Scientists have figured out the worst that could happen if the mammoth chuck of continental ice at the bottom of the world—the West Antarctic Ice Sheet—continues melting. By 2100, ice sheet melt would raise sea levels by 7.9 inches, enough to pose a risk to low-lying nations, according to a study published today in The Cryosphere.

By 2200, ice sheet melt would raise sea levels by 1.6 feet.

The melted water from Antarctica and Greenland, glaciers, and the thermal expansion of the ocean due to higher temperatures are expected to raise sea levels by 3.3 feet in 2100, according to the Intergovernmental Panel on Climate Change. That would be sufficient to submerge 17 percent of Bangladesh.

Currently, the contribution from Greenland is greater than from Antarctica, but that is expected to change soon.

The Cryosphere study focuses on the contribution from West Antarctica, which is particularly vulnerable to melting. A portion of its ice shelves lies below sea level, which is usually not a problem because, due to a quirk, the coldest waters typically occur at the ocean surface and the warmer waters occur at depth.

But in recent years, wind patterns have changed and caused warm waters to rise and melt shelves from below.

Climate scientists use computer models to simulate ice shelves and climate change in the next century. The models break up the world into tiny pieces and assign algorithms representing natural phenomena to each piece. The smaller the size of the piece—that is, the greater the resolution—the more accurate the model would be, Dan Martin, a climate modeler with Lawrence Berkeley National Laboratory (LBNL) and co-author of the study, said in an email.

To accurately model ice sheets, the resolution has to be from less than 0.621 mile away, Martin said.

That’s incredibly detailed, and running such a model for all of Antarctica would be prohibitively expensive, so no one had done it.

Helping computer models predict future impacts

The IPCC’s fourth assessment report that predicts a 7.9-inch sea-level rise by 2100 used a coarse-resolution model that does not accurately represent ice sheet dynamics. This motivated the scientists from the University of Bristol in the United Kingdom and LBNL to develop a method where they could use extremely fine resolution only in the geographies where they needed it.

The resulting model had high resolution and was large scale. It captured the minute physics of how an ice sheet responds in a warming world.

“Much like a higher-resolution digital camera transforms a blur into a flock of birds, higher resolution in a computer model often helps to capture details of the physics involved which may be crucial to the broad picture,” said Martin.

The model showed that the key Pine Island and Thwaites glaciers would retreat by hundreds of miles, as would a number of others if nations continue emitting carbon at present-day rates.

The ice shelves in the Amundsen Sea embayment were the most vulnerable to melting by 2100 because of the typography under the ocean.

The Thwaites Glacier, which feeds into the embayment, may retreat rapidly at some point in the future. Depending on when this begins, it could triple the rate of global sea-level rise, the study found.

Understanding the West Antarctic Ice Sheet is key to helping people understand how to respond to, adapt to and prepare for a warming world, Martin said.

“There is wide consensus in the glaciology community that the West Antarctic Ice Sheet is particularly vulnerable to collapse,” he said.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500