The IPAT-model developed by Ehrlich and Holdren is widespread in ecological economics in order to quantify the impact of population growth on environmental deterioration. We comment on this model and extensions proposed by several authors from a theoretical and empirical point of view.

The performance of market based environmental regulation is affected by patents and vice versa. This interaction is studied for a new type of innovation where new technologies reduce emissions of a specific pollutant but at the same time cause a new type of damage. A robust finding is that the...