SCAR Action Group. The carbon dioxide (CO2) concentration of the Southern Ocean is rising. The dominant source of this increase is in response to partial equilibration with the increasing atmospheric CO2 concentrations, following worldwide fossil fuel combustion and land use changes. Subsequent shifts in chemical equilibria result in a change to the marine carbonate system and a lowering of seawater pH. This process is termed â€œocean acidification (OA). From a limited number of studies to date, it is already clear that OA is causing rapid changes in ocean chemistry. There is concern over the future of polar marine organisms that are uniquely adapted to their extreme and cold surroundings. In an environment where development is ten times slower that that in warmer regions of the world, the ability of these (mostly benthic) organisms to adapt to these changing conditions is questionable, especially over the next 50 to 100 years. Studies investigating the impacts of ocean acidification on polar marine calcifying organisms are extremely limited. The major challenges for understanding Southern Ocean acidification are advancing the observational network and better constraining our understanding of the underlining natural variability and the mechanisms that drive it, both of which are still poor.The socioeconomic and cultural effects of Southern Ocean OA are unknown.