This paper reviews the ideas of measuring physical and economic sustainability of human civilisation proposed by different schools of thought, namely earth sciences, ecological economics, neoclassical economics and engineering, in order to fill the cognitive gaps between the different disciplines. The paper focuses on physical material and energy flows that enable human economic activities and introduces the distinction between flow and stock, as well as that between material and energy. It proposes a revised operational principle of sustainability, or transition towards new state of civilisation: The overall vision of a civilisation based on natural flow and man-made stock, using natural energy stock during the transition phase, supplemented by the following amended operational principle: (a) Ecological services that are needed to maintain life shall be conserved, and waste and pollution levels shall be within the natural assimilative capacity; (b) consumption shall be within the capacity of renewable resources; and (c) consumption of non-renewable resources shall be associated with investment in renewable substitutes. The paper also provides selected indicators, following the revised operational principle: (a) Degree of dependence on natural hydrocarbon stock regarding fuel consumption for heating, transportation and other motive power as well as electricity generation; (b) Energy profit ratio (EPR) for natural hydrocarbon stock relative to natural energy stock; (c) non-energy ecological footprint for biocapacity; and (d) water stress. These could usefully indicate the past and present state and trend of sustainability, thereby suggesting future limits to human activities.
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