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On 23 Sep 2009 at 1:22, frankreed@HistoricalAtlas.com wrote:

> http://tidesandcurrents.noaa.gov/sltrends/sltrends_global.shtml. This is
> "ground truth" data from tide gauges around the world. Sea level IS
> rising, and it is rising at rates which have not changed significantly in
> well over a century.

This is mysterious because temperature data suggest that sea level should 
be rising exponentially, not linearly. Here is a thought: Water has its 
maximum density at 4�C (at standard temperature and pressure). About 80% 
of the column of water in the ocean is below that temperature. So as the 
whole ocean warms, The colder water becomes more dense while the warmer, 
upper section becomes less dense (the familiar thermal expansion). Thus we 
wouldn't expect sea level rise to follow temperature until all the water 
was above the temperature of maximum density.

Now it's not that simple because pressure increases with depth in the 
ocean, and increased pressure lowers the temperature of maximum density, 
so possibly most of the ocean is already on the right hand side of the 
temperature vs density parabola. Also, the change in density between 4�C 
and 0�C is pretty small (I think it's about 0.01% at std T-P, but that's 
just from memory). Even still, if most of the ocean is very close to the 
density maximum, then the first meter, or so, of sea level rise is going 
to be pretty close to linear (given the inherent noise in the data). 

Just my $0.02 worth.

Ken Muldrew.

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