Factors affecting carbon dioxide (CO2) emissions in China's transport sector: a dynamic nonparametric additive regression model

Abstract

With the recent surge in vehicle population, particularly private vehicles, the transport sector has significantly contributed to the increase in energy consumption and carbon dioxide (CO2) emissions in China. Most existing research utilized linear models to investigate the driving forces of the transport sector's CO2 emission, but little attention has been paid to a large number of nonlinear relationships embodied in economic variables. This paper adopts provincial panel data from 2000 to 2012 and nonparametric additive regression models to examine the key influencing factors of CO2 emissions in the transport sector in China. The estimation results show that the nonlinear effect of economic growth on CO2 emissions is consistent with the Environmental Kuznets Curve (EKC) hypothesis. The nonlinear impact of urbanization exhibits an inverted “U-shaped” pattern on account of large-scale population migrations in the early stages and expanding use of non-polluting urban rail public transportation and hybrid fuel vehicles at the later stage. Private vehicles population follows an inverted “U-shaped” relationship with CO2 emissions owing to early surge in private car ownership and late increased use of electric and hybrid cars. The inverted “U-shaped” effect of cargo turnover is due to different modes of freight transport at different stages. But, energy efficiency improvement follows a positive “U-shaped” pattern in relation to CO2 emissions because of the different scale of transportation ownership and the speed of technological progress at different times. Hence, the differential dynamic effects of the driving forces at different times should be taken into consideration in reducing CO2 emissions in China's transport sector.