An ocean observing system to provide the data for climate research, modelling, and forecasting must be designed to high standards of accuracy and continuity. The observations are maintained for many years to develop the criteria for climate forecasting, and hence, in the meantime many of the data can and should be used for short and medium term purposes. When combined with other observations, usually of a local or regional nature, the combined data set provides the full suite of marine and coastal observations needed to serve a wide range of socio-economic and environmental objectives. The diagnostic and forecasting models on different scales are interfaced or nested to produce different analyses and products. This paper reviews the policy analysis which has taken place in Europe, using documentary data also from outside Europe, to develop the case for European investment in ocean observations. The short and medium term systems provide an economic and social return which helps to cover the cost of the long term system. Although there are insufficient economic data to conduct a strictly controlled cost-benefit analysis at present, the effect of this strategy is, in economic terms, to ensure that the net discounted value of benefits minus costs never goes too heavily into deficit, and it may even be possible to maximise short and medium term returns so as to recoup the costs of the permanent long term system. In practice, expenditure and incomes for the various parts of the system to not occur in the same places, or agencies, and so a national or regional view is required, to maximise the net short-term benefits in terms of public good at the European level. Complete global integration of ocean observations is needed for climat
