Sea level is primarily measured using tide stations and satellite laser altimeters. Tide stations around the globe tell us what is happening at a local level—the height of the water as measured along the coast relative to a specific point on land. Satellite measurements provide us with the average height of the entire ocean.  To prove that the sea is rising, this sea level rise map from NOAA shows the elevation trends around the world based on real measurements. Find your location and check the sea level trends near you. You will see that in Finland and Sweden, because of the local evolution of the tectonic plates there, the land is actually rising.