For the last ten thousand years sea levels have been rising. Since the end of the last ice age (or rather the beginning of the interglacial period we are now currently enjoying, since we are clearly STILL in an ice age) the sea levels have risen, with an average during the 20th century of about 1.8 millimeters per year (according to the IPCC) or 1.48 millimeters per year according to Berge-Nguyen et al., give or take a few (they increased in the late '90's due to the unusually warm El Nino but have since dropped back down.)