Joint management of emission abatement and technological innovation for stock externalities

We investigate how emission abatement and technological innovation provide different solutions to reduce pollutant emissions. In the case of a stock externality emission abatement leads to a smooth and continuous adjustment of emissions. Conversely, technological innovation has to be interpreted as an option on a less polluted environment and can justify the use of a pollution threshold above which it is optimal to start a research and development programme for a less polluting technology. It is shown that technological innovation interferes with the traditional emission abatement approach. The optimal abatement level is logically lowered once the less polluting technology is available; nevertheless a temporary increase in emissions is optimal during the research and development period. The usual Pigouvian tax system proves to remain an efficient corrective instrument. A numerical application to the Greenhouse effect is provided.