Quantifying the Synergistic Effects of Sustainable Development Policies: A Quasi-natural Experiment Approach

Sustainable development is inherently systemic and interconnected, yet its policies have often been evaluated in isolation. This study first combines sustainable development goals to construct a comprehensive indicator for measuring high-quality development, incorporating economic sectors, total factor productivity, technological innovation, environmental quality, and living standards. The study then examines the synergistic effects of three distinct types of sustainable development policies—command-and-control, market-based, and socially participatory—using environmental courts, carbon emission trading, and non-governmental organization-led pollution information disclosure as quasi-natural experiment shocks. Utilizing panel data from 285 Chinese cities, the triple-difference model estimates reveal that the synergistic effects of sustainable development policies significantly enhance high-quality development levels by 4.74%, approximately twice the combined marginal effects of individual policies. Event study analysis, dual machine learning, placebo tests, and synthetic triple-difference model estimations confirm the robustness of causal evidence. Green innovation, government attention, and industrial structure drive the effectiveness of these synergistic effects. Top-down environmental inspections by the central government bolster the synergistic impact of sustainable development policies. Simultaneously, these policies help address the resource curse in old industrial base cities. More importantly, the effectiveness of these sustainable development policies is influenced by the personal characteristics of local party secretaries, such as gender, education level, field of study, promotion period, and homophily.