Ecological network analysis of carbon emissions from four Chinese metropoles in multiscale economies

As megacities, metropoles play an important role in carbon emission reduction in China. In this study, four Chinese metropoles (Beijing, Tianjin, Shanghai, and Chongqing) were selected to investigate integral carbon emissions at three scales (city, national, and global) by combining ecological network analysis with input-output analysis. The complex structures and relationships of carbon emission flows in 2010 due to interregional and international trade could be further evaluated. The results showed that, within the metropoles themselves, because of adjustments to the industrial structure and the promotion of tertiary industry, more than 11% of integral carbon emissions input in Beijing and Shanghai derived from the services and construction sectors. At the national scale, Beijing, Tianjin, and Shanghai were the net recipients of carbon emissions, mainly from the northwestern, central, and northern regions, owing to geographic proximity. The integral flow from the northwest region to Shanghai was the highest (22.37 Mt CO2e). At the global scale, carbon emission flows exported from Beijing, Tianjin, and Shanghai were higher than in Chongqing, as the three metropoles are located near harbors. Shanghai’s integral export value was the highest at over 31 Mt CO2e. This analysis aims to provide a scientific foundation for appropriate decarbonization actions, which can help policy makers allocate emission-reduction targets for metropoles and regions. On the one hand, policy makers can mitigate carbon emissions from an integral perspective; on the other, at the city and regional scales, they can guide metropoles or regions to reduce emissions based on their own development status.