4.1. Scenario Analysis
The practice of scenario analysis is commonly employed to examine the future trajectory of carbon emissions. In order to ensure the accuracy of the parameter settings, this paper combines the actual situation with the relevant policy planning, based on the research of previous scholars. Based on the actual situation of the economic and social development of the YEB from 2006 to 2020, the paper summarizes the current situation in regards to development, relevant development planning, policy, and related literature, and hypothesizes the future emissions of the YEB transportation sector. The study proposes four development scenarios, namely the benchmark scenario (BM), the low-carbon scenario (LC), the strengthened low-carbon scenario (ELC), and the high-carbon scenario (HC), and is divided into three forecast intervals: 2021–2025, 2026–2030, and 2031–2035.
The benchmark scenario is guided by natural and related development policies. Under this scenario, the trends in economic development, population growth, energy consumption, and the transportation industry will continue in the current situation and will be developed, to some extent, in accordance with the relevant policy and planning directives already in place.
The low-carbon scenario is based on the benchmark scenario. While implementing regional development policies, provinces and cities have intensified the implementation of energy-saving and emission-reduction policies, and are rapidly moving towards low-carbon socio-economic development and carbon emission scenarios. Under this scenario, in order to realize the early carbon peak as the goal, the focus is on the quality of economic development and economic growth, progressing to the medium and low-speed stage, while enhancing the effectiveness of the energy system and maintaining the total energy consumption at reasonable levels.
The strengthened low-carbon scenario contemplates the completion of the 14th Five-Year Plan for the Target for Dual Control of Energy and Carbon Intensity Reduction and the achievement of the goal of peak carbon emissions by 2030. On the basis of the existing development conditions and policy measures, the scenario strives to achieve the goal of reaching the peak of carbon emissions before 2030, implementing stronger measures to conserve energy and lower emissions, and adopting extraordinary emission reduction policies and measures to significantly improve energy system efficiency and maintain total energy consumption at a low level.
The high-carbon scenario regards economic growth as the main goal, and the realization of green low-carbon goals is regulated by economic development. This scenario is was created due to the impact of the global COVID-19 pandemic, as the recent level of economic development has not been able to meet the expected development goals. Thus, under this scenario, the pursuit of economic growth will be the primary goal of future development, and energy conservation, carbon reduction, and green development goals will become secondary.
The four carbon emission projection scenarios are provided, and the reasons for their impacts are included, as follows:
At present, the population of various regions in China is experiencing a growing trend. On the one hand, the YEB is an important economic development center in China, with residents earning high incomes and the area offering a large number of employment opportunities, attracting many talented individuals to come here for work. On the other hand, as living standards and medical facilities continue to improve, the average life expectancy of people continues to increase. The National Population Development Plan (2016–2030) predicts that China’s population will peak and stabilize around 2030. Most scholars also believe that China may reach its population peak around 2030 [
34], and that the growth trend may decline around the population peak [
35]. Therefore, it is assumed that in the preceding period, the P will remain at a stable low fertility level for a long period of time, will then experience a growth trend, reaching a peak at a certain point, and then will stabilize or even decrease slightly.
- (2)
U:
From 2006 to 2020, the U in all regions of the YEB has increased year by year. On the one hand, the YEB is committed to accelerating the urbanization process and promoting rural revitalization. On the other hand, the outline of the Vision 2023 goal points out that China is in a period of rapid development, with a 30% to 70% urbanization rate, and the Development Research Center of the State Council and other institutions predict that China’s urbanization rate will reach 66% to 73% in 2030. Accordingly, it is assumed that with the sustained development of the YEB, the urbanization growth rate will gradually run out of steam.
- (3)
AGDP:
The AGDP growth rate is mainly influenced by the rate of economic growth. Generally speaking, after economic development reaches a certain stage, it will gradually trend to stabilize at a low and steady growth state. The historical development of AGDP in the YEB has shown an obvious growth trend, which is due to the region’s abundant resources, superior geographical advantages, and the boosting role in China’s continuous economic growth. Therefore, it can be inferred that as the region’s economy continues to develop and the role of national policy planning deepens, AGDP will continue to grow, but the growth rate shows a downward trend.
- (4)
TVA:
The TVA refers to the newly created value of transportation in the process of production and operation over a certain period of time. TVA is an important part of the gross domestic product (GDP) and reflects the development and dynamic degree of the transportation industry in a country or region. From 2006 to 2020, the GDP of the YEB continued to grow in regards to the transportation industry gross domestic product, but the average annual growth rate gradually declined, shifting from a high growth rate in 2006–2010 to a medium-high growth rate in the latter period. Therefore, it is assumed that the TVA will continue to show a declining growth rate year by year.
- (5)
ES:
With the promotion of the high-quality development of the YEB, ES has changed dramatically, and the proportion of clean energy has sustained growth. At the same time, the 14th Five-Year Plan, the Dual Carbon Goals, the YEB Planning and Development Outline, and the current promotion of green transportation, low-carbon transportation, and other policies require a sustained increase in the proportion of clean energy, and they vigorously promote new energy vehicles. Therefore, it is assumed that the ES shows an increasing trend, but the growth rate will decrease with each passing year.
- (6)
EI:
The EI indicates the energy consumption per unit turnover and serves as an indicator of the efficiency of energy-saving and emission-reduction technologies. As the level of these technologies reaches a marginal effect, the difficulty of carbon reduction is gradually increased, with the decline in the rate of energy consumption per unit of turnover gradually slowing down. On the one hand, the Outline of the Planning and Development of the YEB and the Overview of China’s Transportation Energy Conservation and Emission Reduction Related Data and Key Standards and Regulations requires a decrease in energy consumption per unit of turnover. On the other hand, according to the guidance of the 14th Five-Year Plan, China is currently facing many difficulties and challenges in regards to emission reduction. Therefore, it is assumed that the EI is transitioning from the rapid decline stage to the medium-high decline stage and an overall negative growth trend.
- (7)
TI:
As a basic indicator to evaluate the development level of the transportation industry, a decline in TI value can reduce ineffective conveyance in the transportation process, enhancing the organizational management technology level and the efficiency of the transportation industry. The outline proposes to improve the comprehensive transport pattern, speed up the construction of a modern comprehensive transport system, and support relevant policies required to improve transport efficiency and optimize the transport system. Therefore, it is assumed that as the transportation system and infrastructure are consistently optimized and enhanced, transport efficiency will continue to improve, and the TI will gradually decrease.
In summary, the growth rate settings of the model-related parameters, under different scenarios and in different regions of the YEB from 2031 to 2035, are shown in
Table 6.
4.2. Analysis of Prediction Results
According to different scenarios combined with the constructed extended STIRPAT model, the carbon emissions from transportation in the YEB from 2021 to 2035 are predicted. The results of each scenario are shown in
Figure 11,
Figure 12 and
Figure 13.
According to the projected results, there are significant variations in transportation-related carbon emissions across different regions of the YEB under various scenarios, with differing peak levels and carbon emissions. In the upstream region, carbon emissions resulting from transportation under the BM, LC, and ELC scenarios are projected to peak in 2030, followed by slow declines at different rates. In the HC scenario, TCE will not peak in 2030 and will show a low growth trend after that because these provinces and cities focus more on economic growth rather than green, low-carbon, and high-quality development. In the midstream region, the forecast shows that transport carbon emissions will peak in 2030 under all scenarios, with a peak of 136.2 million tons in the BM scenario, 134.57 million tons in the LC scenario, 133.13 million tons in the ELC scenario, and 138.73 million tons in the HC scenario. Therefore, it is predicted that the development of the midstream region is expected to achieve the national targets of peaking carbon emissions by 2030 and carbon neutrality by 2060. In the downstream region, the projections show that all scenarios are able to reach peak carbon emissions by 2030. This is due to the economic prosperity of the downstream cities, the relative prosperity of the residents, and the high degree of advanced modernization, which are the key pilot factors in the important development planning policies for many countries. Therefore, it is predicted that the downstream provinces and municipalities will be able to meet the 14th Five-Year Plan and the national “double carbon” target. In summary, it is predicted that except for the upstream HC scenario, other regions are expected to reach the peak of carbon emissions in 2030 under all scenarios. Therefore, for the sake of realizing the overall peak of carbon emissions in the YEB, it is necessary to focus on the regulation of the upstream region to technically reduce total emissions and carbon emissions.