Investigating the CO2 emission differences among China's transport sectors and their influencing factors

China's transport industry is a priority area for energy conservation and CO2 emission reduction due to its great carbon emissions. Based on the data of 1980-2012, this study first analyzes the CO2 emission differences among China's four transport sub-sectors, i.e., road, waterway, aviation and railway, using the sigma-convergence and beta-convergence methods. Subsequently, it explores the influencing factors for CO2 emissions in China's four transport sub-sectors, respectively, with the logarithmic mean Divisia index method. The following results are obtained. First, road and waterway are the major sources for China's transport CO2 emissions, and the road sector acts as the relatively largest CO2 emitter. In 2012, the CO2 emissions of road, waterway, aviation and railway accounted for 65.21, 29.07, 3.61 and 2.11 % of the total, respectively. Second, the CO2 emission differences among China's transport sectors gradually shrank during the period 1980-1996, while gradually widened during 1996-2012. Third, the economic growth served as one of the most important factors, driving China's transport CO2 emission growth over the period 1980-2012. In this period, the CO2 emissions of road, waterway, aviation and railway sectors increased by 561.71, 265.27, 54.07 and 28.28 Mt, respectively.