'By the end of the century, 13 million Americans will need to move just because of rising sea levels, at a cost of $1 million each, according to Florida State University demographer Mathew Haeur, who studies climate migration.'

I couldn't find any concrete evidence to validate this, it seems more of a prediction? Mr Hauer is a sociologist so this seems a bold claim https://coss.fsu.edu/sociology/mhauer

'his research has focused on how migration induced by sea level rise could reshape the U.S. population distribution'