The new findings, published Monday in the Proceedings of the National Academy of Sciences, come from the analysis of satellite images. They show that a natural buffer system that prevents glaciers from rapidly flowing outward is breaking down, potentially releasing much more ice into the sea over the next few years.
Glacier ‘shear edges’, where their floating ice shelves encounter high levels of friction that restrict the natural flow of the ice, are progressively weakening and in some cases breaking apart.
“The stresses that slow the glacier are no longer in place, so the glacier is accelerating,”
While many of the images have been seen before, the new analysis suggests they are a sign of further disintegration to come.
“We already knew these were glaciers that may matter in the future, but these images indicate to me that these ice shelves are in a very bad state,” Lhermitte said.
It’s just the latest in a flurry of bad news on the planet’s ice.
Arctic sea ice is very close, but probably won’t quite hit an all-time low this time of year. Last month, Canada lost much of its last great Arctic ice shelf.
And in Greenland, the largest still intact ice shelf in the Northern Hemisphere, sometimes known as 79 North due to its latitude (its full name is Nioghalvfjerdsfjorden), has just lost a large chunk of ice, equivalent in size to about two islands of Manhattan, according to the Geological Survey of Denmark and Greenland. Experts attributed the fracture to a strong general warming trend and temperatures that have been “incredibly” high in northeastern Greenland in recent years.
Ice shelves are vast floating platforms that extend over the ocean surface to the outer boundary of marine-based glaciers. As they flow over the water, these shelves freeze on mountain slopes and islands and anchor to the bumps of the sea floor. In this way, the shelves provide a braking mechanism on the natural outward flow of the ice.
The buttress effect occurs in the cutting edges, where the faster flowing ice meets the ice that is more static and stable, often because it is moored somewhere in the landscape. In these places, the ice often curls up and writhes, a visible sign of the strong stresses it is subjected to.
But when these stresses become excessive, the ice breaks. This is what is happening now in West Antarctica, the new research argues, suggesting that warm ocean water has thinned the ice shelves from below enough to make them brittle.
At the same time, and for the same reason, the glaciers themselves began to slide outward faster. The resulting forces have caused the ice at the cutting edge to break apart, meaning the less constrained glacier will now be able to add ice to the ocean even faster.
For the Pine Island glacier, the new study finds that while rupture and fraying at the cutting edge dates back to 1999, they accelerated in 2016. Here is a video based on images from the European Space Agency’s Sentinel satellite, which shows the changes over the past four years:
Even more troubling is the Thwaites Glacier. Again, the cutting edge break has increased in recent years:
“This is important work,” said Richard Alley, a glaciologist at Pennsylvania State University, of the new study.
Alley noted that the ongoing processes in Antarctica appear to have already reached their completion in parts of Greenland, where one of the largest glaciers, Jakobshavn, no longer has any significant ice shelves. When he lost that shelf around 2000, Jakobshavn’s ice loss rate increased dramatically.
The 79 North Glacier still has a major ice shelf, as do some of Greenland’s other northernmost glaciers, but many of these have lost considerable size in recent decades.
“The new document shows that the Amundsen Sea Embayment ice shelves have traversed most, but not all, Jakobshavn crossings,” Alley said in an email. “[A] ocean warming has thinned ice shelves, this reduced buttress, this allowed non-floating ice to move faster, contributing in part to sea level rise and also starting to break up the sides of ice shelves, but additional acceleration could occur if the rest of the passages should occur (further fracture and loss of the ice shelf). “
Multiple ice shelf collapses have already been observed in Canada, Greenland and the warmer Antarctic Peninsula, where the former Larsen A and Larsen B ice shelves have fractured and no longer exist today.
“When ice shelves are damaged by climate change, as we have seen in the Antarctic Peninsula in recent decades, their support effect is reduced and ice currents accelerate and sea level rise,” said Isabella Velicogna, a glaciologist at the ‘University. of California to Irvine, commenting on the new study. “Acceleration increases damage, a positive feedback that’s not good news.”
If a similar process occurs in West Antarctica’s Amundsen Sea, where Pine Island and Thwaites are located, the consequences at sea level could be enormous.
Lhermitte provided calculations showing that over the past six years, the western and central parts of the Pine Island Ice Shelf have shrunk by about 30 percent, from about 1,500 square miles to closer to 1,000 square miles. In other words, an area the size of Los Angeles has been lost.
“This cutting edge is so damaged that we think it preconditions this ice shelf for long-term destabilization,” Lhermitte said. “These are the first signs we see that the Pine Island Ice Shelf is disappearing. This damage is difficult to heal. “