But there is. If it's predicted that the sea level will rise this much by the end of the century, and given how log it's going to take to actually shut down and clear a nuclear power plant site to a level it's safe to let it flood, the time to start is now for those plants we believe to be effected by such a oceanic rise.
The National Oceanic and Atmospheric Administration (NOAA) states clearly that these numbers are not predictions, and are little more than what-if scenarios to get policy makers thinking about what needs to be done. The figures quoted for sea level rise shouldn't be confused with scientific fact.
Quote from the original climate study published by NOAA publication :
This report provides scenarios to help assessment experts and their stakeholders analyze the vulnerabilities and impacts associated with possible, uncertain futures.
Probabilistic projections of future conditions are another form of scenarios not used in this report because this method remains an area of active research. No widely accepted method is currently available for producing probabilistic projections of sea level rise at actionable scales (i.e. regional and local). Coastal management decisions based solely on a most probable or likely outcome can lead to vulnerable assets resulting from inaction or maladaptation. Given the range of uncertainty in future global SLR, using multiple scenarios encourages experts and decision makers to consider multiple future conditions and to develop multiple response options.