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Researchers from the University of Maryland discovered that the melting of ice shelves in Antarctica creates a feedback loop that accelerates the melting itself: the freshwater from the melt weakens the cold barrier at the ocean floor and allows warm currents to reach the base of the ice. The study, published in the journal Nature Geoscience by scientist Madeleine Youngs, suggests that warnings about sea level rise may be conservative.
The research was conducted by Madeleine Youngs from the University of Maryland, with results published in Nature Geoscience this week, with immediate impact on the scientific community studying climate changes in Antarctica. How the cycle works: the cold and dense water that normally sinks and forms a protective barrier at the ocean floor is diluted by the lighter freshwater from the melt, weakening this barrier; with the protection broken, deep and warmer currents reach the base of the ice shelves and melt them from below. This matters because current IPCC models treat the melting as a fixed factor and ignore this feedback loop, which could mean that sea level rise projections are underestimated and that the climate tipping point could arrive sooner than expected.
Youngs was direct in explaining the implications: “It’s a positive feedback loop, where more melting leads to warmer water reaching the ice, which causes even more melting. If we continue business as usual, it’s quite possible that we will reach the climate tipping point sooner than we imagine.” The IPCC estimates that, in high emission scenarios, Antarctic melting could contribute an additional 28 to 34 centimeters to sea level rise by 2100, but any acceleration would expand the reach of storms and permanent flooding in coastal cities from Miami to Mumbai, affecting more than 680 million people in low-lying areas.
The cold barrier that protected the Antarctic ice
The mechanism discovered by the researchers begins with a natural process that acts as a protective shield. Normally, the cold and dense water around Antarctica sinks to the ocean floor and forms a layer that prevents the warmer deep currents from reaching the base of the ice shelves. This cold barrier is what keeps the shelves stable: as long as it exists, the ice is melted only from the surface, at a rate that climate models can predict with reasonable accuracy.
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The problem arises when the melting itself begins to destroy this natural protection. The water resulting from the melting of the ice shelves is fresh and lighter than the salty ocean water. When this fresh water enters the sea, it dilutes the cold and dense layer that forms the protective barrier. With the barrier weakened, warm currents that were previously confined to the depths can rise and reach the base of the ice. More ice melts, more fresh water is released, the barrier weakens further, and more warm water arrives. The cycle is self-sustaining.
The cycle that IPCC models do not calculate
The discovery published in Nature Geoscience has direct implications for the reliability of current climate projections. The Intergovernmental Panel on Climate Change (IPCC) treats the melting of Antarctic ice shelves as a fixed factor in their simulations, not as an interactive process that alters the oceanic environment around it. In other words, the models assume that the melting rate is constant and predictable, when in reality it accelerates as the protective barrier is destroyed.
Youngs argues that this omission can lead to significant underestimations of sea level rise. If the feedback cycle is incorporated into the models, projections of an additional 28 to 34 centimeters by 2100 may be just the optimistic scenario. Any additional centimeter of sea level rise translates into larger extents of coastal flooding, greater reach of storms, and permanent pressure on city infrastructures already facing issues with exceptional tides.
Weddell Sea: where the cycle dangerously accelerates
The study reveals that the effect of the feedback cycle varies according to the region of Antarctica. In the Weddell Sea, the process amplifies worryingly: the melting of upstream shelves erodes the cold barrier and paves the way for warm water to continuously advance, accelerating the melting in a spiral that intensifies each season. In this region, the feedback is positive in the scientific sense of the term, meaning each stage of the cycle reinforces the next.
The Weddell Sea is one of the largest ocean basins around Antarctica and hosts ice shelves whose stability is crucial for the balance of the frozen continent. If the cold barrier in this region continues to be eroded by melting, the volume of ice exposed to warm currents progressively increases, releasing ever-larger amounts of fresh water into the ocean and raising sea levels at a rate that current models do not capture.
The Doomsday Glacier and temporary protection
Not all regions of Antarctica follow the same pattern as the Weddell Sea. In the Western Antarctic Peninsula and the Amundsen Sea, where the so-called “Doomsday Glacier” (Thwaites) is located, the study identified an opposite cycle: the meltwater flowing from higher areas forms a cold barrier that temporarily protects the ice from warm currents. In these regions, the feedback is negative, meaning the melting of one area creates protection for the neighboring area.
Youngs acknowledges that this discovery contradicts the dominant perception of the Thwaites, generally considered the most vulnerable glacier on the planet. “Our study suggests that these regions are actually more protected than we thought in the short term, due to this negative feedback cycle,” she explained. However, the scientist made a crucial caveat: “This protection depends on massive upstream melting, and this upstream melting has its own severe consequences for sea level.” The protection of the Thwaites exists because the surrounding ice is already melting in sufficient volume to create the barrier. It is protection fueled by destruction.
680 million people in risk zones
The practical implications of the discovery about Antarctica go beyond the scientific community and reach directly to coastal cities worldwide. The IPCC estimates that more than 680 million people live in low-lying coastal areas, and any acceleration in sea level rise expands the reach of permanent flooding and storms that already threaten cities like Miami, Mumbai, Jakarta, Shanghai, and dozens of coastal capitals. The 28 to 34 centimeters projected by 2100 are enough to redraw risk maps across the planet.
If the feedback cycle identified by Youngs is confirmed by high-resolution simulations, the projections could rise significantly. The team at the University of Maryland is already developing models that incorporate meltwater cycles, focusing on identifying which ice shelves are closest to the point of no return. “The next step is to understand exactly when and where things change, and what that means for all of us,” concluded the scientist.
A cycle that feeds on its own destruction
Researchers at the University of Maryland discovered that melting in Antarctica weakens the cold ocean barrier and allows warm water to melt even more ice from below, in a cycle that IPCC models do not calculate. If this feedback is incorporated into projections, sea level rise estimates may be revised upwards, and the climate tipping point may arrive sooner than expected. More than 680 million people in low-lying coastal areas would be directly affected.
What do you think of this discovery about melting in Antarctica? Tell us in the comments if you believe current climate models are reliable, how you assess the risk to Brazilian coastal cities, and if this news changes the way you think about climate change. We want to hear your opinion.
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