A single glacier sitting at the bottom of the world may be all that is holding back catastrophic amounts of sea level rise. As it melts away faster than ever, scientists are racing to get a better understanding of when it might fail. Unfortunately, they’ve recently found more bad news.
This Antarctic bulwark known as Thwaites, or the “Doomsday Glacier,” is gargantuan – roughly the size of Florida – and holds enough ice to push the planet’s coastlines up two feet. But the edge of Thwaites also acts as a cork, holding up the rim of the West Antarctic ice sheet, much of which sits below sea level. As Thwaites deteriorates, more ice in this bowl becomes exposed to the ocean a, creating a feedback loop that makes it melt faster. And if Thwaites were to succumb entirely, the whole interior of the sheet might follow suit, rising sea levels by as much as 10 feet.
It’s easy to track Thwaites’ demise from space, but predicting its future has been much trickier. For years, computer models used to simulate Thwaites’ retreat weren’t able to pass the simple test of accurately recreating the retreat that satellites have captured over the last few decades, marking them unreliable tools for looking ahead.
But now, scientists have plugged in a major missing piece. A new paper, published in Nature Communications earlier this month, appears to be the first to account for what’s happening underneath Thwaites to simulate how quickly it may lose ice. Using this model to simulate the future paints a grim picture: Thwaites could contribute twice as much to sea level rise by the end of the century as previously projected.
“There are many other unknowns, but this solves a specific and very important piece of the puzzle,” said Mattia Poinelli, a glaciologist at the University of California Los Angeles and first author of the paper.
The problem area is where the icy underbelly of Thwaites rests on the seabed, known as the grounding zone. Only relatively recently did scientists realize this zone was not a fixed boundary, but one that oscillates with the tides. As it bobs up and down, warm water pushes underneath the glacier — creating cracks and miles-long channels that allow even more melting.
Previous simulations of how Thwaites might melt didn’t account for this dynamic, Poinelli said. By doing so, his team’s model was able to match the changes to the glacier that satellites had observed. It also showed that Thwaites could become permanently unpinned from the seafloor as early as 2038, with a 60 percent chance that this could happen by the end of the century, an eventuality which would likely cause the melting to ratchet up even more.
If the climate remains as warm as it is now, the model shows that Thwaites would be on track to add three centimeters of sea level rise by the end of the century. That may not sound like much, but it doubles the projections made by previous models, according to the study. Thwaites contributes about 4 percent to sea level rise which, over the past three decades, amounts to some 10 centimeters. That’s enough to have sent homes in North Carolina crashing into the sea, while forcing coastal communities in places like the Solomon Islands and Senegal to move to higher ground.
Of course, global warming is not holding steady but rather continuing to ramp up, with each decade expected to be hotter than the one before. As a result, the world should brace for even more melt than the model predicts, Poinelli said.
But what if humans get their act together and slow down climate change, or find a way to safely cool the oceans with geoengineering? A separate study, published in Geophysical Research Letters in July, used a model that tested this kind of hypothetical scenario with Thwaites and its comparably large neighbor, the Pine Island glacier, the fastest melting glacier in Antarctica.
Added together, the two glaciers account for the bulk of sea level rise coming from Antarctica. Ocean melt is the primary culprit, so the researchers “switched it off completely” in their model as a way of understanding the condition of each glacier, said Rosie Williams, an ice sheet modeler at the British Antarctic Survey and lead author of the paper.
For all their similarities, it turns out that Pine Island and Thwaites would respond very differently, according to the study. In cooler ocean temperatures, Pine Island would be able to recover ice within a decade, and eventually regrow to where it was 80 years ago – in part thanks to its relatively intact outer shelf. Thwaites, on the other hand, would keep losing ice and raising sea levels worldwide for at least 150 years. The researchers hypothesize that’s because Thwaites is in much worse shape, with the eastern half significantly diminished and the western half disintegrated into many icebergs. While the speed of ice loss would slow down, the glacier may be doomed even in this fictional best-case scenario.
But “that doesn’t mean there’s nothing we can do,” Williams said. Each fraction of a degree of warming makes a difference in how quickly Thwaites disintegrates, and lowering greenhouse-gas emissions could protect other glaciers around Antarctica. “The more we can slow it down,” she said, “the longer we have to adapt to any change that’s coming.”
