Graph illustrating the Antarctic sea ice extent from February 18 to November 2, for every year in the 45-year satellite data set (represented by myriad colours). The blue line represents the sea ice extent for 2023. The sea ice extent is defined as the area of the ocean covered with at least 15 percent sea ice. In July 2023, it was remarkably low, with a difference of more than 2.6 million square kilometres from the 1981 to 2010 average. This area is almost as big as Argentina. It is also 1.6 million square kilometres lower than the previous record low extent, which was set in 2022. This recent trend is a sudden change from a weakly positive linear trend from 1978 to 2015 to a strongly negative trend since 2016. Recent studies suggest changes in the upper ocean layer as the reason for this phenomenon.