Thread: How is the sea level measured?

I can not understand how scientists are able to accurately measure the 'supposedly' rising sea levels. From what I understand the have 'supposedly' risen 3 cm in the last 40 years. I understand the measurements are done by averaging out the tides, storm surges and various gravity forces from the sun, moon and nearby large mountains.

In order to measure the height of something you need a reference point. What could that be?.. Not the land because it can be rebounding from glacier weight or could be in the process of subduction by plate tectonics... And if you suspect the land is in motion, what is it's reference point??.. (not the sea level I hope)

And what about satellites?.. They too are under the force of gravity, centrifugal forces, solar wind and maybe a few things we do not know about. And if you say they are stable, I would ask, "In relation to what?" .. the Moon? .. the Sun?

And even if the seas have risen 3 cm, how do we know it is not the shifting, sinking and otherwise moving land masses?.. Or how about dark energy gravity forces from deep space?

I am very suspicious of the whole mess and I feel the scientists should spend more time doing something useful for the human race and spend less time in pointless microscopic sea level measurements!

In order to measure the height of something you need a reference point. What could that be?

The center of the planet.

Most ground sea level measurements are averages from a fixed point, that being a gage, usually a stilling well, attached to the bottom. Because of local subsidence and rise of the land surfaces individual points aren't always that useful, but when averaged against many other gages across a region or even the globe it's not bad at all.