Why is the Thwaites Glacier so important?
The Thwaites Glacier drains a huge area of the Antarctic ice sheet-about 74,000 square miles (192,000 square kilometers), an area larger than Florida. When a snowflake falls into that drainage system, it eventually ends up as part of an iceberg in the ocean near Thwaites.
What we are seeing now with the Thwaites Glacier is a disaster in slow motion.
The bedrock beneath Thwaites Glacier is below sea level and slopes inland, causing the glacier to deepen towards the interior of the ice sheet. Once the glacier loses more ice than it gains through new snowfall and begins to retreat, it is very difficult to slow it down because of this slope. And Thwaites is already retreating at an accelerating rate as the climate warms.
Thwaites Glacier contains enough ice to raise global sea levels by more than 2 feet (0.65 meters). Once Thwaites begins to destabilize, it will also destabilize neighboring glaciers. So what happens to Thwaites affects the entire West Antarctic Ice Sheet, and that affects sea level rise along coastlines everywhere.
What is marine ice cliff instability?
Instability of ice cliffs in the sea is a relatively new concept that scientists have proposed over the past decade.
Many of the glaciers around Antarctica have huge floating protrusions called ice shelves that support the glacier and slow the flow of ice to the ocean. As the climate has warmed, we have seen some of these floating protrusions collapse, sometimes very quickly, over the course of weeks or months.
If the Thwaites Ice Shelf were to collapse, it would expose a very high cliff of ice facing the ocean along its 75-mile (120-kilometer) front. There is only so much strength that ice can withstand, so if the cliff is too high, it will collapse into the ocean.
If that happens, a new ice cliff would be exposed further away, and the new cliff would be even higher because it is further inland. The theory of marine ice cliff instability suggests that if the cliffs collapse fast enough, it could have a domino effect of increasingly taller ice cliffs collapsing one after the other.
However, no one has observed sea ice cliff instability in action. We don't know if it will happen, because a lot depends on how quickly the ice collapses.
What have you discovered about the risk to Thwaites?
When the theory of marine ice cliff instability was first introduced, it used a crude approximation of how ice cliffs might collapse if the ice shelf were to disappear.
Studies since then have determined that ice cliffs will not fail systematically until the ice is about 442 feet (135 meters) high. Even at that point, they would fail more slowly than predicted until they were much higher.
Using three high-resolution models, we investigated what this new physical understanding of ice cliff instability would mean for Thwaites Glacier this century.
Our results show that if Thwaites' entire ice shelf collapsed today, the ice front would not advance inland quickly because of the instability of the sea ice cliffs alone. Without the ice shelf, the glacier ice would flow much faster towards the ocean, making the glacier front thinner. As a result, the ice cliffs would not be as high.
We found that Thwaites would remain fairly stable until at least 2100. We also simulated a collapse of the ice shelf 50 years from now, when the glacier's grounding line - where the grounded ice meets the ocean - would have retreated further inland. Even then, we found that the instability of the marine ice cliffs alone would not cause rapid retreat.
The results cast doubt on some recent estimates of how quickly Thwaites could collapse, including a worst-case scenario that the Intergovernmental Panel on Climate Change called out in its latest assessment report but labeled as "low probability."
Thwaites is the glacier that everyone is worried about. If you model the whole ice sheet, this is where the instability of the sea ice cliff starts and spreads far inland. So if Thwaites is not as vulnerable to ice cliff failure as we thought, that is a good sign for the whole ice sheet.
But instability of sea ice cliffs is only one mechanism of ice loss. This finding does not mean Thwaites is stable.
What else is causing glaciers to retreat faster?
There are many processes that make the Antarctic ice sheet unstable, some of which are well understood.
Ice-ocean interactions explain most of the recent loss of ice mass so far. Antarctica is a very cold place, so warming of the atmosphere has not had a big effect yet. But warm ocean currents come under the ice shelves and thin the ice from below, which weakens the ice shelves. When that happens, the ice streams flow faster because there is less drag.
In recent decades, warm water from the Antarctic Circumpolar Current has been invading the Amundsen Sea area, where the Thwaites and Pine Island Glaciers are located, causing the ice to melt from below.
What does climate change have to do with it?
Antarctica may seem like a faraway place, but human activities that are warming the planet - such as burning fossil fuels - are having dramatic effects on the poles. Ice loss is contributing to sea level rise, which is affecting coastal areas around the world.
The choices people make today will determine how quickly the water rises.
This article is republished from The Conversation, a nonprofit, independent news organization that brings you facts and reliable analysis to help you understand our complex world. It was written by: Mathieu Morlighem, Dartmouth College Read more: Mathieu Morlighem receives funding from NASA, the National Science Foundation, the Heising Simons Foundation, and Dartmouth College.