4.1. Classification of Carbon Emission Types Based on Tapio Elasticity Coefficient
Firstly, based on the per capita GDP data and per capita carbon dioxide emissions data of 36 cities in the Yangtze River Delta region, calculate their decoupling elasticity coefficient .
Then, observe the calculated value of the decoupling elasticity coefficient.
, as well as the positive and negative of
and
, found that In 2019, the
of 36 cities are both positive, of which 29 cities belonged to solid or weak decoupling types, and only seven cities, such as Zhoushan belonged to the type of expansive negative decoupling. The detailed decoupling types of 36 cities are shown in
Table 3.
Next, calculate the carbon emission intensity (ES) of 36 cities in 2019 and divide them using ES=1 as the boundary point. When 0<ES<1, it is defined as low-carbon strength; When ES>1, it is defined as high-carbon intensity. Through calculation and induction, it was found that 15 cities, including Ningbo, belong to high-carbon intensity cities, with an average carbon intensity of 1.94 tons every 10000 yuan; Shanghai and 21 other cities belong to low-carbon intensity cities, with an average carbon intensity of 0.63 tons every 10000 yuan. The carbon intensity types are shown in
Table 4.
Finally, combining the Tapio decoupling coefficient and carbon intensity, 36 Yangtze River Delta region cities were classified by growth rate and absolute quantity. This article takes ES=1, =0, =0.8 as the critical value to divide 36 cities into six types of carbon emissions.
The classification results are shown in
Table 5: 36 cities are divided into six carbon emission types, namely carbon emission type I (0<ES<1 and
<0), type II (0<ES<1 and 0<
<0.8), Type III (0<ES<1 and
>0.8), type IV (ES>1 and
<0), type V (ES>1 and 0<
<0.8), and type VI (ES>1 and
>0.8). Carbon emission type I includes seven cities: Wenzhou, Taizhou, Lishui, Nantong, Yancheng, Huzhou, and Yangzhou; Type II consists of 12 cities including Shanghai, Hangzhou, Shaoxing, Jinhua, Jiaxing, Changzhou, Wuxi, Lianyungang, Fuyang, Bengbu, Hefei and Huangshan; Type III includes two cities: Lu'an and Suqian; Type IV consists of 8 cities: Ningbo, Quzhou, Chizhou, Suzhou, Xuancheng, Anqing, Tongling, and Ma'anshan; Type V includes two cities: Nanjing and Huainan; Carbon emission type VI consists of five cities: Zhoushan, Xuzhou, Suzhou, Wuhu, and Zhenjiang.
Based on the classification results, further analysis shows that type I cities have achieved negative per capita carbon emissions growth and low carbon intensity, making it a relatively ideal carbon emission type; The per capita carbon emission growth rate of Type II cities is lower than the per capita GDP growth rate, and the carbon intensity is also at a relatively low level; Although Type III cities have low carbon intensity, their per capita carbon emissions growth rate is greater than the per capita GDP growth rate, indicating that these cities are in a stage of sacrificing the environment for economic development; The per capita carbon emission growth rate of Type IV cities shows negative growth, but the carbon intensity is relatively high; The per capita carbon emission growth rate of Type V cities is lower than the per capita GDP growth rate, and their carbon intensity is higher; The per capita carbon emission growth rate of Type VI cities is higher than the per capita GDP growth rate and the carbon intensity is relatively high, which is an unsatisfactory type of carbon emission.
4.2. Analysis of Regional Characteristics of Carbon Emissions Based on Decoupling Index
The 2019 Tapio decoupling elasticity coefficient and carbon intensity distribution of 41 cities in the Yangtze River Delta region of China are shown in
Figure 1 and
Figure 2, respectively. Next, analyze the spatial distribution of decoupling elasticity coefficient and carbon intensity in various cities 2019.
Figure 1 shows the spatial distribution of decoupling elasticity coefficients for 41 cities in 2019. It can be observed that: five cities located in the central part of the Yangtze River Delta region (Lu'an, Wuhu, Zhenjiang, Suzhou, Zhoushan) and two cities in the north (Xuzhou, Suqian) had high decoupling elasticity coefficients in 2019, which all greater than 0.8, indicating that the economic development of these seven cities still relies on carbon emissions; At the same time, five cities located in the southern part of the Yangtze River Delta region (Ningbo, Taizhou, Wenzhou, Lishui, Quzhou), six cities in the central part (Anqing, Chizhou, Tongling, Xuancheng, Huzhou, Ma'anshan), and four cities in the northern part (Suzhou, Yancheng, Yangzhou, Nantong) have negative decoupling elasticity coefficients, all less than 0, indicating that the economic development and carbon emissions of these 15 cities have achieved decoupling, and carbon emissions have achieved negative growth; The growth rate of per capita carbon emissions in the remaining 14 cities is lower than the growth rate of per capita GDP. Overall, less than 20% of cities in the Yangtze River Delta region have high per capita carbon emissions growth. In comparison, over 80% of cities have low or negative per capita carbon emissions growth. From a spatial perspective, cities with negative per capita carbon emissions growth are often located on the edge of the Yangtze River Delta region. In contrast, cities with low and high per capita carbon emissions growth occupy the interior of the Yangtze River Delta region in an "S" shape.
According to
Figure 2, cities with high carbon intensity are primarily concentrated in Anhui Province, with eight cities with high carbon intensity; Jiangsu Province takes second place, with four high carbon intensity cities; Zhejiang Province takes third place, with three high carbon intensity cities. About 40% of cities in the Yangtze River Delta region are still high carbon intensive, while less than 60% are low carbon intensive. From a spatial perspective, carbon intensity in the Yangtze River Delta region shows "light at the ends and heavy in the middle."
According to the "classification criteria" for carbon emission types in
Table 5, a quadrant diagram for 36 cities in the Yangtze River Delta region in 2019 can be shaped (see
Figure 3). It is found that 53% of cities belong to Type I and Type II, with low-carbon negative growth and low-carbon low growth, respectively. This indicates that in the Yangtze River Delta region, at least half of the cities have carbon emissions at a low level of both total and growth rates, making them the ideal carbon emission type. In addition, 5% of cities belong to Type III, where the total carbon emissions are very low, but the growth rate is high. Technological innovation and upgrading are needed to reduce the growth rate. About 28% of cities belong to Type IV and Type V, with high total carbon emissions but a decreasing growth rate and significant room for emission reduction. However, 14% of cities still belong to Type VI, where the economic development rate is far slower than the increase in industrial energy consumption, and both aggregate and growth rates of carbon emissions are high.
4.3. Analysis of Carbon Emission Reduction Paths Based on the STIRPAT Model
Thirty-six cities were divided into carbon emission types according to the Tapio Model, and the STIRPAT model was further used to analyze panel data of cities with different carbon emission types from 2010 to 2021. Firstly, Eviews was used to perform unit root tests and cointegration tests. Levin, Lin, and Chu (LLC) tests were used to test the stationarity of each variable's time series, and the Pedroni method was used to perform a cointegration test on panel data (as shown in
Table 6 and
Table 7).
The test results indicate that there are no unit roots in lnTC, lnP, lnPGDP, lnLCT, lnIS, lnFDI, lnUR, EI, and the sequences of each variable are stationary, and the sequences are integration of order zero.
According to the cointegration test results, the significance is 0.0000, indicating a long-term equilibrium relationship between variables.
After pre-testing, OLS regression was performed on panel data of six carbon emission types using SPSS26.0, and the regression results are shown in
Table 8. There is a severe collinearity (VIF value much greater than 30) between the explanatory variable
and lnPGDP after regression. After excluding the term
, the regression was conducted again, and it was found that the Durbin Watson (DW) values of cities with carbon emission types I, II, and IV were far less than 2. These results indicate that the autocorrelation between these three carbon emission types of cities is more severe. The reason is that cities with the same carbon emission type have similarities in carbon emission intensity and decoupling.
Table 8 shows the regression results of the STIRPAT Model corresponding to the six-carbon emission types. Based on the regression coefficients and their significance, specific cities can be further refined and targeted to develop carbon emission reduction paths. Based on different types of carbon emissions, the analysis of particular regression results and the setting of effective emission reduction paths are as follows:
Cities belonging to carbon emission type I include Wenzhou, Taizhou, and Lishui. These cities have the characteristics of negative per capita carbon emissions growth and low carbon intensity. Observing the regression results, it was found that the total carbon emissions of such cities are significantly positively correlated with population, per capita GDP, low-carbon technology level, and energy intensity, with regression coefficients of 0.538, 0.819, 0.343, and 0.048, respectively. Since Type I is primarily cities with population outflow and relatively flat economic development, reducing population and suppressing economic growth are ineffective emission reduction measures. Therefore, starting with a low-carbon economy and achieving emission reduction goals through continuous innovation of low-carbon technologies is necessary. At the same time, the city can share low-carbon technologies with other cities and provide them with a carbon reduction experience.
Cities belonging to carbon emission type II include 12 cities such as Shanghai, Hangzhou, and Shaoxing, where the per capita carbon emission growth rate is lower than the per capita GDP growth rate, the carbon intensity is relatively low, and there is still some room for emission reduction. The total carbon emissions of these cities are significantly positively correlated with population, per capita GDP, low-carbon technology level, foreign trade level, and energy structure, with regression coefficients of 0.942, 1.113, 0.081, 0.093, and 0.027, respectively. This type of city has a large population inflow and a relatively high economic level, and carbon emissions cannot be suppressed by sacrificing economic development. These cities have high levels of low-carbon technology and energy efficiency. After comparing other regression coefficients, it was found that the level of foreign trade is the main factor affecting their carbon emissions. For such kinds of cities, it is necessary to focus on adjusting the fields and product types of foreign investment while continuously improving energy efficiency and strengthening the research and development of low-carbon technologies.
Cities of carbon emission type III include Lu'an and Suqian, which have low total carbon emissions but high growth rates. The regression results show that the regression coefficients of variables such as population, per capita GDP, and low-carbon technology level are insignificant, and all variables cannot significantly impact such cities. Therefore, there is currently no effective emission reduction path for such cities, and targeted policies must be taken based on their actual situation to suppress their carbon emission growth rate.
Cities belonging to carbon emission type IV include eight cities, such as Ningbo, Quzhou, and Chizhou, which have achieved negative per capita carbon dioxide emissions growth. However, due to the rapid economic development in the past decade, the total amount of carbon dioxide is large. Observing the regression coefficients, it was found that there is a significant positive correlation between population, per capita GDP, and total carbon emissions, with regression coefficients of 0.667 and 1.318, respectively. Other factors are not significant. Due to the large population inflow, rapid economic development, and large carbon dioxide emissions in these cities, it is necessary to strengthen their carbon sequestration capacity or reduce carbon emissions by enhancing residents' awareness of environmental protection and low-carbon lifestyle.
Cities belonging to carbon emission type V include Nanjing and Huainan, which have sizeable total carbon emissions and high growth rates. Therefore, it is necessary to simultaneously consider "reducing total emissions" and "suppressing growth rates." Observing its regression coefficients, it was found that there is a significant positive correlation between per capita GDP, foreign trade level, and total carbon emissions, with regression coefficients of 1.380 and 0.811, respectively. There is a significant negative correlation between the level of low-carbon technology and the total carbon emissions, with a regression coefficient of -0.472. Therefore, emission reduction can be achieved by suppressing foreign investment in high-energy consumption and high-emission projects in the local area and by accelerating the improvement of low-carbon technology to reduce carbon emissions effectively.
Cities belonging to carbon emission category VI include five cities, such as Zhoushan, Xuzhou, and Suzhou, with significant carbon emissions while also experiencing high carbon emission growth rates. Observing its regression coefficients, it was found that there is a significant positive correlation between urbanization level, population, industrial structure, energy intensity, and total carbon emissions. The regression coefficients from large to small are 1.135, 0.894, 0.645, and 0.029, respectively; There is a significant negative correlation between the level of foreign trade and the total carbon emissions, with a regression coefficient of -0.210. This type of city has a high level of urbanization, with population inflow exceeding population outflow, and cannot effectively suppress carbon emissions through these two variables. However, carbon emissions can be stopped by optimizing the industrial structure and achieving the transformation from industry to service industry as soon as possible. At the same time, improving energy efficiency can reduce energy intensity and carbon emissions in the production process. It is also possible to increase foreign trade to transfer carbon emissions.