On the synergy of environmental policies: A shapley value-based perspective

As countries pursue increasingly ambitious climate targets, an effective and coordinated implementation of environmental policies is becoming vital. While individual policies may yield measurable reductions in pollutant emissions, their combined implementation can lead to synergistic, neutral or even counterproductive effects. This study introduces a game-theory-based approach to evaluate the synergy of environmental policies using the Shapley Value, a game solution mechanism that quantifies each policy's marginal contribution to the collective effectiveness. Focusing on three German environmental policies, we model their interactions across varying achievement levels and assign synergy factors drawn from the literature, rather than empirically estimated, to reflect degrees of complementarity. The results quantitatively suggest that policies can generate positive synergy when implemented together. A particular policy can also act as a catalyst that supports, enhances the cooperative efforts and effectiveness of the others. Our framework then enables policymakers to assess how policy combinations can outperform individual policy efforts, supporting evidence-based resource allocation. This work also delivers a replicable, quantitative methodology for identifying and corroborating policy synergies, while offering insights into strategic policy design and implementation, so that emissions reduction can be maximised through coordination rather than isolated interventions.