Understanding carbon footprint: An evaluation criterion for achieving sustainable development

Abstract

Excessive greenhouse gas emissions lead to global warming, which poses a critical challenge for human society. Worldwide consensus that carbon emissions must be reduced to achieve sustainable development has raised research interest on the topic of carbon footprint, an assessment standard for measuring greenhouse gas emissions. To shed light on this important topic, we introduce carbon footprint-related international standards and domestic policies, and conduct quantitative and qualitative analyses to provide a comprehensive overview of the current carbon footprint literature. Specifically, through a bibliometric analysis of 13 203 carbon footprint publications circulated over the past decade, we quantify the publication volume, influence, and collaboration networks of countries/regions, institutions, and journals. The results show that publications on carbon footprint have been increasing since 2013, and more so after 2017. Regarding domain influence, China and its academic institutions show a strong influence. In addition, a cluster analysis of the keywords of all publications shows seven categories, encompassing carbon footprint accounting methods and research priorities. Furthermore, a qualitative analysis of the research methods and subjects related to carbon footprint reveals the need to increase communication and collaboration among different disciplines and countries/regions to strengthen the construction of carbon footprint systems. Accordingly, this study identifies popular topics and development trends in the carbon footprint literature to provide research direction for promoting green and low-carbon transformation of the social economy to achieve sustainable development.

Headnote

ARTICLE INFO

Keywords:

Carbon footprint

Carbon accounting

Greenhouse gas emissions

Bibliometrics

Sustainable development

ABSTRACT

Excessive greenhouse gas emissions lead to global warming, which poses a critical challenge for human society. Worldwide consensus that carbon emissions must be reduced to achieve sustainable development has raised research interest on the topic of carbon footprint, an assessment standard for measuring greenhouse gas emissions. To shed light on this important topic, we introduce carbon footprint-related international standards and domestic policies, and conduct quantitative and qualitative analyses to provide a comprehensive overview of the current carbon footprint literature. Specifically, through a bibliometric analysis of 13 203 carbon footprint publications circulated over the past decade, we quantify the publication volume, influence, and collaboration networks of countries/regions, institutions, and journals. The results show that publications on carbon footprint have been increasing since 2013, and more so after 2017. Regarding domain influence, China and its academic institutions show a strong influence. In addition, a cluster analysis of the keywords of all publications shows seven categories, encompassing carbon footprint accounting methods and research priorities. Furthermore, a qualitative analysis of the research methods and subjects related to carbon footprint reveals the need to increase communication and collaboration among different disciplines and countries/regions to strengthen the construction of carbon footprint systems. Accordingly, this study identifies popular topics and development trends in the carbon footprint literature to provide research direction for promoting green and low-carbon transformation of the social economy to achieve sustainable development.

1. Introduction

Climate change has brought about global crises, such as extreme weather, melting glaciers, rising sea levels, reduced food production, and the spread of epidemics, posing severe challenges to human survival and development. These phenomena are exacerbated mainly by the carbon emissions generated by human activities (Abulibdeh et al., 2024; Shi and Yin, 2021; Wang et al., 2022). Many climate experts believe that global temperatures will continue to increase over the next 100 years (Li and Zheng, 2020). Hence, the Intergovernmental Panel on Climate Change (IPCC) considers the reduction of greenhouse gas (GHG) emissions important to mitigate climate change. Accordingly, the Paris Agreement, adopted at the 21st Meeting of the Parties to the United Nations Framework Convention on Climate Change, established long-term temperature targets, limiting global average temperature rise to below 2 °C and actual temperature rise to within 1.5 °C (Gong et al., 2023). To this end, the Paris Agreement requires that all parties make nationally determined contributions. China promises to achieve a carbon peak around 2030 and carbon neutrality by 2060. The United States plans to increase GHG emissions reduction by 50%52% on a 2005 benchmark. Japan plans to reduce GHG emissions by 46% from 2013 levels by 2030, and the European Union promises to reduce GHG emissions to 55% of 1990 levels by 2030 (UNFCCC, 2023). Therefore, accounting for carbon emissions has become particularly important.

Carbon accounting, the first step in carbon management and emission reduction, includes a series of activities related to carbon emissions such as measurement, calculation, verification, reporting, and so on (Liu et al., 2023). The concept of carbon footprint arose during the process of measuring GHG emissions, to help gauge the impact of GHG emissions on global climate change more accurately. The term carbon footprint originates from the concept of ecological foot print, which was first proposed by Canadian scientist William Rees in the 1990s. The ecological footprint quantifies the pressure and resource consumption of human activities on the ecosystem by converting the resources consumed and waste generated by a certain population into the required biologically productive land area (Gao, 2020). The currently recognized definition of carbon footprint is the total amount of GHGs directly and indirectly emitted by the studied product, activity, or service throughout its life cycle, expressed in CO, equivalents. GHGs are categorized into six types specified in the Kyoto Protocol: CO,, CH, N,O, HFCs, PFCs, and SF, (Shan et al., 2024; Zhang et al., 2023). As research progressed, the definition of the carbon footprint has incorporated concepts such as implicit carbon, carbon flow, and virtual carbon (Li, 2021). Carbon footprint accounting is the technological foundation for achieving green production, promoting low-carbon consumption, and economic development. It is also an important prerequisite for breaking down green trade barriers and achieving international exchange and mutual recognition of carbon footprint labels. The proposed carbon footprint reveals the impact of human behavior on climate change from a unique perspective, thus providing an effective tool for the scientific measurement of carbon emissions. It has been accepted by governments, organizations, and institutions in various countries and has gradually penetrated various research fields.

At present, research on the accounting and evaluation of carbon footprints has become relatively mature and complete, and has been applied in different scales, fields, and products. Scholars have reviewed the latest progress in single-dimensional carbon footprint research. Onat and Kucukvar (2020) reviewed the carbon footprint of the global construction industry from 2009 to 2020 and conducted a macro supply chain analysis. They believe that carbon reduction policies should consider not only limited regional impacts, but also the indirect, complex, and interrelated global supply chain effects of the construction industry. Xue et al. (2023) reviewed research progress on the carbon footprint of food systems and summarized future research content and hot spots. Li et al. (2022) reviewed the carbon footprint of the automotive battery life cycle, summarized the carbon emissions and the main factors influencing batteries at various stages of production, use, secondary utilization, and recycling, and made relevant suggestions. However, although the aforementioned review elaborates on the research status of the carbon footprint of industries or product systems in a certain region, it lacks a detailed summary of carbon footprint-related research from an overall perspective.

To fill the aforementioned gap in the literature, we first outline the international standards and relevant domestic policies for carbon footprint and then conduct quantitative and qualitative analyses to provide a holistic overview of the existing literature on carbon footprint. We use bibliometric methods to quantify the publication volume, influence, and collaboration network of countries/regions, institutions, and journals and conduct a cluster analysis on keywords to review the development and popular topics of carbon footprint research. Subsequently, the methods and research scope of carbon footprint assessment are summarized, and future research directions are proposed. This study provides a comprehensive summary of knowledge in the field of carbon footprint, helping readers understand the popular topics and development trends of carbon footprint literature, thus providing valuable reference for the selection of research methods and objects, and favorable tools for individuals and organizations to participate actively in climate change mitigation actions.

2. Carbon footprint standards and policies

International carbon footprint standards provide consistent methods and requirements for promoting international cooperation and emission reduction actions. Founded in 1947, the International Organization for Standardization (ISO) is the world's largest standardsetting organization. The ISO 14064 (ISO, 2006a) it released provides detailed principles and requirements for organizing GHG inventories such as determining GHG emission and removal boundaries, identifying and quantifying GHG emission sources, and improving GHG management. ISO 14067 (ISO, 2018) is a quantitative requirement and guideline for product carbon footprint that provides a framework for accounting for GHG emissions generated throughout the life cycle of a product. PAS 2050, published by the British Standards Institute, is used to assess GHG emissions from products and is an important reference for many organizations and countries for product carbon footprint assessment (SMQ, 2022). The GHG Protocol is co-sponsored by the World Resources Institute (WRI) and the World Business Council for Sustainable Development (WBCSD). The core standards include the "Corporate Accounting and Reporting Standard" and the "Product Life Cycle Accounting and Reporting Standard", which are used by organizations to measure and report GHG emissions at the corporate and product levels. These standards are widely recognized and adopted internationally, and should be accurately assessed by selecting the appropriate standard based on the specific needs and context of the organization or industry.

There are few relevant evaluation standards for carbon footprint in China currently (SMQ, 2022). The evaluation primarily cites two standards: ISO 14067 and PAS 2050. However, multiple national standards are currently being planned, such as Carbon Footprint of Products -Requirements and Guidelines for Quantification, Carbon Footprint of Electrical and Electronic Products-Requirements and Guidelines for Quantification, Guideline of Carbon Footprint Calculation and Report for Livestock Product, General Principles for Carbon Footprint Accounting of Plastic Products, and so on. In addition, the State Council and various ministries have issued a series of policy guidance opinions on topics related to carbon footprints such as establishing carbon footprint standards, conducting full lifecycle product carbon footprint accounting and certification services, and meeting regulatory conditions to disclose enterprises' carbon footprints and promote social responsibility construction. In November 2023, the National Development and Reform Commission, Ministry of Industry and Information Technology, State Administration for Market Regulation, Ministry of Housing and Urban Rural Development, and Ministry of Transport jointly issued the "Opinions on Accelerating the Establishment of a Product Carbon Footprint Management System", which systematically deployed various key tasks for managing product carbon footprint, including developing product carbon footprint accounting rules and standards, strengthening the construction of carbon footprint background databases, establishing a product carbon labeling and certification system, enriching product carbon footprint application scenarios, and promoting international connection and mutual recognition of carbon footprints.

3. Carbon footprint bibliometric analysis

Most studies use bibliometric tools to examine journals, disciplines, and research hot spots in specific areas and detect trends and key features (Wang et al., 2022). CiteSpace, used in this study, is a common bibliometric analysis software that systematically draws a knowledge graph; analyzes citation nodes to form a visual network, effectively mines research hot spots, journals, and institutions distributions of specific topics, and tracks the forefront of technological development (Jiang et al., 2023).

Web of Science is the world's leading citation database and includes records of papers, conference proceedings, literature, and books from the world's most influential journals. This study conducted a literature search in the Web of Science core collection, using the search formula TS = (carbon footprint), with the search period set from January 1, 2013 to December 31, 2022. Literature from the past decade provides better coverage of current key research and important findings, thus offering significant reference value. The research language and type were set to "English" and "Article". After CiteSpace deduplication and screening, 13 203 articles were identified. Publication volume, collaborative network, co-citation network, and keyword clustering analyses were performed on the selected literature to showcase development trends, influence, and research hot spots in this field.

3.1. Analysis of publication volume

The filtered articles were categorized according to the year of publication. Figure 1 illustrates the total number of publications and publications by domestic authors on carbon footprint over the past decade. The figure shows that the number of carbon footprint articles has been increasing annually, with the total number of publications increasing from 483 in 2013 to 3 041 in 2022-an increase of more than six times over the past decade. The year 2017 was a key milestone in the growth of carbon footprint publications, as the Paris Agreement officially entered its implementation phase on November 4, 2016. Since then, countries have formulated and strengthened their carbon emission reduction commitments and related policies, making the carbon footprint a popular research topic. The domestic author publication volume has also been increasing annually, consistent with the trend in total publication volume. In September 2020, China proposed the goal of peaking carbon emissions and achieving carbon neutrality. The number of articles published by domestic authors subsequently increased rapidly from 377 in 2020 to 798 in 2022.

3.2. Analysis of national and institutional cooperation networks

The samples of carbon footprint-related research for the period 2013 to 2022 were published in 147 countries/regions. Table 1 lists the top 10 in terms of publication volume. The cooperation network shown in Figure 2 reveals the top-ranking countries/regions in terms of influence. In Figure 2, a node represents a country/region; its size represents the number of publications, and the lines indicate cooperation with others. The top three countries/regions in the ranking and their respective number of articles published (in parentheses) were China (2 764), the United States (2 525), and England (1 174). China accounted for approximately 21% of the total number of articles published and had cooperative relationships with 47 countries/regions worldwide, whereas the United States and England cooperated with 64 and 76 countries/regions, respectively.

Over the past decade, 542 institutions conducted carbon footprint research. Figure 3 illustrates the institutional cooperation network. Owing to the large number of institutions, only institutions with intermediary centrality greater than 0.03 are displayed in Figure 3 to demonstrate the network of connections between institutions more clearly. Mediation centrality measures the sum of the probabilities of nodes appearing on any of the shortest path in a network, and demonstrates the importance of node-bridging roles. The Chinese Academy of Sciences, University of Chinese Academy of Sciences, and Beijing Normal University were the top three research institutions in terms of the number of papers issued. They published 375, 146, and 136 carbon footprint articles and conducted academic cooperation with 25, 14, and 14 institutions, respectively. The Chinese Academy of Sciences and the University of Maryland had high intermediary centrality, indicating that these two institutions were most closely connected to other research institutions and had the most cooperative opportunities.

3.3. Analysis of journal co-citation network

Figure 4 shows the results of a journal co-citation analysis conducted on the cited literature on carbon footprint over the past decade. The cited literature came from 914 journals, with 5 423 journal citation links. Figure 4 shows only the influential journals. The Journal of Cleaner Production (with 7 297 citations), Environmental Science & Technology (3 768 citations), and Renewable and Sustainable Energy Reviews (3 724 citations) were the top three most-cited journals in this field. Journal of Cleaner Production had the highest number of citations, and its intermediary centrality was as high as 0.29, making it a key-node journal. In addition, these three journals had cocitation relationships with 29, 24, and 22 other journals, respectively.

3.4. Analysis of keyword clustering

There were 29 899 keywords in the selected articles, occurring 60 114 times. Among these keywords, the term carbon footprint appeared most frequently (2 367 times), and 2.3% of the keywords appeared more than 10 times. A silhouette is a clustering evaluation indicator used to describe the clustering quality. Usually, a silhouette value greater than 0.5 indicates that the clustering results are reasonable. The silhouette value of this clustering was 0.759 8, indicating a good clustering effect. Figure 5 shows the keyword clustering results, comprising seven cluster categories, namely, life cycle assessment (LCA), CO, footprint, input-output analysis (IOA), carbon sequestration, CO, capture, climate change, and ecological footprint, reflecting the key focus of carbon footprint research over the past decade. The two major clustering categories, LCA and IOA, were the main evaluation methods used for carbon footprint research. The relevant methods are introduced in Section 4.

4. Carbon footprint application and practice

4.1. Evaluation methods and tools

Carbon footprint assessment methods usually include "bottomup" LCA (Chew et al., 2023), "top-down" IOA (Jiang, 2022), and hybrid LCA (Egilmez et al., 2017b), but emission factor methods (Xi et al., 2021) can also be used to account for carbon emissions, generally including direct emissions. Table 2 summarizes the advantages, disadvantages, and corresponding research objects of these four methods.

4.1.1. Life cycle assessment

LCA is a systematic assessment of the entire life cycle of a product, including raw material extraction, transportation, production, use, disposal, and recycling (Fenner et al., 2018). The ISO 14040 (150, 2006b) and ISO 14044 (ISO, 2006с) standards stipulate the necessary principles, frameworks, and guidelines. LCA comprises four stages: goal and scope definition, inventory analysis, impact assessment, and result interpretation (Zhao et al., 2023). In the goal and scope stage, the research objectives are clarified, and appropriate system boundaries and functional units are selected. Inventory analysis is the process of determining the required material inputs and waste outputs within the system boundary (Chen-Glasser et al., 2023). In the impact assessment step, the carbon footprint of a product throughout its life cycle is quantitatively evaluated based on the results of the inventory analysis. Finally, the results are explained, possibilities and potential ways to reduce carbon emissions are explored, and corresponding improvement measures are proposed in the result interpretation stage (Xiao, 2022). LCA is a mainstream method in carbon footprint accounting and is more suitable at the micro level for evaluating the carbon footprint of products or services. The European Commission recommends LCA as the best framework for product evaluation (Pérez-López et al., 2017).

LCA is widely used for product carbon footprint assessments, with chemical, food, building material, battery, and energy production being popular topics in research. For example, Zheng and Suh (2019) conducted a study on the lifecycle GHG emissions of 10 traditional plastics and five bio-based plastics worldwide. They found that if the current development trajectory continues, GHG emissions by 2050 will be more than four times those in 2015. However, the active application of renewable energy, recycling, and demand management strategies may make emissions in 2050 comparable to those in 2015. Dalgaard et al. (2014) calculated the carbon footprint of milk production in Denmark and Sweden, and proposed a model that could apply different modeling assumptions or carbon footprint standards for adjustment and switching. Sameer et al. (2019) tested two scenarios of conventional and ultra-high-performance concrete designs for bridges and compared their carbon footprints, demonstrating that ultra-highperformance concrete reduced the carbon footprint by 14%.

Meanwhile, batteries are widely used in mobile electronic devices, electric vehicles, and renewable energy-storage systems, and calculating the carbon footprints of batteries can guide relevant policy formulations. In this regard, Chen et al. (2022b) investigated the carbon footprint of lithium-ion batteries produced in China using the cradle-to-cradle LCA method and proposed battery recycling as the short-term carbon reduction measure and power greening as the long-term carbon reduction measure. In terms of energy production, Oni et al. (2022) calculated the blue hydrogen carbon footprint and found that among the three different technologies of natural gas reforming, self-thermal reforming, and natural gas decomposition, selfthermal reforming had the lowest GHG emissions.

In summary, LCA research identifies key processes and substances from the perspective of the entire lifecycle of products or services, and proposes emission reduction measures to provide scientific support for environmentally friendly and sustainable development. LCA can be applied to quantify the carbon footprint of specific products or services and compare related products or technologies, thereby helping to select more environmentally friendly production methods. It is also flexible in that the scope and precision of the evaluation can be adjusted to improve the model according to specific circumstances. However, process-based LCA relies on inventory data and requires a comprehensive consideration of data collection, measurement, and processing activities to improve data density and accuracy.

4.1.2. Input-output analysis

IOA was originally proposed by American economist Leontief in 1936. This is an analytical method that reflects the relationships between inputs and outputs in various sectors. By transforming the economic relationship between production sectors into a physical relationship of GHG emissions, IOA reflects the exchange process of direct and indirect emissions and allocates them to various sectors or regions (Zhang et al., 2018). IOA models include single-region input- output analysis (SRIO) and multi-region input-output analysis (MRIO), Which are currently well developed (Wang et al., 2017).

SRIO considers the economic system of a specific region, divides it into different industrial sectors, and evaluates the resource demand and environmental impacts of each industrial sector. For example, Zhang et al. (2021) used a demand-driven IOA to explore, for the first time, the historical consumption-based carbon emissions trajectory of Tianjin, a typical industrial city. Zhou et al. (2019) proposed a carbon analysis framework for the information and communication technology industry that accounts for the carbon emissions of different subsectors, thus revealing the mechanisms of formation and change by determining their source sectors, transfer paths, and economic drivers. MRIO considers resource flows and trade activities between different regions or countries, and is commonly used to study issues such as industrial transfer between regions, global supply chains, and international trade (Su and Ang, 2014). Yang et al. (2024) used an MRIO model to track the environmental costs and economic benefits implicit in inter-provincial trade in the construction industry, and constructed a regional environmental index to assess the degree of inequality between regions. Lin and Guan (2023) identified the main trading partners and corresponding industries in China's food manufacturing industry, using an MRIO model to estimate domestic and international carbon footprints. They then decomposed the determining factors of carbon footprint changes, eventually making policy recommendations.

IOA is often combined with methods such as network and structural decomposition analyses to determine the key sectors and factors influencing the carbon footprint. For example, Xu et al. (2021) combined IOA with ecological network analysis to develop energy, water, and carbon ecological networks, searching for complex relationships between different departments in water use, energy consumption, and carbon emissions. Ma et al. (2019) explored carbon emissions in China's power industry through a structural decomposition analysis and found that consumption was the main driving factor for carbon emission growth, whereas power generation efficiency and internal industrial structure were key factors for emission reduction. Yuan et al. (2022) accounted for the carbon footprints of nine provinces in the Yellow River Basin and used social network analysis to identify key industries in the inter-provincial transfer of implied carbon emissions, thus providing a theoretical basis and data support for the development of carbon emission reduction planning in the Yellow River Basin.

SRIO is generally used to quantify industry carbon footprints to determine the contribution of each sector; it can also evaluate economic structure, inter-industry relationships, and the effectiveness of environmental policies. By contrast, MRIO considers economic connections between multiple regions, and is typically used to analyze global or inter-regional carbon transfer and related impacts. Therefore, IOA is not suitable for micro-level product research, but is more suitable for considering the carbon footprint from a macro-level perspective such as the national, urban, industrial, or inter-industry level because it can reflect the economic and technological structures and relationships between various departments and provide strong data support for formulating relevant policies and strengthening macroeconomic management.

4.1.3. Hybrid life cycle assessment

Although LCA has been widely used to study GHG emissions accounting for products or services, a comprehensive LCA is often timeconsuming and laborious for complex systems. Hybrid LCA is a combination of input-output (IO) and process-based LCA and currently has three forms: tiered hybrid LCA (TH LCA), IO-based hybrid LCA (IOH LCA), and integrated hybrid LCA (IH LCA) (Wang et al., 2015). Hybrid LCA integrates technical processes into the macroeconomic system, ensuring the comprehensiveness of the IO and specificity of the process LCA.

Among the three forms of hybrid LCA, the TH LCA is the most commonly used. This approach selects different methods based on the characteristics of the activity data. A process-based LCA is used for clearer process data, whereas an IO-based LCA is used for unknown processes. For example, when comparing the carbon footprint of soil core rockfill dams and concrete gravity dams of the same scale, Zhang et al. (2015) used process-based LCA to analyze the material transportation and construction stages, and IO to analyze the complex upstream production part. The results showed that rockfill dams have a greater environmental advantage throughout their lifecycle and can help decision-makers choose the appropriate type of hydroelectric system during the design phase. Heinonen and Junnila (2011) also used TH LCA to compare and analyze the carbon footprint of consumers in four different urban structures in Finland. The results showed much higher per capita carbon emissions in cities than in suburban and rural areas. However, migration from cities to rural areas may not reduce carbon emissions. The main issue is understanding the significant impact of income on the overall carbon consumption. By contrast, IOH LCA is a method that better corresponds with the product or service being evaluated, as it further divides the existing IO table into sectors or add new sectors, thereby effectively combining the 10 system with process-specific analytical data (Chen et al., 2022a; Wang et al., 2015). Guan et al. (2016) developed an IOH LCA model to quantify the embodied energy of buildings, using IO tables and process analysis data for major building materials, and ultimately proposed various measures to limit the embodied energy of buildings based on the identification of the most intensive energy flows. Meanwhile, the third combined form, IH LCA, requires both high-matrix operations and dense process data, and has fewer applications than the first two types of hybrid LCAs (Wang et al., 2015).

In short, hybrid LCA can be conducted at different levels-product, industry, and region. However, compared with LCA and IOA, the application of mixed LCA is not widespread, mainly because of the lack of a unified mixed framework and the difficulty of data integration. Nonetheless, a hybrid LCA ensures the completeness of the evaluation boundary while improving the accuracy of the evaluation results. It remains a vital tool for carbon footprint accounting and an important development direction for LCA methodology in the future.

4.1.4. Emission factor method

The emission factor method uses emission factors to calculate the emissions and determine the carbon footprint of a research object (Zhang et al., 2018). Jiang et al. (2020) conducted in-depth research and analysis on the direct carbon footprint of residents in Inner Mongolia Autonomous Region from 2000 to 2016 based on an IPCC method and a logarithmic mean division index decomposition model. Their results showed that energy efficiency and economic development are important factors in stimulating residents' direct carbon footprints. Qiu et al. (2022) established a GHG emission inventory for urban sewage treatment plants in five major urban agglomerations in China from 2015 to 2019 based on the emission factor method. They conducted an in-depth analysis of the spatiotemporal distribution, percapita production, and influencing factors, thus providing basic data and a reference for carbon reduction in the sewage treatment industry. The emission factor method is typically used as a basic tool, in conjunction with other methods. Ma et al. (2024) redefined emission factor values based on the IPCC guidelines, constructed a carbon emission accounting method for the entire life cycle of animal husbandry, quantitatively estimated the carbon footprint, and offered carbon reduction suggestions.

The emission factor values can be determined by referring to pertinent data published by the IPCC or according to data published by relevant institutions in China such as the Chinese Academy of Sciences and the Energy Research Institute of the National Development and Reform Commission (Kong et al., 2017). However, these data use statistical averages, and variations exist in the emission factors depending on the technological level, production condition, and energy use. Therefore, when using the emission factor method for calculations, factors such as geography and time must be considered.

4.2. Research scope and object

Carbon footprint accounting can be conducted on different research scales. This study roughly divides the research objects into three categories according to research scope: individuals and households, products and industries, and regions and countries.

4.2.1. Individuals and households

A household's carbon footprint includes emissions associated with direct energy consumption such as lighting, cooking, showering, and heating, as well as emissions associated with the production of all goods consumed by the household in the supply chain (Long et al., 2017). Household consumption accounted for more than 60% of global GHG emissions and 50%-80% of the total resource use in 2016 (Ivanova et al., 2016). An in-depth analysis of GHGs showed an increasing trend of household carbon footprint contributions, indicating that individual and household carbon footprint accounting is imperative (Huang et al., 2023). O'Malley et al. (2023) conducted a study on the dietary choices of a nationally representative sample of American consumers and analyzed the nutritional quality and carbon footprint of different dietary types. Valdelamar-Villegas and FajardoHerrera (2023) estimated the personal carbon footprint of the city of Cartagena through a carbon footprint calculator and social networks and described its relationship with socio-demographic and spatial dimensions. Owing to differences in consumption scales and patterns between individuals and households, most household carbon footprint studies have focused on analyzing inequality issues and exploring its drivers. Wiedenhofer et al. (2017) proposed a distributed carbon footprint for Chinese households and used the carbon footprints Gini coefficient to quantify inequality. Mi et al. (2020) estimated the household carbon footprints of 12 income groups in 30 regions of China and measured the carbon inequality of households in each province. Liang et al. (2023) measured inequality in household carbon footprints in terms of income and consumption categories. Yu et al. (2022) compared the household carbon footprint and its drivers between China and Japan and explored the impact of economic development level on the household carbon footprint.

In essence, both economic development and urbanization lead to higher household-related carbon emissions, and as the family is the basic unit of society, the sustainable development of society requires the participation of every family. Therefore, accounting for the carbon footprint of families and analyzing the carbon footprint behavior of residents and families from the perspective of consumption, it helps guide families to choose healthy and reasonable consumption patterns and encourage low-carbon behaviors such as green travel.

4.2.2. Products and industries

China is increasingly focusing on the establishment of carbon labels for products. Multiple industries, such as textiles and clothing, daily consumer goods, and electrical appliance manufacturing, have begun to promote carbon labels. Moreover, the calculation and evaluation of products' carbon footprints are becoming increasingly com- mon. Liu et al. (2018) constructed a universal carbon-footprint calculation model and quantified the carbon footprints of household appliances using a cloud service platform. Luo et al. (2022) conducted carbon footprints on three types of jeans, and identified garmenting and weaving as key processes and electricity as the main source of carbon emissions.

In addition, enterprises are the producers of products and potential bearers of carbon emission costs, which makes corporate carbon accounting essential. Zhang et al. (2023) tracked carbon emissions in the value chain of listed Chinese companies and found that their carbon footprints showed an increasing trend from 2010 to 2019. Furthermore, industry sectors are interconnected from a macroeconomic perspective; therefore, it is important to analyze the carbon footprint of an entire industry. In this regard, Egilmez et al. (2017a) developed a time-series carbon footprint estimation model to analyze the annual and cumulative carbon footprints of the US manufacturing industry, and thereby identified industries with the highest carbon emissions and carbon-intensive sectors. An evaluation of the entire industry can reveal the overall characteristics or development trends of the carbon footprint. Dai et al. (2024) conducted a comprehensive bottom-up assessment of the net GHG emissions of the domestic papermaking industry in 30 major countries from 1961 to 2019. Their results showed that by 2050, all countries can achieve net zero emissions from the pulp and paper-making industry. Lenzen et al. (2018) quantified the global carbon footprint of the tourism industry and predicted that it would account for an increasing proportion of global GHG emissions.

In summary, quantifying a product's carbon footprint can force companies to manage and improve supply chain sustainability more appropriately, and thus prompt them to improve technology and optimize processes to enhance market competitiveness. An overall analysis of the industry can determine the intensity of the carbon footprint and development trends, reveal ways to adjust the industrial structure from a macro perspective, and encourage various departments to understand and manage the carbon footprint and take corresponding emission reduction measures to promote sustainable development.

4.2.3. Regions and countries

Regional- and national-level carbon footprint research not only focuses on carbon emission accounting but also pays greater attention to factors affecting carbon emissions, the spatial patterns of carbon footprints, and optimization of carbon reduction pathways. Regarding factors that affect carbon emissions, Bruckner et al. (2022) established multiple scenarios for studying the impact of poverty reduction on carbon emissions. Their study emphasized the differences between countries, highlighting the need to take action to prevent a significant increase in carbon emissions due to poverty alleviation. Ribeiro et al. (2019) proposed a general framework to reveal the coupling effect of population and density on carbon emissions, showing that emission changes related to population density changes not only depend on the magnitude of the changes, but also on the initial level of population density.

Furthermore, dynamic information on the spatiotemporal patterns of carbon footprint is crucial for formulating effective national carbon reduction policies. Zhang et al. (2022) applied an exploratory spatiotemporal data analysis framework and an improved Tapio decoupling model to analyze the spatial patterns and dynamic spatiotemporal interactions of China's carbon footprint from 2001 to 2013. Yang et al. (2020) mapped the hot spot map of China's carbon footprint distribution driven by global trade with a high spatial resolution of 10 km x 10 km. They found that the export-driven carbon footprint is concentrated in key manufacturing centers such as the Yangtze River Delta, the Pearl River Delta, and the North China Plain. Chen et al. (2020) revealed the global low-carbon development path of cities from a metabolic perspective, and for the first time combined the gas carbon footprint derived from physical carbon and fossil fuels to track the carbon flow and stock changes in global cities and their potential impacts on future climate change. Considering the inequality and heterogeneity among different regions of the country, Yu et al. (2023) developed a national energy technology model and a regional collaborative emission reduction path optimization model to study the carbon emissions and energy consumption paths of each region, thereby providing a scientific basis for the design of national and local carbon emission dual-control policies.

In short, identifying the factors that influence carbon emissions and understanding the related mechanisms can help clarify the relationship between various factors and carbon emissions, and thus reveal the key development direction. The study of carbon footprint spatial patterns can help identify key emission reduction areas for developing targeted carbon reduction paths according to the characteristics of different regions. Overall, carbon footprint analysis at the regional and national levels best serves policymaking, as it provides decisionmaking reference for accurately implementing "common but different" carbon reduction goals and policies.

5. Conclusion and policy implication

This article provides an overview of the literature on carbon footprints through a combination of quantitative and qualitative analyses. The release of carbon footprint-related standards and policies demonstrates the global emphasis on carbon footprint accounting. China, in its recent policies, has made systematic arrangements to promote and implement further the carbon footprint of key products. A quantitative analysis of the literature shows that the number of studies on carbon footprints has been continuously increasing over the past decade, with Chinese authors accounting for 21% of the total number of publications. Appropriate carbon footprint assessment methods can be selected based on the specific research content. LCA methods are often used to evaluate micro-perspectives, whereas IOA and other methods are often used to evaluate the macro-perspectives of departments, industries, countries, and so on. Both these methods are widely used. Mixed LCA evaluation results are relatively more reliable and represent an important direction for future development. In terms of the scope and objects of carbon footprint research, individual and household carbon footprint research focuses on exploring inequality issues and their drivers. Product and industry carbon footprint research typically identifies key processes or sectors from a supply chain perspective. Meanwhile, regional- and national-level research has mainly explored spatial development patterns and emission reduction paths of the carbon footprint.

Based on these findings, suggestions for future carbon research on footprints are proposed. Firstly, encourage cooperation and exchange between countries, especially between developed and developing ones, to minimize obstacles caused by unbalanced development between regions and countries and establish a framework for jointly addressing the challenges of carbon footprint. Concurrently, reinforce interdisciplinary cooperation, such as the environment, energy, economy, management, and sociology, to provide more comprehensive perspectives and solutions for the formulation and implementation of policies. Moreover, strengthen data quality and standardization in carbon footprint accounting and develop more accurate and efficient measurement and calculation methods, especially the application of artificial intelligence and big data analytics. Additionally, improve the carbon footprint system, develop certification and labeling services, and accelerate the establishment of an online carbon footprint service platform-this involves accelerating the construction of a data infrastructure and compiling accurate emission factors that are in line with the country, province, and even city. Furthermore, it is essential to consider additional factors such as water footprint, land use, and energy consumption alongside the carbon footprint to provide a more comprehensive assessment of sustainability.

Disclosure statement

No potential conflict of interest was reported by the authors.

Funding

This research was supported by the Shandong Provincial Key Research and Development Program [Grant No. 2023SFGC0101], National Key Research and Development Program [Grant No. 2020YFC1910000], and Mount Taishan Scholar Young Expert Program [Grant No. tsqn202103010].

Sidebar

Received 22 April 2024; Accepted 19 September 2024

Footnote

*Corresponding author.

E-mail address: [email protected] (X. Yuan)

References

References

Abulibdeh, A., Jawarneh, R.N., Al-Awadhi, T., Abdullah, M.M., Abulibdeh, R., El Kenawy, A.M., 2024. Assessment of carbon footprint in Qatar's electricity sector: a comparative analysis across various building typologies. Renewable and Sustainable Energy Reviews 189, 114022.

Bruckner, B., Hubacek, K., Shan, Y.L., Zhong, H.L., Feng, K.S., 2022. Impacts of poverty alleviation on national and global carbon emissions. Nature Sustainability 5, 311- 320.

Chen, K.X., Yang, M.X., Zhou, X.L., Liu, Z.L., Li, P., Tang, J.Y., Peng, C.H., 2022. Recent advances in carbon footprint studies of urban ecosystems: overview, application, and future challenges. Environmental Reviews 30, 342-356.

Chen, Q.W., Lai, X., Gu, H.H., Tang, X.P., Gao, F.R., Han, X.B., Zheng, Y.J., 2022. Investigating carbon footprint and carbon reduction potential using a cradle-to-cradle LCA approach on lithium-ion batteries for electric vehicles in China. Journal of Cleaner Production 369, 133342.

Chen, S.Q., Chen, B., Feng, K.S., Liu, Z., Fromer, N., Tan, X.C., Alsaedi, A., Hayat, T., Weisz, H., Schellnhuber, H.J., Hubacek, K., 2020. Physical and virtual carbon metabolism of global cities. Nature Communications 11, 182.

Chen-Glasser, M., Landis, A.E., DeCaluwe, S.C., 2023. Carbon footprint of Li-Oxygen batteries and the impact of material and structure selection. Journal of Energy Storage 60, 106684.

Chew, Z.L., Tan, E.H., Palaniandy, S.A., Woon, K.S., Phuang, Z.X., 2023. An integrated life-cycle greenhouse gas protocol accounting on oil palm trunk and empty fruit bunch biofuel production. Science of the Total Environment 856, 159007.

Dai, M., Sun, M.X., Chen, B., Shi, L., Jin, M.Z., Man, Y., Liang, Z.Y., de Almeida, C.M.V. B., Li, J.S., Zhang, P.F., Chiu, A.S.F., Xu, M., Yu, H.J., Meng, J., Wang, Y. T., 2024. Country-specific net-zero strategies of the pulp and paper industry. Nature 626, 327-334.

Dalgaard, R., Schmidt, J., Flysjó, A., 2014. Generic model for calculating carbon footprint of milk using four different life cycle assessment modelling approaches. Journal of Cleaner Production 73, 146-153.

Egilmez, G., Bhutta, M.K., Erenay, B., Park, Y., Gedik, R., 2017a. Carbon footprint stock analysis of US manufacturing: a time series input-output LCA. Industrial Management & Data Systems 117, 853-872.

Egilmez, G., Mohamed Abdul Ghani, N.M.A., Gedik, R., 2017b. Layer analysis of CO, sources in the US economic supply chains: an input output LCA study. Industrial Management 8: Data Systems 117, 2171-2193.

Fenner, A. E., Kibert, C.J., Woo, J., Morque, S., Razkenari, M., Hakim, H., Lu, X.S., 2018. The carbon footprint of buildings: a review of methodologies and applications. Renewable and Sustainable Energy Reviews 94, 1142-1152.

Gao, X., 2020. Study on carbon-water-ecological footprint of Chinese dietary changes (Master's Dissertation). Dalian: Dalian University of Technology.

Gong, L., Zhang, Z.B., Chen, M., Taylor, S., Wang, X.L., 2023. Study on the carbon footprint of cold storage units using low-GWP alternative refrigerants. Journal of Cleaner Production 430, 139589.

Guan, J., Zhang, Z.H., Chu, C.L., 2016. Quantification of building embodied energy in China using an input-output-based hybrid LCA model. Energy and Buildings 110, 443-452.

Heinonen, J., Junnila, S., 2011. Implications of urban structure on carbon consumption in metropolitan areas. Environmental Research Letters 6, 014018.

Huang, L.Q., Long, Y., Chen, J.D., Yoshida, Y., 2023. Sustainable lifestyle: Urban household carbon footprint accounting and policy implications for lifestyle-based decarbonization. Energy Policy 181, 113696.

ISO, 2006a. ISO 14064-1. https://www. iso. org/standard/66453. html. Accessed on 25 December, 2023.

ISO, 2006b. ISO 14040. https://www.iso.org/standard/37456.html. Accessed April 18, 2024.

ISO, 2006с. ISO 14044. https://www. iso. org/standard/38498. html. Aaccessed April 18, 2024.

ISO, 2018. ISO 14067. https://www.iso.org/standard/71206.html. Accessed on December 25, 2023.

Ivanova, D., Stadler, K., Steen-Olsen, K., Wood, R., Vita, G., Tukker, A, Hertwich, E.G., 2016. Environmental impact assessment of household consumption. Journal of Industrial Economy 20, 526-536.

Jiang, L.N., Li, Q.W., Zhang, W.C., Lu, L.J., Li, J.H., 2020. Analysis of direct carbon footprint of residents" consumption in Inner Mongolia Autonomous Region. IOP Conference Series: Earth and Environmental Science 585, 012020.

Jiang, T.Y., Li, S.Q., Yu, Y., Peng, Y.F., 2022. Energy-related carbon emissions and structural emissions reduction of China's construction industry: the perspective of input - output analysis. Environmental Science and Pollution Research 29, 39515-39527.

Jiang, Y.L., Yang, G., Li, H.J., Zhang, T., 2023. Knowledge driven approach for smart bridge maintenance using big data mining. Automation in Construction 146, 104673.

Kong, F.W., Wang, X.N., Tian, X., 2017. Comparative study on carbon emission in construction phase between prefabrication and traditional residence based on carbon emission factor method. Ecological Economy 33(8), 81-84.

Lenzen, M., Sun, Y.Y., Faturay, F., Ting, Y.P., Geschke, A., Malik, A., 2018. The carbon footprint of global tourism. Nature Climate Change 8, 522-528.

Li, J., 2021. Study on the carbon footprint of Chinese food consumption in the context of urbanization (Doctoral Dissertation). Dalian: Dalian University of Technology.

Li, P.W., Xia, X.N., Guo, J., 2022. A review of the life cycle carbon footprint of electric vehicle batteries. Separation and Purification Technology 296, 121389.

Li, X.J., Zheng, Y.D., 2020. Using LCA to research carbon footprint for precast concrete piles during the building construction stage: a China study. Journal of Cleaner Production 245, 118754.

Liang, L.W., Chen, M.X., Zhang, X.P., 2023. Measuring inequality of household carbon footprints between income groups and across consumption categories in China. Journal of Cleaner Production 418, 138075.

Lin, B.Q., Guan, C.X., 2023. Assessing consumption-based carbon footprint of China's food industry in global supply chain. Sustainable Production and Consumption 35, 365-375.

Liu, G.L., Liu, J.J., Zhao, J.H., Qiu, J., Mao, Y.R., Wu, Z.X., Wen, F., 2023. Real-time corporate carbon footprint estimation methodology based on appliance identification. IEEE Transactions on Industrial Informatics 19, 1401-1412.

Liu, Y., Pan, X., Zhuang, Z., Peng, L., 2018. Research of carbon footprint calculation based on cloud services platform. Development & Innovation of Machinery & Electrical Products 31, 14-16 (in Chinese).

Long, Y., Yoshida, Y., Dong, L., 2017. Exploring the indirect household carbon emissions by source: analysis on 49 Japanese Cities. Journal of Cleaner Production 167, 571-581.

Luo, Y., Zhou, R., Li, X., Zhu, L., Wang, L., Wu, X., Ding, X., 2022. Carbon footprint calculation and assessment of jeans products based on process modularity. Advanced Textile Technology 30, 204-210 (in Chinese).

Ma, J.J., Du, G., Xie, B.C., 2019. CO, emission changes of China's power generation system: input-output subsystem analysis. Energy Policy 124, 1-12.

Ma, Y., Cao, D., Luo, W., Li, G., Zhang, W., Li, Y., 2024. Carbon emission accounting methodology of livestock and poultry breeding industry in China based on life cycle theory. China Environmental Science (5), 2799-2810 (in Chinese).

Mi, Z.F., Zheng, J.L., Meng, J., Ou, J.M., Hubacek, K., Liu, Z., Coffman, D., Stern, N., Liang, S., Wei, Y.M., 2020. Economic development and converging household carbon footprints in China. Nature Sustainability 3, 529-537.

O'Malley, K., Willits-Smith, A., Rose, D., 2023. Popular diets as selected by adults in the United States show wide variation in carbon footprints and diet quality. The American Journal of Clinical Nutrition 117, 701-708.

Onat, N.C., Kucukvar, M., 2020. Carbon footprint of construction industry: a global review and supply chain analysis. Renewable and Sustainable Energy Reviews 124, 109783.

Oni, A.O., Anaya, K., Giwa, T., Di Lullo, G., Kumar, A., 2022. Comparative assessment of blue hydrogen from steam methane reforming, autothermal reforming, and natural gas decomposition technologies for natural gas-producing regions. Energy Conversion and Management 254, 115245.

Pérez-López, P., Ledda, F.D., Bisio, A., Feijoo, G., Perino, E., Pronzato, R., Manconi, R., Moreira, M.T., 2017. Life cycle assessment of in situ mariculture in the Mediterranean Sea for the production of bioactive compounds from the sponge Sarcotragus spinosulus. Journal of Cleaner Production 142, 4356-4368.

Qiu, D., Chen, C., Guo, L., Liu, D., Ma., J., Lei, M., Li, T., Xu, K., Yan, X., 2022. Characteristics of greenhouse gas emissions from municipal wastewater treatment plants in major urban groups of China based on emission factor method. Environmental Engineering 40, 116-122.

Ribeiro, H.V., Rybski, D., Kropp, J.P., 2019. Effects of changing population or density on urban carbon dioxide emissions. Nature Communications 10, 3204.

Sameer, H., Weber, V., Mostert, C., Bringezu, S., Fehling, E., Wetzel, A., 2019. Environmental assessment of ultra-high-performance concrete using carbon, material, and water footprint. Materials 12, 851.

Shan, S., Liu, H., Liu, M., Wang, S., Cui, Y., 2024. Carbon footprint for thermal power industry in China: a review. Power Generation Technology (4), 575-589 (in Chinese).

Shi, S.Q., Yin, J.H., 2021. Global research on carbon footprint: a scientometric review. Environmental Impact Assessment Review 89, 106571.

SMQ, 2022. Current status of carbon footprint standards at home and abroad research report. https://www. sist. org. cn/fwzl/Biaozhun/szbzllyj/202302/ P020230221455299318533.pdf. Accessed on January 26, 2024.

Su, B., Ang, B.W., 2014. Input-output analysis of CO, emissions embodied in trade: a multi-region model for China. Applied Energy 114, 377-384.

UNFCCC, 2023. NDC Registry. https://unfccc.int/NDCREG. Accessed on December 16, 2023.

Valdelamar-Villegas, J.C., Fajardo-Herrera, R., 2023. An approach to acquiring knowledge of the personal carbon footprint in Cartagena, in the Colombian Caribbean region. Environmental & Socio-economic Studies 11, 65-72.

Wang, C., Zhang, L., Pang, M., 2015. A review on hybrid life cycle assessment: development and application. Journal of Natural Resources 30, 1232-1242 (in Chinese).

Wang, J.T., Zhou, Y., Cooke, F.L., 2022. Low-carbon economy and policy implications: a systematic review and bibliometric analysis. Environmental Science and Pollution Research 29, 65432-65451.

Wang, Y., Zhou, Y., Zhang, R., 2017. A review of the research methods on influencing factors of carbon emissions and carbon footprint. Environmental Engineering 35, 155-159.

Wiedenhofer, D., Guan, D.B., Liu, Z., Meng, J., Zhang, N., Wei, Y.M., 2017. Unequal household carbon footprints in China. Nature Climate Change 7, 75-80.

Xi, J.R., Gong, H., Zhang, Y.J., Dai, X.H., Chen, L., 2021. The evaluation of GHG emissions from Shanghai municipal wastewater treatment plants based on IPCC and operational data integrated methods (ODIM). Science of the Total Environment 797, 148967.

Xiao, X., 2022. Study on life cycle carbon emission and life cycle cost of green buildings. Master's Dissertation. Beijing: Beijing Jiaotong University.

Xu, W.H., Xie, Y.L., Cai, Y.P., Ji, L., Wang, B.S., Yang, Z.F., 2021. Environmentallyextended input-output and ecological network analysis for Energy-Water-CO, metabolic system in China. Science of the Total Environment 758, 143931.

Xue, J., Xu, M., Zhang, J., 2023. Proceedings in carbon footprint research of food systems. Journal of Eco-Agriculture 32(2), 196-205.

Yang, Y.T., Qu, S., Cai, B.F., Liang, S., Wang, Z.H., Wang, J.N., Xu, M., 2020. Mapping global carbon footprint in China. Nature Communications 11, 2237.

Yang, Z.Y., Zhang, B., Yang, Y.T., Qin, B.B., Wang, Z.H., 2024. Interprovincial inequality between economic benefit and carbon footprint: perspective from China's construction industry. Environmental Impact Assessment Review 104, 107293.

Yu, B.Y., Zhao, Z.H., Wei, Y.M., Liu, L.C., Zhao, Q.Y., Xu, S., Kang, J.N., Liao, H., 2023. Approaching national climate targets in China considering the challenge of regional inequality. Nature Communications 14, 8342.

Yu, F., Dong, H.J., Geng, Y., Fang, A.S., Li, H.F., 2022. Uncovering the differences of household carbon footprints and driving forces between China and Japan. Energy Policy 165, 112990.

Yuan, X.L., Sheng, X.R., Chen, L.P., Tang, Y.Z., Li, Y., Jia, Y.S., Qu, D.F., Wang, Q.S., Ma, Q., Zuo, J., 2022. Carbon footprint and embodied carbon transfer at the provincial level of the Yellow River Basin. Science of the Total Environment 803, 149993.

Zhang, C.Y., Zhao, L., Zhang, H.T., Chen, M.N., Fang, R.Y., Yao, Y., Zhang, Q.P., Wang, Q., 2022. Spatial-temporal characteristics of carbon emissions from land use change in Yellow River Delta region, China. Ecological Indicators 136, 108623.

Zhang, M., Zhang, J., Li, W., Zhang, Y., Lin, S., 2023. Review on research of crop carbon footprint accounting in China. Chinese Journal of Agricultural Resources and Regional Planning 44, 148-154 (in Chinese).

Zhang, Q.F., Fang, K., Xu, M., Liu, Q.Y., 2018. Review of carbon footprint research based on input-output analysis. Journal of Natural Resources 33(4), 696-708 (in Chinese).

Zhang, S.R., Pang, B.H., Zhang, Z.L., 2015. Carbon footprint analysis of two different types of hydropower schemes: comparing earth-rockfill dams and concrete gravity dams using hybrid life cycle assessment. Journal of Cleaner Production 103, 854-862.

Zhang, Y., Bai, H.T., Hou, H.M., Zhang, Y., Xu, H., Ji, Y.J., He, G., Zhang, Y.X., 2021. Exploring the consumption-based carbon emissions of industrial cities in China: a case study of Tianjin. Environmental Science and Pollution Research 28, 26948- 26960.

Zhang, Z.K., Li, J.Y., Guan, D.B., 2023. Value chain carbon footprints of Chinese listed companies. Nature Communications 14, 2794.

Zhao, Y.X., Yang, Z.F., Niu, J.J., Du, Z.H., Federica, C., Zhu, Z., Yang, K.C., Li, Y., Zhao, B.F., Pedersen, T. H., Liu, С. G., Emmanuel, M., 2023. Systematical analysis of sludge treatment and disposal technologies for carbon footprint reduction. Journal of Environmental Sciences 128, 224-249.

Zheng, J.J., Suh, S., 2019. Strategies to reduce the global carbon footprint of plastics. Nature Climate Change 9, 374-378.

Zhou, X.Y., Zhou, D.Q., Wang, Q.W., Su, B., 2019. How information and communication technology drives carbon emissions: a sector-level analysis for China. Energy Economics 81, 380-392.