## 1 Introduction
In the joint effect analysis, different scholars selected different impact factors according to the spatial scale of the study and the research purpose, but these generally included the population size, population density, or spatial  
Figure 1: Location and area map of the Yangtze River Delta. (**a**) Location map of the Yangtze River Delta and (**b**) Map of the Yangtze River Delta. distribution of population, economic scale, and industrial structure. From the overall research results, it is generally believed that urbanization, related variables, and carbon emissions have a long-term equilibrium relationship [20; 21]. However, the research results of specific indicators have different conclusions, because of differences in the scales of research, methods, and factors that were included in the model [22]. Although a great deal of literature has strongly demonstrated the strong correlation between urbanization, related factors, and carbon emissions, many meaningful conclusions and inspirations have been obtained. However, the mechanism of urbanization affecting carbon emissions is extremely complicated. On the one hand, urbanization is more indirectly affected by carbon emissions through other factors, such as production and living [23]. The advancement of urbanization has caused the population to continue to gather in urban areas. Large-scale infrastructure construction, such as roads and buildings in urban areas, will generate a large amount of carbon emissions during the construction process and in the future [24], while urbanization is also a process in which the working population flows from the primary industry to the secondary and tertiary industries. For the primary industry, the decrease in the number of primary industry practitioners promotes a significant increase in the logistics activities that are related to the transportation of agricultural products, and to a certain extent it also promotes the mechanization of the primary industry, thereby increasing carbon emissions. For the secondary and tertiary industries, the concentration of population factors has prompted rapid development, while the high-energy consumption production methods of the secondary and tertiary industries increase carbon emissions [25; 26; 27; 28]. In addition, the promotion of urbanization also accelerates the development of fixed assets investment, cement, export trade, and other industries, which indirectly promotes the growth of carbon emissions. On the other hand, there is a strong correlation between land use, industrial expansion, and carbon emissions. Land use and industrial expansion have a stable contribution to economic growth, and the intensive use of land is gradually increasing with the advancement of science and technology [29]. However, a large amount of greenhouse gases are generated in the process of land use [30; 31], which indirectly increase carbon emissions. Throughout the above studies, it can be observed that the current research on the relationship between urbanization and carbon emissions mainly focuses on the study of the total effect (such as \(X\)\(\rightarrow\)\(Y\)) and direct effect (such as \(X\)\(+\)\(M\)\(1\)\(+\)\(M\)\(2\)\(\rightarrow\)\(Y\)), but this is only a part of the mechanism of urbanization-driven carbon emissions, and it is a very important way for urbanization to act on carbon emissions; that is, indirect research (indirect or mediating effects, such as \(X\)\(\rightarrow\)\(M\)\(1\)\(\rightarrow\)\(Y\); \(X\)\(\rightarrow\)\(M\)\(2\)\(\rightarrow\)\(Y\); \(X\)\(\rightarrow\)\(M\)\(1\)\(\rightarrow\)\(M\)\(2\)\(\rightarrow\)\(Y\)) are not enough. Ignoring the specific roles of other factors in this process often makes the interpretation of statistical results ambiguous and it may lead to the wrong conclusions. In terms of research methods, the current research mainly uses traditional econometric study methods, and it ignores the spatial correlation of carbon emissions between regions.