| Since the beginning of the new century,China’s urbanization has stepped into the "fast lane".Not only the size of the urban population has increased rapidly,but also the spatial distribution of the urban population has undergone drastic reconstruction.By 2020,China’s urbanization rate has reached 63.89%,but there is still a certain gap compared with the average urbanization rate of more than 80% in developed countries.Therefore,we can foresee that China’s urbanization development will maintain a high growth rate for a long time in the future.At the same time,on the one hand,cities are the agglomeration areas of population and industry,on the other hand,they are also the main areas of energy consumption and carbon emissions.Among all the sources of urban carbon emission,the carbon emission from urban traffic should be paid more attention.According to the Global Energy Review: Carbon Dioxide Emissions 2020 released by the International Energy Agency(IEA),global carbon emissions mainly come from energy power generation and heating,transportation,manufacturing and construction.Among them,the transportation sector accounts for 26% of carbon emissions,making it the second-largest largest carbon emission sector.Specifically,in China,transport carbon emissions account for about 15% of the total urban carbon emissions,second only to energy and industry.In addition,thanks to the positive results of the transformation and upgrading of China’s industrial structure in recent years,the carbon emissions of most industries have been declining year by year.However,the average growth rate of China’s transport carbon emissions from 2013 to 2020 has remained above 5%,which is the fastest-growing sector of domestic carbon emissions.Especially,urban transportation carbon emissions occupy the absolute mainstream of transportation industry carbon emissions.Therefore,in the process of rapid urbanization in China,it is of great practical significance to study the impact of urban population size and spatial distribution on transportation carbon emissions for the construction of green and low-carbon cities in China.Based on a comprehensive analysis of existing literature at home and abroad,this paper analyzes the effects of urban population size and spatial distribution on transport carbon emissions based on panel data from 209 Chinese cities.Specifically,the first chapter of this paper explains the background and research significance,literature review,research content and framework,and possible innovation points.The second chapter introduces the development process of population urbanization and the transportation industry in China since the reform and opening up.This chapter explains the measurement methods of urban population spatial distribution and transportation carbon emissions,and analyzes the current situation of urban population size,spatial distribution and transportation carbon emissions.The third chapter is the theoretical analysis part.This chapter defines the concepts of urban population size,spatial distribution and transportation carbon emissions,and describes the conceptual framework of the impact of urban population size and spatial distribution on transportation carbon emissions.This chapter also explains the influence mechanism of urban population size and spatial distribution on traffic carbon emissions.The fourth chapter builds an empirical model based on the analysis of characteristic facts.This chapter also conducts regression analysis on the impact of urban population size on traffic carbon emissions.In addition,considering that the influence of urban population size on transportation carbon emissions may still exist spatial spillover,this chapter also analyzes the influence of urban population size on transportation carbon emissions of surrounding cities through the spatial econometric model.In Chapter 5,based on the establishment of the econometric model and the setting of instrumental variables,this chapter empirically analyzes the influence of the spatial distribution of urban population on traffic carbon emissions.At the same time,this chapter studies the nonlinear relationship between urban population and traffic carbon emissions through the threshold effect.In Chapter 6,the interactive effects of urban population size and spatial distribution on transportation carbon emissions are mainly investigated.Based on this,this chapter also analyzes the differential effects of environmental regulation heterogeneity on the regression results.Chapter 7 is the mechanism testing part.This chapter empirically tests the mechanism of urban population size and spatial distribution influencing traffic carbon emissions through the pass-through effect model and the intermediary effect model respectively.The eighth chapter summarizes the research conclusions and puts forward corresponding policy suggestions.The main research conclusions of this paper can be summarized as follows:(1)From the analysis of the current situation,we find that in terms of urban population size,although in the early urbanization development strategy of China,the policy of vigorously developing small and medium-sized cities and restricting the development of big cities was formulated.However,in the process of rapid population urbanization,large cities tend to coincide with regional political,cultural and economic centers and have significant advantages of economies of scale,which leads to an overall decline in the number of small cities while an overall rise in the number of large cities during the study period.In terms of the spatial distribution of urban population,the population continues to gather in the southeast coastal cities and regional central cities.The degree of population spatial agglomeration in big cities is constantly increasing,while that in small and medium-sized cities shows a trend of continuous decline.In terms of urban transport carbon emissions,although the total amount of urban transport carbon emissions increased,the intensity of transport carbon emissions showed a decreasing trend,and there was obvious heterogeneity.(2)Empirical research on transportation carbon emissions based on urban population size found: First of all,although the expansion of urban population size will increase the total traffic carbon emission,it is conducive to reducing the traffic carbon emission intensity.Moreover,the negative relationship between urban population size and traffic carbon emission intensity is U-shaped,that is,with the expansion of urban population size,the negative effect of urban population size on traffic carbon emission intensity will continue to increase.However,when the growth of the population exceeds a certain threshold(4,425,800 by calculation),the continuous expansion of urban population will gradually weaken the negative effect on traffic carbon emission intensity.Secondly,the negative relationship between urban population size and transport carbon emission intensity also has regional heterogeneity.The influence coefficient of urban population size on transport carbon emission intensity in eastern and northeastern China is significantly higher than that in central and western China,which may be related to the fact that the average city size in eastern and northeastern China is larger than that in central and western China.Finally,although urban population expansion is conducive to reducing local transport carbon emission intensity,it has a positive effect on the transport carbon emission intensity of surrounding cities,and the maximum influence range of this regional transmission effect is 500 kilometers.(3)Empirical research on transportation carbon emissions based on urban population spatial distribution found: On the one hand,the increase of the spatial agglomeration degree of urban population is not only conducive to reducing the total carbon emissions from transportation but also hurts the intensity of carbon emissions from transportation.To verify the robustness of the conclusion,methods such as replacing the explained variable,replacing the core explanatory variable,adding other influencing factors and deleting outliers are also used to test the results.The results show that the conclusion that the spatial distribution of urban population has a negative effect on traffic carbon emission intensity is robust.On the other hand,there is a single threshold for the impact of the spatial distribution of urban population on transport carbon emissions.No matter below or above the threshold value,the increase of the spatial agglomeration degree of the urban population is conducive to the reduction of urban transport carbon emissions.However,when the spatial agglomeration degree of urban population exceeds the threshold value,The negative effect of urban population spatial distribution on transportation carbon emissions will be further enhanced.(4)Based on the empirical study on the interaction of urban population size and spatial distribution on traffic carbon emissions,the following findings are found: First of all,urban population size and spatial distribution do have interactive effects on transportation carbon emissions.Secondly,the increase of spatial agglomeration of urban population is conducive to strengthening the negative effect of urban population size on traffic carbon emission intensity.At the same time,the expansion of the urban population is also conducive to strengthening the negative effect of urban population spatial distribution on traffic carbon emission intensity.Finally,stricter environmental regulations can not only enhance the negative impact of urban population size and spatial distribution on transport carbon emissions,but also strengthen their interaction effect on transport carbon emissions.(5)Based on the impact mechanism of urban population size and spatial distribution on traffic carbon emissions,the following findings are found: On the one hand,urban population size will affect urban transport carbon emissions through industrial agglomeration and traffic structure.The expansion of urban population is conducive to promoting industrial agglomeration,which not only promotes urban economic development and increases economic aggregate,but also generates a large amount of traffic demand and increases traffic carbon emissions.Because the economic growth rate brought by industrial agglomeration is often faster than the growth rate of traffic carbon emission,the industrial agglomeration has a negative effect on urban traffic carbon emission intensity.At the same time,the expansion of the urban population is not only conducive to improving the efficiency of urban public transport,but also conducive to the construction of metro rail transit with population threshold.The development of urban public transport is conducive to optimizing the urban traffic structure,reducing the proportion of private car traffic,and thus promoting the reduction of transport carbon emission intensity.On the other hand,the spatial distribution of urban population will affect urban transport carbon emissions through job-housing separation and traffic congestion.The spatial distribution of urban population tends to be dispersed,which intensifies the degree of separation between work and housing of urban residents.The increase of the degree of separation between work and housing of urban residents will not only directly increase the commuting distance and time of urban residents,but also increase the transportation demand of urban residents to enjoy high-quality public services,which leads to the rise of urban transport carbon emissions.In addition,the improvement of urban population agglomeration can reduce residents’ traffic demand and traffic distance,which is conducive to alleviating urban traffic congestion.However,urban traffic congestion will not only prolong the running time of motor vehicles,but also reduce the energy efficiency of transportation,which will have a positive impact on urban traffic carbon emissions.Finally,based on the above research conclusions and the current situation of China’s urbanization development,this paper puts forward several targeted policy suggestions from several aspects,such as promoting the development of big cities,building urban agglomeration-dominated urban forms,strengthening urban population agglomeration,promoting the integrated development of industry and city,deepening inter-regional cooperation and promoting the development of new energy industry. |
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