Antarctica is showing clear physical changes that can now be seen in long satellite records. Grounded ice that once formed a stable barrier around much of the continent has begun to pull back in several key regions, and the scale of this movement is measurable from space. The most extensive records come from three decades of radar observations that trace the boundary between land anchored ice and the floating shelves that extend into the ocean. These boundaries shift when ice lifts free from bedrock, and the pattern across several sectors of West Antarctica is a steady inland retreat. In some places the grounding line has moved back more than forty kilometres since the mid nineteen nineties. The regions with the strongest losses include the Thwaites sector, the Pine Island region, the Smith area and stretches of the East Getz coast. Together these zones account for almost thirteen thousand square kilometres of grounded ice that no longer rests on the continent. This is an area almost half the size of Belgium and it marks a physical change that cannot be reversed by surface weather or seasonal variability.
Radar missions from Europe, Japan, Canada, Italy, Germany, Argentina and commercial operators have produced a continuous view of ice behaviour. Their instruments detect small but measurable vertical changes as floating shelves rise and fall with tidal motion. Grounded ice does not move with the tide. By mapping the point where floating ice begins to react to ocean motion, analysts can determine the precise location of the grounding line at any moment. When these measurements are compared across tens of thousands of satellite passes, they reveal where grounded ice has weakened and where its contact with bedrock has disappeared. The difference between the mid nineteen nineties and the present day is most visible along the Amundsen Sea sector where warm water moves inland through deep channels carved into the seafloor. This water, known for its higher temperature relative to the surrounding polar environment, reaches the underside of the ice and melts it from below. When this happens beneath glaciers that sit on a slope that drops downward toward the interior, retreat can advance without a natural stabilising point. The terrain in this region dips far below sea level which creates an open path for warm water to reach deeper sections.
This behaviour is visible in the record as a smooth inland shift in the grounding zone across multiple sectors. The shelves become thinner as underwater channels expand. Ice that once held firm begins to lift during tidal cycles. Once this lift appears repeatedly in the data, it marks a transition that allows inland ice to accelerate toward the sea. The most significant movement is concentrated in places where deep troughs extend far beneath the glaciers. These features act as conduits for warm currents and keep the base of the ice exposed to water that can melt it efficiently.
Large parts of the coastline, including the Ross region, the Filchner Ronne area and the Amery sector, have remained stable during the same period. Their grounding lines show minimal migration and their shelves maintain thick, cold structures that resist intrusion from warmer currents. These areas currently form the strongest buffer zones on the continent. They hold back significant volumes of inland ice and slow the overall discharge into the Southern Ocean. However, stability in one area does not offset retreat in another. The regions that are losing grounded ice are also the regions where the terrain and ocean pathways create ideal conditions for further change.
The inland slope is one of the most important physical factors in this behaviour. When bedrock rises inland, retreat slows because the ice encounters shallower ground as it pulls back. When the bedrock drops, retreat can accelerate because the ice continues to thin and loses resistance. The Amundsen Sea region has one of the most pronounced downward slopes on the continent. This shape means that once the grounding line begins to move inland it can continue without an obvious point of natural stability. The three decade radar record shows exactly this pattern.
The radar instruments used to build this record operate through cloud and darkness. They map shifts in elevation with precision down to millimetric changes. These measurements accumulate into a dense timeline of ice behaviour. With every pass they record the position of the floating shelf relative to the ocean surface and the fixed land beneath it. Tidal motion creates a dynamic signature that separates grounded ice from floating ice. When this signature appears farther inland than in earlier records, it confirms that grounded ice has thinned enough to lose its support.
The combined mission data reveals a continent with two contrasting behaviours. The majority of Antarctica remains stable, locked to its bedrock and stationary in its coastal configuration. Other sectors are in motion and the trend is consistently inland. These changes are visible in the maps that compare grounding positions from the early nineties to the mid twenty twenties. In regions with significant loss, the earlier grounding line sits far seaward of the current one and exposes long channels of terrain that once held thick ice. These channels are now open paths for continued ocean intrusion.
The physical consequences of losing grounded ice are straightforward. Inland ice begins to move toward the ocean with fewer obstacles. The shelves that once buttressed this flow become thinner and more flexible. Open water moves farther beneath the ice front and extends the zone of melting. Once the grounding line shifts inland, the volume of ice connected to the ocean increases. This connection matters because it influences how much ice can ultimately enter the sea. The radar record provides the clearest proof that this connection has strengthened across several of the most vulnerable sectors.
Antarctica as a whole has not yet entered a phase of continent wide retreat. Most of its outer boundary remains stable. The areas that are shifting, however, hold enough ice to influence global sea level once their retreat reaches deeper interior basins. The present configuration shows that several of these basins are already losing their grounded margins. The current timeline of satellite measurements offers the clearest view yet of how these sectors behave when exposed to sustained warm water contact. The observed inland movement marks a structural change along parts of the coastline that once remained fixed for centuries.
Source:
ESA Press Release: “Antarctica retreat study signals future ice loss”, March 3, 2026
PNAS publication on grounding line change, 1992 to 2025
