Abstract. This paper represents an empirical investigation of the "weak" and "strong" Porter Hypothesis (PH) focusing on the manufacturing sectors of European countries between 1997 and 2009. By and large, the literature has analyzed the impact of environmental regulation on innovation and on productivity generally in separate analyses and mostly focusing on the USA. The few existing studies focusing on Europe investigate the effect of environmental regulation either on green innovation or on performance indicators such as exports. We instead look at overall innovation and productivity impact that are the most relevant indicators for the "strong" PH. This approach allows us to account for potential opportunity costs of induced innovations. As a proxy of environmental policy stringency we use pollution abatement and control expenditures (PACE), which represent one of the few indicators available at the sectoral level. We remedy upon its main drawback, that of potential endogeneity of PACE, by adopting an instrumental variable estimation approach. We find evidence of a positive impact of environmental regulation on the output of innovation activity, as proxied by patents, thus providing support in favor of the "weak" PH in line with most of the literature. On the other front, we find no evidence in favor or against the "strong" PH, as productivity appears to be unaffected by the degree of pollution control and abatement efforts.

The need for a better understanding of future energy scenarios, of their compatibility with the objective of stabilizing greenhouse gas concentrations, and of their links with climate policy, calls for the development of hybrid models. Hybrid because both the technological detail typical of Bottom Up (BU) models and the long run dynamics typical of Top Down (TD) models are crucially necessary. We present WITCH-World Induced Technical Change Hybrid model-a neoclassical optimal growth model (TD) with energy input detail (BU). The model endogenously accounts for technological progress, both through learning curves affecting prices of new vintages of capital and through R&D investments. In addition, the model captures the main economic interrelationships between world regions and is designed to analyze the optimal economic and environment policies in each world region as the outcome of a dynamic game. This paper provides a detailed description of the WITCH model, of its baseline, and of the model calibration procedure.

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