Net Greenhouse Gas Emissions Research Articles

Supplying the ethanol demand for 2030 in Brazil as a land-based climate change mitigation alternative: Implications on greenhouse gases emissions

Transitioning from a fossil-based to a bio-based economy is crucial to climate action and achieving neutrality in greenhouse gas (GHG) emissions. Biofuel production is an essential land-based GHG mitigation alternative. However, it raises concerns about biodiversity conservation, competition with food production, and net GHG emissions associated with direct land-use change (dLUC). This study aims to assess how the location and conversion routes influence GHG emissions for sugarcane expansion in Brazil to supply ethanol demand projections for 2030. A consistent and significant reduction in GHG emissions is achievable by implementing a strategy that prioritizes the spatial distribution for ethanol biorefinery expansions based on georeferenced life cycle emissions, including dLUC emissions associated with sugarcane production. Because of conservative zoning for sugarcane expansion, dLUC emissions are not an overriding factor, representing less than 9.1 % of the total GHG mitigation potential. Despite that, accounting for georeferenced dLUC emissions when prioritizing expansion facilities leads to spatial differences. Regarding conversion routes and land requirements, using cellulosic biorefineries could meet future projected demand based on sugarcane production from 3.1 million hectares, mostly in currently degraded pastureland. Conventional refineries would require 5.5 million hectares to meet the same demand of 71 billion liters. Despite the 77 % higher land demand to produce the same volume of ethanol, conventional refineries with straw recovery could be considered if electricity generation is a priority. This study illustrates how Brazil can achieve GHG mitigation targets while attending to future energy demand and protecting areas with high biodiversity.

Sustainability of biomass pyrolysis for bio-aromatics and bio-phenols production: Life cycle assessment of stepwise catalytic approach

The high-valued utilization of biomass resources remains challenging due to their complex biochemical compositions and limited product selectivity. Herein, we propose a novel biomass stepwise catalytic pyrolysis process to efficiently produce aromatic hydrocarbons and phenols by leveraging the distinct thermal stability of biomass components and their compatibility with ZSM-5 and biochar-based catalysts. A life cycle assessment (LCA) is conducted to evaluate the energy consumption and environmental impact of this innovative process compared to conventional methods. Our findings reveal that this approach significantly reduces the energy consumption by 51.76–90.02 % across different application scenarios of by-product biochar. Additionally, using biochar as a soil amendment contributes to carbon negativity, achieving a net greenhouse gas (GHG) emission reduction of up to 6 t CO2 eq for producing 8.325 t aromatics and 1 t phenol. The first-stage catalytic pyrolysis for producing aromatic hydrocarbons is identified as the major contributor to environmental impact, mainly due to ZSM-5 catalyst usage and loss, while the second stage for phenol production has a comparatively minor impact. Finally, sensitivity analysis of the key parameters highlights areas for process optimization, including reducing catalyst dosage, minimizing energy consumption, and improving phenol yield, which are crucial for enhancing the environmental and economic viability of the entire route. This study provides a detailed LCA and offers insights for future improvements in biomass conversion technology.

Solar‐driven reforming of lignocellulosic biomass to renewable biohydrogen: A review

To date, humans are looking for suitable energy sources to meet the global demand for fuels. Among many candidates, biohydrogen (bio‐H2), a future fuel perspective, is expected to grow critically and receive considerable attention to replace fossil fuels. This review focuses on biohydrogen production via post‐method photocatalytic reforming of ideal feedstock and abundant lignocellulosic biomass. Renewable biomass precursors are used without net greenhouse gas emissions. This idea holds great promise as a sustainable and environmentally friendly energy solution. In particular, many saccharide substrates, including monosaccharides, disaccharides, polysaccharides, etc., have been used as sacrificial reagents in photocatalytic reforming over the past few decades. Among the various substrates, cellulose has attracted worldwide attention since it is the most abundant polymeric biomass resource that can be obtained from many sources. Following, photo‐reforming of renewable lignocellulosic biomass, which aligns with the requirements of sustainable development, is successfully proposed. The overall catalytic efficiency will be discussed regarding biohydrogen evolution rate (mmol·gcat−1·h−1). Finally, the review concluded with challenges and potential opportunities to enhance biohydrogen are also given.

Impacts of Compost Amendment Type and Application Frequency on a Fire-Impacted Grassland Ecosystem

Composting organic matter can lower the global warming potential of food and agricultural waste and provide a nutrient-rich soil amendment. Compost applications generally increase net primary production (NPP) and soil water-holding capacity and may stimulate soil carbon (C) sequestration. Questions remain regarding the effects of compost nitrogen (N) concentrations and application rates on soil C and greenhouse gas dynamics. In this study, we explored the effects of compost with different initial N quality (food waste versus green waste compost) on soil greenhouse gas fluxes, aboveground biomass, and soil C and N pools in a fire-impacted annual grassland ecosystem. Composts were applied annually once, twice, or three times prior to the onset of the winter rainy season. A low-intensity fire event after the first growing season also allowed us to explore how compost-amended grasslands respond to burning events, which are expected to increase with climate change. After four growing seasons, all compost treatments significantly increased soil C pools from 9.5 ± 0.9 to 30.2 ± 0.7 Mg C ha−1 (0–40 cm) and 19.5 ± 0.9 to 40.1 ± 0.7 Mg C ha−1 (0–40 cm) relative to burned and unburned controls, respectively. Gains exceeded the compost-C applied, representing newly fixed C. The higher N food waste compost treatments yielded more cumulative soil C (5.2–10.9 Mg C ha−1) and aboveground biomass (0.19–0.66 Mg C ha−1) than the lower N green waste compost treatments, suggesting greater N inputs further increased soil stocks. The three-time green waste application increased soil C and N stocks relative to a single application of either compost. There was minimal impact on net ecosystem greenhouse gas emissions. Aboveground biomass accumulation was higher in all compost treatments relative to controls, likely due to increased water-holding capacity and N availability. Results show that higher N compost resulted in larger C gains with little offset from greenhouse gas emissions and that compost amendments may help mediate effects of low-intensity fire by increasing fertility and water-holding capacity.

Achieving net zero greenhouse gas emissions critical to limit climate tipping risks

Under current emission trajectories, temporarily overshooting the Paris global warming limit of 1.5 °C is a distinct possibility. Permanently exceeding this limit would substantially increase the probability of triggering climate tipping elements. Here, we investigate the tipping risks associated with several policy-relevant future emission scenarios, using a stylised Earth system model of four interconnected climate tipping elements. We show that following current policies this century would commit to a 45% tipping risk by 2300 (median, 10–90% range: 23–71%), even if temperatures are brought back to below 1.5 °C. We find that tipping risk by 2300 increases with every additional 0.1 °C of overshoot above 1.5 °C and strongly accelerates for peak warming above 2.0 °C. Achieving and maintaining at least net zero greenhouse gas emissions by 2100 is paramount to minimise tipping risk in the long term. Our results underscore that stringent emission reductions in the current decade are critical for planetary stability.

Rethinking environmental sustainability in rainfed cropping systems

Activity data from a 30-year on-farm experiment with six soil-management treatments were used to develop inventory data for environmental partial life-cycle assessment (LCA). The purpose was to compare the treatments based on environmental outcomes and evaluate conservation agriculture (CA) in Australia's dryland cropping zone. Multiple trade-offs were revealed that highlight the need for a nuanced approach to sustainable intensification and show that rules-based CA is not sufficient to guarantee low greenhouse gas (GHG) emissions, nor low overall environmental impact. Nutrient mining in dryland cropping even under CA can lead to losses in soil carbon that can double GHG intensity. In these systems, additional nutrient inputs can reduce the loss of soil carbon as well as net GHG emissions, demonstrating the critical need to include the effects of soil carbon change in LCA to prevent perverse outcomes.The treatment involving strategic tillage and nutrient balancing, along with stubble retention, had the lowest GHG intensity, but there was a trade-off with the higher embedded impacts across several other environmental categories. Higher fertiliser input could lead to toxicity impacts, due to heavy-metal content, that contribute significantly to the Human health endpoint. However, limitations in modelling such local, site-specific impacts were considerable and more research is needed to address this.In general, trade-offs were found to exist between impacts from on-farm activities versus upstream manufacture of inputs; between GHG emissions and land use (yield) versus other environmental categories; and between different on-farm GHG emission sources. Despite these trade-offs, the treatments all had similar overall scores in the Human health and Ecosystems damage categories. There was no single treatment with low, or high, impact scores across all environmental indicators, indicating that trade-offs need to be carefully considered when making farm-management decisions in the context of net-zero or carbon-neutral farming.

Carbon Sequestration in Agricultural Soil: Technique and their Efficiency

Developing technologies to slow the rate of increase in the atmospheric concentration of carbon dioxide (CO2) from annual emissions, such as energy, process industries, land-use change, and soil cultivation, is a major challenge of the twenty-first century. Severe ecological and economic disruptions result from the erratic changes in climate systems caused by the skyrocketing amounts of atmospheric CO2 and other greenhouse gases (GHGs). Through the process of carbon sequestration, net greenhouse gas emissions can be reduced, hence mitigating climate change. Both biotic and abiotic variables can contribute to the long-term sequestration of carbon, or carbon stabilisation. The compilation of past and present methods for sequestering soil organic carbon is crucial, considering the need of measuring and tracking soil carbon at the point, field, regional, and ecosystem levels. This study attempts to provide an overview of the literature about the function of various agricultural management techniques for sequestering carbon and the ways in which they help to stabilize atmospheric carbon.

Alternative uses for urban autumn tree leaves: A case study in profitability and greenhouse gas emissions for the city of Berlin

Autumn tree leaves collect as waste on many city streets every year. In the city of Berlin, they are usually collected and transported for composting as their final treatment, which emits greenhouse gases (GHG) into the atmosphere. This study assesses alternative end uses of autumn tree leaves in order explore the potential of reducing GHG emissions while producing electric energy from residual biomass. It uses a combination of partial life-cycle assessments and net present value (NPV) to explore the different net GHG emissions and economic benefits of using autumn tree leaves for the following scenarios: anaerobic digestion (biogas), gasification, and co-firing. Assuming the use of 36,000 tonnes of leaves per year, co-firing in existing power plants shows the highest NPV, of between 10.3 million and 12.1 million euros for a 10-year lifetime, in line with the phase-out of coal combustion in Germany. It also results in the lowest net GHG emissions, with savings of between 252,000 and 144,000 tonnes of CO2eq. Gasification in new plants resulted in similar NPVs, estimated at between 9.80 and 9.86 million euros over a 20-year investment horizon, but lower emissions savings of 178,000 to 127,000 tonnes of CO2eq. Biogas production showed high emissions savings of 204,000 to 203,000 tonnes of CO2eq, but a much lower NPV of between 2.3 and 2.5 million euros. Composting was the only scenario with positive net GHG emissions. The amount of energy retrieved from the conversion technologies and the electrical tariff applied were the main drivers of these results. Other aspects that can shape the results include the availability of infrastructure and transport distances. The results are highly sensitive in both cases to the dryness of the leaves, while electricity tariffs influenced the economic performance considerably.

High-ambition climate action in all sectors can achieve a 65% greenhouse gas emissions reduction in the United States by 2035

Under the next cycle of target setting under the Paris Agreement, countries will be updating and submitting new nationally determined contributions (NDCs) over the coming year. To this end, there is a growing need for the United States to assess potential pathways toward a new, maximally ambitious 2035 NDC. In this study, we use an integrated assessment model with state-level detail to model existing policies from both federal and non-federal actors, including the Inflation Reduction Act, Bipartisan Infrastructure Law, and key state policies, across all sectors and gases. Additionally, we develop a high-ambition scenario, which includes new and enhanced policies from these actors. We find that existing policies can reduce net greenhouse gas (GHG) emissions by 44% (with a range of 37% to 52%) by 2035, relative to 2005 levels. The high-ambition scenario can deliver net GHG reductions up to 65% (with a range of 59% to 71%) by 2035 under accelerated implementation of federal regulations and investments, as well as state policies such as renewable portfolio standards, EV sales targets, and zero-emission appliance standards. This level of reductions would provide a basis for continued progress toward the country’s 2050 net-zero emissions goal.

Multi-criteria sustainability assessment of solid waste management in Jordan

This study comprehensively evaluates Jordan's municipal solid waste (MSW) management sector from 2022 to 2030, in alignment with Jordan Vision 2030. This study introduces new sustainability indicators and innovative waste management alternatives to address the challenges of rapid industrialization and population growth. Four strategic scenarios—1) recycling, composting, and sanitary landfilling; 2) recycling, anaerobic digestion, and sanitary landfilling; 3) incineration and sanitary landfilling; and 4) sanitary landfilling alone—were assessed against the business-as-usual scenario. Using multi-criteria decision analysis (MCDA) and sensitivity analysis, this study evaluates net greenhouse gas emissions, annual operating expenses, revenue streams, and employment rates to measure environmental, economic, and social sustainability. The results indicate that Scenario 1 is the optimal scenario for integrating a material recovery facility (MRF) with a composting plant and sanitary landfill, achieving the lowest greenhouse gas emissions, annual costs, and employment opportunities. This study offers practical and sustainable solutions to Jordan's waste management challenges, provides novel insights through the developed MCDA and sensitivity analysis, and significantly contributes to sustainability research.

Evaluating the near- and long-term role of carbon dioxide removal in meeting global climate objectives

The 6th Assessment Report from the Intergovernmental Panel on Climate Change lacked sufficient land-sector scenario information to estimate total carbon dioxide removal deployment. Here, using a dataset of land-based carbon dioxide removal based on the scenarios assessed by the Intergovernmental Panel on Climate Change, we show that removals via afforestation and reforestation play a critical near-term role in mitigation, accounting for around 10% (median) of the net greenhouse gas emission reductions between 2020 and 2030 in scenarios that limit warming to 1.5 °C with limited overshoot. Novel carbon dioxide removal technologies such as direct air carbon capture and storage scale to multi-gigatonne levels by 2050 and beyond to balance residual emissions and draw down warming. We show that reducing fossil fuel and deforestation emissions (gross emissions) accounts for over 80% of net greenhouse gas reductions until global net zero carbon dioxide (CO2) independent of climate objective stringency. We explore the regional distributions of gross emissions and total carbon dioxide removal in cost-effective mitigation pathways and highlight the importance of incorporating fairness and broader sustainability considerations in future assessments of mitigation pathways with carbon dioxide removal.

Greenhouse gas mitigation and yield production of Thai fragrant rice cultivation under alternate wetting and drying water management

Abstract Alternate wetting and drying (AWD) water management is being promoted to replace continuous flooding (CF) water regime in rice cultivation for agricultural countries, including Thailand, to achieve the net zero greenhouse gas (GHG) emissions and cope with drought. However, its adoption in different areas yielding variable results that requires the careful approaches to prevent negative impacts on rice yield, particularly the aroma of fragrant rice, along with mitigating GHG emissions, mainly methane (CH4) and nitrous oxide (N2O). This study aims to assess the impacts of AWD on CH4 and N2O emissions, productivity, water use, and soil characteristics of fragrant rice cultivation in Thailand. Khao Dawk Mali (KDML) 105 cultivar was cultivated in the wet season and Pathum Thani (PTT) 1 cultivar was planted in the dry season under CF and AWD at different dry levels of 10 cm (AWD10), 15 cm (AWD15), and 20 cm (AWD20) below the soil surface. The emissions of GHG and water use were measured throughout the study period using closed-chamber technique and water meter equipment, respectively. Rice yields and soil properties were analyzed after crop harvesting. The results showed that rice cultivation under AWD in both wet and dry seasons reduced CH4 emissions (18.4%–27.6%) but stimulated N2O emissions (11.8%–15.0%). However, its global warming potential (GWP) was lower than CF, lowered by an average of 17.7%, 26.8%, and 25.5% under the AWD10, AWD15, and AWD20, respectively. Relative to CF, unsuccessful AWD in the wet season did not change rice yield quantity and aroma (2-acetyl-1-pyrroline: 2AP) of KDML 105. Conversely, successful AWD10 and AWD15 in the dry season promoted rice grain yield and 2AP (0.27–0.33 ppm) of PTT1, while AWD20 did not alter rice yield amount but increased rice aroma (0.47 ppm). AWD can save irrigation water in the range of 12.8%–23.0% and 15.5%–18.7% in the wet and dry seasons, respectively. AWD water regime did not importantly change the soil characteristics after crop harvest. This study concludes that AWD, especially AWD15 and AWD20, has the potential to reduce GHG emissions without affecting the quantity and quality of rice yield, along with saving water.

Europejski Zielony Ład, czyli jak Unia Europejska zamierza uczynić z Europy pierwszy neutralny kontynent dla klimatu?

THE EUROPEAN GREEN DEAL, OR HOW DOES THE EUROPEAN UNION INTEND TO MAKE EUROPE THE FIRST CLIMATE-NEUTRAL CONTINENT? The research aim of the paper is to analyze the objectives of the European Union (EU) climate policy and the instruments for their implementation, as well as to present the challenges on the way to achieving climate neutrality by the EU. In 2015, during the 21st UN Climate Change Conference in Paris, an agreement was agreed, the purpose of which is to limit global warming, aiming, among other things, for limiting the increase in global average temperature to well below 2°C above pre-industrial levels, and preferably to no more than 1.5°C. All EU Member States have ratified the above agreement, while agreeing to take action to make the EU the world’s first climate-neutral economy and society by 2050. To achieve this, the “European Green Deal” strategy was adopted, followed by the European Climate Law and the “Fit for 55” package of legislative proposals. In addition, a more ambitious EU climate target for 2030 has been agreed, namely a reduction of net greenhouse gas emissions by at least 55% compared to 1990 levels. Based on this, the following research hypothesis should be put forward, assuming that if all initiated projects, climate programs and mechanisms are fully implemented, the EU will become the first climate neutral continent by 2050. The first part of the article focuses on the goals of the European Green Deal and their implementation. The second part discusses the assumptions of European Climate Law and the elements of the “Fit for 55” package, as well as presents the most important financial instruments of the EU climate policy. The third part contains an analysis of the challenges standing in the way of the EU achieving climate neutrality by 2050, including the COVID-19 pandemic and the Russian aggression against Ukraine.

Lead-acid battolysers for hydrogen cooking: A comparison with electric cooking for sub-Saharan Africa

A battolyser combines the function of battery and electrolyser in one device, i.e. it provides both electrical energy storage and a means to produce hydrogen. A battolyser with lead-acid chemistry has recently been proposed, and this has potential as a particularly low-cost solution. Here, the battolyser is considered for the production of hydrogen as a cooking fuel (“hCooking”) in sub-Saharan Africa, a region where cooking typically employs polluting fuels (firewood and charcoal). The more conventional approach for decarbonisation of cooking is the introduction of electric cookers (e.g. hotplate, induction hob, pressure cooker) which can be powered by PV and possibly battery storage; accordingly these electric cooking (“eCooking”) systems are considered as the competing decarbonised technology. Multi-objective optimisation is used to design both battolyser and eCooking systems for a notional off-grid community, with solar PV as the main energy source. Objectives are the minimisation of net present cost and lifetime greenhouse gas emissions, and Pareto frontiers are produced to show the play-off between these. Results show that a battolyser system could eliminate 95.6 % of CO2 emissions when compared with a baseline using charcoal, at an annualised cost of $507 per household, over a system lifetime of 20 years. However, eCooking systems appear superior to the battolyser, with the cleanest battery + eCook system achieving 95.8 % emissions reduction at annualised cost $422/household. More generally, hCooking systems are nearly always Pareto dominated by eCooking systems, even under a realistic range of sensitivity scenarios. This result is due to the inherently higher energy intensity of cooking over a flame compared to the eCooking options. Priorities to make the battolyser a more viable solution include extending its lifetime as far as possible, cheaper PV systems, and improved hydrogen burner efficiencies. We also show that eCooking together with some continued use of charcoal may be the cheapest possible cooking solution, whilst simultaneously curtailing 60 % of lifetime greenhouse gas emissions.

Three years of CO2, CH4 and N2O fluxes from different sheepfolds in a semiarid steppe region, China

To better assess greenhouse gas (GHG) emissions from livestock folds in semi-arid steppe zones and reduce uncertainties in regional and national GHG emission inventories, we measured the fluxes of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) from sheepfolds under contrasting management regimes (i.e., summer sheepfolds under continuous and rotational grazing strategies and the winter sheepfold) for 3 consecutive years. Our results showed that these GHG fluxes had high intra-annual and interannual variations, emphasizing the importance of multi-year measurement for achieving temporally representative annual budgets. Sheep presence and temperature appeared to be the key factors driving CH4, CO2 and N2O fluxes from sheepfolds, e.g., higher GHG emissions usually occurred in seasons with sheep presence. However, the sheepfold type exerted a distinct influence on the temperature sensitivity of GHG fluxes, i.e., the Q10 values for GHG fluxes were generally higher in summer sheepfolds than in winter sheepfold. The annual CH4, CO2 and N2O emissions for the 3 sheepfolds were estimated to be 1.5–16.5 kg C ha−1 yr−1 (or 1.9–2.6 g C yr−1sheep−1), 8.6–16.0 t C ha−1 yr−1 (or 5.1–6.6 kg C yr−1sheep−1) and 28.3–41.9 kg N ha−1 yr−1 (or 19.0–26.8 g N yr−1sheep−1), respectively. Averaging across the 3 years, the annual net GHG emissions (CH4 + CO2 + N2O) for all sheepfolds ranged from 47 to 71 t CO2-eq ha−1 yr−1 (or 27–36 kg CO2-eq yr−1 sheep−1), of which CO2 and N2O emissions contributed the most; moreover, the annual net GHG emissions had no significant differences between sheepfold types or grazing strategies. Given that local steppe soils have a lower magnitude of soil respiration (CO2) and N2O emissions and are also net sink for atmospheric CH4, the sheepfold sites in this region are undoubtedly one of the significant hotspots for GHG emissions and could be key areas to focus mitigation action.

Soil carbon sequestration increment and carbon-negative emissions in alternate wetting and drying paddy ecosystems through biochar incorporation

Biochar has been recognized as one of the most important negative emission technologies due to its indirect removal of atmospheric carbon dioxide. However, how biochar incorporation converts rice paddy into carbon negative and enhances soil carbon sequestration (SOCS) remain largely unexplored, especially under alternate wetting and drying irrigation (IAWD). A 3-yr field experiment was conducted utilizing a split-plot design with continuous flooding irrigation (ICF) and IAWD as main plots and two biochar incorporations at the rate of 0 t ha−1 (B0) and 20 t ha−1 (B20) as sub-plots. Results indicated that IAWD reduced CH4 emissions by 73 %, GWP by 69 %, and greenhouse gas emission intensity (GHGI) by 69 % on average, but increased N2O emissions by 109 % over the three years. Biochar inhibited N2O emissions by 31 % over the three years, increased grain yield by 5 % and 11 %, and reduced CH4 emissions by 22 % and 38 % in the 2nd and 3rd year, although a 6 % lower grain yield was observed in the 1st year. Biochar can increase SOCS and SOCS rate more remarkably under IAWD than ICF. Biochar coupled with IAWD obtained the highest SOCS (56.9 t C ha−1) and lowest net GWP (-23.0 t CO2-eq ha−1) and efficiently inhibited the negative effect of IAWD on the increase in N2O emissions. Moreover, compared with ICFB0, ICFB20 and IAWDB20 decreased net GWP by nearly 4 and 8 times, which was mainly attributed to a substantial increase in SOCS (48.3 and 56.9 t C ha−1) through biochar incorporation. The further decline in net GWP comparing IAWDB20 with ICFB20 was caused by decreased GWP under IAWD. Therefore, biochar combined IAWD offers significant benefits in mitigating net greenhouse gases emissions and promoting soil C sequestration in paddy ecosystems.

Indicators of Global Climate Change 2023: annual update of key indicators of the state of the climate system and human influence

Abstract. Intergovernmental Panel on Climate Change (IPCC) assessments are the trusted source of scientific evidence for climate negotiations taking place under the United Nations Framework Convention on Climate Change (UNFCCC). Evidence-based decision-making needs to be informed by up-to-date and timely information on key indicators of the state of the climate system and of the human influence on the global climate system. However, successive IPCC reports are published at intervals of 5–10 years, creating potential for an information gap between report cycles. We follow methods as close as possible to those used in the IPCC Sixth Assessment Report (AR6) Working Group One (WGI) report. We compile monitoring datasets to produce estimates for key climate indicators related to forcing of the climate system: emissions of greenhouse gases and short-lived climate forcers, greenhouse gas concentrations, radiative forcing, the Earth's energy imbalance, surface temperature changes, warming attributed to human activities, the remaining carbon budget, and estimates of global temperature extremes. The purpose of this effort, grounded in an open-data, open-science approach, is to make annually updated reliable global climate indicators available in the public domain (https://doi.org/10.5281/zenodo.11388387, Smith et al., 2024a). As they are traceable to IPCC report methods, they can be trusted by all parties involved in UNFCCC negotiations and help convey wider understanding of the latest knowledge of the climate system and its direction of travel. The indicators show that, for the 2014–2023 decade average, observed warming was 1.19 [1.06 to 1.30] °C, of which 1.19 [1.0 to 1.4] °C was human-induced. For the single-year average, human-induced warming reached 1.31 [1.1 to 1.7] °C in 2023 relative to 1850–1900. The best estimate is below the 2023-observed warming record of 1.43 [1.32 to 1.53] °C, indicating a substantial contribution of internal variability in the 2023 record. Human-induced warming has been increasing at a rate that is unprecedented in the instrumental record, reaching 0.26 [0.2–0.4] °C per decade over 2014–2023. This high rate of warming is caused by a combination of net greenhouse gas emissions being at a persistent high of 53±5.4 Gt CO2e yr−1 over the last decade, as well as reductions in the strength of aerosol cooling. Despite this, there is evidence that the rate of increase in CO2 emissions over the last decade has slowed compared to the 2000s, and depending on societal choices, a continued series of these annual updates over the critical 2020s decade could track a change of direction for some of the indicators presented here.

Winter harvesting reduces methane emissions and enhances blue carbon potential in coastal phragmites wetlands

Enhancing the ability of coastal blue carbon to accumulate and store carbon and reduce net greenhouse gas emissions is an essential component of a comprehensive approach for tackling climate change. The annual winter harvesting of Phragmites is common worldwide. However, the effects of harvesting on methane (CH4) emissions and its potential as an effective blue carbon management strategy have rarely been reported. In this study, the effects of winter Phragmites harvesting on the CH4 and carbon dioxide (CO2) fluxes and the underlying mechanisms in coastal Phragmites wetlands were investigated by comparing the eddy covariance flux measurements for three coastal wetlands with different harvesting and tidal flow conditions. The results show that harvesting can greatly reduce the CH4 emissions and the radiative forcing of CH4 and CO2 fluxes in coastal Phragmites wetlands, suggesting that winter Phragmites harvesting has great potential as a nature-based strategy to mitigate global warming. The monthly mean CH4 fluxes were predominantly driven by air temperature, gross primary productivity, and latent heat fluxes, which are related to vegetation phenology. Additionally, variations in the salinity and water levels exerted strong regulation effects on CH4 emissions, highlighting the important role of proper tidal flow restoration and resalinization in enhancing blue carbon sequestration potential. Compared with the natural, tidally unrestricted wetlands, the CH4 fluxes in the impounded wetland were less strongly correlated with hydrometeorological variables, implying the increased difficulties of predicting CH4 variations in impounded ecosystem. This study facilitates the improved understanding of carbon exchange in coastal Phragmites wetlands with harvesting or impoundment, and provides new insights into effective blue carbon management strategies beyond tidal wetland restoration for mitigating the effects of climate change.

Effect of rice hull biochar treatment on net ecosystem carbon budget and greenhouse gas emissions in Chinese cabbage cultivation on infertile soil

Biochar, with its potential to enhance soil fertility, sequester carbon, boost crop yields and reduce greenhouse gas emissions, offers a solution. Addressing the challenges posed by climate change is crucial for food security and agriculture. However, its widespread adoption in agriculture remains in its infancy. This study assessed the effects of rice hull biochar on cabbage production and greenhouse gas emissions, especially nitrous oxide (N2O). A trial, employing a randomized block design in triplicate was conducted from September 13 to November 23, 2022, where "Cheongomabi" cabbage was cultivated with N-P2O5-K2O fertilization at 32-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-$$\\end{document}7.8-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-$$\\end{document}19.8 kg 10a−1. Additional fertilizer was applied twice post-sowing. The Biochar application rates were control = 0 ton ha−1, B1 = 1 ton ha−1, B3 = 3 ton ha−1, and B5 = 5 ton ha−1. The aboveground biomass of autumn cabbage harvested 82 days after sowing was 2.40–2.70 kg plant−1 in the control and biochar treatments (B1, B3, and B5), with no significant differences (p > 0.05). Cumulative CO2 emissions during cultivation varied across treatment groups, with initial and cumulative emissions of 10.40–17.94 g m−2 day−1 and 3.63–4.43 ton ha−1, respectively. N2O emissions decreased with higher biochar application: reductions of 2.9%, 25.4%, and 41.1% in the B1, B3, and B5 treatments, respectively, compared to the control. The biochar application had no significant impact on yield but curbed soil emissions, Net ecosystem carbon balance during cabbage cultivation ranged from 0.42 to 3.41 ton ha−1 for the B1, B3, and B5 treatments, respectively, compared to control. Overall, the study underscores biochar’s role in mitigating emissions and boosting soil carbon during cabbage cultivation in fall.

Household-scale digesters in Rwanda: Performance analysis and net-greenhouse gas effect

In view of climate change mitigation, the production of biogas through anaerobic digestion has emerged as a prominent renewable fuel source, also in developing countries. The implementation of household-scale digesters in these regions is instrumental in achieving the Sustainable Development Goal 7 of ensuring clean and affordable energy. However, a rigorous quantification of the biogas production and net-greenhouse gas effect of these household digesters, taking into account fuel use, biogas leakage and fertiliser types, is lacking. This study quantified both biogas production and net-greenhouse gas emissions, utilizing Rwanda as a reference region. Through a field survey, biogas measurements, and model simulations, the study revealed that a reference case featuring a fixed dome digester of 4 m3, fed with manure of on average 2 cows produces 0.38 m3 biogas.d−1 which meets 65% of the cooking need of an average family of 4 adults and 2 children. The addition of a toilet to the household-scale digester increased the daily biogas production by 16%. Conversely, the use of a bare soil floor in the cow shed results in a 28% reduction in biogas production, emphasizing the recommendation for a concrete floor. Net-greenhouse gas emissions from a household-scale digester, including an estimated 9% leak percentage, result in a reduction of 2.4 tCO2,eq.year−1 per household compared to wood-only cooking. Besides, using the digestate as a fertiliser further enhances the reduction to a total of 2.5 tCO2,eq.year−1. The main opportunities for minimizing emissions include optimizing temperature, manure flow and reducing leakages, which needs to be considered during design, operation, and policy formulation. In summary, household-scale digesters provide sustainable waste management, renewable energy, and significant greenhouse gas emission reduction, making them a promising technology for decentralized energy solutions in developing regions.