shifted from under 80 gigatonnes of ice per year to 150 gigatonnes or more, all within the span of a couple of decades… half a centimeter to sea level rise—every year. And, as the authors of this paper noted, the Thwaites is only part of the picture for this area of Antarctica. Should sea water enter the deep basin due to the failure of a different glacier, the behavior of the Thwaites would be irrelevant…. Geophysical Research Letters, 2014. DOI: 10.1002/2014GL060140 and Science, 2014. DOI: 10.1126/science.1249055