The idea that problems of declining environmental quality and growing natural resource scarcity are attributable to growth of the economic system occurring in the context of a stable ecosystem is gaining growing acceptance (Costanza 1991) and is a basic premise of this book. As the economic system expands, it places increasing demands on the global ecosystem for energy, materials, and ecosystem services. The global ecosystem, however, has a fixed capacity to provide such services (Daly 1991a). As a consequence of economic expansion, the global ecosystem suffers from excessive exploitation, and, as a result, its capacity to provide inputs to the global economy is diminished. This view is consistent with the central thesis of this book, that the forces driving economic growth are also driving environmental change.