4 March 2022Drawing on the results of two research programs undertaken in France, we consider environmental inequality and regional solidarity in the context of adaptation to sea-level rise, given that there is in France a bespoke national system for natural-disaster solidarity. The analysis makes it possible to address situations of inequality, in particular related to risk, and regional institutional capacities as well as the types of solidarity (at spatial and temporal scales), by studying their impact on motivation and adaptation practices in terms of incentives or behavioral inertia. It also highlights seven interactions and discusses their effects. It emerges that insurance-based solidarity favors the status quo: by compensating or protecting, through dykes construction, the populations whose property is exposed to coastal hazards, this strategy maintains the environmental inequalities present on the coasts; the least well-off social groups participate in this financing without benefiting from better access to the coast (land or recreational activities). It also appears that the recent taxation system for funding the cost of palliative measures reinforces inequalities between coastal municipalities and hinterland municipalities and that differentiated forms of solidarity between the risk of erosion (uncompensated victims) and inundation (compensated victims) generate inequalities. Finally, it is noteworthy that inequalities reduce social, and strengthen intragroup, cohesion. The analysis of these relations reveals their somewhat negative effect on regional adaptation strategies to sea-level rise and calls into question the scales and modalities of solidarity whilst highlighting the key role of social cohesion as a factor of acceptability of regional restructuring programs in the face of sea-level rise.