What is it about?
The Southern Ocean plays a central role in the global uptake of heat and carbon, which is widely thought to be due to its unique upwelling and circulation. We find that for the historical period 1850 to 2005 that the Southern Ocean contributed nearly twice as much to the global ocean uptake of heat compared to that of carbon. The reason for this mismatch is due to differences in the atmospheric sources of heat and carbon. Dust and smoke released in the northern hemisphere has historically led to a cooling contribution opposing the warming contribution from greenhouse gases, so that most of the heat entering the global ocean enters over the Southern Ocean. The carbon dioxide is relatively well mixed over both the northern hemisphere and southern hemisphere, so that there has been carbon uptake over both hemispheres.
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Why is it important?
This work is important in explaining how different parts of our climate and carbon system work together. In the future, there is expected to be weaker carbon emissions, so that the effect of greenhouse gases will be increasingly felt in the heat uptake by both the northern and southern oceans. Hence, the heat uptake is likely to become more similar in both hemisphere and more comparable to what is seen for carbon uptake. The past need not then be a reliable guide to the future when there are changes in the forcing of the climate system.
Perspectives
This work came about through a collaboration of researchers and colleagues at Liverpool University, British Antarctic Survey, Imperial College and National Oceanography Centre. We first did a study analysing the heat and carbon uptake by a suite of climate models that the same climate forcing from an annual rise in atmospheric CO2. We found that the Southern Ocean contribution to global heat and carbon uptake was broadly similar. This result was at odds with a prior study for the historical period. So we turned our attention to understanding what was different about the historical period. The answer turned out to be that aerosol forcing involving dust and smoke has historically led to a cooling over the northern hemisphere. Hence our latest study.
Professor Richard G Williams
University of Liverpool Department of Earth Ocean and Ecological Sciences
Read the Original
This page is a summary of: Asymmetries in the Southern Ocean contribution to global heat and carbon uptake, Nature Climate Change, July 2024, Springer Science + Business Media,
DOI: 10.1038/s41558-024-02066-3.
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