Satellites track Antarctic ice retreat: most of the coastline stable, but alarming “pockets” of rapid withdrawal
Antarctica is home to the largest ice sheet on Earth and is one of the key regulators of global sea level. The latest, multi-decade satellite record of how the continent’s edge “behaves” – where ice stops resting on land and begins to float – delivers a twofold message. On the one hand, a large part of the Antarctic coastline over the past three decades has shown no measurable retreat of that boundary. On the other, researchers have recorded a strong withdrawal at a series of sensitive points, in places greater than 40 kilometers, with an estimate that in the period 1996–2025 about 12,820 square kilometers of “grounded” (bed-supported) ice were lost. This combination of stability and local “breakthroughs” is increasingly cited as a signal that future ice loss could accelerate in places where the ocean most easily reaches the base of glaciers.
What are the “grounding line” and why are they important
At the heart of the research is the concept of the “grounding line” – the line of grounding. It is the transitional boundary between the part of a glacier that lies on bedrock and the part that is already in the status of a floating ice shelf. That boundary is not just a geographic line on a map: it is an indicator of the stability of the ice system and is sensitive to changes in the ocean, especially to the influx of warmer water that can accelerate melting from below. When the grounding line retreats inland, it means that ice that was once “anchored” to the ground is turning into floating ice, which in the long run makes it easier for ice to flow more rapidly toward the ocean.
The authors also emphasize another important nuance: in practice, the grounding line is often a wider “grounding zone” that shifts over time due to tides, changes in sea pressure, and processes beneath the ice, such as the movement of subglacial water. Therefore, in the analysis, alongside the lines themselves, grounding zones were also mapped to capture natural daily and seasonal variability.
Three decades of radar from space
Unlike classic optical satellites, radar systems can “see” through clouds and in complete darkness, which is a decisive advantage in polar conditions. The research relies on synthetic aperture radar (SAR) interferometry and the method of differential interferometry, which compares radar signals recorded over the same point at different times and, from very small changes in height and displacement, can extract information about motion and the elastic “lifting” of floating ice under the influence of tides.
In the long time series, data from multiple missions were used, including the European ERS satellites and Copernicus Sentinel-1, Canadian radar missions (RADARSAT and RCM), Japan’s ALOS PALSAR, Italy’s Cosmo-SkyMed, Germany’s TerraSAR-X, and commercial systems such as ICEYE. The authors note that it was precisely the merging of “legacy” and modern missions that enabled continuity from 1992 to 2025 and comparability of data across three decades.
Stability on 77% of the coastline – but the greatest losses are concentrated in a few key areas
According to the data summary, along more than 77% of the total length of the Antarctic coastline no measurable movement of the grounding line was detected. Stable areas are cited as the vast systems of ice shelves and their upstream basins: Ross, Filchner-Ronne, Amery, and parts of West Antarctic shelves, as well as broad sectors of East Antarctica (including Coats, Queen Maud, Enderby, and Princess Elizabeth Land).
However, the other side of the equation lies in regional “hotspots” of retreat. In three groups of areas – on the Antarctic Peninsula, in Wilkes and George V Land, and in West Antarctica – pronounced grounding-line retreat was recorded, with large differences from glacier to glacier. The Amundsen Sea sector in West Antarctica stands out in particular, where some glaciers experienced tens of kilometers of retreat.
- Largest recorded retreat: up to about 42 km at Smith Glacier (West Antarctica).
- Large retreats: Pine Island about 33 km, Thwaites about 26 km, Pope about 23 km, Haynes about 20 km, Kohler about 12 km.
- Getz sector: retreat at “East Getz” of about 9 km is also mentioned, with higher values on adjacent sections (for example toward Berry about 18 km).
- Antarctic Peninsula: retreat of approximately 2–18 km in the area of the former Larsen A and B ice shelves and 2–6 km on parts of George VI; at the same time, it is stated that on Larsen C and D no change was recorded within the observation framework.
- East Antarctica: in Wilkes and George V Land a retreat of about 6–10 km is reported on a series of large glaciers (including Denman and Totten), with a singled-out value of about 26 km for Vanderford.
How much ice was lost and why it matters for sea level
In estimating the overall effect, the authors state that in the period 1996–2025 about 12,820 km2 of grounded ice were lost (an average of about 442 km2 per year), with most of the loss attributable to West Antarctica (about 62%) and a significant share also to East Antarctica (about 28%). Although the surface area itself is not a direct “conversion” into centimeters of sea level, it is a strong indicator of the retreat of a glacier’s stabilizing point. When that point shifts inward, the conditions of ice flow change: the glacier can “draw out” toward the ocean more quickly, and this is a mechanism that in models often leads to an increased contribution to sea level.
The broader context further underscores why scientists insist on precise monitoring. ESA, in its summaries on the state of polar ice masses, highlights that ice sheets in recent decades have been a significant contributor to global sea-level rise, and that satellite measurements are key to understanding trends and uncertainties. Scientific reviews published in recent years warn that projections for Antarctica are burdened with “deep uncertainty” because they depend on a range of processes at the contact point of ocean, ice, and bed, but also on future greenhouse-gas emissions and the level of warming.
The role of warm ocean currents and submarine channels
One of the most important conclusions of the research relates to the connection between retreat and oceanography. In parts of West Antarctica, especially along the Amundsen Sea, warmer and saltier deep-ocean water – often described as Circumpolar Deep Water – can reach the base of glaciers through submarine channels and depressions. When such water reaches deep glacier “beds,” melting from below weakens the ice, promotes thinning of ice shelves, and reduces their ability to “buttress” the glacier.
The authors also emphasize the geometry of the bed: in many places the ground slopes downward inland (so-called retrograde slope). This is a configuration that in theory and in models can lead to self-sustaining retreat – as the grounding line moves to deeper parts, the ice becomes more susceptible to further ocean intrusion. Recent studies go in the same direction, describing in detail how seawater can “push” beneath ice masses and create dynamic zones of intense melting near grounding, especially in the Thwaites system.
Why the “grounding zone” is the new key term in observing Antarctica
Scientists increasingly warn that observing a single line on a map is not enough. In practice, the transition between grounded and floating ice can shift by kilometers through the tidal cycle, and it is also influenced by subglacial processes. That is precisely why modern radar analyses use the concept of the “grounding zone” – the area in which the boundary “breathes” and changes. In recent years, PNAS has published several papers that, using Thwaites as an example, describe tidal intrusions of seawater beneath the ice and melting processes in that transitional belt, which further explains why certain glaciers are so sensitive to oceanographic changes.
What “mostly stable” means in an age of warming
The finding of stability along most of the coastline may at first glance sound reassuring, but experts warn that stability in this context is an “average” that hides great inequality in glacier behavior. Antarctica is not a single block of ice, but a set of systems that depend on local topography, ocean temperature, the shape of fjords and channels, and the condition of floating ice shelves that act as a “counterforce” slowing the outflow of ice into the sea.
Therefore, in public policy and risk assessments, the need to monitor precisely defined “gateways” through which the ocean has access to the most vulnerable parts of the ice sheet is increasingly emphasized. In that sense, a detailed map of grounding-line retreat serves as a reference framework for models: where changes have already occurred, where they are fastest, and where they could, according to the available geometry and oceanography, continue.
What the future of measurements brings: more satellites, more data, but also greater responsibility
In accompanying materials, the authors of the study emphasize that such continental records would not be possible without long-term funding and open-data policies, especially when it comes to observing polar regions. Linking public European and national missions with commercial radar constellations is an increasingly common trend in climate science: better temporal resolution is obtained, short-lived events are easier to capture, and models can be calibrated more precisely.
At the same time, expanding satellite capabilities does not automatically mean simpler forecasts. Scientific reviews warn that Antarctica is one of the largest sources of uncertainty in projections of sea level by the end of the century. However, that is precisely why measurable facts – such as the speed and spatial pattern of grounding-line retreat – are the foundation on which better estimates are built. And the message of the latest record is clear: while large parts of the continent still show no retreat, a few key areas are already demonstrating mechanisms that, with continued ocean warming, can become a trigger for faster ice loss and a larger contribution to sea-level rise.
Sources:- Dryad (dataset accompanying the study on grounding-line migration 1992–2025, including estimates of retreat and grounded-ice loss) – link- NSIDC (MEaSUREs: high-resolution mapping of Antarctic grounding lines from satellite DInSAR analysis, coverage 1992–2025) – link- Copernicus/ESSD (data paper on changes in ice flux at Antarctica’s grounding line 1996–2024, important context for mass-loss trends) – link- PNAS (paper on seawater intrusion and grounding-zone dynamics at Thwaites Glacier, an example of processes that enhance melting near grounding) – link- Science (review on Antarctica and sources of uncertainty in projections of its contribution to sea level, 2025) – link- ESA Climate Office (summaries and context on polar ice-mass losses and their contribution to sea-level rise based on satellite observations) – link
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