Antarctica Has Lost Nearly 5,000 Square Miles of Grounded Ice in 30 Years as Retreat Concentrates in Vulnerable Western Glaciers

A Continent-Wide Accounting

The first complete circumpolar map of Antarctica’s grounding line retreat, published March 3 in Proceedings of the National Academy of Sciences, shows that the continent lost 12,820 square kilometers of grounded ice between 1996 and 2025, an area roughly ten times the size of Greater Los Angeles. The study, led by Eric Rignot of the University of California, Irvine, and conducted in collaboration with NASA’s Jet Propulsion Laboratory, the University of Washington, the University of Grenoble Alpes, and the Finnish-American satellite company ICEYE, draws on three decades of synthetic aperture radar data from more than a dozen satellite missions.

The grounding line, where a glacier’s base lifts off the bedrock and begins to float on seawater, is the critical boundary that determines how much ice contributes directly to sea level rise. Once a glacier retreats past this line, ocean water gains access to additional ice from below, accelerating thinning and further retreat in a self-reinforcing cycle.

Stability and Vulnerability

The study’s central finding is one of sharp contrast. Fully 77 percent of Antarctica’s coastline has experienced no measurable grounding line migration since satellite records began in the mid-1990s. East Antarctica, which holds the bulk of the continent’s ice, remains largely stable.

But the remaining 23 percent tells a different story. Concentrated retreat in West Antarctica’s Amundsen Sea and Getz sectors, portions of the Antarctic Peninsula, and select areas of East Antarctica accounts for nearly all of the continent’s grounded ice loss. The retreat rate has averaged 442 square kilometers per year over the 30-year period.

The most dramatic individual retreats occurred in the Amundsen Sea Embayment, a region that glaciologists have long identified as the most vulnerable sector of the West Antarctic Ice Sheet. Smith Glacier retreated an extraordinary 42 kilometers, the largest pullback recorded anywhere on the continent. Pine Island Glacier, one of the most closely monitored ice streams in the world, retreated 33 kilometers. Thwaites Glacier, sometimes called the “Doomsday Glacier” because of its potential to raise global sea levels by more than 60 centimeters if it collapses entirely, retreated 26 kilometers.

How the Measurements Were Made

The research team employed synthetic aperture radar differential interferometry, a technique that detects millimeter-scale changes in ice surface elevation caused by tidal flexing. By comparing radar images taken days apart, the method distinguishes between ice that is grounded on bedrock and ice that is floating, effectively mapping the grounding zone with high precision.

The data came from an international constellation of satellite missions spanning European, Canadian, Japanese, Italian, German, and Argentine space agencies, as well as commercial providers. The European Space Agency’s ERS satellites provided the earliest observations in the 1990s, while the Copernicus Sentinel-1 mission and ICEYE’s commercial synthetic aperture radar constellation supplied the most recent data.

“This work would not have been possible without international agencies making polar observations available,” Rignot noted. The collaborative data-sharing approach allowed the team to construct a continuous 30-year record with sufficient temporal resolution to track changes that earlier studies, limited to individual glaciers or shorter time periods, could not capture.

What Drives the Retreat

The pattern of retreat is not random. “Where warm ocean water is pushed by winds to reach glaciers, that’s where we see the big wounds” in Antarctica, according to Rignot. Circumpolar Deep Water, a relatively warm ocean current that circulates around Antarctica at depth, is driven toward the continental shelf by shifting wind patterns linked to climate change. When this water reaches the base of marine-terminating glaciers, it melts ice from below, thinning the glacier and causing the grounding line to retreat inland.

The Amundsen Sea Embayment is particularly susceptible because the bedrock beneath its glaciers slopes downward toward the interior of the continent. As the grounding line retreats into deeper terrain, the ice column above it thickens, exposing a greater cross-section to warm water and further accelerating the process. This marine ice sheet instability mechanism has been theorized for decades, and the new 30-year dataset provides its most comprehensive empirical confirmation to date.

Implications for Sea Level Projections

The circumpolar grounding line map serves as a benchmark for the next generation of ice sheet models used to project future sea level rise. Current models struggle to reproduce observed retreat patterns, in part because they have lacked continent-wide observational constraints at this level of detail.

The study does not itself project future sea levels, but the data it provides will be incorporated into the ice sheet modeling efforts that feed into Intergovernmental Panel on Climate Change assessments. The concentration of retreat in a small fraction of the coastline suggests that targeted monitoring of the most vulnerable sectors, particularly the Amundsen Sea glaciers, will remain essential for narrowing the uncertainty range in sea level projections.

The West Antarctic Ice Sheet contains enough ice to raise global sea levels by approximately 3.3 meters if it were to melt entirely, a process that would unfold over centuries. But even partial retreat of the kind documented in this study has consequences measured in centimeters of global sea level rise per decade, affecting coastal infrastructure and communities worldwide.