Net Carbon Flux Research Articles

Carbon dioxide fertilization enhanced carbon sink offset by climate change and land use in Amazonia on a centennial scale

The Amazon, the Earth's largest tropical forest, plays a critical role in the global carbon cycle, acting as a significant carbon sink. Recent studies, however, indicate a decline in its carbon sequestration capacity due to climate variability, intensive deforestation, and fires. This study aims to examine the impacts of these factors on the carbon dynamics of the Amazon over a centennial scale based on dynamic global vegetation models (DGVMs) of Trendy-v11. It was found that the Amazon region exhibited significant spatiotemporal variations in net land carbon (C) fluxes, and was a net C sink (40.02 ± 242.64 Tg C yr−1) during 1901–2021. The Amazonian net biome productivity (NBP) showed a 6-decades-scale shift from a decreasing trend (−3.78 Tg C yr−2) during 1901–1959 to an increasing trend (2.39 Tg C yr−2) during 1960–2021. The Amazonian NBP was negatively related to air temperature while positively related to dry-season precipitation during 1901–2021. Furthermore, the increase of atmospheric CO2 concentration during 1901–2020 enhanced Amazonian NBP by 36.40 ± 8.39 Pg C, which was largely offset by land use change (−18.84 ± 12.02 Pg C) and climate change (−10.03 ± 5.00 Pg C). Our findings underscore the critical need for sustainable management practices in the Amazon to enhance its C sink and preserve its function in the global climate system.

Description and Evaluation of the CNRM‐Cerfacs Climate Prediction System (C3PS)

AbstractThe CNRM‐Cerfacs Climate Prediction System (C3PS) is a new research modeling tool for performing climate reanalyzes and seasonal‐to‐multiannual predictions for a wide array of Earth system variables. C3PS is based on the CNRM‐ESM2‐1 model including interactive aerosols and stratospheric chemistry schemes as well as terrestrial and marine biogeochemistry enabling a comprehensive representation of the global carbon cycle. C3PS operates through a seamless coupled initialization for the atmosphere, land, ocean, sea ice and biogeochemistry components that allows a continuum of predictions across seasonal to multiannual time‐scales. C3PS has also contributed to the Decadal Climate Prediction Project (DCPP‐A) as part of the sixth Coupled Model Intercomparison Project (CMIP6). Here we describe the main characteristics of this novel Earth system‐based prediction platform, including the methodological steps for obtaining initial states to produce forecasts. We evaluate the entire C3PS initialization procedure with the most up‐to‐date observations and reanalyzes over 1960–2021, and we discuss the overall performance of the system in the light of the lessons learned from previous and actual prediction platforms. Regarding the forecast skill, C3PS exhibits comparable seasonal predictive skill to other systems. At the multiannual scale, C3PS shows significant predictive skill in surface temperature during the first 2 years after initialization in several regions of the world. C3PS also exhibits potential predictive skill in Net primary production (NPP) and carbon fluxes several years in advance. This expands the possibility of applications of forecasting systems, such as the possibility of performing multiannual predictions of marine ecosystems and carbon cycle.

“Pink power”—the importance of coralline algal beds in the oceanic carbon cycle

Current evidence suggests that macroalgal-dominated habitats are important contributors to the oceanic carbon cycle, though the role of those formed by calcifiers remains controversial. Globally distributed coralline algal beds, built by pink coloured rhodoliths and maerl, cover extensive coastal shelf areas of the planet, but scarce information on their productivity, net carbon flux dynamics and carbonate deposits hampers assessing their contribution to the overall oceanic carbon cycle. Here, our data, covering large bathymetrical (2–51 m) and geographical ranges (53°N–27°S), show that coralline algal beds are highly productive habitats that can express substantial carbon uptake rates (28–1347 g C m−2 day−1), which vary in function of light availability and species composition and exceed reported estimates for other major macroalgal habitats. This high productivity, together with their substantial carbonate deposits (0.4–38 kilotons), renders coralline algal beds as highly relevant contributors to the present and future oceanic carbon cycle.

Monitoring the Net Primary Productivity of Togo’s Ecosystems in Relation to Changes in Precipitation and Temperature

Climate variability significantly impacts plant growth, making it crucial to monitor ecosystem performance for optimal carbon sequestration, especially in the context of rising atmospheric CO2 levels. Net Primary Productivity (NPP), which measures the net carbon flux between the atmosphere and plants, serves as a key indicator. This study uses the CASA (Carnegie–Ames–Stanford Approach) model, a radiation use efficiency method, to assess the spatio-temporal dynamics of NPP in Togo from 1987 to 2022 and its climatic drivers. The average annual NPP over 36 years is 4565.31 Kg C ha−1, with notable extremes in 2017 (6312.26 Kg C ha−1) and 1996 (3394.29 Kg C ha−1). Productivity in natural formations increased between 2000 and 2022. While climate change and land use negatively affect Total Production (PT) from 2000 to 2022, they individually enhance NPP variation (58.28% and 188.63%, respectively). NPP shows a strong positive correlation with light use efficiency (r2 = 0.75) and a moderate one with actual evapotranspiration (r2 = 0.43). Precipitation and potential evapotranspiration have weaker correlations (r2 = 0.20; 0.10), and temperature shows almost none (r2 = 0.05). These findings contribute to understanding ecosystem performance, supporting Togo’s climate commitments.

Relationship between eutrophication and greenhouse gases emission in shallow freshwater lakes

In shallow lakes, there are complex relationships between lake eutrophication and greenhouse gas emissions that deserve to be studied, which are important for solving lake eutrophication, slowing down climate warming, and reducing carbon emissions. In order to explore the relationship and mechanism between eutrophication and greenhouse gases (GHGs), the net GHGs emission flux and transformation of carbon, and nitrogen in 45 shallow freshwater lakes were investigated from May to September 2022. Eutrophication facilitated potential denitrification rate (Dt) without increasing nitrous oxide (N2O) production based on the significantly positive relationship between eutrophication and Dt. This should be attributed to the shift from incomplete (N2O producing process) to complete denitrification (N2 producing process). Compared to NarG mediating nitrate (NO3−) to nitrite (NO2−), fewer eutrophication indicators showed a positive relationship with NosZ mediating N2O to N2, suggesting that more stringent conditions are required for complete denitrification, which was achieved in the lakes we investigated. Optimal reduction in net carbon dioxide (CO2) emissions occurs at high levels of primary productivity, as indicated by the V-shaped relationship between chlorophyll a (Chl a) and CO2 emissions. However, in hyper-eutrophic lakes, there is an upward trend in CO2 production. The possible explanations should include CO2 production and fixation as well as methane (CH4) oxidation. The bell-shaped relationship between the net flux of CH4 emission and Chl a could be explained that CH4 was heavily oxidized due to sufficient oxygen caused by algal bloom. This fact gave evidence for the increase of the net flux of CO2 emission in high primary productivity lakes. Therefore, the relationship and mechanism between net GHGs emission flux and eutrophication remained complex and various.

Quantifying water-use efficiency in plant canopies with varying leaf angle and density distribution.

Variation in architectural traits related to the spatial and angular distribution of leaf area can have considerable impacts on canopy-scale fluxes contributing to water-use efficiency (WUE). These architectural traits are frequent targets for crop improvement and for improving the understanding and predictions of net ecosystem carbon and water fluxes. A three-dimensional, leaf-resolving model along with a range of virtually generated hypothetical canopies were used to quantify interactions between canopy structure and WUE by examining its response to variation of leaf inclination independent of leaf azimuth, canopy heterogeneity, vegetation density and physiological parameters. Overall, increasing leaf area index (LAI), increasing the daily-averaged fraction of leaf area projected in the sun direction (Gavg) via the leaf inclination or azimuth distribution and increasing homogeneity had a similar effect on canopy-scale daily fluxes contributing to WUE. Increasing any of these parameters tended to increase daily light interception, increase daily net photosynthesis at low LAI and decrease it at high LAI, increase daily transpiration and decrease WUE. Isolated spherical crowns could decrease photosynthesis by ~60 % but increase daily WUE ≤130 % relative to a homogeneous canopy with equivalent leaf area density. There was no observed optimum in daily canopy WUE as LAI, leaf angle distribution or heterogeneity was varied. However, when the canopy was dense, a more vertical leaf angle distribution could increase both photosynthesis and WUE simultaneously. Variation in leaf angle and density distributions can have a substantial impact on canopy-level carbon and water fluxes, with potential trade-offs between the two. These traits might therefore be viable target traits for increasing or maintaining crop productivity while using less water, and for improvement of simplified models. Increasing canopy density or decreasing canopy heterogeneity increases the impact of leaf angle on WUE and its dependent processes.

Country-level estimates of gross and net carbon fluxes from land use, land-use change and forestry

Abstract. The reduction of CO2 emissions and the enhancement of CO2 removals related to land use are considered essential for future pathways towards net-zero emissions and mitigating climate change. With the growing pressure under global climate treaties, country-level land-use CO2 flux data are becoming increasingly important. So far, country-level estimates are mainly available through official country reports, such as the greenhouse gas inventories reported to the United Nations Framework Convention on Climate Change (UNFCCC). Recently, different modelling approaches, namely dynamic global vegetation models (DGVMs) and bookkeeping models, have moved to higher spatial resolutions, which makes it possible to obtain model-based country-level estimates that are globally consistent in their methodology. To progress towards a largely independent assessment of country reports using models, we analyse the robustness of country-level CO2 flux estimates from different modelling approaches in the period 1950–2021 and compare them with estimates from country reports. Our results highlight the general ability of modelling approaches to estimate land-use CO2 fluxes at the country level and at higher spatial resolution. Modelled land-use CO2 flux estimates generally agree well, but the investigation of multiple DGVMs and bookkeeping models reveals that the robustness of their estimates strongly varies across countries, and substantial uncertainties remain, even for top emitters. Similarly, modelled land-use CO2 flux estimates and country-report-based estimates agree reasonably well in many countries once their differing definitions are accounted for, although differences remain in some other countries. A separate analysis of CO2 emissions and removals from land use using bookkeeping models also shows that historical peaks in net fluxes stem from emission peaks in most countries, whereas the long-term trends are more connected to removal dynamics. The ratio of the net flux to the sum of CO2 emissions and removals from land use (the net-to-gross flux ratio) underlines the spatio-temporal heterogeneity in the drivers of net land-use CO2 flux trends. In many tropical regions, net-to-gross flux ratios of about 50 % are due to much larger emissions than removals; in many temperate countries, ratios close to zero show that emissions and removals largely offset each other. Considering only the net flux thus potentially masks large emissions and removals and the different timescales upon which they act, particularly if averaged over countries or larger regions, highlighting the need for future studies to focus more on the gross fluxes. Data from this study are openly available via the Zenodo portal at https://doi.org/10.5281/zenodo.8144174 (Obermeier et al., 2023).

Evaluation of Water and Carbon Estimation Models in the Caatinga Biome Based on Remote Sensing

The study of energy, water, and carbon exchanges between ecosystems and the atmosphere is important in understanding the role of vegetation in regional microclimates. However, they are still relatively scarce when it comes to Caatinga vegetation. This study aims to identify differences in the dynamics of critical environmental variables such as net radiation (Rn), evapotranspiration (ET), and carbon fluxes (gross primary production, GPP) in contrasting recovered Caatinga (dense Caatinga, DC) and degraded Caatinga (sparse Caatinga, SC) in the state of Paraíba, northeastern Brazil. Estimates were performed using the Surface Energy Balance Algorithm for Land (SEBAL), and comparisons between estimated and measured data were conducted based on the coefficient of determination (R2). The fluxes were measured using the Eddy Covariance (EC) method for comparison with the same variables derived from Moderate Resolution Imaging Spectroradiometer (MODIS) data aboard the Terra satellite. The estimates showed higher Rn values for the DC, indicating that this area should have greater energy availability for physical, biological, and chemical processes. The R2 between daily Rn estimates and observations was 0.93. The ET estimated using the SEBAL showed higher differences in relation to the observed values; however, it presented better spatial discrimination of the surface features. The MOD16A2 algorithm, however, presented ET values closer to the observed data and agreed with the seasonality of the Enhanced Vegetation Index (EVI). The DC generally showed higher ET values than the SC, while the MODIS data (GPP MOD17A2H) presented a temporal behavior closer to the observations. The difference between the two areas was more evident in the rainy season. The R2 values between GPP and GPP MOD17A2H were 0.76 and 0.65 for DC and SC, respectively. In addition, the R2 values for GPP Observed and GPP modeled were lower, i.e., 0.28 and 0.12 for the DC and SC, respectively. The capture of CO2 is more evident for the DC considering the whole year, with the SC showing a notable increase in CO2 absorption only in the rainy season. The GPP estimated from the MOD17A2H showed a predominant underestimation but evidenced the effects of land use and land cover changes over the two areas for all seasons.

Sieving and hydrothermal pre‐treatments for preparing ultra‐high mechanical strength particleboard

AbstractThe application of non woody biomass materials in the manufacture of wood‐based panels has been confirmed as an efficient carbon sequestration approach. In this study, reed straw was recommended to produce reed‐based particleboards (RPs). Sieving and hydrothermal pre‐treatments were conducted on the inner layer reed particles to reduce the adverse influence of the waxy layer on the mechanical strength of RPs. The thickness swelling rate was merely 1.04% (2 h), and the internal bonding strength could reach up to 0.88 MPa, which met the ISO requirements for heavy‐duty load bearing in dry conditions (P‐HLB REG). More importantly, this study constructed the plate forming process that retains the natural morphological characteristics of reed to the maximum extent. Generally, the mechanical strength of RPs was markedly higher than mostly straw‐based and even wood‐based panels. The static bending strength of RPs could reach 35.6 MPa after sieving pre‐treatment. In addition, according to the LCA, the net carbon flux could reach −1227.55 kg CO2 eq. when producing 1 m3 RPs. The obtained RPs could be utilized as wood substitutes to produce furniture and building materials with promising environmental and economic benefits.

Spatiotemporal distributions of air-sea CO2 flux modulated by windseas in the Southern Indian Ocean

The Southern Indian Ocean is a major reservoir for rapid carbon exchange with the atmosphere, plays a key role in the world’s carbon cycle. To understand the importance of anthropogenic CO2 uptake in the Southern Indian Ocean, a variety of methods have been used to quantify the magnitude of the CO2 flux between air and sea. The basic approach is based on the bulk formula—the air-sea CO2 flux is commonly calculated by the difference in the CO2 partial pressure between the ocean and the atmosphere, the gas transfer velocity, the surface wind speed, and the CO2 solubility in seawater. However, relying solely on wind speed to measure the gas transfer velocity at the sea surface increases the uncertainty of CO2 flux estimation. Recent studies have shown that the generation and breaking of ocean waves also significantly affect the gas transfer process at the air-sea interface. In this study, we highlight the impact of windseas on the process of air-sea CO2 exchange and address its important role in CO2 uptake in the Southern Indian Ocean. We run the WAVEWATCH III model to simulate surface waves in this region over the period from January 1st 2002 to December 31st 2021. Then, we use the spectral partitioning method to isolate windseas and swells from total wave fields. Finally, we calculate the CO2 flux based on the new semiempirical equation for gas transfer velocity considering only windseas. We found that after considering windseas’ impact, the seasonal mean zonal flux (mmol/m2·d) increased approximately 10%-20% compared with that calculated solely on wind speed in all seasons. Evolution of air-sea net carbon flux (PgC) increased around 5.87%-32.12% in the latest 5 years with the most significant seasonal improvement appeared in summer. Long-term trend analysis also indicated that the CO2 absorption capacity of the whole Southern Indian Ocean gradually increased during the past 20 years. These findings extend the understanding of the roles of the Southern Indian Ocean in the global carbon cycle and are useful for making management policies associated with marine environmental protection and global climatic change mitigation.

Evaluating Northern Hemisphere Growing Season Net Carbon Flux in Climate Models Using Aircraft Observations

AbstractUnderstanding terrestrial ecosystems and their response to anthropogenic climate change requires quantification of land‐atmosphere carbon exchange. However, top‐down and bottom‐up estimates of large‐scale land‐atmosphere fluxes, including the northern extratropical growing season net flux (GSNF), show significant discrepancies. We developed a data‐driven metric for the GSNF using atmospheric carbon dioxide concentration observations collected during the High‐Performance Instrumented Airborne Platform for Environmental Research Pole‐to‐Pole Observations and Atmospheric Tomography Mission flight campaigns. This aircraft‐derived metric is bias‐corrected using three independent atmospheric inversion systems. We estimate the northern extratropical GSNF to be 5.7 ± 0.3 Pg C and use it to evaluate net biosphere productivity from the Coupled Model Intercomparison Project phase 5 and 6 (CMIP5 and CMIP6) models. While the model‐to‐model spread in the GSNF has decreased in the CMIP6 models relative to that of the CMIP5 models, there is still disagreement on the magnitude and timing of seasonal carbon uptake with most models underestimating the GSNF and overestimating the length of the growing season relative to the observations. We also use an emergent constraint approach to estimate annual northern extratropical gross primary productivity to be 56 ± 17 Pg C, heterotrophic respiration to be 25 ± 13 Pg C, and net primary productivity to be 28 ± 12 Pg C. The flux inferred from these aircraft observations provides an additional constraint on large‐scale gross fluxes in prognostic Earth system models that may ultimately improve our ability to accurately predict carbon‐climate feedbacks.

Decoupling of land-use net carbon flux, economic growth, and population change in China.

In the process of China's modernization, promoting the sustainable development of resource-based cities is a major strategic issue and it has now also become a worldwide issue. This study uses the coupling model to validate the coupling relationship between China's land-use net carbon flux and economic growth and population change during 2009-2017. The study for the first time draws the conclusion that the coupling degree among the three is getting lower, the correlation is gradually weaker, and the independent relationship is becoming more and more prominent. Utilizing the Tapio decoupling model, we obtained the weak decoupling conclusion that the economic growth rate is higher than the growth rate of the land-use net carbon flux, while negative decoupling of sprawl is where the rate of population growth is less than the rate of net land-use carbon flux growth.

Forest liming in the face of climate change: the implications of restorative liming for soil organic carbon in mature German forests

Abstract. Forest liming is a management tool that has and continues to be used extensively across northern Europe to counteract acidification processes from anthropogenic sulfur and nitrogen (N) deposition. In this study, we quantified how liming affects soil organic carbon (SOC) stocks and attempt to disentangle the mechanisms responsible for the often contrasting processes that regulate net soil carbon (C) fluxes. Using a paired plot experimental design we compared SOC stocks in limed plots with adjacent unlimed control plots at 28 experimental sites to 60 cm soil depth in mature broadleaf and coniferous forests across Germany. Historical soil data from a subset of the paired experiment plots were analyzed to assess how SOC stocks in both control and limed plots changed between 1990 and 2019. Overall, we found that forest floor C stocks have been accumulating over time in the control plots. Liming however largely offset organic layer buildup in the L/Of layer, and forest floor C stocks remained unchanged over time in the limed plots. This, in turn, meant that nutrients remained mobile and were not bound in soil organic matter complexes. Results from the paired plot analysis showed that forest floor C stocks were significantly lower in limed plots than the control (−34 %, −8.4 ± 1.7 Mg C ha−1) but did not significantly affect SOC stocks in the mineral soil, when all sites are pooled together. In the forest floor layers, SOC stocks exhibited an exponential decrease with increasing pH, highlighting how lime-induced improvements in the biochemical environment stimulate organic matter (OM) decomposition. Nevertheless, for both forest floor and mineral soils, the magnitude and direction of the belowground C changes hinged directly on the inherent site characteristics, namely, forest type (conifer versus broadleaf), soil pH, soil texture, and the soil SOC stocks. On the other hand, SOC stock decreases were often offset by other processes that fostered C accumulation, such as improved forest productivity or increased carbon stabilization, which correspondingly translated to an overall variable response by SOC stocks, particularly in the mineral soil. Lastly, we measured soil carbon dioxide (CO2) and soil methane (CH4) flux immediately after a re-liming event at three of the experimental sites. Here, we found that (1) liming doubles CH4 uptake in the long-term; (2) soil organic matter mineralization processes respond quickly to liming, even though the duration and size of the CO2 flush varied between sites; and (3) lime-derived CO2 contributed very little to total CO2 emissions over the measurement period (determined using stable isotope approaches).

CARBON STOCK AND FLUX UNDER THE INFLUENCE OF VARIOUS AGRICULTURAL PRACTICES IN TROPICAL SOILS OF SOUTHEASTERN NIGERIA

This study investigated carbon stock under different agricultural practices in tropical soils of Southeastern Nigeria in two distinct seasons. Six agricultural practices {Natural undisturbed forest land (NUFL); Afforestation (AFP); Continuous cultivated land (CCL); Cattle transit (CT); Grassland (GRL) and Uncultivated land (UCL)} were identified. Carbon stock and flux were investigated at three distinct depths (0-30, 30-60 and 60-90 cm). Experimental design adopted was randomized complete block design. Results showed that under NUFL practices, highest concentrations of carbon were obtained from soil aggregates (macro-aggregates: 1.86 and 1.93 g kg-1; micro-aggregates: 4.48 and 4.64 g kg-1) in both raining and dry seasons. Carbon concentrations in the studied sites diminished with depth. Highest soil organic carbon stock (SOCs) contents of 85.77 and 99.86 kg C ha-1 were obtained from site under NUFL practices. Carbon stocks in the study soils declined with depths 99.86 to 27.31 kg C ha-1; 89.49 to 48.13 kg C ha-1 in raining and dry seasons. High values of CO2 (4.96 and 7.77%) were obtained from soil under intensive cultivation (CCL) in both seasons. Maximum Net carbon fluxes (-22.35 and -23.31) were recorded in soils under CCL practices in raining season and dry season. Net carbon flux was consistently negative and significantly lower in soils under NUFL (-84.68 and -97.88) in both seasons. Conclusively, NUFL and AFP practices enhanced vegetation cover which reduced carbon emissions, improved storage of carbon as well as other soil properties with lower risk of soil degradation when compared to soil under other farming practices.

The Transformation and Export of Organic Carbon Across an Arctic River-Delta-Ocean Continuum.

The Arctic Ocean is surrounded by land that feeds highly seasonal rivers with water enriched in high concentrations of dissolved and particulate organic carbon (DOC and POC). Explicit estimates of the flux of organic carbon across the land-ocean interface are difficult to quantify and many interdependent processes makes source attribution difficult. A high-resolution 3-D biogeochemical model was built for the lower Yukon River and coastal ocean to estimate biogeochemical cycling across the land-ocean continuum. The model solves for complex reactions related to organic carbon transformation, including mechanistic photodegradation and multi-reactivity microbial processing, DOC-POC flocculation, and phytoplankton dynamics. The baseline DOC and POC flux out of the delta from April to September 2019, was 977 and 536GgC (∼80% of the annual total), but only 50% of the DOC and 25% of the POC exited the plume across the 10m isobath. Microbial breakdown of DOC accounted for a net loss of 168GgC (17% of delta export) within the plume and photodegradation accounted for a net loss of 46.6GgC DOC (5% of delta export) in 2019. Flocculation decreased the total organic carbon flux by only 6.4GgC (∼1%), while POC sinking accounted for 63.3GgC (10%) settling in the plume. The loss of chromophoric dissolved organic matter due to photodegradation increased the light available for phytoplankton growth throughout the coastal ocean, demonstrating the secondary effects that organic carbon reactions can have on biological processes and the net coastal carbon flux.

Carbon dioxide fluxes of cyanobacterial crusts and underlying soil under different precipitation patterns in the Ulan Buh Desert, China

Cyanobacterial crusts, sensitive to changes in the moisture content, are widely distributed in the Ulan Buh Desert. Changes in precipitation patterns due to global climate change are expected to influence the carbon emission and photosynthetic carbon fixation of soil in areas covered with cyanobacterial crusts. We assessed how changes in precipitation amount and frequency affect carbon processes of Cyanobacterial Crusts. Taking average precipitation amount and frequency in August during the past 30 years as control, we established nine precipitation patterns (three amounts × three frequencies). The net carbon flux (NCF) and dark respiration rate (DRR) of cyanobacterial crusts and underlying soil were investigated. Precipitation could stimulate NCF and DRR immediately. With increasing water application times, the peak values of NCF, DRR and 12 h cumulative carbon emissions gradually decreased. Both precipitation amount and frequency significantly affected cumulative carbon emissions but without an interactive effect. Under the same frequency, cumulative carbon emissions increased with increasing precipitation amounts. Under the same total precipitation amount, cumulative carbon emissions caused by high-frequency events were the highest, followed by those of low-frequency precipitation and the control. However, such changes, against the background of a changing global climate, will result in increased carbon emissions of cyanobacterial crusts and underlying Soil, suggesting that cyanobacteria should be considered in projections of the future carbon budget.

Use of remote sensing and bio-geochemical models to estimate the net carbon fluxes of managed mountain grasslands

The current paper presents a methodology which can simulate the net carbon fluxes of semi-natural grasslands based on the combination of a parametric and a bio-geochemical model. The first model (modified C-Fix) estimates grassland gross primary production (GPP) by driving the light use efficiency approach with remotely sensed normalized difference vegetation index (NDVI) data. The latter model (BIOME-BGC) simulates all main ecosystem processes based on meteorological and ancillary data. The outputs of the two models are finally combined and corrected for the effects of human-induced biomass changes (i.e. mowing, grazing, etc.). The modelling strategy, fed with ancillary and MODIS NDVI data, is tested in two semi-natural grasslands, the first (Amplero) on the Apennines and the second (Monte Bondone) on the Alps (Central and Northern Italy, respectively). The two sites, which show diversified eco-climatic conditions and are managed differently (i.e. Amplero by spring mowing plus cattle grazing and Monte Bondone by summer mowing), were selected for the availability of eddy covariance observations of GPP and net ecosystem production (NEP) collected during several years (from 2003 to 2012). These observations were used to assess the estimates of the modelling strategy, obtaining promising results for both study sites. The greatest estimation errors are found in the Alpine site and are mostly induced by the inaccurate detection of local grassland NDVI values, which is due to the insufficient spatial and temporal resolutions of the used MODIS NDVI imagery. The results of the study highlight the importance of information on the local management practices applied, which is decisive for quantifying medium-term changes in net carbon fluxes.

Performance and environmental implication assessments of green bio-composite from rice straw and bamboo

The clean and eco-efficient utilization of agro-industrial lignocellulose wastes is imperative for social development. This study proposes a viable strategy combining rice straw and waste bamboo particles into bio-composites using green adhesives. These new bio-composites can displace the traditional wood-particle boards, which is a viable strategy to economize on wood resources. The internal bonding strength reached 0.57 MPa, and the thickness swelling rate was 7.00% (24h), which met the ISO requirements for P-FN MR1 particleboard in humid conditions. The characterizations of profile density distribution and microstructure were used to elucidate the mechanical strength and water resistance of bio-composites associated with the surface morphology of biomass and the density variation of bio-composites. The obtained green bio-composites can be utilized with long service life to realize carbon sequestration from agro-industrial lignocellulose wastes. According to the LCA, the net carbon flux could reach −1198.49 kg CO2 eq. when producing 1 m3 bio-composite. Meanwhile, if this strategy is successfully extended to the global particleboard market, the utilization of 23.97 million tonnes of rice straw per year can economize on 1.61 million hm2 of the forest, and decrease the emission of CO2 by 63.76 million tonnes. This study provided a new straw/bamboo-based bio-composite. While using agro-industrial lignocellulose wastes efficiently, this new strategy can appreciably favour carbon neutrality.

Carbon Fluxes during Dansgaard–Oeschger Events as Simulated by an Earth System Model

Abstract The Community Earth System Model with marine and terrestrial biogeochemistry is configured to simulate glacial climate. The integration shows transitions from warm to cold states—interstadials to stadials—and back. The amplitude of the associated Greenland and Antarctica temperature changes and the atmospheric CO2 signal are consistent with ice-core reconstructions, and so are the time lags between termination of a stadial, Antarctic temperature reversal, and the decline of the atmospheric CO2 concentration (for brevity’s sake simply referred to as CO2 from here on). The present model results stand out because the transitions occur spontaneously (without forcing changes like hosing) and because they reproduce the observed features above in a configuration that uses the same parameterizations as climate simulations for the present day (i.e., no retuning has been done). During stadials, precipitation shifts lead to reduced growth on land, which dominates the CO2 increase; the ocean acts as a minor carbon sink during the stadials. After the end of the stadials, however, the sudden reversal of the stadial anomalies in temperature, wind, and precipitation turns the ocean into a carbon source, which accounts for the continued rise of CO2 for several hundred years into the interstadial. The simulations also provide a novel possible interpretation for the observed correlation between CO2 and Antarctic temperature: rather than both being controlled by Southern Ocean processes, they are both controlled by the North Atlantic Ocean, and most of the extra CO2 may not be of Southern Hemisphere origin. If the stadials are prolonged through North Atlantic hosing, the upper ocean comes to an equilibrium, and the CO2 response is dominated by a single process: reduced export production in the North Atlantic as result of the collapsed overturning circulation. This is in contrast to the unforced simulation where the net ocean carbon flux anomaly is the sum of several regional responses of both signs and similar magnitudes. Reducing the aeolian iron deposition by half, to account for the observed reduction of Southern Hemisphere dust fluxes during stadials, reduces biological productivity and export production so that the Southern Ocean emerges as an important carbon source, at least for the three centuries up until a new equilibrium for the upper ocean is reached. Significance Statement The last ice age featured millennial-scale oscillations in CO2 and temperature, the latter being anticorrelated between Greenland and Antarctica. This is often referred to as the bipolar seesaw. Here, an Earth system model is described that reproduces these signals, and its results are used to explain the observed correlation between temperature and CO2. In contrast to previous idealized studies it is found that all ocean basins and the land each contribute equally to the CO2 signal.

Global and regional carbon budget for 2015–2020 inferred from OCO-2 based on an ensemble Kalman filter coupled with GEOS-Chem

Abstract. Understanding carbon sources and sinks across the Earth's surface is fundamental in climate science and policy; thus, these topics have been extensively studied but have yet to be fully resolved and are associated with massive debate regarding the sign and magnitude of the carbon budget from global to regional scales. Developing new models and estimates based on state-of-the-art algorithms and data constraints can provide valuable knowledge and contribute to a final ensemble model in which various optimal carbon budget estimates are integrated, such as the annual global carbon budget paper. Here, we develop a new atmospheric inversion system based on the 4D local ensemble transform Kalman filter (4D-LETKF) coupled with the GEOS-Chem global transport model to infer surface-to-atmosphere net carbon fluxes from Orbiting Carbon Observatory-2 (OCO-2) V10r XCO2 retrievals. The 4D-LETKF algorithm is adapted to an OCO-2-based global carbon inversion system for the first time in this work. On average, the mean annual terrestrial and oceanic fluxes between 2015 and 2020 are estimated as − 2.02 and − 2.34 GtC yr−1, respectively, compensating for 21 % and 24 %, respectively, of global fossil carbon dioxide (CO2) emissions (9.80 GtC yr−1). Our inversion results agree with the CO2 atmospheric growth rates reported by the National Oceanic and Atmospheric Administration (NOAA) and reduce the modeled CO2 concentration biases relative to the prior fluxes against surface and aircraft measurements. Our inversion-based carbon fluxes are broadly consistent with those provided by other global atmospheric inversion models, although discrepancies still occur in the land–ocean flux partitioning schemes and seasonal flux amplitudes over boreal and tropical regions, possibly due to the sparse observational constraints of the OCO-2 satellite and the divergent prior fluxes used in different inversion models. Four sensitivity experiments are performed herein to vary the prior fluxes and uncertainties in our inversion system, suggesting that regions that lack OCO-2 coverage are sensitive to the priors, especially over the tropics and high latitudes. In the further development of our inversion system, we will optimize the data-assimilation configuration to fully utilize current observations and increase the spatial and seasonal representativeness of the prior fluxes over regions that lack observations.