Last reviewed September 2, 2026
Antarctica lost an average of approximately 135 billion metric tons of ice a year from 2002 through 2025, according to NASA’s GRACE and GRACE Follow-On satellite record. NASA estimates that this loss raised global mean sea level by about 0.4 millimetres a year over the same period. Those are observations, not projections. The harder question is how quickly the loss will grow and what it will add to sea level over the coming decades and centuries.
Measuring a continent’s mass
No single instrument can describe the entire ice sheet. Scientists combine several kinds of observation:
- GRACE and GRACE-FO satellites detect changes in Earth’s gravity as ice mass moves or disappears;
- laser and radar altimeters measure changes in surface elevation;
- radar and airborne surveys map ice thickness and the bed beneath it; and
- field instruments measure ocean temperature, ice flow, and the position of grounding lines.
These methods do not measure exactly the same thing, and snowfall can add mass in some places while glaciers lose it elsewhere. Their convergence is what makes the continent-wide conclusion strong: Antarctica is losing mass, with the largest losses concentrated in West Antarctica and the Antarctic Peninsula.
Why West Antarctica is vulnerable
Much of the West Antarctic Ice Sheet rests on bedrock below sea level. In some places the bed becomes deeper farther inland. That geometry permits a retreating grounding line—the point at which ice leaves the bed and begins to float—to move into deeper water and expose thicker ice to the ocean.
Floating ice shelves do not themselves raise sea level when they melt, but they slow the land-based glaciers behind them. Warm water circulating beneath a shelf can thin it and reduce that buttressing. The glacier then flows faster, moving more land ice into the sea.
This feedback is central to research on Thwaites and Pine Island glaciers. It does not mean that every retreat is automatically irreversible, or that the whole West Antarctic Ice Sheet will vanish on a near-term timetable. It means that the shape of the bed can amplify retreat, making the pace of future loss unusually sensitive to ocean conditions and difficult to bound.
What the latest Thwaites work says
The International Thwaites Glacier Collaboration’s 2025 synthesis is sobering without supporting the most sensational version of the story. Thwaites has retreated faster over the past 40 years and is expected to continue retreating through the 21st and 22nd centuries. A complete collapse in the next few decades is considered unlikely, while a wider West Antarctic collapse over the longer period cannot be ruled out.
New high-resolution modelling also finds that one proposed worst-case mechanism—self-sustaining marine ice-cliff instability—is unlikely to drive a catastrophic Thwaites collapse this century. That narrows one pathway; it does not stop ocean-driven retreat or remove the need to plan for rising seas.
What sea-level projections mean
The complete loss of the West Antarctic Ice Sheet would raise global mean sea level by more than three metres, but such a change would unfold over much longer than a single planning horizon. Near-term decisions concern the fraction of that ice that could be lost this century and the much wider range of outcomes after 2100.
Sea level also does not rise evenly. Gravity, ocean circulation, land movement, and coastal geometry produce regional differences. Storm surge and high tides then act on top of the higher baseline. For infrastructure, insurance, and settlement, uncertainty is not an argument for waiting; it is a reason to test plans against more than one plausible future.
What is known—and what is not
Known: Antarctica is losing ice; ocean-driven melting beneath ice shelves is a major cause in West Antarctica; ice loss contributes to present sea-level rise.
Still uncertain: the timing of ice-sheet thresholds, the speed of retreat in the most vulnerable basins, the importance of newly observed processes at grounding zones, and the upper end of Antarctic contribution this century and beyond.