The impact of energy efficiency on carbon emissions: Evidence from the transportation sector in Chinese 30 provinces

Emissions in the transport sector are a rising source of China's carbon emissions. Curbing carbon emissions in the transport sector will be important for China to achieve its carbon peak by 2030 and carbon neutrality by 2060. To better understand the nonlinear effects of carbon emissions in the transport sector, this study investigated carbon emissions caused by the transport sectors of 30 Chinese provinces from 2005 to 2019. It combined the decoupling index with a panel threshold analysis. The results indicate that the inhibitory effect of energy efficiency on carbon emissions in the transportation industry is increasing as energy efficiency improves. Energy efficiency is expressed in terms of the GDP that can be generated by a unit of energy. When energy efficiency is below the threshold value of 0.473 million RMB/ t, carbon emissions are reduced by 0.818% for every 1% increase in energy efficiency. When energy efficiency is higher than the threshold value of 0.473 million RMB/ t, a 1% increase in energy efficiency reduces carbon emissions by 0.926%. The results also show that urbanization curbs carbon emissions from the transportation sector, but the effect of urbanization is lower than the effect of energy efficiency. As the level of urbanization increases, the inhibitory effect of urbanization on carbon emissions ranges from -0.658 to -0.743. Income growth, private cars, and cargo turnover play a nonlinear role in promoting carbon emissions. Studies have shown that carbon emissions in China's transportation sector are generally in three poor decoupling states: strong negative decoupling, declining decoupling, and expansive negative decoupling. This suggests that the inhibitory effect of energy efficiency and urbanization on carbon emissions is less than the promoting effect of income growth, private vehicles, and cargo turnover. To develop more effective policies to curb carbon emissions in the transport sector, the nonlinear effects driving carbon emissions should be carefully considered.