Researchers have raised a fresh alarm on Antarctica’s Thwaites Glacier, warning that it is melting “more aggressively” than previously understood and could contribute twice as much to global sea level rise as current estimates suggest.
The Florida-sized glacier — often called the Doomsday Glacier — is located in one of the least accessible places on Earth, and accounts for about four percent of global annual sea level rise. Spanning roughly 74,000 square miles, the glacier holds enough ice to raise global sea levels by around 65 centimeters if it collapses completely.
Each centimeter of sea level rise exposes an estimated six million people worldwide to coastal flooding.
The warning comes from a new study by researchers at the University of California, Irvine, and NASA’s Jet Propulsion Laboratory, who developed an ice sheet model to better understand how Thwaites is changing. The study projects that the glacier could add up to 30 millimeters to global sea levels by 2100, even without further climate warming.
‘Grounding zone’ reveals historical changes
The researchers reached this conclusion by updating a computer model of Thwaites to account for a wider “grounding zone” instead of the traditionally used “grounding line,” a narrow, relatively stable boundary where ice leaves the land and begins floating on water.
The revised model reconstructed changes in the glacier from the 1990s to the present, revealing changes four times greater than those captured by conventional models.
“Glaciologists have long based their assumptions of ice sheet dynamics on the ‘grounding line’,” said Mattia Poinelli, lead author of the study. “We have come to acknowledge a different arrangement beneath Earth’s major ocean-terminating glaciers. Satellite observations demonstrate the existence of a ‘grounding zone,’ sometimes kilometers wide, where warm ocean water is reaching deep underneath the ice sheets and causing vigorous melting.”
The team, led by UC-Irvine researchers, used synthetic aperture radar readings from the Finnish ICEYE satellite constellation to calibrate ice sheet models against more than 20 years of observations, allowing them to detect kilometer-scale fluctuations in the grounding zone along Thwaites’ main trunk.
Warm seawater accelerates retreat
The data showed that warm seawater travels several kilometers beneath the glacier, lifting the ice during tidal cycles and causing it to melt from below. Researchers found that these processes are also accelerating the glacier’s detachment from stabilizing ridges, leading to more rapid ice flow and deterioration. Climate change has altered the ocean currents that carry this warm water toward Antarctica.
“The Thwaites main trunk is being temporarily stabilized by the Mouginot Ridge. Once that ridge is unpinned, the glacier will continually retreat across a predominantly retrograde seafloor toward its next topographic high, the South Ridge,” said Poinelli, a former UC Irvine postdoctoral scholar who is now a UCLA project scientist and NASA JPL research affiliate.
Simulations accounting for a 4–6-kilometer-wide grounding zone suggest a 60-percent probability that the glacier will become unpinned from the Mouginot Ridge by the end of the century.
“Most projections up-to-present have struggled to match the rapidity of the mass loss because of missing physics; our new model with more complete physics is able to match the record and then produces projections that are twice larger than before. These results predict greater risk of and exposure for coastal flooding than anticipated in the coming decades,” said Eric Rignot, the co-author of the study.
The researchers warned that even if greenhouse gas emissions are reduced, global sea levels will continue to rise because of the damage already caused by climate change.
The study appears in the journal Nature Communications.