Overview of sustainability assessment methods within the input-state-output framework

In order to provide a rational, structural, and thermodynamics-based representation of sustainability, an Input-State-Output framework has been recently introduced [1]. The I-S-O framework has been proposed to investigate different systems by means of systems indicators representative of three components: input indicators show the material and energy flows feeding the system; state indicators represent structural and organizational features of the system; output indicators quantify what systems produce in terms of outflows. The I-S-O framework has been applied to investigate and categorize different kinds of systems. It has been primarily applied to ecosystems [2], using emergy to quantify what is needed for the systems to survive; eco- exergy to describe its structural characteristics; ecosystem services to identify the output in connection with human utility. More recently, the framework has been used to study national economies [1, 3], which allowed to compare, cluster and rank them on the basis of information other than pure economic ones. Moreover, the Input, State and Output. components have been assimilated to the sustainability pillars, namely the environmental, social and economic spheres, respectively, to be assessed for each country. In fact, the I-S-O framework enables to detect these spheres in isolation from, and in connection with each other without losing information (the latter being a problem of extremely aggregated indicators). A crucial role in this proposal is played by the choice of indicators and assessment methods used for each component of the I-S-O framework. Different triads can be chosen in accordance with the kind of information that we need to produce. In particular, several of indicators exist and can be selected to quantify aspects of the input/environmental, state/social and output/economic component of the I-S-O framework.