Green strategy and ecological efficiency: a nonlinear machine learning analysis under institutional quality intervention

Abstract Amid intensifying environmental degradation, the pursuit of effective and evidence-based strategies for promoting sustainability has become a pressing global concern. This study investigates the role of green strategies in enhancing ecological efficiency (EE) across BRICS nations from 2002 to 2022. It further explores how this relationship is shaped by varying levels of institutional quality, offering a novel conceptual framework that integrates green policy measures with governance performance. To operationalise this framework, a new metric for EE is developed based on ecological footprint relative to real gross domestic product. A composite green strategy index (GSI) is constructed using the entropy method, incorporating a broad set of green predictors. Institutional quality is assessed through a distance-based scenario approach to generate an aggregate institutional quality index, along with three key sub-indices: the inclusivity index (ICI), accountability index (ACI), and transparency index (TRI). The empirical analysis employs the kernel-based regularised least squares model to capture complex, nonlinear, and heterogeneous relationships. Robustness is ensured through the application of the random forest algorithm and the generalised additive model. The findings reveal that GSI exerts a consistently positive effect on EE, with the impact intensifying at higher percentiles. Institutional quality further amplifies this relationship, although diminishing returns emerge beyond certain thresholds. Among the governance dimensions, ACI plays the most significant moderating role, while ICI and TRI demonstrate potential for further enhancement. In addition, per capita real GDP and the globalisation index are positively associated with EE, whereas urbanisation, population density, and industrial energy consumption exert negative effects. The study concludes with tailored policy recommendations for BRICS nations, emphasising the importance of institutional reinforcement in maximising the ecological benefits of green strategies.