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...
Yearly variation in heat content of the world oceans. Data from NOAA. WO = world
oceans total.
The same heat data as in the previous graph, corrected for the
difference in area.
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