Antarctic sea ice reached its annual winter maximum on September 14, NASA says, covering 6.79 million square miles. The apparent tension in that sentence matters: this is the yearly maximum, but it is also the third-lowest maximum in the satellite record.
“Extent” is a measurement convention, not a map of solid white ice. Scientists count regions where satellites detect at least 15% ice concentration. Passive microwave instruments can distinguish sea ice from open water through clouds, making regular observation possible during Antarctic weather.
The longer record also resists a simple straight-line story. Antarctic total sea ice increased about 1% per decade from 1979 through 2014, with record winter highs from 2012 to 2014. The rise ended in 2015; large declines began in 2016; and both the record-low annual minimum and maximum arrived in 2023. NASA’s appropriately narrow conclusion is that continued observation is needed to tell long-term change from variability.
NASA Earth Observatory — “Antarctic Sea Ice Grows to Its 2026 Maximum,” October 12