1. Introduction
While the development of industrialization and urbanization has promoted the development of economic globalization, it has also exacerbated the climate change crisis caused by the increase in CO2 emissions that stem largely from energy consumption. In the global context of tackling climate change, how to effectively suppress CO2 emissions while promoting economic growth has become a challenge that most countries are facing in the development process. The Paris Agreement, which entered into force in 2016, is a legally binding global emission reduction agreement that plans the global climate governance pattern after 2020. Different countries and regions have accordingly proposed specific action plans for CO2 emission reduction based on the principle of common but differentiated responsibilities, in order to achieve the pursuit of economic development and emission reduction synergistically.
In recent years, research on the relationship between economic growth and CO
2 emissions has been increasing drastically. In terms of research methods, the related literature can be classified into four categories. The first category explores the contribution of the influencing factors of CO
2 emissions including economic scale through decomposition models. Since the logarithmic mean Divisia index (LMDI) method has the advantages of path independence and provides perfect decomposition results without residual terms [
1], it has been widely adopted in the decomposition analysis regarding CO
2 emissions, and most studies have demonstrated that economic growth is the main contributor to the increase in CO
2 emissions. For example, Ma et al. [
2] took advantage of the LMDI method to quantify the driving factors of CO
2 emissions in China from 2005 to 2016, showing that rapid economic growth is the most important reason for the increase in CO
2 emissions. Du et al. [
3] identified the drivers of changes in energy-related CO
2 emissions of high-energy intensive industries in China during 1986–2013 based on the LMDI method, verifying that the expansion of economic scale was the leading force explaining why CO
2 emissions increased. In addition, Dong et al. [
4] and Wang et al. [
5] also confirmed that economic output was the dominantly positive driving factor of CO
2 emissions by using the LMDI model.
The second category is the quantitative or qualitative analysis of the impacts of the factors including economic growth on CO
2 emissions through econometrics and statistical models. Quantitative analysis models mainly reflect the influence degree and influence direction through fitting model coefficients, including the stochastic impacts by regression on population, affluence and technology (STIRPAT) model [
3,
6,
7], the vector autoregressive (VAR) model [
8,
9], the autoregressive distributed lag (ARDL) model [
10,
11], the generalized method of moments (GMM) model [
12,
13], etc. For example, Li et al. [
6] used the STIRPAT model to investigate the effect of the rationalization and upgrading of manufacturing structure on CO
2 emissions in China, and the simulation coefficients show that the greater the ratio of industrial output to GDP, the weaker the restricting effect of resource dependence on the emissions reduction of manufacturing structure. The qualitative analysis models such as the vector error correction model (VECM) and Granger causality analysis mainly explain the relationship between economic growth and CO
2 emissions by judging the causal relationship. Jian et al. [
14] applied VECM to investigate the long-term equilibrium and short-term causality relationship among influencing factors and CO
2 emissions, and the results show the long-term cointegration relationship between them. Mirza et al. [
15] used VECM to explore the existence of Grangers’ long run, short run and strong causalities between economic growth, energy consumption and CO
2 emissions for Pakistan.
The third category investigates the relationship between economic growth and CO
2 emissions based on the EKC model. Compared with other methods that qualitatively determine the causality between variables or quantitatively determine the degree of impact by calculating model coefficients, the EKC proposed by Grossman and Krueger can better reflect the dynamic relationship between economic growth and CO
2 emissions at different stages of economic development [
16]. The results of some studies conform to the EKC hypothesis characterized by an inverted U-shape [
5,
17,
18], while others do not, showing an N-shaped [
19,
20,
21] or even M-shaped, curve [
22]. In general, the reasons leading to this phenomenon lie in three aspects. The first reason is the difference in the study objects and corresponding time series data. Most of these studies showed that the relationship between economic growth and CO
2 emissions in underdeveloped regions does not meet the EKC hypothesis compared with developed regions [
23,
24]. Besides, specific time periods parallel specific socioeconomic conditions, leading to different results even for the same research object [
5,
8]. The second reason stems from whether gross domestic product (GDP), as an independent variable, is quadratic or cubic when building the model [
25,
26]. The last reason derives mainly from different methods for estimating the coefficients of the model, among which FMOLS, DOLS and ARDL have been most commonly used [
27,
28,
29].
The fourth category detects the decoupling relationship between economic growth and CO
2 emissions based on the Tapio decoupling model. The determination of the decoupling relationship is achieved by calculating the decoupling elasticity, which can be specifically expressed as strong decoupling, weak decoupling, expansive coupling, negative decoupling, strong negative decoupling and so on [
30]. Wu et al. [
31] conducted a Tapio decoupling analysis of economic growth and CO
2 emissions with reference to 30 Chinese provinces from 2001 to 2015, finding that there is a strong decoupling relation between GDP and CO
2 emissions. Taking Beijing and Shanghai from 2005 to 2015 as examples, Wang et al. [
32] used decoupling analysis to explore the relationship between sectoral economic output and carbon emissions. Both cities experienced weak decoupling in construction, expansive negative decoupling in transport and expansive coupling in trade.
In terms of research object, it can be basically divided into developed or developing countries or regions from the perspective of development level. Among them, the discussions with regard to developed countries have not been frequently seen, and most of the related studies aim to verify that economic growth and CO
2 emissions are in line with the EKC hypothesis [
33,
34]. Conversely, more empirical studies with developing countries as targets, especially China, have been extensively conducted. In terms of research content, it involves sector perspectives such as construction sector [
35,
36], transportation sector [
37], manufacture sector [
38], etc., or sub-region perspectives such as Beijing [
39,
40], Shanghai [
41] and other provincial regions.
There are two deficiencies in the reviewed studies. The first one is the lack of explanation of what causes the dynamic changes in the correlation between economic growth and CO
2 emissions. As discussed above, the majority of the studies only quantified the impact of economic growth as one of the influencing factors on CO
2 emissions, or analyzed the correlation between economic growth on CO
2 emissions from the perspective of EKC hypothesis and decoupling status. Very few studies explored what factors drive the formation of the correlation, especially with a focus on the dynamic impacts of structural effects on the correlation. As mentioned by Grossman and Krueger [
42], structural effects, including the effects of both industrial structure and energy structure, have important impacts on economic growth and CO
2 emissions. They are indispensable factors to conduct a comprehensive analysis of the driving mechanism of CO
2 emissions.
The second deficiency is the lack of research on the traditional industrial regions, which refer to those whose industrial structure is dominated by traditional industrial sectors (such as steel, machinery or electricity). These regions are currently undergoing industrialization, but in a desperate need for transformation in the pattern of economic development from the originally traditional industrial mode to a modern development mode. The structural characteristics of such regions are generally reflected in two aspects. The industrial structure has begun to transit from high-energy-consuming and high-emitting traditional industries toward service and emerging industries, but the main driving force of economic development is still traditional industries. The energy structure has begun to transit from coal to oil, gas and renewable energy, but it is still dominated by coal consumption, with relatively lower energy efficiency. Many countries and regions in the world have experienced this transformation stage, such as the Ruhr area in Germany, the central part of the United Kingdom, and the Great Lakes area in the northeast of the United States. More developing regions are now undergoing such a stage. On the one hand, different from developed regions, such regions generally face the dual pressures of CO2 emission reduction while promoting high-quality economic growth. On the other hand, CO2 emission reduction practices in such regions play a critical role in reducing global CO2 emissions due to their large emission reduction potential.
Therefore, there are some questions that have not yet been thoroughly discussed in previous studies, especially for the large number of traditional industrial regions experiencing transformation in the world represented by China, that is, how will the dual structural effects, represented by industrial structure and energy structure, affect the future correlation between economic growth and CO2 emissions? To what extent should industrial structure and energy structure be adjusted to make CO2 emissions decouple from GDP growth? In-depth research on these issues is conducive to providing a path reference for carbon emission reduction in these regions while ensuring stable economic development.
To fill the gaps, this study selects Jilin Province, a typical transformation region in the Northeast China as the empirical target. First, we built an integrated simulation model based on the evolution of various factors from 1995 to 2015. The indicator CO2 emission intensity (CEI) (CO2 emissions per unit GDP) functions as a bridge connecting economic growth and CO2 emissions, on which basis we decomposed CEI into multiple factors through the Kaya identity and transformed the simulation model to contain only structural effects by the dynamic ordinary least squares (DOLS) method. Secondly, we simulated the correlation between economic growth and CO2 emissions, and the peaking pathways of CO2 emissions in four different scenarios were set according to different development patterns from 2016 to 2050. Finally, through introducing the concepts of marginal utility and total utility, we took advantage of variance decomposition analysis (VDA) based on the VAR model to explore the impacts of dual structural effects on the correlation between economic growth and CO2 emissions. The methods and results of the study are expected to provide reference for coordinating economic growth and CO2 emissions in the underdeveloped countries/regions undergoing structural transformation, especially in the context of CO2 emission reduction globally.
5. Discussion and Policy Implications
Jilin Province is a typical transformation region implementing a dual adjustment of both industrial structure and energy structure. In this study, an integrated simulation model is built based on the interactions among the socioeconomic, industrial, energy and CO2 emission variables in Jilin from 1995 to 2015, using CEI as a bridge connecting GDP and CO2 emissions. There is an inverted U-shaped dynamic correlation between GDP and CO2 emissions. The turning points appearing in the four scenarios indicate that CO2 emissions can decouple from GDP in Jilin once it has undergone sufficient development. However, the states at the turning points in the four scenarios differ significantly. The slower the adjustment of energy structure and industrial structure is, the more significant the upward trend appears before the turning point; furthermore, the slower the decrease in CEI is, the later CO2 emissions decouple from GDP.
The turning point of the correlation between economic growth and CO
2 emissions reflects the beginning of relative emissions reduction, while the CO
2 emission peak is the beginning of absolute emissions reduction. The reduction in CO
2 emission intensity is the main representation of relative emissions reduction, which is reflected in the gradual slowdown of the increase in CO
2 emissions before the emission peak. GDP drives the increase in CO
2 emissions, while CEI suppresses the increase in CO
2 emissions. Only when the reduction rate of CEI is greater than GDP growth rate can CO
2 emissions change from rising to falling, thereby forming the peak. Lower GDP growth rate and greater decrease in CEI caused by more aggressive adjustment of energy structure and industrial structure results in an earlier arrival of the emission peak, which is similar to the findings of Du et al. [
35] and Shuai et al. [
53].
In order to explore the dynamic influence mechanism of structural effects on the correlation between GDP and CO
2 emissions, CO
2 emissions and CUG were analogized to TU and MU in the process of economic development. CIS and CES have opposite effects on CUG with different intensities of influence. When the turning point occurs,
SI in the four scenarios is similar (about 41%), while
RN in the four scenarios is distinct (37%, 26%, 21% and 17%, respectively). Even if the levels of GDP and CO
2 emissions in the four scenarios are different, also with differences in energy structure, the industrial structure tends to be similar, which is also in line with the socio-economic development characteristics of developed countries that have peaked CO
2 emissions in their peak years [
54]. With regard to the contribution to CUG, industrial structure and energy structure each makes similar contributions in the four scenarios. With the development of emerging industries and the optimization of energy utilization models, the positive contribution of CIS on CUG will gradually weaken while the negative contribution of CES to CUG will gradually increase. Although the turning points corresponding to different scenarios occur at different times, the contributions of structural effects to CUG are almost similar, which shows that structural adjustment plays a relatively fixed and irreplaceable role in the process of peaking CO
2 emissions.
Based on the findings, the following policy implications are proposed. As a traditional industrial region that is undergoing transformation in terms of both industrial structure and energy structure, Jilin should strive to coordinate the relationship between economic growth and CO2 emission reduction. CEI is an important link to measure the relationship between economic growth and CO2 emissions. Currently, the CEI in Jilin Province is relatively high, which still has a large potential for emission reduction. Structural adjustment is the key to realizing the transformation of economic development mode in Jilin Province.
The adjustment of industrial structure is the prerequisite for development. As one of the typical representatives of the heavy industrial base, under the impact of emerging industries such as information technology at home and abroad, Jilin has gradually lost its previous development advantages. The industrial mode characterized by high energy consumption, high emissions and low added value cannot provide an impetus for the sustainable development of economy and society. At the same time, due to the limitations of geographical location and resource endowment, emerging industries and service industries with high added value and low energy consumption have not been effectively developed, which causes the lag of regional development [
55]. Therefore, Jilin Province should reduce energy-intensive industries while eliminating backward production capacity, and vigorously develop technology-intensive and capital-intensive industries.
The adjustment of energy structure is the guarantee of industrial transformation. In accordance with the characteristics of high energy consumption and high emissions of traditional industries, fossil energy consumption accounts for more than 90% of total energy consumption in Jilin Province, of which coal consumption accounts for more than 65%, which obviously does not meet the development requirements of a low-carbon economy. In order to meet the development needs of emerging industries and the requirements of CO2 emission reduction, according to the simulation results, the energy structure adjustment of Jilin Province should be carried out in two steps. The first step is to gradually replace some coal energy consumption with oil and natural gas. However, considering the shortage of fossil energy, the second step is to continuously increase the proportion of renewable energy consumption in order to gradually replace fossil energy consumption.
Taking Jilin Province as an example, this study reveals the correlation between economic growth and CO2 emissions under dual structural effects attributed to the Kaya identity of CEI. Owing to scenario analysis, the dynamic impacts of structural effects can be explored. However, the setting of the scenarios is based on the local development status and future planning. It is impossible to ensure the universal applicability for the transformation regions. Although each factor for future development is set as far as possible from the perspective of rationality and feasibility, there are still uncertainties, especially considering the periodicity of policy implementation. We used a five-year interval as a unit of parameter setting, which may induce deviations compared with the actual development situation. In addition, due to the lack of relevant planning, this study did not introduce technological factors into the simulation model, without further exploring the impacts of technological effects on the correlation between economic growth and CO2 emissions. In the future, we will further improve our research in the following two respects. The first is to expand the scope of the research and take other transformation regions as targets, so as to make the research more widely representative. The second is to continuously update the scenario settings according to the actual development situation to ensure the accuracy of the prediction results.
6. Conclusions
This study aims to unravel the dynamic driving mechanism of dual structural effect on the correlation between economic growth and CO2 emissions in a typical transformation region represented by Jilin province. We built an integrated simulation model to cover the interrelationships among the variables, and the prediction of CO2 emissions was based on the combination of GDP and CO2 emission intensity. The determination of the latter was based on the Kaya identity which is built incorporating the structural factors including industrial structure and energy structure. In order to quantitatively analyze the influence of structural effects on CUG, the concepts of marginal utility and total utility were introduced, and VDA based on the VAR model was employed to quantify the effects. The specific conclusions derived from the present study can be listed as follows:
(1) In terms of the impacts of structural effects on the changing trend in the correlation between GDP and CO2 emissions, the slower the adjustment of energy structure and industrial structure is, the more significant the growth trend in GDP will be before the turning point, resulting in significant differences in GDP and CO2 emissions at the turning point. The slower decrease in CEI is, the later CO2 emissions decouple from GDP.
(2) Lower GDP growth rate and greater decrease in CEI caused by more aggressive adjustment of energy structure and industrial structure results in earlier arrival of the emission peak. The faster GDP grows, the larger CO2 emissions, and the later the corresponding turning point appears.
(3) Even under different socio-economic development modes, when CO2 emissions peak, the energy structure is different while the industrial structure tends to be similar. Meanwhile, the contribution of the dual structural effects to CUG is basically the same (around 23–24%). The change in industrial structure has a positive driving effect on CUG, while the change in energy structure has a negative driving effect. With the transformation of the socio-economy, the positive driving effect of the industrial structure will gradually weaken, while the negative driving effect of the energy structure will increase.