The great ice sheet of West Antarctica is as big as Mexico and holds enough volume of ice to raise the sea level by 12 feet. A refined model based on equations which accurately reproduced sea level rise events from hundreds of thousands of years ago suggests this massive ice sheet is disintegrating faster then previously thought. It could raise the sea level by an extra three feet, bringing the total projected sea level rise to five to six feet by 2100 — twice as much than the estimates reported in a worse case scenario by the U.N.

Two Antarctic ice shelves on the verge of collapsing—the Pine Island Glacier (shown) and the Thwaites Glacier—will cause the ultimate collapse of the entire West Antarctic Ice Sheet. Credit: NASA

Robert M. DeConto of the University of Massachusetts, Amherst, and David Pollard, a researcher at Pennsylvania State University, led the new research.

Modeling the effects of global warming on Antarctica’s ice sheets is a complex affair. Compared with the coupled ocean-atmosphere climate system, an ice sheet might seem a rather simple system to model numerically. Ice sheets are composed of a single, largely homogeneous material.  But it is in specifying the stress boundary conditions on  two of the ice sheet interfaces—its base and its seaward margin—that the difficulty arises.

Determining whether small changes could trigger a substantial deglaciation in a complex chain of events is thus very difficult. It’s clear that global warming is exacerbating the melting of Antarctica’s ice sheet, but by how much and when will the critical point be reached? These sort of questions keep climate scientists awake at night. Results may be skewed due to the sheer complexity, but the best way to check if results touch reality is to compare with the past.

For the first time, a climate model accurately reproduced high sea level rise from the past

DeConto and Pollard had a very sophisticated climate model at their disposal, but it proved woefully inadequate when they used it to explain the behaviour of ice sheets in the past. Specifically, that from a climatic period about 125,000 years ago when the seas rose to levels 20 to 30 feet higher than today. Something was missing to piece the model together.

The missing link proved to be the huge shelves of floating ice that acts like a buffer and protect the West Antarctic ice sheet from melting.Without them, glacial ice enters the ocean faster and accelerates the pace of global sea level rise.  In 2002, an ice shelf the size of Rhode Island, the Larsen B, partially collapsed. This happened in only two weeks.

When the researchers factored in global warming’s attack on floating ice shelves, vast, sheer cliffs of ice facing the sea formed. Many are high and unstable, so collapse is imminent. This results in a rapid shrinkage of the ice sheet as the cliffs collapse. The researchers note similar effects are being observed already in Greenland and, at a smaller scale, in Antarctica.

The new version of the model allowed the scientists, for the first time, to reproduce high sea levels of the past, the New York Times reports. Another interesting finding was that the ice sheet shrinkage can be avoided if the planet decarbonizes. This is contrary to other study who reported the disintegration of the West Antarctic ice sheet has already begun and is irreversible. To prevent the collapse, however, carbon emissions need to be lowered far more aggressively than currently agreed up by U.N. states in Paris, last year.