The Environment and Directed Technical Change
在环境约束的增长模型中引入内生和定向技术变革，发现当清洁与肮脏投入可替代时，临时税收或补贴可引导创新转向清洁技术，延迟干预代价高昂。
This paper introduces endogenous and directed technical change in a growth model with environmental constraints. The final good is produced from “dirty” and “clean” inputs. We show that: (i) when inputs are sufficiently substitutable, sustainable growth can be achieved with temporary taxes/subsidies that redirect innovation toward clean inputs; (ii) optimal policy involves both “carbon taxes” and research subsidies, avoiding excessive use of carbon taxes; (iii) delay in intervention is costly, as it later necessitates a longer transition phase with slow growth; and (iv) use of an exhaustible resource in dirty input production helps the switch to clean innovation under laissez-faire.