In recent papers from Levitus e.a. and announcements from Barnett the ocean's heat content was discussed. According to Barnett, this is the proof that man-made greenhouse gases are responsible for the increased heat content of the oceans. But there are problems with the distribution of the heat content increase...

If we may believe current climate models, the amount of aerosols emitted (and circulating) in the NH (northern hemisphere) is much larger than in the SH (southern hemisphere). This should reduce the influence of greenhouse gases (GHGs) mainly in the NH and therefore globally, especially in the 1945-1975 period. But the heat content increase of the oceans is mainly in the NH! Moreover, melting ice needs a lot of heat too. There is a decrease in yearly ice cover in the Arctic, while there is no obvious decrease in Antarctica.

The difference is striking, if one corrects for ocean area. Ocean volume would give a better indication, but I haven't found figures for the volumes of the oceans in the NH and SH parts. But as the main difference in heat storage is in the upper 300/700 m, that doesn't make much difference. What will make a difference is the difference in latitude/area of the oceans, as insolation and/or heat reflection from clouds/GHGs changes with latitude (and temperature). But I have no figures that may be used to integrate for the different oceans.
Oceans are located for 43% in the NH, for 57% in the SH. While the heat content increase of the NH and the SH oceans is near equal, due to the difference in area (volume) between the SH and NH, the relative heat increase is some 50% larger in the NH... There is not much exchange between SH and NH wind and surface ocean currents and the global deep water current (the "conveyor belt") has an overtake of some 1,500 years. And even large scale changes in ocean heat distribution like El Niño have not much influence on the hemispherical heat content.

Further, while the general trend is increasing over the past 50 years, there are very large variations, which can't be explained by GHGs, neither aerosols. The heat content peaks are more or less following the solar cycle peaks, while several of the troughs combine with explosive volcanic eruptions... This all points to a much higher influence of natural origin (solar, volcanic, cloud cover) than of GHGs...

World oceans heat content
Yearly variation in heat content of the world oceans. Data from NOAA. WO = world oceans total.

world oceans heat content corrected for area
The same heat data as in the previous graph, corrected for the difference in area.

On the net: 9 March, 2005.
Last update: 6 August, 2007.

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