The Pine Island Glacier on the West Antarctic Ice Sheet is responsible for more than a quarter of Antarctica’s contribution to global sea level rise over the past decades. Now, a new study shows it is more vulnerable to rapid melting than thought, because climate change is weakening its natural braking system.

Why it matters: At stake is the future of a glacier containing about 160 trillion tons of ice, which if it were all to melt into the ocean would cause about 1.6 feet of global sea level rise.

• The study, published Friday in the journal Science Advances, uses satellite measurements and a computer model to find that there was a more than 12% increase in the speed that this glacier is flowing into the sea from late 2017 to 2020, a period when the glacier’s floating ice shelf shed several large icebergs.

Threat level: Intense scientific scrutiny is focused on this glacier and the neighboring Thwaites Glacier, which is also called the “doomsday glacier,” due to the possibility that it may already be past a tipping point into a virtually unstoppable, runaway melt.

Image: Ian Joughin et al./Science Advances

The details Scientists from the University of Washington and British Antarctic Survey combined sophisticated satellite data with a computer model of ice movement to determine what is driving the speed up.

• Until late 2017, the glacier had been melting mainly due to relatively mild ocean water infiltrating the underbelly of its floating ice shelf.
• Such shelves act like a doorstop, holding back inland ice. However, they can be a glacier’s achilles’ heel when they break up or weaken, due to melting from above, below, or both.
• From Sept. 2017 to March 2020, the Pine Island Glacier’s ice shelf lost 20% of its area, reducing its ability to buttress the inland ice.
• In total, the shelf retreated inland by about 12.4 miles during this period, and the glacier sped its flow into the sea, as well.

What they found: Rather than melting from below, as it did during a previous period of relatively rapid melt, the scientists found the ice shelf is retreating due to calving, or the breaking off of large icebergs at the shelf’s edge.

• This introduces a greater level of risk that scientists hadn’t previously considered. What had looked like an ice shelf loss in 100 years or more has now been pushed up to as short as the next couple of decades, lead author Ian Joughin told Axios.

What they’re saying: The shelf appears to be the victim of the glacier’s own climate change-related speedup in motion from the 1990s to 2009.

• “What our study is showing is that the shelf [is] maybe breaking up in response to the earlier-melt-induced speedup, so perhaps we have to worry about loss of the shelf perhaps sooner (this decade possibly) rather than later,” Joughin told Axios via email.
• “It may be a long shot that the shelf could completely collapse, but not that big [of] one.”

What’s next: Researchers are anxiously waiting to see what the glacier and its ice shelf does next, which could help determine the future of some coastal communities around the world.

• “A big question… is will this breakup cease or will it continue over the next few years?” said study coauthor Pierre Dutrieux of the British Antarctic Survey.