evidence: Sea ice covers the ocean surrounding Antarctica, forming a key component of the coupled ocean-atmosphere-cryosphere system in southern high latitudes that helps regulate climate, ocean circulation, and marine ecosystems. The extent of Antarctic sea ice varies greatly from year to year, but 40 years of satellite records show a long-term trend. Although some Antarctic regions have experienced reductions in sea ice extent, the overall trend since 1979 shows increased ice. The increase in Antarctic sea ice extent stands in stark contrast to conditions in the Arctic, where sea ice extent has declined significantly—by about 2 million square kilometers, or about 20%, over the past 40 years. Much of the observed loss of Arctic sea ice, which is in general agreement with expectations from climate models, has been attributed to anthropogenic global warming. [...] Antarctic sea ice is bordered by the ice-free Southern Ocean, which itself has experienced cooling SSTs over recent decades. This cooling trend is partly due to natural variability and partly due to upwelling currents that bring to the surface deep waters that have not yet warmed because of anthropogenic climate change [e.g., Armour et al., 2016].