Definitions of the environmental dimension of sustainable development are usually general and the variety of impacts rarely considered. A correct representation of the full range of effects is necessary for an accurate and transparent environmental sustainability assessment. Environmental impacts and their characteristics are described through the concept of causal chains between a source and a final target. Its parameters are the source target, time and distance scales, and the final target. The scientific disciplines involved in defining indicators are considered. This analysis is based on research on environmental impacts resulting from transport. It allows us to define 49 independent causal chains that address all effects. They are organized into a hierarchy of 27 aggregated chains and 8 groups, as the usual binary classification (quality of life/natural heritage, present/future generations, reversibility, local/global) lacks meaning.