Like many other seas, the ecosystems of the North Sea and Baltic Sea are under severe pressure from eutrophication and climate change. To counteract this pressure, the countries around the Baltic Sea have decided to set upper limits for nutrient inputs into the coastal waters in order to restore good environmental status. The international conventions, which include water quality management and eutrophication control, require up-to-date environmental information and knowledge, which can only be derived from robust, coherent, freely accessible and directly applicable data sets. However, the data sets and model simulations available to date do not fully meet these criteria. Instead, the latest holistic assessments show that the measures implemented to date in the North-East Atlantic and the Baltic Sea are not uniformly effective and therefore do not fulfil the requirements for achieving good environmental status. In addition, there are gaps in knowledge about the effects of climate change on eutrophication and the interaction with nutrient reduction measures, which complicates current measures and the development of future management plans. The central questions of CodeBlue, which are to be answered with a comprehensive modelling ensemble, arise from this context and the knowledge gaps. The IOW sub-project will primarily contribute to answering 2 points:

a) Was climate change in combination with increased nutrient loads a significant factor in the development of today's eutrophication in the Baltic Sea?

b) Will the ‘maximum permissible nutrient inputs’ into the Baltic Sea fulfil the objective of achieving good environmental status if climate change intensifies further?