A new study suggests Antarctica’s ice shelves may be caught in a cycle that makes melting feed on itself. As more ice melts, fresh water changes the ocean near the continent and allows warmer water to reach the underside of the ice, where the damage is harder to see but deeply important.
Led by Madeleine K. Youngs of the University of Maryland, the research points to a blind spot in climate projections used to estimate future sea level rise. The concern is simple enough to understand and hard to ignore. If the ocean response to melting is stronger than models assume, the warning signs for coastal cities may be arriving earlier than expected.
The cold shield under the ice
Ice shelves are floating extensions of glaciers. They do not raise sea levels much when they melt directly, but they act like braces that slow the flow of land ice into the ocean. When those braces weaken, more ice can move from land to sea.
Under normal conditions, cold and salty water near Antarctica becomes dense and sinks. That cold water can help block warmer deep-ocean currents from reaching the base of the ice shelves. It is not a wall you can see, but it works like one.
The problem begins when meltwater enters the ocean. Fresh water is lighter than salty seawater, so it can dilute and weaken the cold barrier below. Once that protection thins out, warmer currents can reach the ice from underneath and melt even more of it.
A loop climate models miss
The team used an Antarctic ocean and sea ice model that includes interactive ice shelves. That matters because the model does not treat melting as a one-way event. Instead, it tests how meltwater changes the nearby ocean, and how that changed ocean then affects the ice.
The findings show that melt-driven feedback can be as important as the direct effects of a warming ocean in some regions. In the study, the positive melt feedback accounted for two-thirds of the increased melt rate across Antarctic ice shelves.
Youngs was blunt about the modeling gap. “Most current climate models that inform international policy don’t consider this feedback loop at all,” she said. This means some sea level projections may be missing a moving part that changes the system while it is being measured.
Why the Weddell Sea matters
In dense shelf regions such as the Weddell Sea, the cycle can become especially worrying. More melting releases more fresh water, which weakens the cold layer, which then opens a path for warmer water to reach the ice. The cycle feeds itself.
That is the kind of process scientists call a positive feedback. It does not mean “good.” It means each step reinforces the next one, like a small leak that slowly turns into a bigger one.
This also changes the way people should think about Antarctic risk. The story is not only about the most famous glaciers or the places that already make headlines. Some cold, dense-water regions may become much more important once the ocean’s own response is included.
The Thwaites twist
The picture is more complicated in the West Antarctic Peninsula and the Amundsen Sea, where the Thwaites Glacier sits. There, meltwater moving from upstream can create a cold freshwater barrier that temporarily shields ice from warm currents. That is called a negative feedback because it can slow the next stage of melting for a while.
That, however, does not make the region safe. The short-term protection depends on heavy melting elsewhere, and that upstream loss still adds water to the ocean. It is a strange kind of shield, built from damage already underway.
A separate Nature Climate Change study in 2023 found that rapid ocean warming and widespread ice shelf melting in the Amundsen Sea are likely committed through the 21st century. So the new finding adds nuance, not comfort. One area may be shielded for a time while another pays the price.
What it means for coasts
The Intergovernmental Panel on Climate Change says the low-lying coastal zone was home to around 680 million people in 2010 and could hold more than one billion people by 2050. These are the places where sea level rise turns from a chart into water in streets, damaged roads, higher insurance costs, and worse storm flooding.
Current estimates cited by the researchers suggest Antarctic ice melt could add roughly 11 to 13 inches of sea level rise by 2100 under high-emissions scenarios. Even a few extra inches can make storm surges reach farther inland, especially in cities such as Miami, Mumbai, Jakarta, and Shanghai.
That is why this feedback loop matters beyond Antarctica. For coastal families, the question is not whether a computer model got every detail right. The question is whether the water keeps coming higher than expected, faster than city planning can keep up.
What scientists do next
The research team included Andrew L. Stewart, Yidongfang Si, Andrew F. Thompson, and Michael P. Schodlok, with affiliations spanning UCLA, MIT, Caltech, and JIFRESSE at UCLA. The work was supported by the U.S. National Science Foundation.
Youngs and her colleagues are now developing higher-resolution simulations that follow meltwater feedback from today through 2100. The goal is to identify which ice shelves are closest to a point of no return and what that could mean for sea level rise.
At the end of the day, the study does not say every part of Antarctica will respond the same way. It says the ocean around the ice is active, connected, and capable of making melting faster or slower depending on where the water goes.
That is a big deal.The official study has been published in Nature Geoscience.
