Exploring the drivers for the synergy of pollutant mitigation and carbon reduction: Evidence from Chinese cities

Global climate change, marked by persistent warming trends, has emerged as one of the foremost challenges confronting human society in the 21st century. Systematically promoting carbon peak and neutrality has become a critical priority for governments in China. As the most active urbanization region in the country, metropolitan areas assume a pivotal leadership and exemplary role in executing carbon peak and neutrality initiatives. Consequently, we focus our research on the Chang-Zhu-Tan Metropolitan Area (CMA). The STIRPAT and CA-Markov models are employed to forecast carbon sinks and carbon emissions under various scenarios in 2030 and 2060, respectively, to explore pathways to carbon neutrality under various conditions. The findings indicate that the carbon surplus and deficit (CSD) values have consistently been negative from 2000 to 2020, signifying a persistent carbon deficit in the region, which has exhibited an upward trend. Notably, the CSD in Yuelu, Ningxiang, and Changsha experienced the most significant increases, particularly in Yuelu, where it reached - 11.22 × 106 t by 2020. Depending on the combinations of scenarios, the CSD values are anticipated to range from - 130.75 × 106 t to - 98.22 × 106 t in 2030, and from - 63.28 × 106 t to - 21.22 × 106 t in 2060. Furthermore, the carbon emissions under different scenarios are projected to reach peaks in 2030, with a maximum of 66.54 × 106 t in 2060. The prediction results of carbon neutrality in the CMA indicate that carbon emission is expected to reach peaks before 2030 across various scenarios. However, carbon emissions will significantly exceed the carbon sink capacity by 2060, and there is still a carbon emission gap of at least 2122.44 × 104 t from achieving carbon neutrality, highlighting the necessity of accelerating emission reduction in the industrial and energy sectors. Consequently, the critical challenge to achieve carbon neutrality lies in the substantial reduction of carbon emissions.

Summary Cities, contributing more than 75% of global carbon emissions, are at the heart of climate change mitigation. Given cities' heterogeneity, they need specific low-carbon roadmaps instead of one-size-fits-all approaches. Here, we present the most detailed and up-to-date accounts of CO2 emissions for 294 cities in China and examine the extent to which their economic growth was decoupled from emissions. Results show that from 2005 to 2015, only 11% of cities exhibited strong decoupling, whereas 65.6% showed weak decoupling, and 23.4% showed no decoupling. We attribute the economic-emission decoupling in cities to several socioeconomic factors (i.e., structure and size of the economy, emission intensity, and population size) and find that the decline in emission intensity via improvement in production and carbon efficiency (e.g., decarbonizing the energy mix via building a renewable energy system) is the most important one. The experience and status quo of carbon emissions and emission-GDP (gross domestic product) decoupling in Chinese cities may have implications for other developing economies to design low-carbon development pathways.

Studying the spatiotemporal evolution and inequality characteristics of the marginal cost of carbon reduction at the city level is crucial for formulating effective and fair carbon reduction policies. Using panel data from 236 prefecture-level cities in China during the period 2006-2019， this study employed a directional distance function parameter estimation method to measure the marginal carbon dioxide reduction costs in cities in China. Building on this result， the study analyzed the temporal and spatial evolution， classification， inequality， and spatial convergence characteristics of these marginal reduction costs using models such as kernel density functions， the Dagum Gini coefficient， and spatial convergence. The key findings are as follows： ①From 2006 to 2019， China's marginal carbon reduction cost （measured in CO2e） showed a trend of first declining and then rising. The average value first decreased from 7.45 thousand yuan per ton to 5.58 thousand yuan per ton and then increased to 20.36 thousand yuan per ton. ②The curve of China's marginal carbon reduction cost showed a U-shaped trend over the period 2006-2019， with the majority of cities positioned to the left of the lowest point. ③The inequality in China's marginal carbon reduction costs followed a pattern of initial increase followed by decrease. The overall Gini coefficient declined from 0.220 in 2006 to 0.151 in 2019. ④From 2006 to 2019， China's city-level marginal reduction costs demonstrated σ-convergence characteristics and supported the β-spatial convergence mechanism. There was significant heterogeneity in reduction costs across different economic regions， and the classification of city-level marginal reduction costs showed a trend toward polarization. Although China has achieved some results in carbon reduction， the task difficulty and cost have gradually increased as carbon reduction action has increased. Therefore， to facilitate the coordinated reduction of carbon reduction costs across cities in China， the government should establish inter-city collaborative mechanisms for emissions reduction， promote the coordinated development of green and low-carbon industries among cities， enhance the collaborative application of energy efficiency and energy-saving technologies across urban areas， deepen the collaborative advancement of environmental education and public participation， and innovate the design of inter-city financing models and incentive mechanisms. This would not only help to reduce emission reduction costs but also promote the balanced development of the regional low-carbon economy， helping to achieve the Twin Carbon Targets.

In the pursuit of China’s environmental targets to achieve a carbon peak by 2030 and carbon neutrality by 2060, the carbon emission trading scheme (CETs) has emerged as a critical policy instrument. Since the 14th Five-Year Plan, China has been on a two-wheel drive to prevent pollution and combat climate change and proposes to fight the Blue Sky Defense. Therefore, this study focuses on prefecture-level cities in China and employs a spatial difference-difference (SDID) model to investigate the spatial spillover effects of CETs on urban total factor carbon emission efficiency (TFCEE). Furthermore, a mediating effect model is constructed to explore the channels through which CETs influence carbon emission efficiency. The results show that (1) implementing urban CETs can significantly improve urban itself and the surrounding carbon emission efficiency. (2) The CETs can indirectly promote the improvement of carbon efficiency by optimizing the allocation of labor resources and strengthening the level of green technology innovation. (3) Compared with the cities in central and western China, implementing the CETs has a stronger promotion effect on the carbon emission efficiency of the cities in eastern China.

A dimensional perspective-based analysis on the practice of low carbon city in China

This paper aims to establish a more standardized and regulated carbon emission accounting model for sponge cities by unifying the accounting content for carbon emissions and clarifying the relationships between carbon reduction benefits, carbon reduction effects, and carbon sequestration, in order to evaluate the carbon reduction outcomes and mechanisms of sponge city construction. Based on a Life Cycle Assessment (LCA) carbon emission accounting model using the carbon emission factor method, a newly constructed residential area in Tianshui City, Gansu Province, was selected as a case study, and the carbon emission reduction effect of sponge city construction was then investigated. Results indicated that the 30-year full life cycle carbon emissions for sponge city construction in the newly constructed residential area amounted to 828.98 tons, compared to 744.28 tons of CO2 reduction in traditional construction, representing a 47.31% reduction in carbon emissions. Over a 30-year life cycle, this equated to a total carbon emission reduction effect of 1460.31 tons. Additionally, under various rainfall scenarios in a typical year, the carbon emission reduction effect of sponge city construction exceeded the carbon emissions, achieving carbon neutrality within 22 to 30 years of operation. This demonstrates that the carbon emission reduction effect of sponge city communities is significant. The findings of this study provide data and a theoretical basis for the low-carbon construction of sponge cities in China.

How does digital economy empower pollution mitigation and carbon reduction? Evidence from Chinese cities

Synergistic effects of pollution and carbon reduction forms the core of ecological civilization construction in the “14th Five-Year Plan” period. Based on the panel data of prefecture-level cities in China from 2012 to 2023, first, the baseline regression model and the spatial panel Durbin model are used to discuss the direct and spatial effects of industrial digitization on synergistic effects of pollution and carbon reduction. Second, based on whole-process management, through the construction of a multiple intermediary effects model, the indirect impact of industrial digitization on synergistic effects of pollution and carbon reduction was explored. Third, heterogeneity tests from multiple perspectives are conducted. It is found that: (1) industrial digitalization has a remarkable positive impact on synergistic effects of pollution and carbon reduction, and there is a positive spillover effect. (2) Industrial digitization can indirectly promote synergistic effects of pollution and carbon reduction by strengthening “Source prevention” through renewable energy substitution, enhancing “process control” through green process innovation, and strengthening “end-of-pipe treatment” through environmental regulations. (3) Industrial digitization has a more remarkable promoting effect on synergistic effects of pollution and carbon reduction in energy basins, higher-level cities, large cities, and urban agglomerations. The research conclusions promote traditional industries to use the “digital cloud” to help the combined development of pollution and carbon reduction and offer a scientific foundation and theoretical reference for promoting industrial digitization to empower synergistic effects of pollution and carbon reduction.

Now, China has made it clear that it will strive to have CO2 emissions peak before 2030 and achieve carbon neutrality before 2060 (the “dual carbon” goals), based on the logic that carbon peaking is a prerequisite for carbon neutrality. The year 2021 is the first year of China’s 14th Five-Year Plan period. As the main battlefields to achieve the “dual carbon” goals, cities are also required to build on their pathways towards such goals under new conditions. Based on the progress China has made with pilot cities for low-carbon development and the discussion on 60 cities by category, this paper identifies the commonalities and differences between Chinese cities’ pathways towards carbon peaking, and concludes that Chinese cities need to peak their carbon emissions in an organized and step-wise way on the basis of classification and according to their own development level and emission characteristics. In light of the above conclusion, this paper provides feasible suggestions for Chinese cities’ carbon peaking.

As one of a number of crucial policies for achieving the goal of "double carbon", it is crucial to investigate the "carbon neutral" effect of the carbon trading market (CTM) in the pilot phase, which is an essential reference for the development of a future CTM. Based on panel data of 283 cities in China in the period from 2006 to 2017, this paper examines the impact of the Carbon Trading Pilot Policy (CTPP) on the achievement of the "carbon neutrality" target. The study shows that the CTPP market can promote an increase in regional net carbon sinks and further accelerate the achievement of the "carbon neutrality" goal. The findings of the study remain valid after a series of robustness tests. The mechanism analysis finds that the CTPP can help achieve the carbon neutrality target through three mechanisms: the effect on concern for the environment, the effect on urban governance, and the effect on energy production and consumption. Further analysis reveals that enterprises' willingness and productive behavior, as well as the internal elements of the market, have a positive moderating effect on the achievement of the carbon neutrality target. In addition, there is heterogeneity among regions with different technological endowments, CTPP regions, and regions with different shares of state-owned assets in the CTM. This paper provides important practical references and empirical evidence that can help China to better achieve the "carbon neutrality" target.

Collaborative governance of pollution reduction and carbon reduction is the core path and key starting point to promote green and low-carbon transformation, and helps to achieve two-way empowerment of environmental quality improvement and carbon peak and carbon neutrality. In the face of the prominent contradiction between the current distribution of energy resources and the reverse mismatch of demand, solving the contradiction of energy spatial mismatch and optimizing the geographical layout of energy have become the strategic fulcrum to ensure energy security and efficiency. Based on this, this study uses the panel data of 77 prefecture-level cities in China from 2012 to 2022, and firstly uses the fixed effect model to explore the direct relationship between energy spatial mismatch and collaborative governance of pollution reduction and carbon reduction. Secondly, this paper explores the transmission mechanism of energy spatial mismatch in collaborative governance of pollution reduction and carbon reduction with energy consumption intensity as the constraint variable. The results show that: (1) The energy spatial mismatch has a significant inhibitory effect on the collaborative governance of pollution reduction and carbon reduction. (2) Alleviating energy spatial mismatch can reduce energy consumption intensity and indirectly improve collaborative governance of pollution reduction and carbon reduction. The research conclusions provide theoretical basis and practical path reference for optimizing the collaborative development mechanism of environmental protection industry and clean energy industry in energy rich areas, and promoting the construction of sustainable collaborative governance system of pollution reduction and carbon reduction.

The synergistic development of digital transformation and carbon neutrality is a key path to global sustainable development. This study utilized the Broadband China pilot policy and a multi-period Difference-in-Differences (DID) design to comprehensively evaluate the impact of digital infrastructure on carbon neutrality using panel data from 291 prefecture-level cities in China from 2008 to 2021. The results indicate that regional digital infrastructure contributed to carbon neutralization innovation, carbon-intensive industry innovation, and carbon-emission efficiency in the pilot areas. This held true after analyzing the results with propensity score matching, coarsened exact matching, robust estimators, and instrumental variable regression. Specifically, the results of the mediation effect model indicate that digital infrastructure promotes the process of carbon neutrality through several mechanisms, including promoting the rationalization of industrial structure, promoting digital economic development, and inducing innovation in digital technology. In addition, cities with better economic development, lower resource dependence, and weaker environmental constraints have a greater carbon neutrality dividend effect from regional digital infrastructure. These findings indicate a need to optimize policies to unleash the dividends of digital infrastructure in carbon neutrality, which can drive technological, structural, and efficiency changes through digital empowerment. In addition, cities with heterogeneous endowments need to develop targeted measures.

Does the digital economy contribute to carbon emissions reduction? A city-level spatial analysis in China

The synergy between carbon neutrality and urbanization is essential for effective climate governance and socio-ecological intelligent transition. From the perspective of coupled urban dynamic evolution and carbon metabolism systems, this study integrates the Sen-MK trend test and the geographical detector model to explore the spatial–temporal differentiation patterns and driving mechanisms of carbon balance across 337 prefecture-level cities in China from 2012 to 2022. The results reveal a spatial–temporal mismatch between carbon emissions and carbon storage, forming an asymmetric carbon metabolism pattern characterized by “expansion-dominated and shrinkage-dissipative” dynamics. Carbon compensation rates exhibit a west–high to east–low gradient distribution, with hotspots of expansionary cities clustered in the southwest, while shrinking cities display a dispersed pattern from the northwest to the northeast. Based on the four-quadrant carbon balance classification, expansionary cities are mainly located in the “high economic–low ecological” quadrant, whereas shrinking cities concentrate in the “low economic–high ecological” quadrant. Industrial structure and population scale serve as the dual-core drivers of carbon compensation. Expansionary cities are positively regulated by urbanization rates, while shrinking cities are negatively constrained by energy intensity. These findings suggest that differentiated regulation strategies can help optimize carbon governance within national territorial space.

Can China's carbon trading policy help achieve Carbon Neutrality? — A study of policy effects from the Five-sphere Integrated Plan perspective