The Southern Ocean in the Coupled Model Intercomparison Project phase 5.

Area of Science:

• Climate Science
• Oceanography
• Climate Modeling

Background:

• The Southern Ocean is crucial to the global climate system.
• Its complex nature presents challenges for climate modeling and predicting future responses.
• Previous model intercomparisons (CMIP3) identified trends in wind, sea ice, and ocean properties.

Purpose of the Study:

• To review recent analyses of historical and projected Southern Ocean conditions using the CMIP5 ensemble.
• To assess improvements in climate models and their impact on Southern Ocean projections.
• To understand the projected changes in wind, sea ice, circulation, and water mass properties.

Main Methods:

• Analysis of the Coupled Model Intercomparison Project phase 5 (CMIP5) ensemble.
• Review of historical and projected data for wind, sea ice, ocean circulation, and bulk properties.
• Comparison of CMIP5 results with previous CMIP3 findings.

Main Results:

• CMIP5 models show improvements over CMIP3 with reduced biases and inter-model spread.
• Projected changes include poleward-shifting winds, warming and freshening waters, decreasing sea ice, and a shallowing surface mixed layer.
• The upper overturning circulation is projected to intensify, while bottom water formation decreases.
• Significant model disagreement exists regarding the Antarctic Circumpolar Current's future strength.

Conclusions:

• CMIP5 provides a more refined view of Southern Ocean climate change projections.
• Despite model improvements, uncertainties remain, particularly concerning the Antarctic Circumpolar Current.
• The projected changes underscore the sensitivity of the Southern Ocean to future climate forcing.