Anticipated costs for this vary widely. For example, Hinkel et al.  calculate that adaptation costs to maintain current global levels of coastal flood protection would be 1.2-9.3% of gross world product but protect assets in human settlements of USD 21-210 billion; Tiggeloven et al.  calculate the cost of adaptation to be USD 176 billion ; while Nicholls et al.  estimate that global coastal protection would cost substantially more, up to USD 18.3 trillion between 2015 and 2100 for RCP8.5 .
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report