SUSTAINABILITY AND TECHNICAL PROGRESS

A rigorous model connects together the following three basic concepts: (1) ''sustainability'' - meaning the generalized future power of an e conomy to consume over time; (2) ''Green NNP'' - meaning a current mea sure of national income that subtracts off from GNP not just depreciat ion of capital but also, more generally, depletion of environmental as sets evaluated at current efficiency prices; (3) ''technological progr ess'' - meaning a projection onto the future of the so-called ''Solow residual''. A simple general formula is derived. Some crude calculatio ns suggest a possibly strong effect of the residual, which hints that our best present estimates of long-term sustainability may be largely driven by predictions of future technological progress.