Setting the Frames of Expected Future Sea Level Changes by Exploring past Geological Sea Level Records

Past sea level changes are reconstructed by geological means. Present relative sea level changes are recorded by geodetic means. In order to estimate possible future changes in sea level, we have to use the past as a key to the future. Ice melting and water heating are two processes that may lead to a present sea level rise. Both factors are controlled by strict physical processes. After the last glaciation maximum at around 20,000 BP (LGM), ice melted at a maximum rate and climate improved drastically and rapidly. Still, sea level did not rise more that 10 mm per year or 1.0 m per century. Neither glacial melting nor water heating can be stronger today than during the post-LGM period of maximum deglaciation. Therefore, the value of 10 mm per year (1.0 m in a century) may be used as a frame-value between possible and not possible values of a future sea level rise by year 2100. Such a frame value seems urgently needed in today’s discussions.