The planet’s widest glacier is melting “more aggressively” than previously predicted, meaning its impacts on global sea level rise could double current estimates, according to new research by a team of glaciologists. The Thwaites Glacier in West Antarctica, nicknamed the Doomsday Glacier because of the catastrophe its collapse would trigger, is a big wild card when it comes to forecasting global sea level rise. The Florida-sized glacier, which lies in one of the least accessible places on Earth, has been receding for decades and its melting ice currently contributes about 4% to global sea level rise. But the mechanisms behind its withdrawal are exceptionally complex, making it difficult to precisely chart its future. However, it is a vital task, as Thwaites contains enough water to raise sea levels by more than 2 feet if it were to collapse. Because it also acts as a cork holding back Antarctica’s vast ice sheet, it could ultimately cause a rise of about 10 feet in sea level, devastating coastal communities from Miami to Manila. Glaciologists at the University of California, Irvine and NASA’s Jet Propulsion Laboratory have developed a new ice sheet model that they say better reflects what’s happening beneath this ice giant. Thwaites’ rapid retreat is driven by processes at its “grounding line,” the point at which ice rises from the seafloor and begins to float in the ocean as an ice shelf. But while typical ice sheet models have tended to view the ground line as fixed and largely stable, “we have come to recognize a different arrangement beneath Earth’s major glaciers that terminate in the oceans,” said the report’s lead author, Mattia Poinelli, a project scientist at UCLA who was an Earth system research scientist at UC Irvine at the time of the study. ⛅ Get CNN Weather in your inbox. The forecast is just the beginning. We’ll send you expert coverage and the stories behind the weather, so you always know more than just the number. Subscribe to the newsletter Satellite data reveals that the land line is actually a “zone of land,” sometimes kilometers wide, where seawater constantly moves in and out with the tides, lifting and lowering the thick ice in a process known as “tidal pumping.” This allows relatively warm ocean water to penetrate “deep beneath the ice sheets and cause vigorous melting,” Poinelli said. When scientists adjusted the models to include the grounding zone concept, they found that Thwaites could contribute up to 1.2 inches of sea level rise by 2100 (double previous estimates) even without further global warming, according to findings published Monday in the journal Nature Communications. The land Thwaites sits on slopes downward, meaning that as the glacier melts, more ice is exposed to warm ocean water. However, the topography is complicated by two key underwater ridges, which “pin” the ice, preventing it from flowing into the ocean more quickly. The study found that melting processes in the Thwaites stranding zone are accelerating the “lifting off” of ice from a large ridge called Mouginot Ridge. According to the study, there is a 60% chance it will be released by the end of the century, after which the glacier is likely to retreat rapidly down the tilted bedrock towards the next major ridge. The findings suggest that the impacts of the loss of Thwaites may have been underestimated. A sea level rise of 1.2 inches may not seem like much, but it is enough to greatly magnify the dangers to coastal populations. The results “predict greater risk and exposure to coastal flooding than expected in the coming decades,” said Eric Rignot, an author of the report and a professor of Earth system sciences at UC Irvine. Ted Scambos, senior research scientist at the University of Colorado Boulder’s Earth Science and Observation Center, who was not involved in the research, said the findings could be “a real game-changer for sea level forecasting since Thwaites.” But he and other experts warn that more research is needed to understand the impacts of different melting processes on land areas, including by obtaining direct data beneath the glacier. “The reality is that there is still a lot to discover about the processes of the stranding zone to be able to make confident predictions about how quickly the ice will be lost,” said Robert Larter, a marine geophysicist at the British Antarctic Survey, who was also not involved in the study. The environment beneath Thwaites, which is very difficult to access, is even more complex than the document describes, he added. Obtaining ground line observation data from Thwaites is the next step, Rignot said. Scientists plan to travel there in 2028 to deploy instruments capable of documenting the entry and exit of seawater. “We have been aware of the impacts of climate change on our planet’s sensitive ice sheets for decades,” Rignot said, “but in recent years the growing understanding of what is really happening at the bottom of glaciers like Thwaites is generating an even greater sense of alarm.” He said the world must reduce planet-warming pollution now to limit the impacts, but warned that “even if we do, we can expect higher sea levels in the future as a result of the damage that has already been caused.”
