Since 2015, Antarctica has lost sea ice equivalent in area to Greenland – and it has not returned, according to new satellite data. This event is now considered one of the most significant global environmental changes of the past decade.
Melting ice typically freshens seawater. But this time, the opposite is happening: The ocean surface is becoming saltier. This unexpected increase in salinity draws heat from deeper ocean layers up to the surface, making it harder for new ice to form. Scientists warn that this is creating a powerful feedback loop, further accelerating ice melt.
Researchers from the University of Southampton, the Barcelona Expert Center and the European Space Agency monitored temperature, salinity and sea ice changes in the Southern Ocean over a 15-year period. Using advanced satellite technology and autonomous underwater vehicles, they found that ocean surface salinity began rising sharply in 2015, coinciding with the period of accelerated sea ice loss.
Under normal conditions, cold, fresh water remains at the surface, insulating the warmer, saltier layers beneath. But as surface water becomes saltier, it grows denser and sinks, pulling heat up from the depths. This process melts sea ice from below and makes it difficult for ice to form, even during winter.
Sea ice is vital not only for local ecosystems but also for the global climate. It functions like a giant mirror, reflecting sunlight back into space. When sea ice disappears, the darker ocean surface absorbs more heat, speeding up global warming, intensifying storms and contributing to rising sea levels.
Threat to wildlife
The disappearance of sea ice also endangers species like emperor penguins, which breed on the ice, and krill, a key food source for whales, that depend on icy habitats to survive. These species now face a heightened risk of extinction.
Scientists emphasize that changes in Antarctica are unfolding more rapidly and differently than previously predicted. Climate models had assumed that melting ice would freshen surface waters, but the unexpected increase in salinity challenges that assumption.
As a result, researchers stress the urgent need to update climate models to reflect these new dynamics. They also warn that potential funding cuts to satellite and ocean monitoring systems could jeopardize the scientific community’s ability to track these critical changes. “If we don’t monitor these signals,” they caution, “we’ll be caught unprepared for the changes ahead.”