The undesirable impact of China's "national sustainable development plan of resource-based cities" on CO2 intensity

China's numerous resource-based cities have confronted severe environmental and economic problems, which were substantial impediments to the regional sustainable development. In 2013, China started to implement its 'National Sustainable Development Plan of Resource-Based Cities', in order to transform the previous development patterns. This study employs the difference-in-differences (DID) method to evaluate the policy's impact on the city-level carbon dioxide (CO2) emission intensity. CO2 intensity is defined as the scale of CO2 emitted per unit of GDP. The research sample covers 326 Chinese cities during 2008-2017. Research results indicate that the policy significantly increased the CO2 intensity in resource-based cities. Moreover, it is found that the policy dampened resource-based cities' innovation levels and these cities did not strengthen their environmental regulations, which can be provided as the explanations of why the policy effect on carbon intensity was positive. Furthermore, this study reports the discrepancies in policy effects when cities have different development stages, spatial locations and marketization levels. Overall, this research discovers an undesirable policy effect. More actions should be taken to reduce the carbon intensity during the structural transformation in resource-based cities.