## 6 Conclusions and Policy Implications
### Policy Implications  
To establish an effective carbon governance system, we propose a theoretical framework that integrates mandatory regulatory tools with market-based mechanisms. This approach combines carbon taxation and emissions trading systems with voluntary measures such as GPP. Carbon pricing provides legally binding economic incentives for emission reductions by internalizing environmental externalities, while GPP leverages market demand signals to drive low-carbon innovation and shape sustainable consumption patterns. \begin{table}
\begin{tabular}{l l l l} \hline  & **(1) Excluding 2020** & **(2) Trim the Tail** &
\begin{tabular}{l} **(3) Replace with the** \\ **Economic Geography** \\ **Nested Matrix** \\ \end{tabular} \\ \hline Direct Effects & \(-1.754\)*** & \(-0.961\)** & \(-1.553\)*** \\  & (0.426) & (0.392) & (0.391) \\ Indirect Effects & \(-50.20\)*** & \(-13.330\)*** & \(-2.256\)** \\  & (18.99) & (2.526) & (0.897) \\ Total Effects & \(-51.95\)*** & \(-14.29\)*** & \(-3.809\)*** \\  & (19.13) & (2579) & (0.974) \\ N & 2280 & 2565 & 2565 \\ \hline \end{tabular} Notes: * \(p\) < 0.05, *** \(p\) < 0.01.  
\end{table} 
Table 11: Results of robustness tests for the spatial effects. To maximize the decarbonization potential of GPP, a coordinated implementation mechanism should be established, with a focus on three key dimensions: (1) Accelerate green technological innovation through dedicated R&D funding, expedited patent examination for low-carbon technologies, and targeted subsidies for strategic emerging industries (e.g., renewable energy, carbon capture); (2) Integrate the carbon footprint of suppliers into procurement evaluations, offer preferential prices for green SCs, and foster a \"leading enterprise--small and medium-sized enterprise\" cooperation model to enhance the overall level of cooperate sustainable performance; (3) Stimulate social engagement by implementing transparent emission reporting requirements and public oversight platforms. This integrated framework ensures synchronized progress in low-carbon transformation across technological, corporate, and societal levels. A regional synergistic compensation mechanism is critical to address the spatial spillover effects of urban carbon emissions. Key measures include: (1) Establish a Green Supply Chain City Alliance to facilitate cross-regional low-carbon technology transfer and collaborative innovation, enabling tiered diffusion of green technologies from eastern to central and western regions; (2) Pilot mutual recognition of green certifications in major urban agglomerations (e.g., Yangtze River Delta, Beijing-Tianjin-Hebei), while imposing carbon intensity thresholds for industrial relocation to mitigate carbon leakage risks; (3) Enhance green labeling systems and introducing inter-regional environmental tax adjustments to curb high-carbon demand displacement through price signals. These measures would strengthen coordinated emissions reduction while addressing spillover externalities. Finally, a robust data infrastructure and cross-departmental policy coordination are essential. A nationally unified carbon accounting database should be established to support the cross-regional trading of GPP quotas and carbon allowances, ultimately facilitating jurisdictional alignment. By integrating big data and national platforms, a multi-tiered GPP governance framework can evolve from localized pilot programs to regional coordination and ultimately national integration, thereby optimizing emissions reduction synergies. We must admit that this study focuses primarily on the Chinese context, yet GPP effectiveness can vary significantly across institutional settings. In highly marketized economies such as United States and European countries, GPP tends to yield stronger outcomes when integrated with complementary instruments such as corporate innovation incentives and carbon-footprint accounting.