ECOLOGICAL ECONOMICS Ecological Economics 17 (1996) 147-156 Commentary The concept of weak sustainability Maite Cabeza Gut& Departament d ‘Economia i Histhria Econbmica, Universitut Autbnoma de Barcelona, Barcelona, Spain Received 7 March 1995; accepted6 December 1995 zyxwvutsrqponmlkjihgfedcbaZYXWVUTS Abstract This paper surveys the links between growth theory with exhaustible resources and the concept of weak sustainability. It examines the underlying assumptions behind this concept, and questions the usefulness of the weak sustainability index as an indicator of sustainable development. Keywords: Production functions; Sustainability; Growth theory; Exhaustible resources; Natural capital 1. Introduction The need to develop sustainability indicators is central if we are interested in assessing whether an economy is sustainable. Within the field of eco- nomics, this search for an operational definition of sustainable development has led, among many other contributions, to the concepts of strong and weak sustainability. Strong sustainability regards natural capital as providing some functions that are not substitutable by man-made capital. These functions, labeled ‘criti- cal natural capital’, are stressed by defining sustain- ability as leaving the future generations a stock of natural capital not smaller than the one enjoyed by the present generation. That is, sustainability is viewed in terms of non-decreasing natural capital. Counter to this concept, is the concept of weak sustainability. Following the definition proposed in Pearce and Atkinson (19931, an economy is consid- ered sustainable if its savings rate is greater than the combined depreciation rate on natural and man-made capital. Under this notion, sustainability is equivalent to non-decreasing total capital stock. This is referred to as ‘weak’ sustainability since no restrictions on the degree of substitutability between natural and man-made capital are introduced, and thus natural capital receives no special treatment. Consistent with this interpretation, Pearce and Atkinson (1993) pre- sent a weak sustainability index as an economic indicator of sustainable development. The weak sus- tainability index proposed is defined as the differ- ence between the savings rate and the sum of the depreciation rate of natural and man-made capital. That is, an economy is considered to be ‘weakly’ sustainable if and only if the weak sustainability index is greater than zero. The strong and weak concepts just outlined can be considered to represent two opposing ends in the quest to give a workable dimension to sustainability. ’ This article focuses on the second of these views, with the purpose of emphasizing the key role that the I For a more complete classification of views of sustainability, see Turner et al. (1994). Chapter 2. 0921-8009/96/$15.00 0 1996 Elsevier Science B.V. All rights reserved. SSDI 0921-8009(95)00112-3