Robustness test using PSM-DID method.

As the foundation and cornerstone of the digital economy, digital infrastructure construction is an indispensable engine for realizing China’s energy-saving and emission-reduction, innovation-driven and low-carbon transformation and development. Investigating the carbon unlocking effect of digital infrastructure construction might hasten the achievement of the dual-carbon goal and the “win-win” scenario of environmental protection and economic growth. However, there is still a gap between whether and how digital infrastructure construction can break the carbon lock-in (CLI). Based on the panel data of 266 prefecture-level cities from 2006 to 2019, this paper takes “Broadband China” policy (BCP) as a quasi-natural experiment, constructs a spatial difference-in-difference (SDID) model to explore its impact on CLI, and further analyzes its transmission mechanism, spatial spillover effect and heterogeneity. The results show that: (1) BCP can break the carbon lock-in in the pilot cities and remains valid after a series of robustness tests. (2) There is a lag in the carbon unlocking effect of BCP, and the effect is gradually significant after 3 years of policy implementation. (3) BCP has a spatial spillover impact on CLI, and it significantly contributes to both nearby and local cities. (4) By encouraging green technical advancement and upgrading industrial structure, BCP breaks the CLI. (5) There is regional heterogeneity and urban characteristic heterogeneity in the carbon unlocking effect of BCP. On this basis, we propose a series of policy recommendations to hasten the implementation of low-carbon transformation and sustainable urban development.

作为数字经济的基础与基石，数字基础设施建设是实现我国节能减排、创新驱动及低碳转型发展不可或缺的核心引擎。探究数字基础设施建设的碳解锁效应（Carbon Unlocking Effect），有助于加快双碳目标的达成以及环境保护与经济增长的双赢格局实现。然而，当前关于数字基础设施建设能否以及如何打破碳锁定（Carbon Lock-In, CLI）仍存在研究空白。本文基于2006-2019年266个地级市的面板数据，以“宽带中国”政策（Broadband China Policy, BCP）为准自然实验，构建空间双重差分（Spatial Difference-in-Difference, SDID）模型探究其对碳锁定的影响，并进一步分析其传导机制、空间溢出效应（Spatial Spillover Effect）与异质性。研究结果表明：（1）“宽带中国”政策可打破试点城市的碳锁定，且经过一系列稳健性检验后结论依然成立；（2）“宽带中国”政策的碳解锁效应存在时滞，在政策实施3年后效果逐渐显著；（3）“宽带中国”政策对碳锁定具有空间溢出影响，可显著惠及本地与周边城市；（4）“宽带中国”政策通过激励绿色技术进步与产业结构升级打破碳锁定；（5）“宽带中国”政策的碳解锁效应存在区域异质性与城市特征异质性。在此基础上，本文提出一系列政策建议，以加快推进低碳转型与城市可持续发展。