[LINK] Sea levels rising at ~20mm per decade and ocean acidification

Robin Whittle rw at firstpr.com.au
Sun Feb 26 12:02:28 AEDT 2012

There are various arguments about where to measure atmospheric
temperature and how to average current and historical measurements.
Likewise about the validity of various computer models and their
projections for the future.

However, I think it is hard to argue with the oceans and the icecaps,
which behave like a giant, slow-responding, global averaging
thermometer.  There is a well-documented rise in ocean levels and in
ocean acidity in the last century or so which seems to be completely out
of step with anything in the last few thousand years, and which also
seems to be closely correlated with the well-documented rise in
atmospheric CO2 levels in the last few hundred years.

Still, I guess some people will do the extreme mental gymnastics
required to believe and argue that we shouldn't be worried by our
historically unprecedented levels of fossil fuel burning.

There are some graphs, apparently based on well-researched data:


1.85cm per century = 1.85mm per annum in the last hundred years or so.
This is from tide gauge records of sites not affected by glacial
rebound.  Satellite altimetry between 1993-01 and 2011-12 shows a
somewhat greater rate: 3.1mm per annum:

  (I wasn't able to interpret jb_iby_sry_gtn_giy.nc.gz)

Long-term average sea level rises are driven primarily or solely by the
ocean heating and expanding and by imbalance between the amount of snow
which falls on icecaps, glaciers etc. and the rate at which they melt.


This graph presumably ignores the last century or so.  Eyeballing the
presumably hand-drawn average curve, I get the impression sea levels
have risen 10 to 20cm or so in the last 2000 years.  That's 0.05 to
0.1mm per annum.

Sea levels seem to have risen a metre since 3000 to 4500 years ago.
That's 0.33mm per annum from 3000 years ago, but the rate seems to have
been higher at first and flattened out about 2000 years ago.

Between 4000 and 7000 years ago, the graph shows a rise of about 2.5
metres.  That's just under 1mm per annum.  Before that:


there were drastic changes, with ~110 metres in the 6000 years to 8000
years ago.  That's 37mm per annum.

1.85, 2.0mm or 3.0mm per annum is a big deal compared to ~0.1mm per
annum of the past 2000 years.  As far as I know it can only be explained
by increasing global atmospheric and oceanic temperatures.

There may be some negative feedback effects - and positive feedback
through release of methane stored in permafrost and hydrates at the
bottom of the ocean.  Vulcanism contributes CO2 as well, but according to:


which cites: http://www.agu.org/pubs/crossref/1991/90EO10192.shtml
volcanic activity releases about 1% of the CO2 released by human

There's lots of research on solar variation and global temperatures:


however, according to the graph at:



solar variation is likely to account for only a very small proportion of
the temperature rise which are currently occurring.  According to this
chart, the anthropogenic contributions to warming are over ten times
what they attribute to solar variation.  These anthropogenic
contributions are primarily increased atmospheric levels of carbon
dioxide, methane and other greenhouse gasses, reduced significantly by
aerosols (sulphur dioxide, I guess - which is more in the northern
hemisphere) having a cooling effect.

The ocean soaks up CO2 from the atmosphere, leading to ocean
acidification - another very scary subject: a 30% change in hydrogen ion
concentration already.  This is in surface waters and I think the
acidification varies with different oceans.  Over time, I guess this
will spread to all oceans and depths.


     The level of CO2 in the atmosphere seems likely to double
     over its pre‐industrial value  by the middle of this century: in
     response the chemistry of the ocean is changing more rapidly than
     at any time in the past 20 million years (Feely et al., 2004).
     Indeed this process of ocean acidification has reduced the surface
     ocean pH by about 0.11 already (a change of about 30% in hydrogen
     ion concentration), and is expected to reduce pH by up to another
     0.3 units this century if nothing is done to curb the release of
     CO2 to the atmosphere from human activities (Orr et al., 2005).

  - Robin

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