In this study, we use patent count data for overall Climate Change Mitigation Technologies, and for those related to energy production and distribution to evaluate the relationship between the sizable oversupply of European Union emissions Allowances and a policy shift marked by the transition from Phase I to Phase II under the European Union Emission Trading System, on the one hand, and on 'green' patenting, on the other. According to our results, the expected negative impact of this oversupply on technological change seems to be confirmed. Thus, stakeholders take the actual supply of certificates into account when determining their innovative activity. In the same vein, they do so with respect to policy changes related to greater stringency, which generated a sizeable increase in patenting activity when controlling for other economic factors. Our results suggest that a critical evaluation of emission caps and allowances distribution must be undertaken.