Tracking the CO₂ Emissions of China’s Coal Production via Global Supply Chains

Abstract

Coal’s green mining and scientific utilization is the key to achieve the national vision of carbon peak by 2030 and carbon neutrality by 2060. Clarifying the CO₂ flow of coal production is the core part of decarbonization. This study uses an environmental extended multi-regional input–output (EEMRIO) model to analyze the impact of embodied emissions on the indirect CO₂ emission intensity of coal production between China’s coal mining sector and 141 countries/regions. It is found that the CO₂ emission intensity of China’s coal production was 34.14 gCO₂/MJ in 2014, while the direct and indirect emission intensities were 16.22 gCO₂/MJ and 17.92 gCO₂/MJ, respectively. From 2007 to 2014, the direct emission intensity of China’s coal production increased by 23%, while the indirect emission intensity decreased by 30%. The key material and service inputs affecting indirect carbon emissions of coal production in China are electricity service, metal manufacturing, chemical products, coal mining, and transport, which accounted for 85.5% of the total indirect emission intensity of coal production in 2014. Globally, a large portion of CO₂ from Chinese coal production is emitted to meet foreign direct and indirect demands for material and service inputs. Policy implications related to this outcome are further discussed in the study.

1. Introduction

On 22 September 2020, Chinese President Xi Jinping addressed, at the General Debate of the General Assembly’s seventy-fifth session, that China would scale up its Intended Nationally Determined Contributions (NDCs) by adopting more vigorous action plans and policies and aim to have CO₂ emissions peak before 2030 and achieve carbon neutrality before 2060. After that, the Chinese government developed detailed plans and programs in a series of summits [1]. The goal of carbon neutrality opens the way to deep decarbonization of China’s energy system, including accelerating the increase in non-fossil energy development and consumption and reducing coal consumption as the main path to achieve carbon neutrality [2,3].

Due to China’s rich coal, poor oil, and less gas energy resource endowment, coal accounts for more than half of China’s primary energy sources. Although the scale of coal in China’s total energy consumption continues to decline, the short term is still inseparable from coal due to the characteristics of China’s resource endowment and the current stage of economic and social development. Xie et al. (2019) reported that in 2025 China’s energy consumption demand will be 5.5–5.6 billion tons of standard coal, of which the coal consumption measure is 2.8–2.9 billion tons of standard coal, commanding 50–52% of total energy consumption [4]. Carbon emissions associated with energy production and consumption are an important source of carbon emissions in China, and carbon emissions from coal production and consumption make up 70–80% of China’s total carbon emissions [5]. As coal is the largest producer of China’s greenhouse gas emissions, the energy conservation and emission reduction in the coal industry will be the most crucial measure for China to respond to global climate change and solve current long-term environmental problems, which promotes the development of a comprehensive understanding of the direct and indirect carbon emissions of coal mining.

1.1. Review of Earlier Works

The research method for direct coal-related carbon emissions is mainly to compute carbon emissions by obtaining activity data of emission sources and the corresponding carbon emission factors. The carbon emission factors are mainly derived from the 2006 IPCC Guidelines for National Greenhouse Gas Inventories released by the United Nations Intergovernmental Panel on Climate Change (IPCC) in April 2006 [6]. There are some scholars who have conducted studies on direct CO₂ emissions from coal-fired power plants using a direct monitoring approach from an engineering perspective [7]. However, none of these studies considered indirect emissions.

Life Cycle Assessment (LCA) is an important environmental management tool, which not only can direct environmental impacts caused by the implementation of the activity being considered but can also analyze the relevant indirect impact. Fossil fuels, mainly coal, release waste substances into the environment as they power the world’s economy. Assessing chains of the processes inside the system with environmental analyses such as LCA is crucial [8]. Wang et al. (2018) used the LCA method to evaluate the direct and indirect environmental problems of mining, washing, and transportation in the process of coal mining in China. The indirect emissions mainly involve the impact of carbon emissions caused by fugitive gas in the production process [9]. The research on the boundary of coal-fired power generation systems includes three different stages: coal production, coal transportation, and coal burning. From the perspective of sensitivity analysis, the environmental impact of the coal carbon supply chain can be reduced [10]. Zhou et al. (2020) further refined the coal mining process based on the whole life cycle model, considering the carbon emissions from mining, ventilation, drainage, power consumption, transportation, and post-mining activities. Indirect carbon emissions from post-mining activities were also taken into account [11]. Burchart-Korol et al. (2016) developed an environmental LCA model applied to coal mining operations, which not only applies to greenhouse gas (GHG) emission assessment but is also connected with the ReCiPe system to identify damage categories such as human health, ecosystem, and resources [12].

Input–output (IO) analysis is commonly used to quantify embodied energy [13], embodied CO₂ [14], and embodied PM_2.5 emissions [15]. There are many databases that provide IO tables of embodied energy, such as GTAB and EXIOBASE [16]. Compared with the EXIOBASE database, the input–output model of GTAB includes more inter-country trade and is more suitable for studying national emissions. All goods and services produced by an economy are directly or indirectly linked to energy use and, depending on the type of fuel used, to carbon dioxide emissions [17]. Davis and Caldeira (2010) calculated carbon emissions at the global sectoral scale using an EEMRIO [18]. Zhou et al. (2010) combined an IO table with the energy consumption data by sector to estimate embodied carbon emissions in the international trade of China in 2007 [19]. Daly et al. (2015) estimated upstream CO₂ emissions from current and future energy technologies in the UK using a multi-regional environment extended input–output (EEMRIO) model, and explicitly simulated direct and indirect CO₂ emissions from energy supply and infrastructure technologies within the national ESOM (TIMES model) [20]. Some studies account for sector-specific direct and indirect carbon emissions based on sectoral emission intensity and intersectoral economic linkages. Pan et al. (2020) used an IO model to account for the sectoral-scale CO₂ emissions of China, including the oil and gas sector [21]. In addition, a system considering material flow to analyze the embodied carbon emissions of aluminum-containing commodities in China’s international trade from 2008 to 2017 has also been developed [22].

1.2. Aim of This Study

Green mining and the scientific utilization of coal are key to achieving the national vision of carbon peaking by 2030 and carbon neutrality by 2060. Coal-based energy structure is the main source of carbon emissions in China, which requires the coal industry and other industries closely connected with the coal mining sector to adjust their structure and accelerate transformation. Therefore, this paper selects the coal mining sector as the research subject, calculates the CO₂ emission intensity of the sector based on the EEMRIO approach, and explores the sustainable development model of the coal industry. This paper is organized as follows: Section 2 explains the method and data, Section 3 describes the results and discussion, and Section 4 presents conclusions and policy implications.

2. Materials and Methods

2.1. Methodology for Accounting CO₂ Emission Intensity

The input–output (IO) model was proposed by Leontief in the 1930s [23], which is mainly through the formulation of the IO table and establishes the corresponding mathematical model to reflect the national economic system of interdependence and the restriction relationship between different departments. Multi-regional input–output models are gradually used to quantitatively analyze the environmental impacts of trade activities between countries or regions, including PM_2.5, CO₂ [15,17]. This method is used to analyze the direct and indirect CO₂ emissions of coal production in major coal-producing countries (Figure 1). The basic equation is shown in Equation (1):

$$C=E{(I-A)}^{-1}M=\mathit{ELM}$$

(1)

where there are 141 countries or regions and each region has 57 sectors, and C is an 8037 × 8037 vector representing the complete CO₂ emissions. $E=\frac{e}{x^{\prime }}$, which is the CO₂ direct emission coefficients of economic sectors; L is an 8037 × 8037 Leontief inverse, which is also called complete emission factor matrix; M is an 8037 × 8037 matrix of intermediate demand. The Equation (2) is expressed as a matrix:

$$\left(\begin{array}{ccc}\begin{array}{cc}{C}_{1 1}& C_{1 2}\end{array}& \cdots & C_{1 8037}\\ \begin{array}{cc}{C}_{2 1}& C_{2 2}\end{array}& \cdots & C_{2 8037}\\ \begin{array}{cc}\begin{array}{c}⋮\\ C_{8037 1}\end{array}& \begin{array}{c}⋮\\ C_{8037 2}\end{array}\end{array}& \begin{array}{c}\ddots \\ \dots \end{array}& \begin{array}{c}⋮\\ C_{8037 8037}\end{array}\end{array}\right)=\left(\begin{array}{ccc}\begin{array}{cc}{E}_1& 0\end{array}& \cdots & 0\\ \begin{array}{cc}0& E_2\end{array}& \cdots & 0\\ \begin{array}{cc}\begin{array}{c}⋮\\ 0\end{array}& \begin{array}{c}⋮\\ 0\end{array}\end{array}& \begin{array}{c}\ddots \\ \dots \end{array}& \begin{array}{c}⋮\\ E_{8037}\end{array}\end{array}\right)\left(\begin{array}{ccc}\begin{array}{cc}{L}_{1 1}& L_{1 2}\end{array}& \cdots & L_{1 8037}\\ \begin{array}{cc}{L}_{2 1}& L_{2 2}\end{array}& \cdots & L_{2 8037}\\ \begin{array}{cc}\begin{array}{c}⋮\\ L_{8037 1}\end{array}& \begin{array}{c}⋮\\ L_{8037 2}\end{array}\end{array}& \begin{array}{c}\ddots \\ \dots \end{array}& \begin{array}{c}⋮\\ L_{8037 8037}\end{array}\end{array}\right)\left(\begin{array}{ccc}\begin{array}{cc}{M}_{1 1}& M_{1 2}\end{array}& \cdots & M_{1 8037}\\ \begin{array}{cc}{M}_{2 1}& M_{2 2}\end{array}& \cdots & M_{2 8037}\\ \begin{array}{cc}\begin{array}{c}⋮\\ M_{8037 1}\end{array}& \begin{array}{c}⋮\\ M_{8037 2}\end{array}\end{array}& \begin{array}{c}\ddots \\ \dots \end{array}& \begin{array}{c}⋮\\ M_{8037 8037}\end{array}\end{array}\right)$$

(2)

Indirect emissions from production in the coal sector in each country are summed in the corresponding columns of the C matrix in Equation (2). Take China as an example: ${{\displaystyle \sum }}_{i=1}^{8037}{C}_{i 186}$ is indirect emissions from China’s coal production. The MRIO model endogenously calculates not only the domestic output, but also the output in all other regions resulting from intermediate products, which is embodied in international trade. The summation by sector and country can be used to analyze the embodied emissions from coal production of different sectors and countries.

Indirect emission intensity from China’s coal production is shown in Equation (3):

$$I_{ind,CHN}=\frac{{{\displaystyle \sum }}_{i=1}^{8037}{C}_{i 186}}{Q_{coal,CHN}}$$

(3)

where $I_{ind,CHN}$ is the indirect emission intensity of China’s coal production, ${{\displaystyle \sum }}_{i=1}^{8037}{C}_{i 186}$ is the indirect emissions from coal production in China, and $Q_{coal,CHN}$ represents the annual coal production in China.

Direct emission intensity from China’s coal production is shown in Equation (4):

$$I_{d,CHN}=\frac{C_p}{Q_{coal, CHN}}$$

(4)

where $I_{d,CHN}$ is the direct emission intensity of China’s coal production and $C_p$ is the production-based CO₂ emissions in China.

2.2. Data

In this study, the global production-based CO₂ emissions data and world IO tables were obtained from the latest GTAP 10 [24], which is commonly used in health and environmental research [25], for example, PM_2.5 and CO₂ accounting studies [26,27]. The Global Trade Analysis Project (GTAP) database provides the world economy for 4 reference years (2004, 2007, 2011, and 2014) and distinguishes 65 sectors, up from 57 in the previous release, in each of the 141 countries/regions. For each country/region, the database presents values of production and intermediate and final consumption of materials and services in millions of US dollars. We mainly analyze intermediate consumption data for the coal sector in 11 countries, as shown in Figure 2. Annual data on coal production by country come from the IEA [28].

3. Results and Discussion

3.1. CO₂ Emission Intensity of Coal Production in Major Coal-Producing Countries

According to the model and data advantage of the input–output approach, we can obtain the CO₂ emission intensity of the world’s major coal production in 2014, as shown in Figure 2. The CO₂ emission intensity of coal production in different countries is between 2.21 gCO₂/MJ and 34.14 gCO₂/MJ. China, South Africa, and Russia have large coal production emission intensities, which are 34.14 gCO₂/MJ, 28.61 gCO₂ /MJ, and 28.41 gCO₂/MJ, respectively. At the same time, the CO₂ emission sources from coal production vary widely in different countries. The direct and indirect emission intensity of coal production can be distinguished by the input–output method, as shown in Figure 1. Direct emission intensity refers to the CO₂ emissions of different resource productions, while indirect emission is associated with the material and service inputs in the production process.

The direct CO₂ emission intensity of coal production in 11 coal-producing countries ranges from 0.01 gCO₂/MJ to 16.22 gCO₂/MJ, which is related to the differences in coal mining exploitation in each country. For instance, although China is rich in coal resources, its resource endowment and long-term strong demand have led to the increasing depth of coal mining [29]. Deep coal mine development activities are an important reason for China’s direct CO₂ emission intensity ranking first in 2014. Russia’s underground coal resources account for 37% of the total resources [30]. Under the circumstance of increasing mining difficulty, the direct carbon emission intensity of coal production was 7.89 gCO₂/MJ in 2014. However, the direct CO₂ emission intensity of coal mining in South Africa is only 0.02 gCO₂/MJ, which has rich open-pit coal resources and superior mining conditions. The indirect CO₂ emission intensity of coal production in 11 coal-producing countries ranges from 1.89 gCO₂/MJ to 28.59 gCO₂/MJ, which is mainly associated with the material and service inputs of the coal mining sector. In addition, the differences in industrial structure, trade structure, and energy structure between countries play more important roles in indirect emissions. Indirect CO₂ emissions from coal production are high in South Africa, Russia, and China, with carbon emission intensities of 28.59 gCO₂ /MJ, 20.52 gCO₂ /MJ, and 17.92 gCO₂ /MJ, respectively.

Figure 3 illustrates the distribution of direct and indirect CO₂ emission intensity in major coal-producing countries in 2014. South Africa, Mongolia, and Kazakhstan are coal producers with high indirect emission intensities. China and Russia are coal producers, which both have high direct and indirect emissions intensities. In general, indirect emissions are higher than direct emissions in most coal-producing countries. In 2014, indirect CO₂ emission intensity accounted for more than 80% of total CO₂ emission intensity in each coal-producing country. Therefore, indirect carbon emission intensity has a significant effect on the overall carbon intensity of coal production. The next section analyzes the differences in indirect emission intensity of coal production between countries from the import/export trade.

3.2. Indirect CO₂ Emission Intensity of Coal Production from Material and Service Inputs

Compared to the bottom-up approach, the top-down input–output method can also find the key factors affecting the CO₂ emission intensity of coal production.

Table 1. Distribution of indirect CO₂ emission intensity of China’s coal production in 2014.

Ranking	Material and Service Input	Indirect CO2 Emission Intensity
1	Electricity	9.18
2	Ferrous metal	2.31
3	Machinery and equipment	1.07
4	Chemical products	0.75
5	Metal products	0.73
6	Coal	0.65
7	Transport	0.62
8	Wood products	0.40
9	Business services	0.35
10	Petroleum, coal products	0.35
11	Financial services	0.31
12	Mineral products	0.27
13	Trade	0.17
14	Construction	0.08
15	Sea transport	0.08
16	Electrical and electronic equipment	0.06
17	Water	0.04
18	Manufactures	0.03
19	Air transport	0.02
20	Other extraction (mineral)	0.02

shows the 20 major material and service inputs, which accounted for 97.56% of the total indirect CO₂ emission intensity of China’s coal production in 2014. Electricity ranks first with 9.18 gCO₂/MJ indirect emission intensity, accounting for half of the total indirect emission intensity. Above all, China’s power mix is dominated by coal, which accounted for more than 75% of the total power generation in 2014 [28], resulting in high overall emissions from the power sector. Secondly, the depth of coal mining in China has been increasing as shallow coal resources are depleted [31], leading to an increment in electricity consumption as coal mining becomes harder. The indirect emission intensities caused by ferrous metals, machinery and equipment, chemical products, and metal products are also relatively high, which are 2.31 gCO₂/MJ, 1.07 gCO₂/MJ, 0.75 gCO₂/MJ, and 0.73 gCO₂/MJ, respectively. It shows that there is a great demand for steel and chemicals. In addition, it can also be found in Table 1 that China’s coal production leads to the indirect emission intensity of the coal mining sector reaching 0.65 gCO₂/MJ, which further reflects China’s current coal-based energy structure.

In this study, 20 major inputs of material and service are combined into 7 categories of material and service inputs to further analyze the temporal variation trend of indirect CO₂ from coal mining in China and the differences in indirect emission intensity among major coal-producing countries. Electricity service includes electricity; transportation services comprise transport, air transport, and sea transport; extraction services involve coal, water, and other extractions (mineral); metal manufacturing covers ferrous metal, metal products, machinery and equipment, and electrical and electronic equipment; other manufacturing includes wood products, mineral products, and manufactures; support services incorporate business services, trade, financial services, and construction; and refining and chemicals comprise petroleum and coal products and chemical products.

Comparing the CO₂ emission intensity of China’s coal production in 2007 and 2014, it can be found that the emission intensity of coal production in 2007 was 38.75 gCO₂/MJ, of which the direct emission intensity was 13.20 gCO₂/MJ, and the indirect emission intensity was 25.55 gCO₂/MJ. In 2014, the emission intensity of coal production was 34.14 gCO₂/MJ, of which the direct emission intensity was 16.22 gCO₂/MJ and the indirect emission intensity was 17.92 gCO₂/MJ. With the depletion of shallow coal resources, the depth of coal mining in China has been increasing, and the direct emission intensity has increased by 23%. Figure 4 shows that the indirect emission intensity of coal production in China decreased by 30% from 2007 to 2014, and embodied emission intensity of electricity service, transportation services, extraction services, metal manufacturing, and other manufacturing decreased by 26%, 62%, 41%, 30%, and 35%, respectively. The decline in the embodied emission intensity of the real economy sector is potentially due to technological progress, energy efficiency improvement, and the adjustment of China’s energy structure. The end consumption of coal decreased from 43% in 2007 to 39% in 2014, among which the share of coal power in China’s power structure dropped from 81% in 2007 to 73% in 2014 [28]. For support services, including financial services, business services, and trade, the proportion of embodied CO₂ emission intensity of coal production increased by 31%, reflecting the increasing vitality of China’s financial market and commercial services as well as the increasing participation of financing activities in the coal sector [32].

Figure 5 portrays that the structure of the embodied carbon emission intensity from coal production is significantly different between China and the US. China’s electricity service accounts for 51% of embodied emission intensity, compared with 31% for the United States. Due to China’s coal resource endowment and long-term strong demand, coal mining depth continues to increase, resulting in increased electricity consumption in production activities. Meanwhile, there are differences in the power generation structure between China and the United States. In 2014, 73% of China’s electricity came from coal, compared to 39% in the United States [28]. China’s embodied emission intensity from extraction services was 4%, while that from USA was less than 1%, which further reflects China’s coal-based energy structure. Transportation services is another difference between China and the United States in the structure of embodied emission intensity from coal production. The United States accounted for 35% of embodied emission intensity in transportation serves, while China only accounted for 4%. This is mainly due to China’s developed public transportation system and the large number of coal power plants in China, which facilitate local consumption of coal production.

3.3. Coal Production CO₂ Emissions Embodied in Trade

In this section, the representative coal-producing countries in each continent are selected to analyze the embodied CO₂ emissions caused by the participation of the coal mining sector in international trade. In 2014, the embodied emissions from international trade related to China’s coal mining sector were mainly in Asia, accounting for 64.1%, and are closely related to trade with Japan, South Korea, Thailand, and India, contributing 0.8% of China’s total indirect emissions from coal production. Outside Asia, countries with high trade links to China’s coal mining sector include the US, Russia, and Australia. However, the indirect carbon emissions of China’s coal contributed by international trade only accounts for 1.13%, and most of the embodied emissions of material and service inputs are in China.

As shown in Figure 6, the embodied emissions from international trade related to Russia’s coal mining sector are mainly in Asia and Europe, accounting for 42% and 41.7%, respectively. The international trade emissions associated with South Africa’s coal mining sector are mainly in Asia, accounting for 66.3%. The embodied emissions from international trade associated with the US’s coal mining sector are mainly in Europe and Asia, accounting for 53.2% and 41.7%, respectively. Asia accounts for 76% of international-trade-related emissions from Australia’s coal mining sector. In the coal mining sectors of Russia, South Africa, the US, and Australia, China is the largest importer of trade, accounting for 1.24%, 1.28%, 4.34%, and 3.58% of their total indirect emissions from coal production, respectively. Therefore, coal production in Russia, South Africa, the United States, and Australia contributed 0.2 Mt, 0.23 Mt, 0.94 Mt, and 0.41 Mt of CO₂ emissions in China in 2014.

4. Conclusions and Policy Implications

(1)

In 2014, the CO₂ emission intensity of China’s coal production was 34.14 gCO₂/MJ, of which the direct and indirect emission intensities were 16.22 gCO₂/MJ and 17.92 gCO₂/MJ, respectively. From 2007 to 2014, the direct emission intensity of China’s coal production increased by 23%, while the indirect emission intensity decreased by 30%. Compared with other coal-producing countries, China has high direct and indirect emission intensity in coal production mining.

(2)

The key material and service inputs affecting indirect carbon emissions of coal production in China are electricity, ferrous metal, machinery and equipment, chemical products, metal products, coal mining, and transport, which accounted for 85.5% of the total indirect emission intensity of coal production in 2014. It is worth noting that China’s coal mining sector contributes 4% of indirect emissions to coal production, which is much higher than other coal-producing countries.

(3)

China’s coal production sector is mainly traded with Japan, South Korea, Thailand, and India. All import trade accounts for 0.8% of the total indirect emissions from coal production in China. However, China is the largest import source of material and service inputs for coal production in South Africa, the United States, Russia, Australia, and other coal-producing countries, accounting for 1.24%, 1.28%, 4.34%, and 3.58% of their total indirect emissions from coal production, respectively.

Based on the conclusion of this study, policy recommendations are given for the reduction in CO₂ direct emissions from coal production and CO₂ embodied emissions from trade, respectively. First, on the production side, China’s mining difficulty aggravated by resource exhaustion actively promote the research, development, and application of carbon-negative technology represented by carbon capture, utilization, and storage (CCUS) in coal mining. This can alleviate CO₂ emissions in the coal supply chain and industrial chain from the source. Secondly, more than half of the indirect emissions of China’s coal production come from electricity service. In 2007 and 2014, the proportion of coal power in China reached 81% and 73%, respectively. However, the proportion of coal power in China bucked the trend and rose to more than 70% during 2021. While China is aggressively pursuing carbon neutrality, its coal-based electricity mix is unlikely to change radically anytime soon. Because of China’s vast territory, wind, light, biomass, and other resources are rich. By enhancing the complementary supply of distributed renewable energy electricity including wind power, solar, and biomass in coal production areas in accordance with local conditions, the embodied emissions of the electricity service input in coal mining can be reduced and energy structure adjustment can also be promoted.