What happens in the Antarctic affects the whole planet. The Southern Ocean has a key role in global ocean circulation; a frozen sea surface alters the exchange of heat and gases, including carbon dioxide, between ocean and atmosphere. Sea ice reflects sunlight and influences weather systems, the formation of clouds and precipitation patterns. These in turn affect the mass of the Antarctic ice sheet and its contribution to sea-level rise.
Antarctic sea-ice cover has been stable or increasing for decades. Record maxima were recorded in 2012, 2013 and 2014. But on 1 March 2017, a historic low in the extent of Antarctic sea-ice cover was recorded. 2 million square kilometres or 27% below the mean annual minimum was the smallest extent observed since satellite monitoring began in 1978.
Explaining the recent variability in Antarctic sea ice requires projects that bridge many disciplines. Satellite observations of Antarctic sea-ice only reach back about four decades. Information from ships’ logbooks, coastal stations, whale-catch records, early satellite imagery and chemical analyses of ice cores suggest that sea-ice coverage might have been 25% greater in the 1940s to 1960s. Better information about the Southern Ocean and its sea ice must now be a priority. The research communities involved in ice-core analysis and historical data rescue need to collaborate to track sea-ice variability over timescales longer than the satellite record. This will be crucial to the next assessment of the Intergovernmental Panel on Climate Change, which is due around 2020–21.