The input-state-output model and related indicators to investigate the relationships among environment, society and economy

• An input-state-output model is used to represent national economies.
• Emergy, Gini index of income distribution and GDP are considered in this case.
• Different sets of indicators can be applied to the model.
• This framework describes the environmental–social–economic aspects of sustainability.

Economic systems can be studied as thermodynamic open systems that rely upon inputs of energy and materials, processed through human labor and a structured organization, and eventually transformed into useful outputs (i.e., goods and services). In this vein, a generic input-state-output model can be used to represent the relations among environment, society, and economy as well as their dynamics. This approach, that implies the use of holistic and systemic approaches, allows the description and understanding of the evolution of the level of sustainability of national economies through the use of three different metrics computed for world countries in time-series: emergy flow as input-based indicator, Gini index of income distribution as a state descriptor, and gross domestic product as a measure of outputs produced by the economic system. This whole framework depicts a synthetic representation of the environmental, social, and economic dimensions that characterize national systems. It aims at being highly informative to better understand complex relationships between quality and amount of energy and resources used, equity in income distribution, and the overall value of economic production.