Abstract

Global warming is one of the focus issues of common concern in the international community.The assessment report of the United Nations Intergovernmental Panel on Climate Change shows that the increase of carbon dioxide concentration is the main cause of global warming.As major carbon emitter，China faces enormous pressure to reduce carbon emissions.China's rapid urbanization has provided powerful impetus for economic and social development.As a gathering place of population and industrial activities，the city is a concentration place of resource consumption on the one hand.On the other hand，it is the place of social transformation，institutional innovation and technological innovation，which can bring energy saving and emission reduction technologies.So will urbanization drive carbon emissions or curb them？From the current research，the academic circle has not reached a consistent conclusion on the relationship between the two.In view of this，this book studies the mechanism of urbanization's impact on carbon emissions，the regional differentiation of urbanization's impact on carbon emissions，and the threshold effect of urbanization's impact on carbon emissions，so as to draw comprehensive and objective conclusions and provide theoretical support for the formulation and implementation of urbanization strategies and energy conservation and emission reduction policies.

On the basis of reviewing and summarizing domestic and foreign research literature，this book first discusses the mechanism of urbanization's impact on carbon emissions from three aspects：transmission mechanism，spatial effect and impact of different stages of urbanization on carbon emissions.Secondly，based on the analysis of urbanization and carbon emissions，the panel vector autoregression model（PVAR）is constructed，and the spatial panel model is used to analyze the impact of urbanization on carbon emissions，and the stepwise regression method is used to verify the transmission channel of urbanization on carbon emissions.Thirdly，based on the analysis of regional differences between urbanization and carbon emissions，the difference of urbanization's impact on carbon emissions in the eastern，central and western regions is empirically analyzed，and the transmission channel of urbanization's impact on carbon emissions in the three regions is further verified.Finally，the threshold effect of urbanization on carbon emissions is empirically analyzed in order to find out the reason why urbanization has different impacts on carbon emissions in the eastern，central and western regions.The main conclusions of this book are as follows：

First，the impact of urbanization on carbon emissions is the indirect transmission result of intermediate variables.In this process，the spatial effect and the stage of urbanization will affect the direction and intensity of the effect of urbanization on carbon emissions.Specifically，urbanization affects carbon emissions mainly through affecting intermediate variables such as human capital，technological innovation，industrial structure and household consumption.Considering the spatial effect，it can be seen that the carbon emission in this region is affected not only by the relevant factors in this region，but also by the carbon emission and related factors in neighboring regions.Different stages of urbanization have different impacts on human capital，technological innovation，industrial structure and household consumption.As a result，the impacts of urbanization level on carbon emissions in different stages of urbanization are different.

Second，panel vector autoregression model，impulse response function and variance decomposition results show that urbanization has a continuous driving effect on carbon emissions.Urbanization is the Granger cause of carbon emission，but carbon emission is not the Granger cause of urbanization.

Third，the Gini coefficient of urbanization and carbon emissions shows that there are obvious regional differences between urbanization and carbon emissions.In terms of urbanization level，there are significant regional differences in urbanization at provincial level，but the regional differences are gradually narrowing.From the perspective of the differences and evolution trends in the three regions，the urbanization level differences in the eastern and central regions showed a downward trend，while the urbanization level differences in the western region did not change significantly.From the perspective of carbon emissions，the Gini coefficient of carbon emissions at the provincial level in China indicates that there is little change in regional differences of carbon emissions.Within the three regions，the differences within the eastern and western regions are expanding，but the differences among provinces in the central region are gradually narrowing.

Fourth，at the national level，urbanization drives carbon emissions，which have a significant spatial positive correlation.From the perspective of transmission channels，the improvement of urbanization level will lead to the increase of human capital，technological innovation，industrial structure and household consumption，which drive carbon emissions.

Fifth，at the regional level，there are significant differences in the impact of urbanization on carbon emissions.Urbanization in eastern China significantly inhibits carbon emissions，while urbanization in central and western China increases carbon emissions.From the perspective of transmission channels，the improvement of urbanization level will bring the increase of human capital，technological innovation，industrial structure and resident consumption in the eastern，central and western regions，but the intensity of urbanization's promotion effect on each intermediate variable is different in the eastern，central and western regions.From the perspective of the influence of intermediate variables on carbon emissions，the driving intensity of industrial structure and household consumption on carbon emissions in eastern China is not strong，while the inhibiting effect of human capital and technological innovation on carbon emissions is obvious.Therefore，urbanization generally inhibits carbon emissions.The inhibiting effect of human capital and technological innovation on carbon emissions in central China is less than the driving effect of industrial structure and household consumption on carbon emissions，so urbanization will increase carbon emissions eventually.In western China，except that technological innovation can restrain carbon emissions，other intermediate variables will increase carbon emissions.Therefore，urbanization level will increase carbon emissions.

Sixth，urbanization has a significant threshold effect on carbon emissions.When the urbanization level is below a certain threshold value，urbanization has a significant driving effect on carbon emissions，while when the urbanization level exceeds a certain threshold value，urbanization will inhibit carbon emissions.

Based on the above research conclusions，the book argues that the impact of urbanization on carbon emissions is not always a driving effect or a restraining effect，but an obvious threshold feature.Different urbanization levels have different impacts on human capital，technological innovation，industrial structure and household consumption，leading to different impacts of intermediate variables on carbon emissions.Therefore，this book proposes to promote balanced development of urbanization，optimize human capital structure，promote energy-saving technology innovation，advocate low-carbon consumption mode and other aspects，and actively create an environment conducive to urbanization to reduce carbon emissions.

Key words： urbanization；carbon emissions；transmission mechanism；regional differences；threshold effect