Coastal erosion and flooding are projected to increase during the 21^st century due to sea-level rise (SLR). To prevent adverse impacts of unmanaged coastal development, national organizations can apply a land protection policy, which consists of acquiring coastal land to avoid further development. Yet, these reserved areas remain exposed to flooding and erosion enhanced by SLR. Here, we quantify the exposure of the coastal land heritage portfolio of the French Conservatoire du littoral (Cdl). We find that 30% (~40%) of the Cdl lands owned (projected to be owned) are located below the contemporary highest tide level. Nearly 10% additional surface exposure is projected by 2100 under the high greenhouse gas emissions scenario (SSP5-8.5) and 2150 for the moderate scenario (SSP2-4.5). The increase in exposure is largest along the West Mediterranean coast of France. We also find that Cdl land exposure increases more rapidly for SLR in the range of 0–1 m than for SLR in the range 2–4 m. Thus, near-future uncertainty on SLR has the largest impact on Cdl land exposure evolution and related land acquisition planning. Concerning erosion, we find that nearly 1% of Cdl land could be lost in 2100 if observed historical trends continue. Adding the SLR effect could lead to more than 3% land loss. Our study confirms previous findings that Cdl needs to consider land losses due to SLR in its land acquisition strategy and start acquiring land farther from the coast.

Sea level rise (SLR) will affect Europe's coasts over the coming decades and beyond, giving rise to ongoing challenges in governing coastal and marine areas. Progress is being made in adapting to and addressing these challenges at both national and sub-national levels across all major European sea basins. This paper assesses progress in coastal adaptation governance in Europe by, first, characterising the socio-economic and political contexts in European sea basins and then by reviewing coastal-adaptation-relevant policy frameworks in place at regional and national levels within each of these sea basins. The regional frameworks reviewed are derived from regional sea conventions and are assessed for their legal status and their inclusion of SLR information. The national coastal policy frameworks reviewed include national adaptation plans focusing on coastal areas and marine spatial planning instruments for all European member states, as well as public financing arrangements for coastal adaptation, focusing on flood risk reduction measures. Key national policies for coastal adaptation are assessed for which coastal hazards they address, the extent to which they incorporate sea level rise information and their inclusion of SLR-specific adaptation measures. Finally, the paper presents governance challenges that arise due to the complexity of adaptation to SLR, i.e. time horizon and uncertainty, cross-scale and cross-domain coordination, and equity and social vulnerability, and discusses examples illustrating how each of these challenges is being addressed in different European sea basins. The paper finds that for all basins, regional policy frameworks generally do not include specific provisions for SLR or coastal adaptation, while at the national level, significant progress on SLR governance is being made. For all basins except for the Black Sea, all countries have reported observed and future SLR hazards and have adopted adaptation strategies. The inclusion of adaptation measures specific to SLR is less advanced, as most sea basins have at least one country that does not include specific SLR adaptation measures in either their adaptation strategies or their marine spatial plans. Regarding SLR governance challenges, key examples of how these are being addressed include approaches for incorporating flexibility into coastal planning, e.g. dynamic adaptation pathways in the Netherlands or dike crest widening in Germany, as well as co-development of nature-based adaptation solutions in Italy. Examples of addressing equity and social vulnerability challenges include the emerging issue of climate ligation illustrated through several court cases on liability for SLR-related damage.

Coastal areas are highly diverse, ecologically rich, regions of key socio-economic activity, and are particularly sensitive to sea-level change. Over most of the 20th century, global mean sea level has risen mainly due to warming and subsequent expansion of the upper ocean layers as well as the melting of glaciers and ice caps. Over the last three decades, increased mass loss of the Greenland and Antarctic ice sheets has also started to contribute significantly to contemporary sea-level rise. The future mass loss of the two ice sheets, which combined represent a sea-level rise potential of ∼65 m, constitutes the main source of uncertainty in long-term (centennial to millennial) sea-level rise projections. Improved knowledge of the magnitude and rate of future sea-level change is therefore of utmost importance. Moreover, sea level does not change uniformly across the globe and can differ greatly at both regional and local scales. The most appropriate and feasible sea level mitigation and adaptation measures in coastal regions strongly depend on local land use and associated risk aversion. Here, we advocate that addressing the problem of future sea-level rise and its impacts requires (i) bringing together a transdisciplinary scientific community, from climate and cryospheric scientists to coastal impact specialists, and (ii) interacting closely and iteratively with users and local stakeholders to co-design and co-build coastal climate services, including addressing the high-end risks.