Comparative policy studies face a number of methodological challenges where conceptualization of the object of comparison—policy output—is the most fundamental. On the basis of three common approaches of the study of policy output, we reconsider this widely applied concept and propose a refined measure as a function of both density (number of policy instruments) and intensity (content of policy instruments). We theoretically derive six policy‐intensity measures (objectives, scope, integration, budget, implementation, and monitoring), which are used for weighting national policy instruments on an Index of Climate Policy Activity. The article presents an empirical application of this measurement approach. Focusing on national climate policy instruments in the energy production sector in Austria, Germany, and the United Kingdom, we investigate changes in the countries' policy portfolios from 1998 to 2010. The article demonstrates that our Index of Climate Policy Activity provides a reliable and valid measurement for national policy output that can be applied for comparative analyses of policy output.

To determine whether innovations in policy concerning climate-change mitigation are symbolic or truly radical in the sense of 'tipping' existing policy portfolios towards a new instrumental logic, we study policy innovations in the context of pre-existing policy portfolios and analyse the associated dynamics over time. Our analysis is facilitated by a new measurement of policy output, the Index of Climate Policy Activity. This new approach sheds light on the relative importance of policy innovations in complex policy portfolios, and serves as a blueprint for further analyses of the politics of policy innovation. Empirically, we analyse policy innovations within the policy portfolios of energy production in Austria, Germany, and the UK between 1998 and 2010. We find high stability in the instrumental logic but substantial change in policy settings and calibrations.