Sustainability: an ill-defined concept and its assessment using fuzzy logic

Sustainability is an inherently vague concept whose scientific definition and measurement still lack wide acceptance. Fuzzy logic is well suited to handle such a vague, uncertain, and polymorphous concept. In this paper, we develop a model called Sustainability Assessment by Fuzzy Evaluation (SAFE), which provides a mechanism for measuring development sustainability. Ecological (land, water, air, and biodiversity) and human (economical, social, educational, and political) inputs are treated individually and then combined with the aid of fuzzy logic to provide an overall measure. The output of the model is a degree (%) of sustainability of the system under examination (locality, state, country, etc.). The model is open to new inputs as reality and experience change, and it weighs all inputs' according to their impact. A number of selected economies are tested and respective degrees of sustainability are derived and analyzed. It should be stressed that this method in itself is both a new definition and numerical assessment of sustainability. The SAFE model may become a useful aid to policy and decision-makers as they strive towards increasingly sustainable policies. (C) 2001 Elsevier Science B.V. All rights reserved.