Greenhouse Gas Budget Research Articles

High soil carbon sequestration rates persist several decades in turfgrass systems: A meta-analysis

Managed turfgrass is a common component of urban landscapes that is expanding under current land use trends. Previous studies have reported high rates of soil carbon sequestration in turfgrass, but no systematic review has summarized these rates nor evaluated how they change as turfgrass ages. Here we conducted a meta-analysis of soil carbon sequestration rates from 63 studies globally, comprised mostly of C3 grass species in the U.S., including 24 chronosequence studies that evaluated carbon changes over 75 years or longer. We showed that turfgrass established within the last ten years had a positive mean soil C sequestration rate of 5.3 Mg CO2 ha−1 yr−1 (95% CI = 3.7–6.2), which is higher than rates reported for several soil conservation practices. Areas converted to turfgrass from forests were an exception, sometimes lost soil carbon, and had a cross-study mean sequestration rate that did not differ from 0. In some locations, soil C accumulated linearly with turfgrass age over several decades, but the major trend was for soil C accumulation rates to decline through time, reaching a cross-study mean sequestration rate that was not different from 0 at 50 years. We show that fitting soil C timeseries with a mechanistically derived function rather than purely empirical functions did not alter these conclusions, nor did employing equivalent soil mass versus fixed-depth carbon stock accounting. We conducted a partial greenhouse gas budget that estimated emissions from mowing, N-fertilizer production, and soil N2O emissions. When N fertilizer was applied, average maintenance emissions offset 32% of C sequestration in recently established turfgrass. Potential emission removals by turfgrass can be maximized with reduced-input management. Management decisions that avoid losing accrued soil C—both when turfgrass is first established and when it is eventually replaced with other land-uses—will also help maximize turfgrass C sequestration potential.

Nitric oxide: A core signaling molecule under elevated GHGs (CO2, CH4, N2O, O3)-mediated abiotic stress in plants.

Nitric oxide (NO), an ancient molecule with multiple roles in plants, has gained momentum and continues to govern plant biosciences-related research. NO, known to be involved in diverse physiological and biological processes, is a central molecule mediating cellular redox homeostasis under abiotic and biotic stresses. NO signaling interacts with various signaling networks to govern the adaptive response mechanism towards stress tolerance. Although diverging views question the role of plants in the current greenhouse gases (GHGs) budget, it is widely accepted that plants contribute, in one way or another, to the release of GHGs (carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and ozone (O3)) to the atmosphere, with CH4 and N2O being the most abundant, and occur simultaneously. Studies support that elevated concentrations of GHGs trigger similar signaling pathways to that observed in commonly studied abiotic stresses. In the process, NO plays a forefront role, in which the nitrogen metabolism is tightly related. Regardless of their beneficial roles in plants at a certain level of accumulation, high concentrations of CO2, CH4, and N2O-mediating stress in plants exacerbate the production of reactive oxygen (ROS) and nitrogen (RNS) species. This review assesses and discusses the current knowledge of NO signaling and its interaction with other signaling pathways, here focusing on the reported calcium (Ca2+) and hormonal signaling, under elevated GHGs along with the associated mechanisms underlying GHGs-induced stress in plants.

One year of spectroscopic high‐frequency measurements of atmospheric CO2, CH4, H2O and δ13C‐CO2 at an Australian Savanna site

AbstractWe provide a 1‐year dataset of atmospheric surface CO2, CH4 and H2O concentrations and δ13C‐CO2 values from an Australian savanna site. These semi‐arid ecosystems act as carbon sinks in wet years but the persistence of the sink in dry years is uncertain. The dataset can be used to constrain uncertainties in modelling of greenhouse gas budgets, improve algorithms for satellite measurements and characterize the role of vegetation and soil in modulating atmospheric CO2 concentrations. We found pronounced seasonal variations in daily mean CO2 concentrations with an increase (by 5–7 ppmv) after the first rainfall of the wet season in early December with peak concentrations maintained until late January. The CO2 increase reflected the initiation of rapid microbial respiration from soil and vegetation sources upon initial wetting. As the wet season progressed, daily CO2 concentrations were variable, but generally decreased back to dry season levels as CO2 assimilation by photosynthesis increased. Mean daily concentrations of CH4 increased in the wet season by up to 0.2 ppmv relative to dry season levels as the soil profile became waterlogged after heavy rainfall events. During the dry season there was regular cycling between maximum CO2/minimum δ13C‐CO2 at night and minimum CO2/maximum δ13C‐CO2 during the day. In the wet season diel patterns were less regular in response to variable cloud cover and rainfall. CO2 isotope data showed that in the wet season, surface CO2 was predominantly a two‐component mixture influenced by C3 plant assimilation (day) and soil/plant respiration (night), while regional background air from higher altitudes represented an additional CO2 source in the dry season. Higher wind speeds during the dry season increased vertical mixing compared to the wet season. In addition, night‐time advection of high‐altitude air during low temperature conditions also promoted mixing in the dry season.

High-resolution vertical biogeochemical profiles in the hyporheic zone reveal insights into microbial methane cycling

Abstract. Facing the challenges of climate change, policy making relies on sound greenhouse gas (GHG) budgets. Rivers and streams emit large quantities of the potent GHG methane (CH4), but their global impact on atmospheric CH4 concentrations is highly uncertain. In situ data from the hyporheic zone (HZ), where most CH4 is produced and some of it can be oxidized to CO2, are lacking for an accurate description of CH4 production and consumption in streams. To address this, we recorded high-resolution depth-resolved geochemical profiles at five different locations in the stream bed of the river Moosach, southern Germany. Specifically, we measured pore-water concentrations and stable carbon isotopes (δ13C) of dissolved CH4 as well as relevant electron acceptors for oxidation with a 1 cm vertical depth resolution. Findings were interpreted with the help of a numerical model, and 16S rRNA gene analyses added information on the microbial community at one of the locations. Our data confirm with pore-water CH4 concentrations of up to 1000 µmol L−1 that large quantities of CH4 are produced in the HZ. Stable isotope measurements of CH4 suggest that hydrogenotrophic methanogenesis represents a dominant pathway for CH4 production in the HZ of the river Moosach, while a relatively high abundance of a novel group of methanogenic archaea, the Candidatus “Methanomethyliales” (phylum Candidatus “Verstraetearchaeota”), indicate that CH4 production through H2-dependent methylotrophic methanogenesis might also be an important CH4 source. Combined isotopic and modeling results clearly implied CH4 oxidation processes at one of the sampled locations, but due to the steep chemical gradients and the close proximity of the oxygen and nitrate reduction zones, no single electron acceptor for this process could be identified. Nevertheless, the numerical modeling results showed potential not only for aerobic CH4 oxidation but also for anaerobic oxidation of CH4 coupled to denitrification. In addition, the nitrate–methane transition zone was characterized by an increased relative abundance of microbial groups (Crenothrix, NC10) known to mediate nitrate and nitrite-dependent methane oxidation in the hyporheic zone. This study demonstrates substantial CH4 production in hyporheic sediments, a potential for aerobic and anaerobic CH4 oxidation, and underlines the high spatiotemporal variability in this habitat.

Electric Mobility Emission Reduction Policies: A Multi-Objective Optimization Assessment Approach

The passenger transportation sector is notoriously sticky to decarbonize because it is interlinked with urban form, individual choice, and economic growth. As the urgency to respond to climate change increases and the transport sector disproportionally increases its contributions to global GHG emissions, there is a need for a more meaningful and transparent application of tools to cost GHG emission reduction. This study presents a multi-objective integer optimization (MIO) model to support the costing and GHG reduction estimation of electric mobility road passenger transportation policies. The model considers both cost and GHG emission minimization under resource constraints and background changes in policy interventions within interval ranges for the province of Ontario’s (Canada) in year 2030. All Pareto optimal solutions are included but results that indicate the optimal policy allocation for two discrete targets are discussed in detail; one scenario where $3 billion spending over ten years is the target and another scenario where the target is 40% GHG reduction in year 2030 (relative to 2005 levels). The MIO approach offers an out-of-the-box solution to support the GHG-reducing decision-making process at all levels of government by implementing optimal policy combinations to achieve GHG emission reductions under a target GHG emission reduction target and/or budget.

How do land cover changes affect carbon-nitrogen-phosphorus stocks and the greenhouse gas budget of ecosystems in southern Chile?

Agricultural land use changes are expected to modify the carbon (C), nitrogen (N) and phosphorus (P) stocks compared to the native ecosystems they replace and result in changes in greenhouse gas (GHG) fluxes. To quantify these effects, we measured C-N-P stocks in four land cover classes (cropland, grassland, native shrubland and invaded shrubland) together with their ecosystem-level CO2, CH4 and N2O fluxes for one year using the closed-chamber technique, in three locations on Chiloé Island, southern Chile. As a reference, given that most of the original ecosystems were derived from forest clearance, we monitored CO2 fluxes in a native forest site in the same area using the eddy covariance technique, and used published data of its C-N-P stocks and CH4 and N2O fluxes. We found that compared to the forest, the other land cover classes represented a 60 % loss of total ecosystem C, which was explained mainly by the loss of 98 % in above ground biomass and a 42 % reduction in soil C, but with a relatively unchanged N stock and an increase in soil P. While croplands were net GHG emitters (901 g CO2-eq m-2 year-1), grasslands, native shrublands and invaded shrublands were net sinks (−1350, −1154 and −2088 g CO2-eq m-2 year-1, respectively). The invaded shrublands (invaded by the N-fixing species Ulex europaeus and Cytisus scoparius) showed higher aboveground and root biomass compared to the other land cover classes, but somewhat lower C-N-P soil stocks, possibly because of lower litter decomposition, reduced root turnover/rhizodeposition and/or greater dissolved elemental losses, as the invasion occurred on degraded lands. Although the invasive shrublands acted as a stronger GHG sink, driven by their higher CO2 fixation, this might change in the longer term through the additional accumulation of fixed N, with a potential increase in N2O emissions.

The Paris Target, Human Rights, and IPCC Weaknesses: Legal Arguments in Favour of Smaller Carbon Budgets

The Paris Climate Agreement (PA) provides an overall target which limits global warming to “well below 2 °C above pre-industrial levels” and “pursuing efforts to limit the temperature increase to 1.5 °C above pre-industrial levels” (Art. 2 para. 1 PA). This article assesses the extent to which new insights can be derived from recent IPCC reports for the interpretation of Art. 2 para. 1 PA from a legal perspective. To this end, the article analyses the contributions of Working Groups I and III of the sixth assessment report. Methodologically, we compare the findings with previously published IPCC reports, namely the 1.5 °C report and the fifth assessment report. A legal interpretation of the Paris Agreement and of core concepts of human rights follows. Several empirical indications show that current global greenhouse gas budget calculations are quite generous. We provide five empirical arguments that clearly point in that direction. These empirical arguments, combined with legal arguments, demonstrate that the budgets must be smaller than those estimated by the IPCC. The legal arguments are based on Art. 2 of the Paris Agreement, as well as on human rights and the precautionary principle. These norms contain an obligation to minimise the risk of significant damage, i.e., to take rapid and drastic climate protection measures. This implies: 1.5 °C is the legally binding temperature target; adherence requires a very high probability of achieving the target; temperature overshoot and geoengineering tend to be prohibited, and budget calculations must be based on sceptical factual assumptions. These findings have also been confirmed by recent rulings of supreme courts, such as the ground-breaking climate decision of the German Federal Constitutional Court. The Paris Agreement and human rights underline a legally binding obligation for smaller global greenhouse gas budgets as those estimated in the greenhouse gas budgets of the IPCC—even compared to the 83 percent scenario in the latest assessment. Thus, climate policy will have to raise its ambitions towards zero fossil fuels and a drastic reduction of livestock farming in times of the Ukraine war.

Life cycle assessment of tunnel structures: Assessment of the New Austrian Tunnelling Method using a case study

One important measure to combat progressing climate change is compliance with and under no circumstances to exceed the decreasing greenhouse gas budget. Every economic sector must strive to make its ecological contribution to achieve this objective. The construction sector is largely responsible for these negative environmental burdens. Although tunnels are considered to have extensive energy and material consumptions the literature has failed to present their environmental impacts. Aimed at this knowledge gap, the objective of this study is to present the life cycle assessment (LCA) of a tunnel construction project situated in Bulgaria. The study analyzes the impacts of the New Austrian Tunnelling Method (NATM) using the case study “Modernization of Railway Section Elin Pelin-Kostenets – Lot 3”. Moreover, by applying dominance and sensitivity analyses, the environmental drivers and optimization potential for reducing greenhouse gas emissions are identified. The results show that steel, shotcrete, and concrete, contribute the most to the global warming potential indicator and are responsible for 85% of this. Furthermore, the life cycle stages for the production of materials and components have a share close to 85 % of the total global warming potential. These findings may help future tunnelling construction projects to improve the environmental performance and thus to combat the alarming development of climate change.

Initial effects of post-harvest ditch cleaning on greenhouse gas fluxes in a hemiboreal peatland forest

Ditch cleaning (DC) is a well-established forestry practice across Fennoscandia to lower water table levels (WTL) and thereby facilitate the establishment of tree seedlings following clear-cutting. However, the implications from these activities for ecosystem-atmosphere greenhouse gas (GHG) exchanges are poorly understood at present. We assessed the initial DC effects on the GHG fluxes in a forest clear-cut on a drained fertile peatland in hemiboreal Sweden, by comparing chamber measurements of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) fluxes from soil and ditches in DC and uncleaned (UC) areas over the first two post-harvest years. We also evaluated spatial effects by comparing fluxes at 4 m and 40 m from ditches. We found that 2 years after DC, mean (±standard error) WTL of −65 ± 2 cm was significantly lower in the DC area compared to −56 ± 2 cm in the UC area. We further observed lower gross primary production and ecosystem respiration in the first year after DC which coincided with delayed development of herbaceous ground vegetation. We also found higher CH4 uptake but no difference in N2O fluxes after DC. Greater CH4 uptake occurred at 4 m compared to 40 m away from both cleaned and uncleaned ditches. Model extrapolation suggests that total annual GHG emissions in the second year were reduced from 49.4 ± 17.0 t-CO2-eq-ha−1-year−1 in the UC area to 27.8 ± 10.3 t-CO2-eq-ha−1-year−1 in the DC area. A flux partitioning approach suggested that this was likely caused by decreased heterotrophic respiration, possibly because of enhanced soil dryness following DC during the dry meteorological conditions. CH4 and N2O fluxes from clear-cut areas contributed <2 % to the total (soil, ditches) GHG budget. Similarly the area-weighted contributions by CO2 and CH4 emissions from both cleaned and uncleaned ditches were <2 %. Thus, our study highlights that DC may considerably alter the post-harvest GHG fluxes of drained peatland forests. However, long-term observations under various site conditions and forest rotation stages are warranted to better understand DC effects on the forest GHG balance.

Multiple Facets of Nitrogen: From Atmospheric Gas to Indispensable Agricultural Input.

Nitrogen (N) is a gas and the fifth most abundant element naturally found in the atmosphere. N’s role in agriculture and plant metabolism has been widely investigated for decades, and extensive information regarding this subject is available. However, the advent of sequencing technology and the advances in plant biotechnology, coupled with the growing interest in functional genomics-related studies and the various environmental challenges, have paved novel paths to rediscovering the fundamentals of N and its dynamics in physiological and biological processes, as well as biochemical reactions under both normal and stress conditions. This work provides a comprehensive review on multiple facets of N and N-containing compounds in plants disseminated in the literature to better appreciate N in its multiple dimensions. Here, some of the ancient but fundamental aspects of N are revived and the advances in our understanding of N in the metabolism of plants is portrayed. It is established that N is indispensable for achieving high plant productivity and fitness. However, the use of N-rich fertilizers in relatively higher amounts negatively affects the environment. Therefore, a paradigm shift is important to shape to the future use of N-rich fertilizers in crop production and their contribution to the current global greenhouse gases (GHGs) budget would help tackle current global environmental challenges toward a sustainable agriculture.

Mismatch of N release from the permafrost and vegetative uptake opens pathways of increasing nitrous oxide emissions in the high Arctic.

Biogeochemical cycling in permafrost-affected ecosystems remains associated with large uncertainties, which could impact the Earth's greenhouse gas budget and future climate policies. In particular, increased nutrient availability following permafrost thaw could perturb the greenhouse gas exchange in these systems, an effect largely unexplored until now. Here, we enhance the terrestrial ecosystem model QUINCY (QUantifying Interactions between terrestrial Nutrient CYcles and the climate system), which simulates fully coupled carbon (C), nitrogen (N) and phosphorus (P) cycles in vegetation and soil, with processes relevant in high latitudes (e.g., soil freezing and snow dynamics). In combination with site-level and satellite-based observations, we use the model to investigate impacts of increased nutrient availability from permafrost thawing in comparison to other climate-induced effects and CO2 fertilization over 1960 to 2018 across the high Arctic. Our simulations show that enhanced availability of nutrients following permafrost thaw account for less than 15% of the total Gross primary productivity increase over the time period, despite simulated N limitation over the high Arctic scale. As an explanation for this weak fertilization effect, observational and model data indicate a mismatch between the timing of peak vegetative growth (week 26-27 of the year, corresponding to the beginning of July) and peak thaw depth (week 32-35, mid-to-late August), resulting in incomplete plant use of nutrients near the permafrost table. The resulting increasing N availability approaching the permafrost table enhances N loss pathways, which leads to rising nitrous oxide (N2 O) emissions in our model. Site-level emission trends of 2mg N m-2 year-1 on average over the historical time period could therefore predict an emerging increasing source of N2 O emissions following future permafrost thaw in the high Arctic.

A new index on agricultural land greenhouse gas emissions in Africa.

Africa emits the lowest amounts of greenhouse gases (GHGs) into the global GHG budget. However, the continent remains the most vulnerable continent to the effects of climate change. The agricultural sector in Africa is among the most vulnerable sectors to climate change. Also, as a dominant agricultural sector, African agriculture is increasingly contributing to climate change through GHG emissions. Research has so far focused on the effects of GHG emissions on the agricultural and other sectors with very little emphasis on monitoring and quantifying the spatial distribution of GHG emissions from agricultural land in Africa. This study develops a new index: African Agricultural Land Greenhouse Gas Index (AALGGI) that uses scores and specific scale ranges for carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) to map the spatial variations in regional GHG emissions across Africa. The data for the three main GHGs (CO2, CH4, and N20) were downloaded from FAOSTAT. The data were analyzed through the newly developed African Agricultural Land Greenhouse Gas Index (AALGGI). This is an empirical index with scores ranging from 0 to 10, with higher scores indicating higher levels of emissions. The results show that Southern and North African regions have the lowest amounts of agricultural land GHG emissions, with AALGGIs of 3.5 and 4.5, respectively. East Africa records the highest levels of GHG emissions, with an AALGGI of 8 followed by West Africa with an AALGGI of 7.5. With the continental mean or baseline AALGGI being 5.8, East and Middle Africa are above the mean AALGGI. These results underscore the fact that though Africa, in general, is not a heavy emitter of GHGs, African agricultural lands are increasingly emitting more GHGs into the global GHG budget. The low AALGGIs in the more developed parts of Africa such as Southern and North Africa are explained by their domination in other GHG emitting sectors such as industrialization and energy. The high rates of emissions in East Africa and Middle Africa are mainly linked to intensive traditional farming practices/processes and deforestation. These findings underscore the need to further leverage climate change mitigation actions and policy in Africa and most importantly the co-benefits of mitigation and adaptations in the most vulnerable regions.

Methane and carbon dioxide cycles in lakes of the King George Island, maritime Antarctica

Freshwater ecosystems are important contributors to the global greenhouse gas budget and a comprehensive assessment of their role in the context of global warming is essential. Despite many reports on freshwater ecosystems, relatively little attention has been given so far to those located in the southern hemisphere and our current knowledge is particularly poor regarding the methane cycle in non-perennially glaciated lakes of the maritime Antarctica. We conducted a high-resolution study of the methane and carbon dioxide cycle in a lake of the Fildes Peninsula, King George Island (Lat. 62°S), and a succinct characterization of 10 additional lakes and ponds of the region. The study, done during the ice-free and the ice-seasons, included methane and carbon dioxide exchanges with the atmosphere (both from water and surrounding soils) and the dissolved concentration of these two gases throughout the water column. This characterization was complemented with an ex-situ analysis of the microbial activities involved in the methane cycle, including methanotrophic and methanogenic activities as well as the methane-related marker gene abundance, in water, sediments and surrounding soils. The results showed that, over an annual cycle, the freshwater ecosystems of the region are dominantly autotrophic and that, despite low but omnipresent atmospheric methane emissions, they act as greenhouse gas sinks.

Impacts of stump harvesting on carbon dioxide, methane and nitrous oxide fluxes

During 2010-2013, we investigated the effects of stump harvesting on greenhouse gas (GHG) fluxes of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) with the flux-gradient technique at four experimental plots in a hemiboreal forest in Sweden. All plots were clear-cut and soil scarified and two of the plots were additionally stump harvested. The two clear-cut plots served as control plots. Due to differences in topography, we had one wetter and one drier plot of each treatment. All plots exhibited substantial emissions of GHGs and we noted significant effects of wetness on CO2, CH4 and N2O fluxes within treatments and significant effects of stump harvesting on CO2 and N2O fluxes at the dry plots. The CO2 emissions were lower at the dry stump harvested plot than at the dry control, but when estimated emissions from the removed stumps were added, total CO2 emissions were higher at the stump harvested plot, indicating a small enhancement of soil respiration. In addition, we noted significant emissions of N2O at this plot. At the wet plots, CO2 emissions were higher at the stump harvested plot, also suggesting a treatment effect but differences in wetness and vegetation cover at these plots make this effect more uncertain. At the wet plots, we noted sustained periods (weeks to months) of net N2O uptake. During the year with simultaneous measurements of the abovementioned GHGs, GHG budgets were 1.224×103 and 1.442×103 gm-2 of CO2-equivalents at the wet and dry stump harvested plots, respectively, and 1.070×103 and 1.696×103 gm-2 of CO2-equivalents at the wet and dry control plots, respectively. CO2 fluxes dominated GHG budgets at all plots but N2O contributed with 17% at the dry stump harvested plot. For the full period 2010-2013, total carbon (CO2+CH4) budgets were 4.301×103 and 4.114×103 g m-2 of CO2-eqvivalents at the wet and dry stump harvest plots, respectively and 4.107×103 and 5.274×103 gm-2 of CO2-equivalents at the wet and dry control plots, respectively. Our results support recent studies suggesting that stump harvesting does not result in substantial increase in CO2 emissions but uncertainties regarding GHG fluxes (especially N2O) remain and more long-term measurements are needed before robust conclusions can be drawn.

Changes in Soil Microbial Community and Carbon Flux Regime across a Subtropical Montane Peatland-to-Forest Successional Series in Taiwan

Subtropical montane peatland is among several rare ecosystems that continue to receive insufficient scientific exploration. We analyzed the vegetation types and soil bacterial composition, as well as surface carbon dioxide and methane fluxes along a successional peatland-to-upland-forest series in one such ecosystem in Taiwan. The Yuanyang Lake (YYL) study site is characterized by low temperature, high precipitation, prevailing fog, and acidic soil, which are typical conditions for the surrounding dominant Chamaecyparis obtusa var. formosana forest. Bacterial communities were dominated by Acidobacteriota and Proteobacteria. Along the bog-to-forest gradient, Proteobacteria decreased and Acidobacteriota increased while CO2 fluxes increased and CH4 fluxes decreased. Principal coordinate analysis allowed separating samples into four clusters, which correspond to samples from the bog, marsh, forest, and forest outside of the watershed. The majority of bacterial genera were found in all plots, suggesting that these communities can easily switch to other types. Variation among samples from the same vegetation type suggests influence of habitat heterogeneity on bacterial community composition. Variations of soil water content and season caused the variations of carbon fluxes. While CO2 flux decreased exponentially with increasing soil water content, the CH4 fluxes exhibited an exponential increase together with soil water content. Because YYL is in a process of gradual terrestrialization, especially under the warming climate, we expect changes in microbial composition and the greenhouse gas budget at the landscape scale within the next decades.

A Modeling Approach for Addressing Sensitivity and Uncertainty of Estuarine Greenhouse Gas (CO2 and CH4) Dynamics

AbstractEstuaries make an important contribution to the global greenhouse gas budget. Yet modeling predictions of carbon dioxide (CO2) and methane (CH4) emissions from estuaries remain highly uncertain due to both simplified assumptions about the underpinning hydrologic and biologic processes and inadequate data availability to uniquely define parameters related to CO2 and CH4 processes. This study presents a modeling framework to quantify the sensitivity and uncertainty of predicted CO2 and CH4 concentrations and emissions, which is demonstrated through application to a subtropical urban estuary (Brisbane River, Australia). A 3D hydrodynamic‐biogeochemical model was constructed, and calibrated using the model‐independent Parameter ESTimation software (PEST) with field data sets that captured strong gradients of CO2 and CH4 concentrations and emissions along the estuary. The approach refined uncertainty in the estimation of whole‐estuary annual emissions, and enabled us to assess the sensitivity and uncertainty of CO2 and CH4 dynamics. Estuarine CO2 concentrations were most sensitive to uncertainty in riverine inputs, whereas estuarine CH4 concentrations were most sensitive to sediment production and pelagic oxidation. Over the modeled year, variance in the daily fluctuations in carbon emissions from this case‐study spanned the full range of emission rates reported for estuaries around the world, highlighting that spatially or temporally limited sampling regimes could significantly bias estuarine greenhouse gas emission estimates. The combination of targeted field campaigns with the modeling approach presented in this study can help to improve carbon budgeting in estuaries, reduce uncertainty in emission estimates, and support management strategies to reduce or offset estuary greenhouse gas emissions.

Large alpine deep lake as a source of greenhouse gases: A case study on Lake Fuxian in Southwestern China

Freshwater lakes are recognized as potential sources of greenhouse gases (GHGs) that contribute to global warming. However, the spatiotemporal patterns of GHG emissions have not been adequately quantified in large deep lakes, resulting in substantial uncertainties in the estimated GHG budgets in global lakes. In this study, the spatial and seasonal variability of diffusive GHG (CO2, CH4, and N2O) emissions from Lake Fuxian located on a plateau in Southwestern China were quantified. The results showed that the surface lake water was oversaturated with dissolved GHG concentrations, and the average concentrations were 24.25 μM CO2, 0.044 μM CH4, and 14.28 nM N2O, with diffusive emission rates of 8.82 mmol CO2 m−2 d−1, 31.94 μmol CH4 m−2 d−1, and 4.94 μmol N2O m−2 d−1, respectively. Diffusive CH4 flux exhibited high temporal and spatial variability similar to that in most lakes. In contrast, diffusive CO2 and N2O flux showed distinct seasonal variability and similar spatial patterns, emphasizing the necessity for increasing the temporal resolution in GHG flux measurements for integrated assessments. Water temperature and/or oxygen concentrations were crucial in regulating seasonal variability in GHG emissions. However, no limnological parameter was found to govern the spatial GHG patterns. The frequent advection mixing caused by wind-driven currents might be the reason for the low spatial heterogeneity in GHGs, in which the inconspicuous mechanism requires further research. It was recommended that at least 11 locations were needed for representative whole lake flux estimates at each sampling campaign. In addition, the maximum peak of CH4 in the oxycline from Lake Fuxian indicated that low CH4 oxidation occurred in oxic waters. Overall, this study suggests that, compared to other tropical and temperate lakes, this alpine deep lake is a minor CO2 and CH4 source, but a moderate N2O source, which are horizontally uniform.

The Impact of Modifications in Forest Litter Inputs on Soil N2O Fluxes: A Meta-Analysis

Although litter can regulate the global climate by influencing soil N2O fluxes, there is no consensus on the major drivers or their relative importance and how these impact at the global scale. In this paper, we conducted a meta-analysis of 21 global studies to quantify the impact of litter removal and litter doubling on soil N2O fluxes from forests. Overall, our results showed that litter removal significantly reduced soil N2O fluxes (−19.0%), while a doubling of the amount of litter significantly increased soil N2O fluxes (30.3%), based on the results of a small number of studies. Litter removal decreased the N2O fluxes from tropical forest and temperate forest. The warmer the climate, the greater the soil acidity, and the larger the soil C:N ratio, the greater the impact on N2O emissions, which was particularly evident in tropical forest ecosystems. The decreases in soil N2O fluxes associated with litter removal were greater in acid soils (pH &lt; 6.5) or soils with a C:N &gt; 15. Litter removal decreased soil N2O fluxes from coniferous forests (−21.8%) and broad-leaved forests (−17.2%) but had no significant effect in mixed forests. Soil N2O fluxes were significantly reduced in experiments where the duration of litter removal was &lt;1 year. These results showed that modifications in ecosystem N2O fluxes due to changes in the ground litter vary with forest type and need to be considered when evaluating current and future greenhouse gas budgets.

Nitrogen application at a lower rate reduce net field global warming potential and greenhouse gas intensity in winter wheat grown in semi-arid region of the Loess Plateau

With the intensification of crop production pressure and the urgency of mitigating greenhouse gas emissions, semi-arid regions have increasingly become one of the key areas of research. However, due to the relatively low indigenous soil organic matter (SOM), it is worth pondering whether the long-term introduction of cropland management measures will affect the soil organic carbon (SOC), greenhouse gases (GHGs) and global warming potential (GWP) in the semi-arid areas. This long-term fertilization experiment was conducted for four years during 2017–2021 to assess fertilization impacts on net global warming potential (NGWP) including estimation of SOC change, N 2 O and CH 4 emissions and indirect emissions (IE), and the greenhouse gas intensity (GHGI) on the winter wheat in a semi-arid region of China. The treatments included five levels of N application including non-N-fertilized control (N0), 75 kg N·ha −1 (N75), 150 kg N·ha −1 (N150), 225 kg N·ha −1 (N225) and a traditional N application rate, 300 kg N·ha −1 (N300). In comparison with N300, N225 caused a significant increase in SOC content and SOC sequestration rates and reduced the N 2 O and CH 4 emissions and N 2 O emission factor (EF N2O ) followed by N150, N75 and N0. Indirect emissions from farm inputs were highest in the N300 treatment due to excessive N application. The higher grain yield, during all study years, was recorded in N225 treatment and there was no significant difference between N150 and N300 treatments. However, the lowest grain yield was recorded from N0, followed by N75. The lowest mean NGWP and net greenhouse gas intensity (NGHGI) were recorded from the N150 and N225 treatments than all other treatments. The results of this study suggested that N application at 150–225 kg·ha −1 is an effective method to enhance SOC sequestration and grain yield and to reduce the GHGI. • Net ecosystem carbon and greenhouse gas budgets are evaluated for four years. • Soil organic carbon (SOC) content and N 2 O emissions were increased and CH 4 absorption decreased with increasing N rates. • Compared with N300, N150 and N225 has the highest NGWP and GHG emissions. • N150 and N225 treatments can record maximum SOC sequestration than low and higher N rates.

Implications of the consumption-based accounting for future national emissions budgets

ABSTRACT As a complement of production-based accounting (PBA), consumption-based accounting (CBA) provides an alternative perspective to understand national emissions and responsibilities for global climate change. Existing studies assessed historical national emissions under CBA. However, how CBA might guide future mitigation under the Paris Agreement goals has not been well understood. By combining global multi-region input-output analysis and the equity principle of ‘equal cumulative per capita emissions’ (ECPCE), this study explores potential implications of CBA for future national emissions budgets to limit global warming to below 1.5°C. Historically, consumption-based greenhouse gas (GHG) emissions were higher than production-based emissions in most developed countries while lower in many developing countries. When CBA is used instead of PBA to allocate emissions budgets by ECPCE, future GHG mitigation burdens would become more stringent in 70% of Annex I (mostly developed) countries but slightly smaller in 55% of non-Annex I (mostly developing) countries. In particular, more than half of Annex I countries might need to achieve negative GHG budgets under 1.5°C. Our analysis emphasizes that, as net emission importers, developed countries could strive to pay equal attention to achieving consumption-based and production-based emissions reductions, and strengthen technological and financial support to developing countries that undertake production outsourcing. As net emission exporters, with international support and domestic investment, developing countries could pragmatically promote energy structure optimization and technological innovation to accelerate the decarbonization of production. To support the Paris Agreement goals, mitigation contributions initiated from the perspective of CBA could also be welcomed. Key policy insights Developed countries shift emissions to developing countries through international trade. CBA increases historical responsibilities of developed countries for climate warming from the PBA assessments. Compared to PBA, CBA has clear implications on future national emissions budgets under responsibility-based allocations, but does not change the urgency of national mitigation required to achieve the Paris Agreement goals. Allocated by ECPCE, future GHG budgets for over 50% of the world’s countries would be run out before 2040 under 1.5°C at the 2015 emissions rates, using either CBA or PBA. According to different roles in global supply chains, developed countries should step up support to help developing countries improve emissions and energy intensities, which is a key to reducing emissions embodied in trade.