Science works best when it catches its own mistakes. That is exactly what is happening with a new study suggesting that current models of Antarctic ice loss may be systematically overestimating how fast the ice sheet will contribute to sea level rise — because they have been missing a crucial geological feedback that works, to a modest degree, in the ice sheet's favour.
I want to lead with the framing, because it matters enormously: this is not a discovery that sea level rise is not happening. It is not a finding that Antarctica is safe. It is science doing precisely what science is supposed to do: examining its own models with rigour, identifying an underrepresented physical process, and updating projections accordingly.
The missing variable is called glacial isostatic adjustment — or, in more intuitive terms, bedrock rebound. Here is the physics: ice is enormously heavy. The West Antarctic Ice Sheet has been pressing down on the bedrock beneath it for millennia, causing the underlying ground to sag under the load. As ice melts and that weight is removed, the bedrock slowly rises — a process that can unfold over centuries to millennia. This rebound turns out to matter for ice sheet dynamics in ways that current sea level models have not fully accounted for.
When bedrock rises beneath a thinning glacier, it alters the geometry of the ice sheet's grounding zone — the critical boundary where the glacier lifts off the seafloor and begins floating as an ice shelf. That geometry directly governs how fast ice flows into the ocean and becomes available to raise sea levels. Published in PNAS, the research found that properly factoring in bedrock rebound could reduce projected Antarctic contributions to sea level rise by up to 20 percent in certain model scenarios. The ground, quite literally, pushes back.
The physical mechanism itself — isostatic rebound — is thoroughly established geology. Much of northern Europe and Canada has been visibly rising for 10,000 years as the weight of kilometre-thick Pleistocene ice sheets has been removed by melting. What is new here is the systematic incorporation of this feedback into the specific ice sheet models used for sea level forecasting, and the quantification of how much difference it makes to the projections.
Now for the careful accounting of what actually means. Ice sheet modelling is fiendishly complex, involving interactions between ocean temperatures, ice flow dynamics, atmospheric warming, and now bedrock response. , not uniformly to all sea level projections. Some ice loss pathways are less sensitive to the bedrock rebound effect — particularly in regions where underlying rock is stiffer, or where ice is losing mass faster than the bedrock can respond mechanically.
