Integrated assessment

The development of environmental policy with respect to the current and future quality of air, water and soil cannot be considered in isolation. Alleviation of one environmental problem may lead to an increase in the importance of another problem. For example, the reduction of nitrogen oxide emissions may decrease the risk of acidification but can, under particular circumstances, lead to an increase in the formation of tropospheric ozone. Climate change may lead to changes in land cover that may affect biodiversity. Another example often mentioned is the relationship between sulphur dioxide emissions in which the risk of acidification is increased, while the enhanced greenhouse effect is, through the formation of sulphate aerosols, decreased. This is why relationships between environmental problems need to be recognised by policies aimed at reducing these problems. This also holds true for policies affecting socio-economic activities, since these can generate externalities in the environment. For example, both the fifth and the sixth Environmental Action Programmes of the European Commission identify five target sectors (industry, energy, transport, agriculture and forestry, and tourism), all having an important -- but different -- impact on the environment. Environmental science -- applied to support policy development -- addresses different target sectors and a variety of environmental issues in facing the challenge of meeting both disciplinary and inter-disciplinary scientific requirements for formulating adequate hypotheses for verification and validation. Conflicts that may arise between the theories developed to understand environmental problems and their linkages, and the knowledge based on data, calls for a multi-disciplinary approach to relationships between environmental issues and socio-economic developments. This in turn puts high demands -- possibly with significant variations -- on data requirements. Scientific experiments to test hypotheses on climate change, for example, are not easy, considering the wide range of spatial and temporal scales involved. The availability of data is limited. This applies both to the impact of climate change, of which the risks can be simulated to occur over several decades, and the socio-economic causes, which may change dramatically during that time. Spatial and temporal scales of environmental problems will vary, depending on regional, national, continental or global characteristics. National environmental policy may be adequate to deal with environmental issues related to such factors as waste water, whereas formulating policies to influence transboundary environmental problems -- such as air pollution -- requires synchronization of national policies