Southern Ocean (SO) physical processes influence the hemispheric and global climate, the dynamics of the Antarctic ice sheet and thus pattern and rate of sea-level rise, the distribution of nutrients and productivity of marine ecosystems, and ocean uptake and storage of carbon dioxide. Recent studies document the variability of the SO environment and its impact on water mass characteristics, contributing to the global meridional overturning circulation, the regional climate, and marine organisms. Climate models predict that the SO overturning circulation will slow down as a result of global warming, causing a decrease in the amount of carbon dioxide absorbed by the ocean and a positive feedback on climate change. The Southern Ocean is remote, the environment is hostile, and historical data are scarce, thus hypotheses regarding the impact of SO processes on the fringing ice sheet, regional ecosystems, and the global climate are difficult to validate. However, new tools (e.g. autonomous floats, animal mounted oceanographic sensors, new and more accurate satellite sensors, improved numerical models) and additional measurements from the last decade now allow to determine changes in the Southern Ocean and to describe the processes responsible for the variability in space and time.