Knowledge spillovers from clean and dirty technologies

How much should governments subsidize the development of new clean technologies? We use patent citation data to investigate the relative intensity of knowledge spillovers in clean and dirty technologies in two technological fields: energy production and transportation. We introduce a new methodology that takes into account the whole history of patent citations to capture the indirect knowledge spillovers generated by patents. We find that conditional on a wide range of potential confounding factors clean patents receive on average 43% more citations than dirty patents. Knowledge spillovers from clean technologies are comparable in scale to those observed in the IT sector. The radical novelty of clean technologies relative to more incremental dirty inventions seems to account for their superiority. Our results can support public support for clean R&D. They also suggest that green policies might be able to boost economic growth through induced knowledge spillovers.