Peaks of transportation CO2emissions of 119 countries for sustainable development: Results from carbon Kuznets curve

Transportation has significantly boomed energy consumption and carbon dioxide (CO2) emissions. Understanding and forecasting the dynamic statuses of transportation CO(2)emissions is a necessary step before making strategies to decrease CO(2)emissions. Carbon Kuznets curve (CKC) hypothesis has been frequently validated properly to present the changing statuses of CO(2)emissions in the literature. This study tests the CKC hypothesis using the data recording the CO(2)emissions of transportation sectors of 119 countries over the period of 1995-2014, then turning points (TPs) are calculated for the countries where CKC hypothesis is turned out supported. Based on the CKC models, this study identifies different types of TPs, i.e. TP of carbon intensity (TPCI), TP of per capita CO(2)emissions (TPPC), and TP of total CO(2)emissions (TPTC) of the countries whose data support the CKC hypothesis. According to the earliness of the turning years (TYs) (TYCI, TY(PC)and TYTC) - the years when CO(2)emissions peak - of individual countries, this study identified a step-wise decoupling strategy for different countries, i.e. (1) first to reach the TPCI, (2) then to reach the TPPC, and (3) finally to reach the TPTC. As a result, the CKC hypothesis was supported by the data of 58 countries, among which, there are still seven countries having not reached any of the three TPs, 23 countries have reached the first-step TP (TPCI), 9 countries have reached the second-step TP (TPPC), and 19 countries have reached the third-step TP (TPTC).