Anthropogenic Carbon Research Articles

Soil respiration across a variety of tree-covered urban green spaces in Helsinki, Finland

Abstract. As an increasing share of the human population is being clustered in cities, urban areas have swiftly become the epicentres of anthropogenic carbon (C) emissions. Understanding different parts of the biogenic C cycle in urban ecosystems is needed in order to assess the potential to enhance their C stocks as a cost-efficient means to balance the C emissions and mitigate climate change. Here, we conducted a field measurement campaign over three consecutive growing seasons to examine soil respiration carbon dioxide (CO2) fluxes and soil organic carbon (SOC) stocks at four measurement sites in Helsinki, representing different types of tree-covered urban green space commonly found in northern European cities. We expected to find variation in the main drivers of soil respiration – soil temperature, soil moisture, and SOC – as a result of the heterogeneity of urban landscape and that this variation would be reflected in the measured soil respiration rates. In the end, we could see fairly constant statistically significant differences between the sites in terms of soil temperature but only sporadic and seemingly momentary differences in soil moisture and soil respiration. There were also statistically significant differences in SOC stocks: the highest SOC stock was found in inactively managed deciduous urban forest and the lowest under managed streetside lawn with common linden trees. We studied the impacts of the urban heat island (UHI) effect and irrigation on heterotrophic soil respiration with process-based model simulations and found that the variation created by the UHI is relatively minor compared to the increase associated with active irrigation, especially during dry summers. We conclude that, within our study area, the observed variation in soil temperature alone was not enough to cause variation in soil respiration rates between the studied green space types, perhaps because the soil moisture conditions were uniform. Thus, irrigation could potentially be a key factor in altering the soil respiration dynamics in urban green space both within the urban area and in comparison to non-urban ecosystems.

Arctic Oceanic Carbon Cycle: A Comprehensive Review of Mechanisms, Regulations, and Models

Understanding the oceanic carbon cycle, particularly in the Arctic regions, is crucial for addressing climate change. However, significant research gaps persist, especially regarding climate effects on the oceanic carbon cycle in these regions. This review systematically explores Arctic-related research, focusing on mechanisms, regulatory frameworks, and modelling approaches in the oceanic carbon cycle, carbon sink, climate change impact, and maritime shipping. The findings highlight the Arctic’s limited observer presence and high operational costs, hindering the data availability and studies on carbon-cycle changes. This underscores the need to integrate real-time Arctic Ocean monitoring data. Carbon sink research urgently requires direct methods to measure anthropogenic carbon uptake and address uncertainties in air–ocean carbon fluxes due to sea ice melting. Unlike terrestrial carbon cycling research, carbon-cycle studies in the oceans, which are essential for absorbing anthropogenic emissions, receive insufficient attention, especially in the Arctic regions. Numerous policies often fall short in achieving effective mitigation, frequently depending on voluntary or market-based approaches. Analyzing carbon-cycle and sink models has uncovered limitations, primarily due to their global perspective, hampering in-depth assessments of climate change effects on the Arctic regions. To pave the way for future research, enhancing Arctic Ocean climate data availability is recommended, as well as fostering international cooperation in carbon-cycle research, enforcing carbon policies, and improving regional modelling in the Arctic Ocean.

A novel integrated gas-cooled fast nuclear reactor and vanadium chloride thermochemical cycle for sustainable fuel production

The continuous growth of anthropogenic carbon emissions from the aviation industry has emphasized the urgent request to substitute traditional aviation fuels with Sustainable Aviation Fuels (SAFs) because SAFs can potentially reduce carbon emissions by around 50–90% as compared to traditional kerosene-based fuels. In this paper, a novel SAF production pathway is developed which is based on biomass processing, nuclear energy, and thermochemical reactions of the vanadium chloride cycle for SAF, clean power, and hydrogen production. The entire system is assessed thermodynamically in terms of energy and exergy performances. Various sensitivity analyses are computed to determine the reliable operating parameters. The study concludes that biomass-to-SAF energetic and exergetic performance is achieved to be 76.72% and 74.35%. The energetic and exergetic performance values, through efficiencies, of the V–Cl cycle are calculated to be 68.08% and 53.50%, respectively. For hydrogen production and storage, an energy penalty of around 16.83 kJ/kg H2 is calculated, which results in an efficiency penalty of 6.18%. The overall energetic and exergetic efficiencies of the proposed integrated system are found to be around 59.79% and 23.78%, respectively.

Bilayer Porous Electrocatalysts for Stable and Selective Electrochemical Reduction of CO2 to Formate in the Presence of Flue Gas Containing NO and SO2.

The development of stable and selective electrocatalysts for converting CO2 to value-added chemicals or fuels has gained much interest in terms of their potential to mitigate anthropogenic carbon emissions. Most of the electrocatalysts are tested under pure CO2; however, industrial outlet flue gas contains numerous impurities, such as NO and SO2, which poison the electrocatalysts and alter the product selectivity. Developing electrocatalysts that are resistant to such impurities is essential for commercial implementation. Herein, we prepared bilayer porous electrocatalysts, namely, Sn, Bi, and In, on porous Cu foam mesh (Sn/Cu-f, Bi/Cu-f, and In/Cu-f) by a two-step electrodeposition process and employed these electrodes for the electrochemical reduction of CO2 to formate. It was observed that the bilayer porous electrocatalysts exhibited high CO2 reduction activity compared to catalysts coated on a Cu mesh. Among bilayer porous electrocatalysts, Sn/Cu-f and Bi/Cu-f electrocatalysts showed more than 80% faradaic efficiency (FE) toward formate production, with a formate partial current density of around -16 and -10.4 mA cm-2, respectively, at -1.02 V vs RHE. In/Cu-f electrocatalyst showed nearly 40% formate FE with formate partial current density of -15 mA cm-2 at -1.22 V vs RHE. We investigated the effect of NO and SO2 impurities (500 ppm of NO, 800 ppm of SO2, and 500 ppm of NO + 800 ppm of SO2) on these electrocatalysts' selectivity and stability toward formate. It was observed that the Bi/Cu-f electrocatalyst showed 50 h stability with 80 ± 5% formate FE, and Sn/Cu-f showed 18 h stability with above 80 ± 5% efficiency in the presence of NO and SO2 mixed with CO2. Furthermore, we studied the effect of CO2 concentration with Sn/Cu-f and Bi/Cu-f catalysts in the range of 15-100% CO2, for which formate FEs of 45-80% were observed.

Promoting low-carbon land use: from theory to practical application through exploring new methods

Cities are main carbon emissions generators. Land use changes can not only affect terrestrial ecosystems carbon, but also anthropogenic carbon emissions. However, carbon monitoring at a spatial level is still coarse, and low-carbon land use encounters the challenge of being unable to adjust at the patch scale. This study addresses these limitations by using land-use data and various auxiliary data to explore new methods. The approach involves developing a high-resolution carbon monitoring model and investigating a patch-scale low-carbon land use model by integrating high carbon sink/source images with the Future Land Use Simulation model. Between 2000 and 2020, the results reveal an increasing trend in both carbon emissions and carbon sinks in the Shangyu district. Carbon sinks can only offset approximately 3% of the total carbon emissions. Spatially, the north exhibits net carbon emissions, while the southern region functions more as a carbon sink. A total of 14.5% of the total land area witnessed a change in land-use type, with the transfer-out of cropland constituting the largest area at 96.44 km2, accounting for 50% of the total transferred area. Land-use transfer resulted in an annual increase of 77.72 × 104 t in carbon emissions between 2000 and 2020. Through land-use structure optimisation, carbon emissions are projected to increase by only 7154 t C/year from 2000 to 2030, significantly lower than the amount between 2000 and 2020. Further low-carbon land optimisation at the patch scale can enhance the carbon sink by 129.59 t C/year. The conclusion drawn is that there is considerable potential to reduce carbon emissions through land use control. The new methods developed in our study can effectively contribute to high-resolution carbon monitoring in spatial contexts and support low-carbon land use, promoting the application of low-carbon land use from theory to practice. This will provide technological guidance for land use planning, city planning, and so forth.

In the Wake of Deeper Convection: Nonsteady State Anthropogenic Carbon in the Greenland Sea

AbstractWe evaluate changes in dissolved inorganic carbon (DIC) in the Greenland Sea between 2002 and 2016, a period characterized by increasing convection depths. We find a mid‐depth maximum in anthropogenic carbon (Cant) accumulation that occurred as waters at these depths were rejuvenated by deeper reaching convection; broadly, these waters have caught up with the atmospheric CO2 rise that had happened between the last time they were ventilated and 2002 and also tracked the atmospheric CO2 rise 2002–2016. The overlying waters only tracked the atmospheric CO2 rise 2002–2016. The mid‐depth maximum in Cant accumulation was not evident in estimates generated with commonly used multiple linear regression (MLR) methods. We analyze the reasons why and show that the eMLR(C*) method may not fully capture nonsteady state changes in Cant when applied along a single hydrographic section as done here. This nonsteady component equates to redistribution of C*, whose spatial gradients in the Greenland Sea are dominated by Cant. We also show that the regular extended multiple linear regression method is sensitive to loss of spatial DIC gradients, which now happens as more and more Cant enters the ocean. Our findings demonstrate that MLR‐based estimates of the Cant accumulation rate should not be taken at face value in highly dynamical ocean regions, such as the Greenland Sea, and the need for also considering the total change in DIC and how this is affected by natural processes. Further investigations into the ability of MLR methods to reproduce nonsteady state changes in Cant are encouraged.

Policies promoting decarbonisation of energy supply under uncertainty: Where, how and when to abate

Energy supply is responsible of more than 80% of anthropogenic carbon emissions whose rapid accumulation in the atmosphere is in turn responsible of unsustainable global warming (overshoot of 1.5 °C) to avoid which carbon neutrality should be achieved in a few decades. "Accelerating" the (supposed) decarbonization of energy supply in sectors different of power generation is commonly considered a necessary step to reach such a goal. Nevertheless, this article points out that (at least in principle) this kind of "acceleration" (e.g. through indis- criminate targets and stringent policy provisions, including over-subsidies for RES producers) might not be desirable. In fact, the allocation of renewables (among different uses, different abatement carriers and over time) is by no means a trivial choice. To explain why, we focus on thermal and transport sectors and analyse the main energy carriers of abatement (electrifi- cation, biomethane and hydrogen), looking for intertemporal and interspatial optimization of renewables allocation, by estimating the LSCOA (levelized social cost of abatement), and by accounting for uncertainty about energy prices and renewable costs. The principal conclusion is that, before electricity supply is fully decarbonised, only greenfield biomethane should be allocated to thermal and transport uses, in the meantime "accelerating" the allocation of elec- tric renewables to power generation. Only when this latter is almost completely decarbonised, policies should promote deep green (now really) electrification of thermal (not "hard to abate") and transport (light-duty) uses. Otherwise, the risk is to significantly slow down the entire process of energy supply decarbonization, and even to undermine the achievement of the climate targets. Finally, regarding green hydrogen, it should be allocated to the so-called "hard to abate" uses (including heavy transport) and to improve (as storage option) electric renewable competitiveness

Estimating the CO2 Fertilization Effect on Extratropical Forest Productivity From Flux‐Tower Observations

AbstractThe land sink of anthropogenic carbon emissions, a crucial component of mitigating climate change, is primarily attributed to the CO2 fertilization effect on global gross primary productivity (GPP). However, direct observational evidence of this effect remains scarce, hampered by challenges in disentangling the CO2 fertilization effect from other long‐term confounding drivers, particularly climatic changes. Here, we introduce a novel statistical approach to separate the CO2 fertilization effect on photosynthetic carbon uptake using eddy covariance (EC) records across 38 extratropical forest sites. We find the median stimulation rate of GPP to be 3.2 ± 0.9 gC m−2 yr−1 ppm−1 (or 16.4 ± 4.2% per 100 ppm) under increasing atmospheric CO2 across these sites, respectively. To validate the robustness of our findings, we test our statistical method using factorial simulations of an ensemble of process‐based land surface models. We address additional factors, including nitrogen deposition and land management, that may impact plant productivity, potentially confounding the attribution to the CO2 fertilization effect. Assuming these site‐specific effects offset to some extent across sites as random factors, the estimated median value still reflects the strength of the CO2 fertilization effect. However, disentanglement of these long‐term effects, often inseparable by timescale, requires further causal research. Our study provides direct evidence that the photosynthetic stimulation is maintained under long‐term CO2 fertilization across multiple EC sites. Such observation‐based quantification is key to constraining the long‐standing uncertainties in the land carbon cycle under rising CO2 concentrations.

Rice husk biochar for carbon sequestration, soil fertility and plant health improvement: A review

Carbon dioxide (CO2) is considered one of the ozone layer gases that contribute to climate change. As the area under agricultural use expands, the level of CO2 from soil as an agricultural by-product increases in the atmosphere. Burning rice husks in open air, decomposing plant materials among other activities release CO2 directly to the atmosphere. Rice husks as a by-product of rice production in Kenya has both the potential to be a source of greenhouse gas (GHG) and production of biochar. Production and deposition of rice husk biochar (RHB) into soil is thought to be one of the viable options for permanent carbon storage with related benefits to soil fertility. This review seeks to consolidate information from various studies that highlight the innovative way of using RHB in combating climate change, improving soil fertility, plant health and crop yields. Studies that have demonstrated beneficial use of RHB were evaluated to prepare this review. When RHB is used as a soil amendment, it has the ability to increase soil carbon storage, mitigate 10% of the current anthropogenic carbon emissions, improve pH and raise Cation Exchange Capacity (CEC), increase available plant nutrients, enhance inherent plant immunity, increase crop yields and improve water quality by increasing retention of nutrients and agrochemicals for plant utilization. A review of the benefits of RHB use in agriculture and climate change mitigation will enhance its adoption. The review further emphasizes the usefulness of pyrolysis in turning organic waste into bioenergy, compost and other beneficial products while protecting the environment. Key Words: Carbon dioxide, climate change, global warming, innovation, ozone layer, temperature.

Assessing the impact of urban expansion on carbon emission

Urban expansion is not only a driving force for economic growth and development but also a perilous element for anthropogenic carbon emission coinciding with population growth, urban expansion, land use pattern, urban sprawl. The study compares urban expansion and its impact on the carbon emission pattern for Rajshahi, a city of Bangladesh where land cover data is an important determinant. At first, the study aims to evaluate the pattern of urban expansion and the second step quantifies the carbon emission trend. The satellite images are used for land cover detection of urban expansion and Support Vector Machine (SVM) algorithm is applied for its classification. Similar carbon emission data are examined to relate carbon emission quantification rate by remote sensing algorithm. It indicates that urban expansion significantly explains carbon emission by comparing with similar secondary data to extract carbon emission and energy consumption. After accentuating urban expansion and carbon emission rate, the spatiotemporal pattern is analyzed in 16 different directions revealing that the urban expansion and emission trend expands to north-western and north-eastern directions of Rajshahi, turning it into a low carbon absorbed city. The responsible landmarks are real estate housing complex, educational institutions, student dormitories, industrial areas, brickfields and mango wholesale business. In order to understand the effects of uncontrolled urban expansion, this study will assist policymakers and urban planners in developing a comprehensive and well-organized strategy.

Implications of Defect Density and Polymer Interactions for CO2 Capture on Amine-Functionalized MIL-101(Cr).

Rising anthropogenic carbon emissions have dire environmental consequences, necessitating remediative approaches, which includes use of solid sorbents. Here, aminopolymers (poly(ethylene imine) (PEI) and poly(propylene imine) (PPI)) are supported within solid mesoporous MIL-101(Cr) to examine effects of support defect density on aminopolymer-MOF interactions for CO2 uptake and stability during uptake-regeneration cycles. Using simulated flue gas (10 % CO2 in He), MIL-101(Cr)-ρhigh (higher defect density) shows 33 % higher uptake capacity per gram adsorbent than MIL-101(Cr)-ρlow (lower defect density) at 308 K, consistent with increased availability of undercoordinated Cr adsorption sites at missing linker defects. Increasing aminopolymer weight loadings (10-50 wt.%) within MIL-101(Cr)-ρlow and MIL-101(Cr)-ρhigh increases amine efficiencies and CO2 uptake capacities relative to bare MOFs, though both incur CO2 diffusion limitations through confined, viscous polymer phases at higher (40-50 wt.%) loadings. Benchmarked against SBA-15, lower polymer packing densities (PPI>PEI), weaker and less abundant van der Waals interactions between aminopolymers and pore walls, and open framework topology increase amine efficiencies. Interactions between amines and Cr defect sites incur amine efficiency losses but grant higher thermal and oxidative stability during uptake-regeneration cycling. Finally, >25 % higher CO2 uptake capacities are achieved for aminopolymer/MIL-101(Cr)-ρhigh under humid conditions, demonstrating promise for realistic applications.

Opinion: A research roadmap for exploring atmospheric methane removal via iron salt aerosol

Abstract. The escalating climate crisis requires rapid action to reduce the concentrations of atmospheric greenhouse gases and lower global surface temperatures. Methane will play a critical role in near-term warming due to its high radiative forcing and short atmospheric lifetime. Methane emissions have accelerated in recent years, and there is significant risk and uncertainty associated with the future growth in natural emissions. The largest natural sink of methane occurs through oxidation reactions with atmospheric hydroxyl and chlorine radicals. Enhanced atmospheric oxidation could be a potential approach to remove atmospheric methane. One method proposes the addition of iron salt aerosol (ISA) to the atmosphere, mimicking a natural process proposed to occur when mineral dust mixes with chloride from sea spray to form iron chlorides, which are photolyzed by sunlight to produce chlorine radicals. Under the right conditions, lofting ISA into the atmosphere could potentially reduce atmospheric methane concentrations and lower global surface temperatures. Recognizing that potential atmospheric methane removal must only be considered an additive measure – in addition to, not replacing, crucial anthropogenic greenhouse gas emission reductions and carbon dioxide removal – roadmaps can be a valuable tool to organize and streamline interdisciplinary and multifaceted research to efficiently move towards understanding whether an approach may be viable and socially acceptable or if it is nonviable and further research should be deprioritized. Here we present a 5-year research roadmap to explore whether ISA enhancement of the chlorine radical sink could be a viable and socially acceptable atmospheric methane removal approach.

Analysis Of Carbonate Chemistry Parameters And Impact Of Anthropogenic CO2 On Ocean Acidification In Selected Coastline Sites Of Ghana

Anthropogenic carbon dioxide (CO2) dissolved into seawater at coastline has shown some effect on oceanic acidification after the preindustrial period. The coastline surrounded with human activities results to oceans acidity that has proven to affect the oceans’ calcifying organisms. This study was conducted in three selected landing beach sites of Ghana coastline to determine the concentrations of CO2, carbonate ions (CO32- ), partial pressures of carbon dioxide (pCO2) and pH for 12 months, and the impact of anthropogenic CO2 on oceanic the oceanic acidification from the sampled sites within the year. The result from sampled sites showed that dissolved CO2 concentration and other evaluated parameters were clearly different in each month and at every sampled site. High CO2 concentration was determined in the months of January and February, and June from different sites. Total mean amount per a year for the sites showed a dissolved CO2 concentration of 16.19 ± 1.73, CO32- concentration of 143.21 ± 21.12 µmol/kg, pCO2 of 600.36 ± 131.92 and pH of 8.01 ± 0.20. Correlation relationship showed an increase of anthropogenic CO2 dissolved into seawater decreased pH at all the study sites, indicating that ocean acidification of seawater at the sites had increased from earlier projections. It was therefore concluded that the anthropogenic CO2 at sites induces rise of ocean acidification, which could pose danger to marine organisms in the studied areas. Continue decrease of pH low harvest of fishes and the calcification rates of other sea organisms

Photothermal CO2 Catalysis toward the Synthesis of Solar Fuel: From Material and Reactor Engineering to Techno-Economic Analysis.

Carbon dioxide (CO2), a member of greenhouse gases, contributes significantly to maintaining a tolerable environment for all living species. However, with the development of modern society and the utilization of fossil fuels, the concentration of atmospheric CO2 has increased to 400ppm, resulting in a serious greenhouse effect. Thus, converting CO2 into valuable chemicals is highly desired, especially with renewable solar energy, which shows great potential with the manner of photothermal catalysis. In this review, recent advancements in photothermal CO2 conversion are discussed, including the design of catalysts, analysis of mechanisms, engineering of reactors, and the corresponding techno-economic analysis. A guideline for future investigation and the anthropogenic carbon cycle are provided.

The carbonate pump feedback on alkalinity and the carbon cycle in the 21st century and beyond

Abstract. Ocean acidification is likely to impact all stages of the ocean carbonate pump, i.e. the production, export, dissolution and burial of biogenic CaCO3. However, the associated feedback on anthropogenic carbon uptake and ocean acidification has received little attention. It has previously been shown that Earth system model (ESM) carbonate pump parameterizations can affect and drive biases in the representation of ocean alkalinity, which is critical to the uptake of atmospheric carbon and provides buffering capacity towards associated acidification. In the sixth phase of the Coupled Model Intercomparison Project (CMIP6), we show divergent responses of CaCO3 export at 100 m this century, with anomalies by 2100 ranging from −74 % to +23 % under a high-emission scenario. The greatest export declines are projected by ESMs that consider pelagic CaCO3 production to depend on the local calcite/aragonite saturation state. Despite the potential effects of other processes on alkalinity, there is a robust negative correlation between anomalies in CaCO3 export and salinity-normalized surface alkalinity across the CMIP6 ensemble. Motivated by this relationship and the uncertainty in CaCO3 export projections across ESMs, we perform idealized simulations with an ocean biogeochemical model and confirm a limited impact of carbonate pump anomalies on 21st century ocean carbon uptake and acidification. However, we highlight a potentially abrupt shift, between 2100 and 2300, in the dissolution of CaCO3 from deep to subsurface waters when the global-scale mean calcite saturation state reaches about 1.23 at 500 m (likely when atmospheric CO2 reaches 900–1100 ppm). During this shift, upper ocean acidification due to anthropogenic carbon uptake induces deep ocean acidification driven by a substantial reduction in CaCO3 deep dissolution following its decreased export at depth. Although the effect of a diminished carbonate pump on global ocean carbon uptake and surface ocean acidification remains limited until 2300, it can have a large impact on regional air–sea carbon fluxes, particularly in the Southern Ocean.

Rapid shoaling of aragonite saturation horizon in the northern Indian Ocean

Anthropogenic carbon dioxide (CO2) penetrates up to 1000 m of water column in the Indian Ocean resulting in acidification and corrosion of aragonite skeletal material. The shallowest aragonite saturation horizon (ASH) was observed in the Bay of Bengal (BoB; 219 ± 10 m) within the tropical Indian Ocean. The ASH shoaled at the rate of 6.3 ± 5 and 4.4 ± 3 m yr−1 in the past four decades in the BoB and Arabian Sea respectively. As a result, an increase in total alkalinity (TA) was observed at the rate of 0.5 ± 0.3 and 0.25 ± 0.2 μmol kg−1 yr−1 at the depth of ASH in the BoB, and Arabian Sea respectively. While the shoaling rate of ASH remained the same in the Arabian Sea over the past four decades, in contrast, rapid shoaling was observed in the BoB in the recent decades due to higher accumulation of anthropogenic CO2 in the upper ocean associated with an increase in river discharge and decomposition of riverine organic matter. These two processes decreased the pH resulting in corrosion of aragonite skeletal material and increased TA at the depth of ASH in the BoB. Under a business-as-usual scenario, aragonite-secreting organisms will be seriously affected by the middle of this century in the BoB.

Microalgal biorefinery as a sustainable and cost-effective platform for co-production of high-value-added products/metabolites: An insight into emerging trends, challenges, and opportunities

In biorefining, biomass is processed sustainably to produce multiple high-value products. The biorefinery concept has been acknowledged as the most promising tactic for creating a biomass-based business/industry. Biomass from microalgae includes a variety of beneficial bioactive elements like pigments, proteins, polyunsaturated fatty acids, and polyhydroxyalkanoates (PHAs). In addition, microalgal cells can also be utilized as a source of raw materials to make biofuel. In order to reduce overall process costs, these value-added chemicals can be extracted concurrently or sequentially with biodiesel. Further, to promote microalgae in the industrial sector, a biorefinery approach is crucial. Researchers have been eager to use the bio-refinery strategy for obtaining the high-value constituents entrapped by microalgae. Microalgae not only contain a variety of valuable chemicals but also contribute in lowering the atmospheric levels of anthropogenic carbon dioxide. These advantages make microalgae a viable resource for bio-refinery strategy. This review intends to emphasize the valuable properties of microalgae together with their significance to people. This article also highlights the recent as well as upcoming developments that will increase the viability of bio-processing for microalgal-based bio-refinery.

Forest-floor respiration, N2O fluxes, and CH4 fluxes in a subalpine spruce forest: drivers and annual budgets

Abstract. Forest ecosystems play an important role in the global carbon (C) budget by sequestering a large fraction of anthropogenic carbon dioxide (CO2) emissions and by acting as important methane (CH4) sinks. The forest-floor greenhouse gas (GHG; CO2, CH4, and nitrous oxide (N2O)) flux, i.e., from soil and understory vegetation, is one of the major components to consider when determining the C or GHG budget of forests. Although winter fluxes are essential to determine the annual C budget, only very few studies have examined long-term, year-round forest-floor GHG fluxes. Thus, we aimed to (i) quantify seasonal and annual variations of forest-floor GHG fluxes; (ii) evaluate their drivers, including the effects of snow cover, timing, and amount of snowmelt; and (iii) calculate annual budgets of forest-floor GHG fluxes for a subalpine spruce forest in Switzerland. We measured GHG fluxes year-round during 4 years with four automatic large chambers at the ICOS Class 1 Ecosystem station Davos (CH-Dav). We applied random forest models to investigate environmental drivers and to gap-fill the flux time series. The forest floor emitted 2336 g CO2 m−2 yr−1 (average over 4 years). Annual and seasonal forest-floor respiration responded most strongly to soil temperature and snow depth. No response of forest-floor respiration to leaf area index or photosynthetic photon flux density was observed, suggesting a strong direct control of soil environmental factors and a weak, or even lacking, indirect control of canopy biology. Furthermore, the forest floor was a consistent CH4 sink (−0.71 g CH4 m−2 yr−1), with annual fluxes driven mainly by snow depth. Winter CO2 fluxes were less important for the CO2 budget (6.0 %–7.3 %), while winter CH4 fluxes contributed substantially to the annual CH4 budget (14.4 %–18.4 %). N2O fluxes were very low (0.007 g N2O m−2 yr−1), negligible for the forest-floor GHG budget at our site. In 2022, the warmest year on record with below-average precipitation at the Davos site, we observed a substantial increase in forest-floor respiration compared with other years. The mean forest-floor GHG budget indicated emissions of 2319 ± 200 g CO2 eq. m−2 yr−1 (mean ± standard deviation (SD) over all years), with respiration fluxes dominating and CH4 offsetting a very small proportion (0.8 %) of the CO2 emissions. Due to the relevance of snow cover, we recommend year-round measurements of GHG fluxes with high temporal resolution. In a future with increasing temperatures and less snow cover due to climate change, we expect increased forest-floor respiration at this subalpine site modulating the carbon sink of the forest ecosystem.

Energy efficiency of hydrogen production via gasification from lignocellulosic residual biomass blend

Facing the challenges of environmental sustainability and energy security caused by anthropogenic carbon emissions, there is a need to adopt cleaner energy generation technologies, leveraging Colombia's existing national resources. In this context, hydrogen emerges as a promising source of renewable energy. Therefore, this project explores the use of a blend of residual lignocellulosic biomass as raw material for hydrogen production through gasification for energy purposes. Initially, a screening of residual lignocellulosic biomass in the study region was conducted, a blend was selected, and a simulation of the synthesis gas production process was carried out prospectively using Aspen Plus Dynamics® software. The results revealed that, by using the selected biomass blend, a synthesis gas with a hydrogen molar fraction of 38.7% and an ER of 0.19 was obtained. According to sensitivity analyses, the optimal parameters identified to achieve this hydrogen concentration were: gasification temperature of 707°C, oxygen flows of 484 kg/h, steam at 420 kg/h, and gasification pressure of 1 atm. These findings support the potential of the studied lignocellulosic biomass blend as an alternative for hydrogen production, while also offering an opportunity for the valorization of lignocellulosic residual biomass.

Electricity climate-compatibility index: Measuring global progress towards decarbonising the power sector

This paper proposes a novel index, ECI (Electricity Climate-Compatibility Index), to measure global fossil fuel electricity generation alignment with climate targets. Net anthropogenic carbon dioxide emissions (CO2) must approach zero by mid-century to stabilise the mean temperature to well below 2°C. Pursuing carbon neutrality will require immediate action if we are to avoid the economic risks associated with a delayed, more abrupt energy transition. This paper reviewed the existing literature and found insufficient indicators for country-level climate targets in electricity generation. Therefore, the paper proposes a novel electricity climate-compatibility index (ECI) to address the gap. The index computes climate compatibility or incompatibility as the difference between fossil fuel electricity generation permitted in the Integrated Assessment Model (IAM) country-level climate scenarios and that which is generated from operational, under-construction and planned power generation assets. The ECI correlates positively in specific instances with relatable metrics such as Energy Transition Index (ETI) and Climate Change Performance Index (CCPI) but provides a better understanding of the climate-incompatible generation of fossil fuel plants for a decarbonised power sector.