Characterization of Spatial and Temporal Divergence and Coupling of Net Agricultural Carbon Sinks in China: A Case Study from 2000 to 2022

Developing policies to reduce carbon emissions in agriculture is crucial for achieving the ‘dual carbon’ goal. Therefore, scientifically analysing the temporal and spatial distribution characteristics of agricultural carbon sinks and their driving factors holds paramount importance for the coordinated and integrated development of regional agriculture and the realization of sustainable development. Based on the perspective of carbon cycle in agricultural production, the measurement system of agricultural net carbon sink was established from the perspective of carbon sink/carbon source, this study conducted an analysis of the temporal and spatial variation characteristics as well as driving mechanisms of agricultural net carbon sinks. The findings are as follows: (1) The agricultural net carbon sink exhibited an increasing trend from 2009 to 2020, with favourable intensity and level. (2) Agricultural land use and livestock and poultry production constituted the primary sources of agricultural carbon emissions. Notably, agricultural carbon emissions demonstrated a decreasing trend during the study period. (3) The net agricultural carbon sink displayed local spatial aggregation, indicating significant regional differences. (4) Factors such as rural economic level, urbanization level and agricultural employment significantly promoted the net carbon sink. In contrast, the rural industrial structure, technical level and crop seeding had inhibitory effects. Therefore, it is imperative to promote the reduction of agricultural carbon emissions in the Beijing-Tianjin-Hebei region. This entails accelerating the construction of new agriculture and rural areas, facilitating industrial upgrading, promoting the development of low-carbon-sink regions into high-carbon-sink regions and actively fostering the coordinated and integrated development of regional agriculture.

Analysis of the spatial mismatch pattern of net carbon in agriculture and its influencing factors

Based on the panel data of prefecture-level cities and above and provincial-level cities in the Yangtze River Economic Belt, respectively, this study measured the agricultural carbon emissions, carbon sinks, and carbon offset rates from 2006 to 2021 and analyzed their evolution characteristics. Based on the STIRPAT model and ridge regression analysis, this study identified the factors affecting agricultural carbon emissions in the 11 provinces and municipalities in the Yangtze River Economic Zone, combined them with the scenario analysis method to predict the agricultural carbon emissions under the baseline scenario in the period of 2022 to 2025, and analyzed the process of "carbon peaking." Simultaneously, this study predicted the agricultural carbon sinks of 11 provinces and cities from 2022 to 2025 and then speculated their agricultural "carbon neutral" process under the framework of agricultural carbon compensation rate, so as to summarize the effective paths for different provinces and cities to achieve agricultural "carbon peak and carbon neutral." The results showed that： ① Changes in agricultural carbon emissions in the Yangtze River Economic Zone during the observation period followed an inverted U-shape and peaked in 2015 at 33 312.65×104 tons. The fluctuation of agricultural carbon sinks was relatively small, with an overall upward trend. The upward trend of the agricultural carbon offset rate was obvious, but it still belonged to the "net carbon emission" region. ② Regional differences of agricultural carbon offsetting rate were prominent, and there was a polarization phenomenon, with "net carbon sink" cities significantly less than "net carbon emission" cities. ③ Shanghai, Zhejiang, and Sichuan reached the peak of agricultural carbon emissions in 2006, which Anhui and Chongqing reached in 2012, and the rest of the provinces and municipalities showed a clear upward trend. ④ Anhui, Chongqing, Sichuan, and Yunnan crossed the "agricultural carbon neutral line" and achieved agricultural carbon neutrality. Jiangsu was expected to achieve this in 2026-2030, whereas the remaining provinces and municipalities faced greater difficulties.

The farmland system in the global terrestrial ecosystem has dual attributes as both a carbon source and a carbon sink, playing a crucial role in controlling carbon emissions and mitigating global warming. Using carbon source and sink accounting of farmland ecosystems, we applied methods such as standard deviation ellipse, Tapio decoupling theory, and Markov chain to analyze the spatiotemporal changes, response mechanisms, and evolutionary trends of regional carbon effects. The results indicated that from 2011 to 2021, the farmland ecosystem in the middle and lower reaches of the Yangtze River consistently acted as a carbon sink. However, the net carbon sink showed slight fluctuations and significant spatial differences. The migration range of the net carbon sink center in the farmland ecosystem of the middle and lower reaches of the Yangtze River was relatively small, ranging from 115.52 to 115.77° E and 30.14 to 30.27° N. The decomposition of the Tapio decoupling index between the net carbon sink of the farmland ecosystem and agricultural output value showed the order of effects on their coupling relationship as follows: agricultural mechanization level > agricultural mechanization efficiency > agricultural output value > planting scale. The probability of maintaining the original state of net carbon sink in various cities in the middle and lower reaches of the Yangtze River (over 77%) was much higher than the probability of transfer, making it difficult to achieve a leapfrog growth in net carbon sink. The net carbon sink at the city scale exhibits the Matthew effect and spatial spillover effect. The above research results clarify the spatiotemporal changes in carbon effects in agricultural production at multiple levels, including city, province, and region. They also provide a theoretical basis for formulating differentiated regional emission reduction and sink enhancement strategies in the middle and lower reaches of the Yangtze River, promoting the rapid development of low-carbon agriculture in China.

Modelling the impact of future changes in climate, CO 2 concentration and land use on natural ecosystems and the terrestrial carbon sink

Exploring the impact of digital inclusive finance on agricultural net carbon sink efficiency has theoretical and practical significance for enriching the theoretical system of digital finance and promoting the quality and efficiency of agricultural low-carbon development. Based on the data of 30 provinces and municipalities in China from 2011 to 2020, the Malmquist index method is used to measure the carbon emission efficiency, the panel threshold model is used to explore the direct impact of digital inclusive finance on the efficiency of agricultural net carbon sink, and the stepwise regression method is used to explore the indirect impact of technological innovation as an intermediary. In view of geographical location and policy inclination, the heterogeneity of its impact effect is further studied. Digital inclusive finance has a positive effect on the efficiency of agricultural net carbon sinks, and the effect is different in different threshold ranges of digital inclusive finance. The effect in the low value area of digital inclusive finance is greater than that in the high value area. There is a nonlinear relationship between the two. Technological innovation is an important channel to affect the efficiency of agricultural net carbon sinks. There are time differences in the impact of digital inclusive finance and agricultural net carbon sink efficiency, and the positive promotion effect at this stage is significantly higher than that before 2016. The impact of digital inclusive finance in regions with low economic development is higher than that in regions with high economic development. It is proposed to strengthen digital financial services and promote the promotion of digital inclusive finance in the agricultural field; reduce regional development differences and implement heterogeneous governance strategies to appropriately regulate digital financial supervision; through financial subsidies and other ways to encourage farmers and agricultural enterprises to adopt low-carbon agricultural technology and management methods, improve the efficiency of net carbon sinks and other recommendations.

People are the fundamental purpose and driving force of agricultural development. The changes in population structure can directly affect social and economic development of rural areas and the entire process of agricultural production. This paper takes Huan County in the Loess Hilly Region of China as the evaluation object, the townships as the evaluation unit, the change of rural population structure as the key point, and the agricultural production as the mediating factor, to study the mechanism of agricultural net carbon sinks. The results show: 1) From 2009 to 2018, the number of rural labor force in Huan County was seriously lost, the quality of the labor force was steadily improved, and the age of the labor force was increased. The number of agricultural employees dropped from 72.6 to 49.4%. The number of people with high school education or above increased from 9.7 to 15.1%. Those over working age who participated in the labor force rose from 5.2 to 8.3%. 2) The Loess Hilly Region in the northwest of Huan County was “grain-trending,” and the River Valley and Plain Area in the southeast was “grain-removing.” The input structure index both increased first and then decreased. and the Loess Hilly Region was more dependent on the fertilizer. 3) The rural population structure affects the agricultural net carbon sink by affecting the planting structure index and the input structure index. The rural population quantity and quality structure have a significant positive effect on the agricultural net carbon sink, while the population age structure has a significant negative effect on the agricultural net carbon sink. 4) From the mediating effect, the loss of population can cause fluctuations in the agricultural net carbon sink. The improvement of population quality will promote the growth of the agricultural net carbon sink, and the aging of the population will cause the decline of the agricultural net carbon sink. 5) The return of the labor force, the improvement of labor force quality, the improvement of production methods, technological innovation, and skill training are the main ways to increase agricultural net carbon sinks and reduce emissions. This paper can lay a solid foundation for realizing the overall emission reduction target of agricultural production in the Loess Hilly Region.

Effects of land-use conversion from Masson pine forests to tea plantations on net ecosystem carbon and greenhouse gas budgets

Considering the comparative perspective of the net agricultural carbon effect in China’s three major functional grain production areas, the Dagum Gini coefficient, kernel density estimation and Markov chain analysis are used to investigate the spatial disequilibrium and dynamic evolution characteristics of the net agricultural carbon effect in China from 2000 to 2019. The results show that the overall net agricultural carbon sink in China is on a fluctuating upward trend, and the net agricultural carbon sink in the main production areas is higher than that in main marketing areas and balanced production and marketing areas. There are obvious differences in the net agricultural carbon sink between different areas, and the differences are expanding; inter-regional differences are the most significant, with the contribution of intra-regional differences second and the contribution of intensity of transvariation the least. The kernel density curve shows that the absolute differences are increasing and that there are gradients and multipolar differentiation within the area. The Markov transfer matrix reflects that the net agricultural carbon effect in China is highly volatile and has a strong internal mobility. The probability of upward shift in an area increases when it is adjacent to a high-level area, and the net carbon effect of agriculture in high-level areas has a strong stability. Based on this, each area should build on its own comparative advantages and explore targeted pathways to reducing emissions and increasing sinks in agriculture while strengthening inter-regional communication and cooperation. It is necessary to build a synergistic mechanism to enhance the net carbon effect of agriculture, which will ultimately help to achieve the “double carbon” target.

As an important industry in ecologically fragile areas, the synergy of agricultural pollution control and carbon reduction is vital for the balanced development of industries and regional synergy. This paper aims to explore the synergistic result of agricultural pollution control and carbon reduction in ecologically fragile areas so as to clarify the weak links and solve carbon pollution in ecologically fragile areas. Leveraging the 2006–2021 municipal data of ecologically fragile areas, this paper calculates the coupling coordination degree (CCD) of agricultural non-point source pollution and agricultural carbon emission in ecologically fragile areas; calculates the decoupling relationship between agricultural carbon emissions, pollutants, and gross agricultural output based on the Tapio decoupling index; and quantitatively depicts the synergy of agricultural pollution control and carbon reduction in ecologically fragile areas. From 2006 to 2021, agricultural carbon emissions in ecologically fragile areas depicted a fluctuating and increasing trend. Agricultural non-point source pollution depicted an “inverted U-shaped” growth trend. The emission trends of agricultural carbon emissions and agricultural pollutants depict that although agricultural pollutants and carbon emissions are homologous, there is heterogeneity in the trend and change in emissions. The synergistic results of agricultural pollution control and carbon reduction show a fluctuating upward trend in ecologically fragile areas, and the coordination degree of ecologically fragile areas increased from 0.32 to 0.89, indicating that the level of coordinated development between agricultural pollution control and carbon reduction increased significantly. Taking into account the decoupling effect, the decoupling state of agricultural carbon pollution synergistic economic growth in ecologically fragile areas has changed from negative decoupling to strong decoupling to weak decoupling, mainly in the state of strong decoupling, negative decoupling of expansion, and weak decoupling; in addition, the synergistic capacity of agricultural pollution control and carbon reduction needs to be further optimized. Based on the research results, there is some room for improvement in agricultural carbon pollution synergy in ecologically fragile areas, and regions should strengthen regional cooperation.

Peatlands are important global stores of carbon. However, peatland disturbance, including climate change, can cause stored carbon to be released, shifting peatlands from net carbon sinks to net carbon sources. Yet, there is a paucity of data on the carbon cycling of Australian peatlands from which to inform effective management of the peatland carbon store. Here, we present the first estimation of the seasonal and annual net ecosystem carbon balance (NECB) of an intact Sphagnum-dominated peatland in the Australian Alps. We measured the net ecosystem exchange of CO2 (NEE), methane emission (CH4), and aquatic fluxes of dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC), over a two-year period. Overall, the ecosystem acted as a strong net carbon sink of -292.5gCm-2yr-1. The annual NECB exhibited distinct intra-annual variability, shifting from a strong carbon sink in the growing period (-444.1gCm-2period-1) to a carbon source in the non-growing period (151.6gCm-2period-1). Estimates of non-CO2 fluxes were relatively small: emission of CH4 was 2.4g CH4-C m-2yr-1; DOC flux was 8.7gCm-2yr-1; and evasion flux was 18.5gCm-2yr-1; together comprising <10% of annual NECB. The large observed net carbon uptake suggests that the carbon sequestration potential of the study site is exceptionally high, likely due to its occurrence in a temperate region with a relatively long growing period.

CO2 fluxes were measured continuously for three years (2003–2005) using the eddy covariance technique for the canopy layer with a height of 27 m above the ground in a dominant subtropical evergreen forest in Dinghushan, South China. By applying gapfilling methods, we quantified the different components of the carbon fluxes (net ecosystem exchange (NEE)), gross primary production (GPP) and ecosystem respiration (Reco) in order to assess the effects of meteorological variables on these fluxes and the atmospherecanopy interactions on the forest carbon cycle. Our results showed that monthly average daily maximum net CO2 exchange of the whole ecosystem varied from −3.79 to −14.24 μmol m−2 s−1 and was linearly related to photosynthetic active radiation. The Dinghushan forest acted as a net carbon sink of −488 g C m−2 y−1, with a GPP of 1448 g Cm−2 y−1, and a Reco of 961 g C m−2 y−1. Using a carboxylase-based model, we compared the predicted fluxes of CO2 with measurements. GPP was modelled as 1443 g C m−2 y−1, and the model inversion results helped to explain ca. 90% of temporal variability of the measured ecosystem fluxes. Contribution of CO2 fluxes in the subtropical forest in the dry season (October-March) was 62.2% of the annual total from the whole forest ecosystem. On average, 43.3% of the net annual carbon sink occurred between October and December, indicating that this time period is an important stage for uptake of CO2 by the forest ecosystem from the atmosphere. Carbon uptake in the evergreen forest ecosystem is an indicator of the interaction of between the atmosphere and the canopy, especially in terms of driving climate factors such as temperature and rainfall events. We found that the Dinghushan evergreen forest is acting as a carbon sink almost year-round. The study can improve the evaluation of the net carbon uptake of tropical monsoon evergreen forest ecosystem in south China region under climate change conditions.

To achieve the goal of urban carbon dioxide emission reduction, how to increase carbon sequestration has become a top priority. The biological sink is mainly divided into green carbon sink and blue carbon sink. Coastal cities have two kinds of carbon sinks. There, the study of carbon sinks in coastal cities is the primary choice to cope with climate change. Therefore, this study chooses coastal cities with primary industries including agriculture, fishery, and forestry as the study subjects. The LMDI (Log-Mean Divisia Index) method and multiple regression prediction models were used to explore the low-carbon countermeasures which increase urban net carbon sink from the perspective of influencing factors and future potential. The study found that the average output value of employees in the primary industry is the main driving factor, and the change in the purchasing power of unit carbon sinks and the change in the proportion of employees in the primary industry have inhibited the increase in net carbon sinks. Projections based on the primary industry's output and afforestation area as independent variables show an overall upward trend in net carbon sinks, reaching 15.70 million tons of net carbon sinks in 2060, offsetting 10-20% of total carbon emissions in the same year. Based on the calculation results, this paper puts forward some corresponding countermeasures to increase carbon sinks. This paper provides a theoretical reference for the low-carbon development of coastal cities in China, and the strategies can be also expanded to other cities with similar resources around the world.

Promoting the improvement of agricultural ecological efficiency (AEE) under the “dual carbon” goals is an important way to drive the high-quality development of the Yangtze River Economic Belt (YEB). This study, based on panel data from 11 provinces and cities along the YEB from 2008 to 2023, first accounts for agricultural carbon sources and sinks, then incorporates them into a non-desired output super-efficiency SBM model to measure the AEE of the YEB, and finally uses the Tobit model to analyze the factors influencing AEE. The study found that (1) the net agricultural carbon sink of the YEB increased from 108.160 million tons in 2008 to 142.890 million tons in 2023, and the net agricultural carbon sinks of Anhui, Jiangsu, and Sichuan ranked among the top three in the basin. (2) The AEE of the YEB gradually increases from 0.625 in 2008 to 1.024 in 2023, and the AEE accelerates after 2020; In 2008, most provinces and cities were primarily located in areas characterized by low surplus and low efficiency, but by 2023, they had predominantly transitioned to areas with high surplus and high efficiency, along with some remaining in low-surplus, high-efficiency zones. In terms of the type of AEE, in 2008, provinces and municipalities were mainly concentrated in low-surplus low-efficiency zones, low-surplus low-efficiency zones, and high-surplus low-efficiency zones, while in 2023, provinces and municipalities were primarily focused in high-surplus high-efficiency zones and low-surplus high-efficiency zones. (3) In terms of influencing factors, the living standard of farmers, the level of financial support for agriculture, and the level of agricultural marketization will promote the improvement of AEE, while the level of farmland water conservancy facilities, the rate of disaster, and the level of urbanization will hinder the improvement of AEE. Therefore, this paper proposes optimizing the structure of agricultural production factors, implementing differentiated low-carbon agricultural development strategies, and strengthening governmental collaborative governance. This study aims to offer a fresh viewpoint on how to better assess AEE, provide a Chinese approach to achieving agricultural carbon neutrality in global river basins, and suggest practical steps to reach the “Carbon Peak and Carbon Neutrality” goal in the YEB.

Abstract. We show here an updated estimate of the net land carbon sink (NLS) as a function of time from 1960 to 2007 calculated from the difference between fossil fuel emissions, the observed atmospheric growth rate, and the ocean uptake obtained by recent ocean model simulations forced with reanalysis wind stress and heat and water fluxes. Except for interannual variability, the net land carbon sink appears to have been relatively constant at a mean value of −0.27 Pg C yr−1 between 1960 and 1988, at which time it increased abruptly by −0.88 (−0.77 to −1.04) Pg C yr−1 to a new relatively constant mean of −1.15 Pg C yr−1 between 1989 and 2003/7 (the sign convention is negative out of the atmosphere). This result is detectable at the 99% level using a t-test. The land use source (LU) is relatively constant over this entire time interval. While the LU estimate is highly uncertain, this does imply that most of the change in the net land carbon sink must be due to an abrupt increase in the land sink, LS = NLS – LU, in response to some as yet unknown combination of biogeochemical and climate forcing. A regional synthesis and assessment of the land carbon sources and sinks over the post 1988/1989 period reveals broad agreement that the Northern Hemisphere land is a major sink of atmospheric CO2, but there remain major discrepancies with regard to the sign and magnitude of the net flux to and from tropical land.