the most seriously threatened european seas are the north sea, the baltic and the black sea. here the rapid degradation of these marine environments is examined comparatively to identify similarities and differences in the driving forces and responses of the marine systems. although it is difficult to distinguish between anthropogenic changes and those due to natural climate fluctuations, an attempt is made here to define possible effects based on a multidisciplinary mix of recent observations and modelling. the systems studied range from almost totally enclosed domains to marginal seas adjoining a large ocean body, and from shallow, dissipative and tidally dominated shelf regions to deep, relatively stagnant basins with adjoining energetic shelf regions, and from completely anoxic to oxygen-saturated chemical environments. climate control appears as a background theme, while the most significant human effect is eutrophication, which is leading to rapid changes in these systems.