Natural Carbon Sinks Research Articles

Decarbonization potential of fuel cell technologies in micro-cogeneration applications: spotlight on SOFCs in a Belgian case study

Abstract There is a plethora of fuel cell technologies, many of which hold great promise in terms of their decarbonization potential, which this paper aims to explore. In fact, this paper discusses the only two existing technologies on the market, Polymer Exchange Membrane Fuel Cells (PEMFCs) and Solid Oxide Fuel Cells (SOFCs). Unfortunately, these commercial systems mainly use natural gas as primary fuel due to its cost and practicality (easy transport and storage, existing infrastructures, etc.). Using Belgium as a case study, this paper shows that their GHG mitigation potential remains rather insignificant compared to the average individual carbon footprint if their fuel is not decarbonised. Even so, their mitigation potential would still be far from sufficient, and other measures, including behavioural changes, would still need to be implemented. Nevertheless, some emerging fuel cell technologies, such as Direct Carbon Solid Oxide Fuel Cells (DC-SOFCs) or Direct Formic Acid Fuel Cells (DFAFCs), offer the possibility of facilitating pure CO2 capture at their anode outlet, thus allowing for potential negative emissions. Using a case study of the electricity demand of an average Belgian home (with two adults) supplied by an efficient biomass-fuelled DC-SOFC, this paper shows that these negative emissions could be up to about 4 tCO2eq/year. By comparison, the IPCC's Sixth Assessment Report estimated the emissions footprint that could never be mitigated, even with future net-zero CO2 emissions, to be 1 tCO2eq/year per capita, implying that climate neutrality will require similar levels of carbon sequestration. In populous Western countries, natural carbon sinks are unlikely to be sufficient, and the potential negative emissions of emerging fuel cell technologies will be welcome.

Surplus or deficit? Quantification of carbon sources and sinks and analysis of driving mechanisms of typical oasis urban agglomeration ecosystems

The relationship between carbon sources and sinks, along with their balance, is a crucial indicator for assessing ecosystem health. Ecosystem protection mitigates climate change and promotes the carbon cycle balance. Consequently, to effectively assess the status of carbon sources and sinks in an oasis ecosystem, this study utilized remote sensing and statistical data to estimate the natural carbon sources and sinks, energy carbon emissions(ECE), and carbon surpluses or deficits in the urban agglomeration of the northern slopes of the Tianshan Mountains(UANSTM) for a period 2000–2022 from a perspective of the natural-social-economic system. The driving mechanisms were analyzed using the optimal geodetector model (OPGD) and generalized divisia index method (GDIM). The results show(1) throughout the study period, natural carbon sources and sinks in the UANSTM exhibited a distribution pattern that diminished from the Tianshan Mountains axis northward and southward, accompanied by a fluctuating increase over time. ECE predominantly occurred in urban built-up areas and adjacent cultivated lands, totaling an increase of 88.48 × 104 TgC. (2) The change trend showed an overall predominance of carbon sources, with the rate of increase of carbon sources being greater than that of carbon sinks. Grassland-cultivated land and construction land interaction area exhibited significant changes in carbon sources and sinks. (3) During the study period, the UANSTM experienced a consistent carbon deficit, averaging −68.11 TgC annually. Spatially, this deficit evolved from discrete points to linear and then to areal patterns. (4) Precipitation and elevation were the primary determinants of natural carbon sources and sinks. Whereas GDP with a contribution of 50.4%,was the predominant driver of ECE across each prefecture-level city. Development of policies that synergize regional natural and socioeconomic systems is an important means of achieving a carbon balance. The results of this study provide a reference for adding a research paradigm on carbon sources and sinks in oasis urban agglomerations and for low-carbon development.

Legal pathways for China’s blue carbon conservation: a perspective of synergizing ocean and climate rule of law

Blue carbon serves as a significant natural carbon sink and presents substantial opportunities for greenhouse gas mitigation actions. This study first elucidates the importance of blue carbon conservation and its basis in international law, and then analyzes the progress and shortcomings of China’s efforts in blue carbon protection in the areas of legislation, enforcement, and judicial practices related to ocean governance and climate change mitigation. Finally, from the perspective of coordinating ocean and climate governance, this paper proposes legal pathways to improve blue carbon conservation. In terms of legislation, it advocates for the explicit inclusion of the legal concept of “blue carbon” in the legal frameworks governing ocean and climate governance, and for the clarification of the legal status of “blue carbon credits”. In terms of regulatory enforcement, it recommends developing a detailed implementation plan to integrate blue carbon into the China Certified Emission Reduction (CCER) system, designating a regulatory body for blue carbon trading, and establishing a multi-stakeholder governance mechanism involving government, market, and society. In the judicial realm, the paper suggests issuing judicial interpretations to clarify the scope, prerequisites, and implementation of “purchasing blue carbon credit” to prevent such purchases from becoming a “free pass” that could damage marine ecosystems

Green turtle tracking leads the discovery of seagrass blue carbon resources.

Seagrass meadows are natural carbon sinks, and their conservation and restoration play a crucial role in climate change mitigation and adaptation. However, blue carbon projects are hindered, in most nations, by major gaps in understanding the distribution and extent of seagrasses. Here, we show how satellite tracking of green turtles (Chelonia mydas) provided a major advance in identifying novel seagrass blue carbon resources in the Red Sea. By tracking 53 nesting green turtles, we identified 38 distinctive foraging sites. All ground-truthed foraging sites (100%) identified a seagrass meadow, surpassing the 40% (n = 30) accuracy of satellite imagery-based inferences. Sampling from these turtle-derived locations represents a greater range of depths than previously sampled in the Red Sea providing a carbon stock estimate of 4.89 ± 0.83 kg Corg (organic carbon) m-2. By improving estimates of seagrass extent and associated blue carbon, our approach can support the conservation of blue carbon resources in data-deficient regions worldwide.

Analysis of emission reduction strategies for the use of alternative fuels and natural carbon sinks in international bulk shipping

This research examines four categories of international bulk carriers and forecasts their ability, from 2025 to 2050, to meet the IMO targets for emission reduction: a 20% reduction by 2030 and a 70% reduction by 2040 compared to 2008 levels, with the ultimate aim of achieving net-zero emissions by 2050, utilizing a life cycle assessment (LCA) methodology. It evaluates various scenarios involving different rates of ship demolition and alternative fuel adoption to achieve these targets. Additionally, it investigates the potential costs associated with carbon credits and natural carbon sinks (such as seagrass) in cases where emissions targets are not met. The findings suggest that, under the baseline scenario and Scenario 1, despite increased usage of alternative fuels and declining emission factors, none of the four ship types meet the IMO targets in terms of life cycle greenhouse gas (GHG) emissions. However, in Scenario 2, where the ship demolition rate steadily increases until the usage of traditional fuel ships reaches zero, and with concurrent reductions in emission factors, emissions decrease substantially and approach the desired targets, though they still fall short. Furthermore, the study analyzes the financial implications of employing carbon credits versus natural carbon sinks to offset emission shortfalls, indicating that Scenario 2 is comparatively less costly. It also demonstrates that leveraging natural carbon sinks is more cost-effective in reducing emission expenses compared to relying solely on carbon credits. Consequently, the research recommends prompt adoption of alternative fuels, acceleration of ship demolition rates, and utilization of natural carbon sinks not only to meet international shipping emission reduction objectives but also to rejuvenate marine ecosystems, thereby fortifying marine environments.

The importance of natural land carbon sinks in modelling future emissions pathways and assessing individual country progress towards net-zero emissions targets

Nature-based solutions (NBS), in the form of active ecosystem conservation, restoration and improved land management, represent a pathway to accelerate net-zero emissions (NZE) strategies and support biodiversity. Meaningful implementation and successful accounting depend on the ability to differentiate between anthropogenic and natural carbon fluxes on land. The United Nations Framework Convention on Climate Change (UNFCCC) land carbon accounting methods currently incorporate all CO2 fluxes on managed land in country inventories without distinguishing between anthropogenic and natural components. Meanwhile, natural land carbon sinks are modelled by earth system models but are mostly reported at global level. Here we present a simple yet novel methodology to estimate the present and future progression of natural land sinks at the country and regional level. Forests dominate the uptake of CO2 on land and as such, our analysis is based on allocating global projections of the natural land carbon flux to individual countries using a compilation of forest land areas for a historic and scenario range spanning 1960–2100. Specifically, we use MIT’s carbon cycle model simulations that are set in the context of emissions pathways from the Shell Energy Security Scenarios (2023). Our natural land carbon flux estimates for individual countries and regions such as the European Union (EU) show generally good agreement with independent estimates from recent land-use harmonisation studies for 2000–2020. Hence, our approach may also provide a simple, first-order exploration of future natural land fluxes at country level—a potential that other studies do not yet offer. In turn, this enables better understanding of the anthropogenic and natural components contributing to country NZE targets under different scenarios. Nevertheless, our findings also suggest that models such as the Shell World Energy Model (WEM) would benefit from further improvements in the apportionment of land carbon sources and sinks to evaluate detailed actions to meet country targets. More importantly, uncertainties remain regarding the resilience of land ecosystems and their capacity to store increasing amounts of carbon under progressive global warming. Therefore, we recommend that the carbon cycle modelling and energy modelling research communities continue to collaborate to develop a next generation of relevant data products to distinguish anthropogenic from natural impacts at local, regional and national levels.

Towards carbon neutral cities: An insight for Istanbul, Turkey

AbstractTurkey pledged net‐zero emissions by 2053 under the Paris Agreement. Istanbul, its largest city, aims to be carbon‐neutral by 2050. To accomplish this goal, the first step involves identifying emissions and devising reduction plans, with a focus on utilizing natural carbon sinks. This study assessed emissions and potential reductions across Istanbul's 39 districts. Greenhouse gas emissions were calculated using Intergovernmental Panel on Climate Change guidelines. Despite limited data on sink efficacy, a practical approach was adopted. According to the results, Istanbul emitted 58.5 million tons of CO2 equivalent, varying by district in 2022. In Istanbul, 32% of emissions come from electricity consumption, 29% from heating, 29% from transportation, and 10% from waste disposal. High emissions were observed near waste sites or airports. Carbon sinks reduced emissions by 11.5%, with only two districts achieving neutrality. Natural processes alone are not enough; urgent reduction strategies are needed, prioritizing high‐emission districts over citywide measures.

Study of Carbon Sequestration in Forest Ecosystems in DRC

Purpose: The aim of the study was to investigate the study of carbon sequestration in forest ecosystems in DRC. Methodology: This study adopted a desk methodology. A desk study research design is commonly known as secondary data collection. This is basically collecting data from existing resources preferably because of its low cost advantage as compared to a field research. Our current study looked into already published studies and reports as the data was easily accessed through online journals and libraries. Findings: Research on carbon sequestration in DRC's forests underscores their crucial role as significant carbon sinks. These forests store substantial amounts of carbon in biomass and soils, contributing significantly to global climate regulation efforts. However, challenges like deforestation and illegal logging threaten this capacity, highlighting the importance of sustainable forest management and conservation. Enhancing carbon sequestration in DRC's forests is essential for mitigating climate change impacts and preserving biodiversity. Unique Contribution to Theory, Practice and Policy: Ecological succession theory, resource allocation theory & social-ecological systems theory may be used to anchor future studies on the study of carbon sequestration in forest ecosystems in DRC. Encourage the adoption of sustainable forestry practices that enhance carbon sequestration while supporting biodiversity conservation and local livelihoods. Align forest management policies with national and international climate change mitigation goals, emphasizing the role of forests as natural carbon sinks.

On the irrelevance of (peat-free) substrates - Qualitative insights into the social practices of hobby gardeners in Germany

Reducing peat consumption in hobby gardening offers considerable potential for reducing CO2 emissions, since peatlands are one of the most important natural carbon sinks. While existing research focuses on the products and their diffusion, we focus on people and their practices of gardening. So we conducted 44 interviews with hobby gardeners in Germany from three different contexts: gardening at home, in an allotment garden, and in an urban gardening initiative. Our findings show that substrates are not a major part of gardeners' social interactions. Purchasing substrates is a utility-driven process with, compared to gardening itself, mostly passive information behavior. Although (basic) knowledge about peat is widespread among hobby gardeners, price is the dominant purchase criterion for substrates; sustainability does not play an important role. Our results suggest that communication campaigns by governments and companies should convey substrate-related messages in those places where gardeners go to seek information, e.g. gardening-related publications. Communication should focus on the functional value of peat-free substrates and not just explain environmental benefits. Lastly, campaigns should target home gardeners rather than urban gardeners and allotment gardeners who rarely buy any substrates but rely on their own production.

Terrestrial inputs boost organic carbon accumulation in Mexican mangroves

Despite their ability to mitigate climate change by efficiently absorbing atmospheric carbon dioxide (CO2) and acting as natural long-term carbon sinks, mangrove ecosystems have faced several anthropogenic threats over the past century, resulting in a decline in the global mangrove cover. By using standardized methods and the most recent Bayesian tracer mixing models MixSIAR, this study aimed to quantify source contributions, burial rates, and stocks of organic carbon (Corg) and explore their temporal changes (∼100 years) in seven lead-210 dated sediment cores collected from three contrasting Mexican mangrove areas. The spatial variation in Corg burial rates and stocks in these blue carbon ecosystems primarily depended on the influence of local rivers, which controlled Corg sources and fluxes within the mangrove areas. The Corg burial rates in the cores ranged from 66 ± 16 to 400 ± 40 g m−2 yr−1. The Corg stocks ranged from 84.9 ± 0.7 to 255 ± 2 Mg ha−1 at 50 cm depth and from 137 ± 2 to 241 ± 4 Mg ha−1 at 1 m depth. The highest Corg burial rates and stocks were observed in cores from the carbonate platform of Yucatan and in cores with reduced river influence and high mangrove detritus inputs, in contrast to patterns identified from global databases. Over the past century, the rising trends in Corg burial rates and stocks in the study sites were primarily driven by enhanced inputs of fluvial-derived Corg and, in some cores, mangrove-derived Corg. Despite their decreasing extension, mangrove areas remained highly effective producers and sinks of Corg. Ongoing efforts to enhance the global database should continue, including mangrove area characteristics and reliable timescales to facilitate cross-comparison among studies.

Seagrass decline weakens sediment organic carbon stability

Seagrass meadows are globally recognized as critical natural carbon sinks, commonly known as ‘blue carbon’. However, seagrass decline attributed to escalating human activities and climate change, significantly influences their carbon sequestration capacity. A key aspect in comprehending the impact of seagrass decline on carbon sequestration is understanding how degradation affects the stored blue carbon, primarily consisting of sediment organic carbon (SOC). While it is widely acknowledged that seagrass decline affects the input of organic carbon, little is known about its impact on SOC pool stability. To address this knowledge, we examined variations in total SOC and recalcitrant SOC (RSOC) at a depth of 15 cm in nine seagrass meadows located on the coast of Southern China. Our findings revealed that the ratio of RSOC to SOC (RSOC/SOC) ranged from 27 % to 91 % in the seagrass meadows, and the RSOC/SOC increased slightly with depth. Comparing different seagrass species, we observed that SOC and RSOC stocks were 1.94 and 3.19-fold higher under Halophila beccarii and Halophila ovalis meadows compared to Thalassia hemprichii and Enhalus acoroides meadows. Redundancy and correlation analyses indicated that SOC and RSOC content and stock, as well as the RSOC/SOC ratio, decreased with declining seagrass shoot density, biomass, and coverage. This implies that the loss of seagrass, caused by human activities and climate change, results in a reduction in carbon sequestration stability. Further, the RSOC decreased by 15 %, 29 %, and 40 % under unvegetated areas compared to adjacent Halophila spp., T. hemprichii and E. acoroides meadows, respectively. Given the anticipated acceleration of seagrass decline due to climate change and increasing coastal development, our study provides timely information for developing coastal carbon protection strategies. These strategies should focus on preserving seagrass and restoring damaged seagrass meadows, to maximize their carbon sequestration capacity.

О поглощении антропогенного диоксида углерода лесами и степной растительностью Республики Тыва

INTRODUCTION. Currently, a coal mining territory is being formed in the Republic of Tyva, the volume of coal mining, the “carbon intensity” of production, and СО2 emissions into the atmosphere are increasing. Emissions of the man-made СО2 into the atmosphere caused by combustion of hydrocarbon fuels, wildfires, deforestation and land use development change the natural СО2 balance in the atmosphere, which is manifested in the photosynthesis and respiration processes of plants with the formation of natural carbon sinks. OBJECTIVES. The research aims to correlate the calculated data on the degree of atmospheric pollution by carbon dioxide emissions from stationary and mobile sources with the sequestration potential (with respect to СО2) of the forest and steppe ecosystems of the Republic of Tyva. RESULTS. The sequestration potential of the ecosystems of the Republic of Tyva makes it possible to capture both its own carbon dioxide emissions (fuel combustion) and those introduced from other regions. CONCLUSIONS. The total impact of the man-made СО2 on the atmosphere in the city of Kyzyl relative to other regions is low, amounting to 1,41 million t-eq СО2/year; currently, the territory of the Republic of Tyva is characterized by an excess of the sequestration capacity of man-made СО2 (7,46 million t-eq СО2/year).

Structure and composition of rehabilitated mangrove in Lubuk Kertang Village, North Sumatra, Indonesia

Mangroves are generally distributed in tidal zones along tropical and subtropical coasts and are known as woody halophytes. Mangroves are one of the most productive and efficient long-term natural carbon sinks. Deforestation and mangrove degradation produced substantial carbon emissions that account for the majority and salt marshes emissions. Mangroves play an important role in protecting against storms and sea level rise, preventing coastline erosion, regulating coastal water quality, providing habitat for commercial interests. This study was conducted to measure the diversity, structure and composition of forests in the rehabilitation of abandoned pond mangrove forests in Lubuk Kertang Village, West Brandan District, Langkat Regency, North Sumatra. The method used was to conduct a census in a 1.6 ha restoration forest by measuring the overall diameter, height and species found. Fourteen species were found, namely Aegiceras corniculatum, Avicennia marina, Acrostichum aureum, Bruguiera gymnorrhiza, Ceriops tags, Exoecaria agallocha, Finlaysonia maritimea, Nypa fruticans Rhizophora apiculata, Rhizophora mucronata, Rhizophora stylosa, Sonneratia alba, Scyphiphora hydrophyllacea, Sesuvium portulacastrum.

Enhancing wood efficiency through comprehensive wood flow analysis: Methodology and strategic insights

Wood, an essential natural resource in human civilization, remains widely used despite advances in technology and material substitution. The surge in greenhouse gas emissions and environmental concerns accentuates the need for optimizing wood utilization. Material flow analysis is a powerful tool for tracking material flows and stocks, aiding resource management and environmental decision-making. However, the full extent of its methodological dimensions, particularly within the context of the wood supply chain, remains relatively unexplored. In this study, we delve into the existing literature on wood flow analysis, discussing its primary objectives, materials involved, temporal and spatial scales, data sources, units, and conversion factors. Additionally, data uncertainty, data reconciliation and crucial assumptions in material flow analysis are highlighted in this paper. Key findings reveal the significance of wood cascading and substitution effects by replacing non-wood materials, where they can reduce greenhouse gas emissions more than the natural carbon sink of forests and wood products. The immediate impact of short-term wood cascading might not be as robust as the substitution effect, with energy substitution showcasing better results than material substitution. However, it's crucial to note that these conclusions could experience significant reversal from a long-term and global perspective. Strategies for improving wood efficiency involve maximizing material use, advancing construction technologies, extending product lifespans, promoting cascade use, and optimizing energy recovery processes. The study underscores the need for standardized approaches in wood flow analysis and emphasizes the potential of wood efficiency strategies in addressing environmental challenges.

Focused recharge enhances soil carbon leakage and carbonate weathering in groundwater: Implications for subsurface carbon sinks

Soil carbon leakage into groundwater is a crucial and natural carbon sink process in the subsurface carbon cycling. However, the primary driving force for soil carbon downward leakage and the following fate of the carbon in groundwater remains elusive. Here, we investigated multi-seasonal hydrodynamics, hydrogeochemistry and environmental isotopes (δ13C, δ2H and δ18O) in groundwater wells in a humid region. Frequent water-table rise (1 ∼ 3 m) and isotopic signature fluctuation after the concentrated rainfall supported evidence for the occurrence of focused groundwater recharge. We found that focused recharge during the shorter and wetter season induced the increase of groundwater DOC (306.5 ± 231 μmol/L) and CO2 (2154 ± 726.6 μmol/L), the dilution of CH4 (1.75 ± 1.2 μmol/L) and DIC (4486 ± 790.8 μmol/L) as well as depleted δ13C signatures (−17‰ ∼ −18‰). These variations jointly elucidated accelerated soil carbon downward leakage and hydrodynamic mixing driven by focused recharge. Saturation index calculation and PHREEQC simulations confirmed that massive groundwater CO2 from soil carbon leakage during focused recharge exerted positive perturbations on carbonate weathering, and ultimately stored in a more stable form by transforming into HCO3−. Carbon isotope analysis further identified carbonate weathering accounted for approximately one third of DIC dynamics compared to biogenic sources. This study highlights that focused recharge has a disproportional contribution to flushing soil-derived carbon into groundwater and activating carbonate weathering in the groundwater, with important implications for temporal variability of non-negligible subsurface carbon sinks in the global carbon budget.

Carbon Sequestration Through Forestry: A Differential Equation Approach

Carbon sequestration through forestry represents a promising approach to partially counteract anthropogenic greenhouse gas emissions driving climate change. Tree growth naturally removes carbon dioxide from the atmosphere, storing it as biomass. Sustainably managed forests can effectively function as carbon sinks. However, determining optimal forestry policies involves balancing complex ecological dynamics with economic constraints. This study develops differential equation models quantitatively capturing forest growth, timber harvesting, and carbon sequestration dynamics. Logistic models are first adapted to simulate biomass accumulation of representative tree species. Lifecycle growth patterns spanning juvenile to mature phases are incorporated, along with climate effects. Biomass levels are proportionally related to carbon dioxide removal rates from the atmosphere. Deforestation impacts are analyzed by incorporating harvesting-induced biomass reductions. Sustainability constraints are implemented to ensure minimum viable tree densities across harvest rotations. Optimization techniques then identify management guidelines maximizing economic returns given ecological stability considerations. The goal is providing quantitative insights into rotation lengths, planting densities, and allowable cuts upholding both climate change mitigation and commercial demands. Findings can inform science-based forestry policies to leverage forests as sustainable natural carbon sinks.

Carbon stock potential in rehabilitated mangrove in Lubuk Kertang Village, North Sumatra, Indonesia

Mangrove forests are one of the most productive and efficient long-term natural carbon sinks, tropical natural resources that have social, economic and ecological benefits. Even though the area of mangrove forests is relatively large in of the world, the consequences of various anthropogenic cause various damages. Given their global significance as a large carbon sink, preventing mangrove loss would be an effective climate change adaptation and mitigation strategy. This research was conducted to analyze carbon stocks in mangrove forests resulting from the rehabilitation of former pond land in Lubuk Kertang Village, West Brandan District, Langkat, North Sumatra, Indonesia. The census method was applied in this study, to calculate the value of carbon stocks using an allometric equation with DBH > 5cm. The aboveground biomass was 15.54 Mg/ha. Soil sampling for organic carbon content by collecting a sub-sample 5 cm from the center of the core. The total value of the total carbon stock above and below the soil surface is 9.42 Mg/ha1 and soil carbon is 685 MgC/ha1.

Abandoned cropland compensates the decrease in net ecosystem productivity of impervious surface expansion in China

Abandoned cropland and impervious surface expansion are generally considered to have positive and negative impacts on net ecosystem productivity (NEP), respectively. However, the comprehensive comparison of the impacts of these two land use changes on NEP remains lacking. We use multi-year land cover data, NEP data, and statistical data to track the interannual variability of abandoned cropland and impervious surface expansion in China, and subsequently estimate their impacts on NEP. From 2000 to 2019, 30.8 × 106 ha of cropland in China was abandoned, while the impervious surface area expanded by 8.97 × 106 ha over the period. The average annual abandonment rate and impervious surface expansion rate were 0.83% and 2.96%, respectively. The average annual NEP of abandoned cropland and impervious surface expansion were 39.9 g C/m2 and 16.2 g C/m2, respectively. Using the space-for-time method to estimate NEP changes, results showed that the carbon sink of 0.013 Tg C accumulated by abandoned cropland not only offset the carbon source of 0.01 Tg C from impervious surface expansion but sequestered additional 0.003 Tg C during the study period. Further analysis of the relationships between NEP and natural and anthropogenic factors revealed that temperature had the most significant positive impact on NEP (0.35, p < 0.01), while the urbanization rate had the most significant negative impact on NEP (−0.33, p < 0.01). This study provides a new insight for regulating the effects of land use changes on natural carbon sink/source, and highlights the importance of abandoned cropland to enhancing natural carbon sink.

Committed Global Warming Risks Triggering Multiple Climate Tipping Points

AbstractMany scenarios for limiting global warming to 1.5°C assume planetary‐scale carbon dioxide removal sufficient to exceed anthropogenic emissions, resulting in radiative forcing falling and temperatures stabilizing. However, such removal technology may prove unfeasible for technical, environmental, political, or economic reasons, resulting in continuing greenhouse gas emissions from hard‐to‐mitigate sectors. This may lead to constant concentration scenarios, where net anthropogenic emissions remain non‐zero but small, and are roughly balanced by natural carbon sinks. Such a situation would keep atmospheric radiative forcing roughly constant. Fixed radiative forcing creates an equilibrium “committed” warming, captured in the concept of “equilibrium climate sensitivity.” This scenario is rarely analyzed as a potential extension to transient climate scenarios. Here, we aim to understand the planetary response to such fixed concentration commitments, with an emphasis on assessing the resulting likelihood of exceeding temperature thresholds that trigger climate tipping points. We explore transients followed by respective equilibrium committed warming initiated under low to high emission scenarios. We find that the likelihood of crossing the 1.5°C threshold and the 2.0°C threshold is 83% and 55%, respectively, if today's radiative forcing is maintained until achieving equilibrium global warming. Under the scenario that best matches current national commitments (RCP4.5), we estimate that in the transient stage, two tipping points will be crossed. If radiative forcing is then held fixed after the year 2100, a further six tipping point thresholds are crossed. Achieving a trajectory similar to RCP2.6 requires reaching net‐zero emissions rapidly, which would greatly reduce the likelihood of tipping events.

Urban Flora Structure and Carbon Storage Potential of Woody Trees in Different Land Use Units of Cotonou (West Africa)

Urbanization is a current concern, particularly in Africa, where it is expected to continue and increasingly threaten the effectiveness of plant biodiversity, natural carbon sinks, and the sustainability of cities. This paper investigates the structural parameters and carbon storage potential of trees in the land use units of the city of Cotonou in southern Benin. A total of 149 plots at 2500 m2 each were randomly generated, and trees with a diameter ≥ 10 cm were inventoried. ANOVA revealed that the means of structural parameters (diameter and height classes) and carbon stock rate varied significantly (p &lt; 0.001) across land use units in the city. Tree basal area is estimated at 4.52 ± 5.24 m2 ha−1, with an average of 12.72 (13) feet ha−1. The average diameter of the trees is estimated at 57.94 ± 29.71 cm. Approximately 1000 kg ha−1 (0.94 × 103 kg ha−1) of carbon is stored in the city of Cotonou. Green spaces (1.21 × 103 kg ha−1) and roads (1.19 × 103 kg ha−1) are the units that recorded the highest carbon stocks. Khaya senegalensis, Mangifera indica, and Terminalia mentally lead the top ten species with high stock potential. This study demonstrates the contribution of urban trees to global atmospheric carbon reduction, which varies by species, land use units, and tree density. Future research could investigate an i-Tree Landscape approach for urban carbon estimation. This could reinforce urban carbon data availability for urban ecological planning.