Croissance durable : mesurons-nous bien le défi ?

Macro-measurement is a long and arduous process that involves the system of national accounts. The challenge it raises is driven by the requirements of economic policy. Today, there is a need for a sustainable growth path that couples environmental concerns and development policy. This calls for nothing less than a sea change in national accounting, implying a shift from a system of income and expenditure accounts focused on GDP to a system of wealth accounts. The latter lays emphasis on an extended concept of capital, encompassing all assets that contribute to social well-being and an associated measure of ?genuine? saving. This paper analyses the problems involved in measuring different types of capital that are either ignored or barely dealt with per se by the accepted rules of national accounting. Yet, in developed countries, intangible assets are worth as much as productive fixed capital and constitute the most important factors of growth for the knowledge economy. Moreover, natural capital needs to be priced according to its scarcity given its function as a source of primary resources, an absorber of greenhouse gases and a means of conserving biodiversity. Since the inherent nature of these types of capital means that they are measured at the discounted value of future rents, the choice of discount rates is critical to the valuing process. The discount rate is as important for estimating the cost of depleting non-renewable resources and the damage due to anthropogenic production of carbon dioxide as it is for valuing pension liabilities. The paper shows that the process of valuing the different types of capital and estimating their substitutability in the production of social welfare is beset with radical uncertainty. There are multiple growth paths whose sustainability is open to question due to ?unknown unknowns? in the interactions between economic and ecological factors, which may be linked to disruptive highly non-linear feedbacks. Therefore, the choice of discount rates is a deeply ethical matter and needs to espouse a widely applied precautionary principle, given that the future of the generations to come is at stake. This principle holds true as long as there are situations of exposure to unlimited risk. Societies facing a catastrophic crisis of unknown probability need to engage immediate discussions about how to organise collective decisions on the appropriate policies to adopt.