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Never has the 'Battle of Semantics' been more powerful than with sea level. We used to have 'absolute sea level' which was the level measured in respect to the centre of the Earth (as best they could). Then we had 'relative sea level' which was local sea level, which was up or down depending on tectonic or isostatic uplift. Darwin on his voyage with the Beagle, did a great job on this. Basically, that sea level goes up and down like a toilet seat.
Those of us looking at isostatic uplift always referred to absolute sea level, as just plain sea level. Over recorded history it has remained nearly constant. May have been a big disturbance during continental glaciation, but that is difficult to tell.
Just in the past few years, desperate nosa has gone full tilt with sea level meaning local or relative sea level, as measured by a tide gauge. This is totally useless for geophysics, because who knows what that means? They also take all the local measurements and average them for some reason. Meaningless.
We expect absolute sea level to rise, with rising ocean temperatures. That's basic physics - the expansion of water. The only tide gauge that shows this, is the one above.
This chart shows all the short cycle variation, since 1930. You can see the 1930 'Dust Bowl', and the huge drop for Hitler's invasion of Russia. The temperature likes to drop for huge invasions by dictators.
Had this chart gone back to 1600, we would see the 'Little Ice Age'. I would hate to see how low that would go. We might see it soon. Alas, we have no measurements for the rest of the world.
