## 4 Discussion
This clearly points out the limitation of assessments addressing hypothetical future environmental states. Future state assessments might cause wrong expectations and, if wrong, could motivate false decisions. Another lesson learnt from the Huttelmoor scenarios is that the comparison of 20-year time periods is problematic. In the Huttelmoor, policy changes (abandonment of agriculture) and the stepwise implementation of measures (increase in freshwater levels, coastal realignment) caused significant environmental changes. These changes are reflectedin the ecosystem service assessments, but the changes in scores between consecutive time-slices are, with respect to many ecosystem services, very limited. We can conclude that for systems with a natural development, 20-year assessment time intervals are too short. The natural changes taking place in an area would hardly be strong and apparent enough that they could be represented with our ecosystem service assessment approach. In general, our assessments represent changes in the potential ecosystem service provision. Whether these changed potentials are utilized depends on human behavior, traditions, fashions and other socio-economic factors. These aspects can hardly be predicted over decades and hardly be taken into account in future scenarios. However, the retrospective discussions with participants revealed that there is always a risk that the scorings of future ecosystem service changes are affected by the personal view of the experts with respect to the utilization of the potentials. Another aspect that caused difficulties for the participants was that habitats and uses changed. For example, in the Ahrenshoop 2070 scenario, meadows are largely replaced by wetland and/or underwater habitats such as reed areas. A comparison of ecosystem service potentials between systematically different habitats adds uncertainty to the results. Considering the limitations of our comparative qualitative ecosystem service assessments raises the question of alternative approaches. We additionally applied and tested the matrix approach, which focuses on spatial changes between habitats [33]. This approach turned out to be too coarse. The scale indicating ecosystem services and the land-use units was too general. Further, this terrestrial approach insufficiently addresses coastal water habitats and their ecosystem service potentials. It insufficiently reflected the changes in the Huttelmoor. Recent approaches with better resolved habitats and a better consideration of coastal water habitats might provide better results [40; 41]. The InVEST models for ecosystem service assessments [34] provide spatially resolved quantitative information. InVEST Coastal Blue Carbon was the only suitable model applicable to our case studies. The model well reflects the consequences of moor restoration on carbon sequestration. However, it addresses only one ecosystem service, and only for the moor without the coastal zone. Further, the calculations strongly depend on assumptions, field study data and the available literature. InVEST is a suitable, but thematically narrow, complement to our approach. Climate adaptation is a task for society as a whole and the decision of how to adapt, e.g., to sea level rise is a societal one. In the Huttelmoor, the decision--for coastal realignment--has already been taken. The Ahrenshoop case is different. It is a built-up area and coastal protection measures are in place. However, the projections for the future show that some parts of the municipal area will likely be flooded. So, a question that will need to be tackled is whether or not Ahrenshoop will be protected at all costs. At the moment, this is mainly a question in the responsibility of the coastal protection authority. The case studies also show that the implementation of measures is in the hands of sectorial planning. Spatial planning, on the other hand, sets a frame and requirements at a larger scale, which sectorial planning has to take into account.