Accelerated Warming of the Southern Ocean and Its Impacts on the Hydrological Cycle and Sea Ice

The observed sea surface temperature (SST) variability in the Southern Ocean shows a substantial warming trend for the second half of the 20th century. As a result, there has been an enhanced hydrological cycle in the Southern Ocean that helps to maintain the Antarctic sea ice through the reduced upward ocean heat transport and increased snow flux. The simulated SST variability from two global coupled climate models for the second half of the 20th century is dominated by natural internal variability associated with the Antarctic Oscillation1, suggesting that the models' internal variability is too strong, leading to a response to anthropogenic forcing that is too weak. With increased loading of greenhouse gases in the atmosphere through the 21st century, the models show an accelerated warming in the Southern Ocean, and indicate that anthropogenic forcing exceeds natural internal variability. The increased heating from below (ocean) and above (atmosphere) and increased liquid precipitation associated with the enhanced hydrological cycle results in a projected decline of the Antarctic sea ice.