Given the high costs of coastal adaptation, benefit-to-cost ratios  are often used to determine the value of investing in adaptation. BCR are high for urbanised coastal areas with high concentrations of assets , covering 90% of the global coastal floodplain population and 96% of assets in the global coastal floodplain . A global assessment shows a BCR for investing in flood protection of up to ~120 . For Europe, at least 83% of flood damages could be avoided by elevating dikes along ~23-32% of Europe's coastline and BCR vary from 8.3 to 14.9, with higher ratios for higher concentration pathways . Globally, 40% of damages can be reduced with levees of 1 m and costs lower than avoided damage . For a mix of expensive storm surge barriers, nature-based solutions and flood-proofing measures for New York City, Aerts et al.  found BCRs <1 for the current situation, but >2 for a SLR scenario of +1 m.
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report