Migration, land loss and costs to 2100 due to coastal flooding under the IPCC AR6 sea-level rise scenarios and plausible adaptation choices

Caridad Ballesteros ^1* Daniel Lincke ² Robert J Nicholls ¹ Jack Heslop ¹ Jochen Hinkel ² Víctor Malagón-Santos ³ Aimée B A Slangen ^3,4

• ¹ Tyndall Centre for Climate Change Research, Faculty of Science, University of East Anglia, Norwich, United Kingdom
• ² Global Climate Forum, Berlin, Berlin, Germany
• ³ Royal Netherlands Institute for Sea Research (NIOZ), Texel, Netherlands
• ⁴ Department of Physical Geography, Faculty of Geosciences, Utrecht University, Utrecht, Netherlands, Netherlands

Sea-level rise (SLR) through the 21 st century and beyond is inevitable, threatening coastal areas and their inhabitants unless there is appropriate adaptation. We investigate coastal flooding to 2100 under the full range of IPCC AR6 (2021) SLR scenarios assuming plausible adaptation. The adaptation chooses the most economically robust adaptation option, protection or retreat. People living in unprotected coastal areas that are inundated frequently (below 1-in-1 year flood) are assumed to migrate and the land is considered lost. Globally, from across the range of SLR and related socioeconomic scenarios, we estimate between 4 million and 72 million people could migrate over the 21 st century, and a net land loss in the range of 2,800 km 2 to 490,000 km 2 . India and Vietnam consistently show the highest absolute migration, while Small Island Developing States are the most affected when considering relative migration and land loss. Protection is the most robust adaptation option under all scenarios for 2.8% of the global coastline, but this protects 78% of global population and 91% of assets in coastal areas. Climate stabilisation (SSP1-1.9 and SSP1-2.6) does not avoid all coastal impacts and costs as sea levels still rise albeit more slowly. The impacts and costs are also sensitive to the socio-economic scenario: SSP3-7.0 experiences higher migration than SSP5-8.5 despite lower SLR, reflecting the larger population and lower GDP. Our findings can inform national and intergovernmental agencies and organizations on the magnitude of SLR impacts and costs and guide assessments of adaptation policies and strategies.