Through Time Sea level has oscillated greatly in earth history.
Sea level is mainly a function of amount of water tied up in ice caps.
Relative vs. Eustatic Sea Level rise relative sea level rise - is sea level rise that occurs at a particular place. Tectonic forces or glacial unloading may cause this to vary from one place to another. Hudson Bay example. There has been a general rise of about 125 meters in sea level since end of last glaciation. Current rate of rise is 20-30 cm per hundred years.