Sea levels are rising. Mountains’ heights are quoted “above (mean?) sea level”. What are the implications for this and other measurements of rising sea levels (if any)?
And as broader question, is “mean sea level” internationally understood to be the same everywhere on the planet, in the same way as a metre or a kilo is?
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The sea level that gets used is not an actual level that changes with measurements but a fixed definition.
Somebody defined altitude zero at some point and everyone else refers back to that definition.
Without that trying to survey anything or build anything would lead into chaos as tides and normal variations messed with the actual sea level.
To make matters worse we don’t just have a single standard but many competing ones.
Usually a single country will use the same definition and everyone knows the difference between different countries definitions, but sometimes people still run into trouble like when they tried to build a bridge between Germany and Switzerland remembered the difference in what each side considered zero, but added when they should have subtracted the difference and almost ended up with a step in the middle of their border crossing bridge.
So no mountains don’t get smaller because we measure them based on a fixed point that is not bound to the actual average sea level.
At some point in the future we might have to adjust the definitions we all use, but not any time soon.
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