The characters, control and cost-benefits of methane emissions
The coal sector, which is the largest anthropogenic methane source in China, accounts for 38% of the country’s total anthropogenic methane emissions. Studies have identified significant uncertainties in existing inventories, indicating the urgency to enhance the accuracy of China’s coal methane inventory. Using a self-built dynamic mine-level database and high-tier methodologies in emission calculation recommended by IPCC (Intergovernmental Panel on Climate Change) inventory guidelines, this work improved China’s coal methane inventory and revised the estimation of coal methane emissions in 2012 and 2014. The results show consistency of coal methane emissions in 2012 between this work (23.33 Tg) and China’s national greenhouse gas inventory (23.85 Tg). However, it is important to note that the consistency observed in 2012 does not guarantee the accuracy of China’s national inventory due to significant discrepancies among sub-sources. In fact, coal methane emissions in 2014 were found to be 25.87 Tg, or 23% higher, compared to the national inventory. Further analysis reveals that abandoned mine methane (AMM) is the most significant source of this discrepancy, which has emerged as the second largest contributor of coal methane emissions, accounting for a share of 10%?20%, but has been substantially underestimated in previous studies. Additionally, this work identifies the dynamic variation of key parameters, such as the emission factor, as having a significant impact on inventory accuracy. It highlights the importance of timely updates to fundamental data, such as the timely measurements of mine gas gushing rates. Overall, this work makes significant contribution to improving the accuracy of coal methane inventory, supporting policy decisions of methane mitigation, and ensuring high-quality compliance.
The status, trends and key sources of CH4 emissions in Annex I countries are explored, based on GHGs emissions data from Parties submitted by Annex I countries to the United Nations Framework Convention on Climate Change (UNFCCC) from 1990 to the most recent inventory year (2020). The results show that: (1) In 2020, the total CH4 emissions of the 42 countries in Annex I of the UNFCCC were 1872231.01 kt CO2-eq, and the combined CH4 emissions of the United States, the Russian Federation and Australia accounted for 60% of the total emissions. (2) Compared with 1990, the overall CH4 emissions of Annex I countries/groups of UNFCCC showed a downward trend in 2020, of which United States, the Russian Federation, Australia, the European Union (Convention) and the European Union (Kyoto Protocol) decreased by 14.79%, 29.69%, 24.01%, 40.56% and 40.34% respectively, while Turkey, Spain, New Zealand and Ireland increased by 50.62%, 2.49%, 3.97% and 7.91% respectively. (3) CH4 emissions in major developed countries mainly come from the agricultural and energy sectors, followed by the waste sector. Among them, in the agricultural sector mainly from enteric fermentation, followed by manure management; CH4 emissions from the energy sector come mainly from escape emissions from fuels; The main source of emissions in the waste sector is solid waste landfills.
Compared with carbon dioxide, methane has a shorter lifetime and higher global warming potential (GWP) and also acts as a key ingredient of ground-level ozone pollution, so it is of great significance to control its emissions regarding climate change and air pollution mitigation. However, methane emissions are still growing up, in which livestock and oil/gas system are key categories. Regarding emission by parties, it shows a downward trend in Annex I parties to the United Nations Framework Convention on Climate Change while non-Annex I parties face challenges. The major policies and measures (PaMs) implemented and adopted are regulatory ones (e.g. standards) to control methane emissions, supplemented by market-based measures. In the meantime, voluntary agreement and partnership are critical to find the most cost-effective options. China has achieved effectiveness in methane controlling by bunches of PaMs, as low growing rate of overall emission and even declining in some sectors is observed. Nevertheless, challenges are ahead, including high cost, emission growing induced by structural factors and weak supporting systems. Based on these findings, policy recommendations are raised.
In order to systematically understand the characteristics and management status of methane (CH4) emissions in Guangdong’s municipal waste disposal sector, the CH4 emissions of solid waste landfill disposal, domestic sewage treatment and industrial wastewater treatment in 2010-2020 in Guangdong province were calculated, and the implementation of control policies in Guangdong was analyzed based on the emission results. Results indicated that from 2010 to 2020, CH4 emissions accounted for more than 70% in the field of municipal waste disposal in Guangdong, mainly from solid waste landfill disposal. Although CH4 emissions from wastewater treatment still showed an upward trend, the increase in CH4 emissions from solid waste landfill treatment in Guangdong has been initially reversed, and the emissions in 2020 were reduced by about 381 and 13 kt respectively compared with 2018 and 2010. The growth trend of CH4 emissions in the field of waste treatment was reversed during the “13th Five-Year Plan” period, denoting that Guangdong’s waste treatment CH4 emission management work has achieved certain results. In addition, in order to deepen the national and provincial CH4 emission reduction action under the goal of carbon peak and carbon neutrality, measures such as issuing an integrated CH4 emission reduction plan, refining the CH4 emission reduction management mechanism of municipal waste disposal and continuously improving the operation and management level of waste treatment facilities were also strongly recommended to the governments.
Methane emission control and reduction is considered as one of the important measures for effectively mitigating global warming effect, which has attracted widespread attention both domestically and internationally. In this paper, based on the EDGAR database, the decoupling index and Logarithmic Mean Divisia Index (LMDI) decomposition method were used to quantitatively analyze the relationship between methane emissions from solid waste treatment and economic development in G7 countries. It is found that methane emissions from solid waste treatment in G7 countries have already peaked, with the per capita GDP of the US, Canada, France, Germany, the UK and Japan being concentrated in the range of 30000-40000 US dollars when reaching the peak, and Italy’s per capita GDP just exceeded 20000 US dollars. No country has achieved absolute decoupling between emissions and economic development. As for the structural decomposition results driven by population, per capita GDP, solid waste generation intensity, and methane emission coefficient, the growth of population and per capita GDP sustainably drives the increase in methane emissions from solid waste treatment in G7 countries, but the driving force significantly weakens as the development speed slows down. The reduction of methane emission coefficient is the most important factor in achieving methane control, and the decrease in solid waste generation intensity can also suppress the increase in methane emissions in most periods. By continuously strengthening solid waste classification and recycling and promoting methane collection and utilization in landfills, methane emission coefficient is expected to continue to decline. Combining with the main methane control policies and actions taken by G7 countries, some suggestions are proposed to help China achieve methane control in the field of solid waste treatment, including formulating emission reduction strategies, controlling the intensity of solid waste generation, reducing organic matter entering landfills, and strongly promoting landfill gas recovery and utilization or disposal.
Based on the inventory method, the agricultural CH4 emissions in China from 1981 to 2060 were calculated, and the agricultural CH4 emission reduction effects of five healthy dietary patterns were analyzed based on scenario design. Results show that CH4 emissions from agriculture in China increased from 18.46 Mt to 22.23 Mt from 1981 to 2021, with enteric fermentation, rice cultivation and freshwater aquaculture being the main sources of CH4 emissions. Under the baseline scenario, China’s agricultural CH4 emissions will reach a peak of 24.91 Mt in 2036, and the cumulative emissions from 2022 to 2060 are 940.40 Mt. The five healthy dietary scenarios will promote the early peak of CH4 in China before 2030 (2021-2027), and the cumulative emission reduction potential from 2022 to 2060 is 170.22-343.31 Mt (18%-37%) CH4. Among them, the healthy dietary scenario with relatively less consumption of animal sources food has greater CH4 emission reduction potential.
As the largest staple food crop, rice plays a pivotal role in China’s stable and safe supply system of grain and important agricultural products. It can be seen that low-carbon rice production is not only related to the promotion of the national dual-carbon strategy, but also of great significance for the improvement of the national grain self-sufficiency rate, the improvement of national dietary nutrition and the implementation of climate diplomacy. This paper systematically discusses the realization path of low-carbon sustainable rice production system from the aspects of China’s rice field methane emission status, emission reduction technology and low-carbon production strategy. In recent years, although the rice planting area in China has fluctuated, the yield per unit area of rice has continued to increase. In 2021, the average yield per mu (1 mu≈667 m2) reached 474.2 kg, a record high in history. At the same time, rice fields are also the main source of methane (CH4) emissions in China (187 Mt CO2e), accounting for 40.1% of the total methane emissions from agricultural activities in China. Therefore, facing the multiple challenges of sustainable rice production, adverse impacts of climate change in the future, and climate diplomacy, CH4 emission reduction in paddy fields must fully consider the comprehensive planning of water, fertilizers, varieties, tillage, and inoculum products. It is necessary to establish a technical system based on human-enhanced measures supplemented by Nature-based Solutions, for inhibiting growth, improving production and increasing efficiency based on near-natural regulation and artificial enhancement, which is applicable to the main rice-producing areas. On this regarding, the implementation of cover crop planting, no-tillage rotation, high-yield and low-emission variety breeding, mulching and moisture conservation, bacterial agent synergistic products, intelligent machinery, reasonable dense planting, decoupling of tillers, alternating wet and dry, and aerobic farming, etc., to ensure the effective supply of rice, reduce emissions and increase carbon, and achieve sustainable, green and high-quality development of rice.
