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A good quantitative knowledge of regional sources and sinks of atmospheric carbon dioxide (CO2) is essential for understanding the global carbon cycle. It is also a key prerequisite for elaborating cost-effective national strategies to achieve the goals of the Paris Agreement. However, available estimates of CO2 fluxes for many regions of the world remain uncertain, despite significant recent progress in the remote sensing of terrestrial vegetation and atmospheric CO2. In this study, we investigate the feasibility of inferring reliable regional estimates of the net ecosystem exchange (NEE) using column-averaged dry-air mole fractions of CO2 (XCO2) retrieved from Orbiting Carbon Observatory-2 (OCO-2) observations as constraints on parameters of the widely used Vegetation Photosynthesis and Respiration model (VPRM), which predicts ecosystem fluxes based on vegetation indices derived from multispectral satellite imagery. We developed a regional-scale inverse modeling system that applies a Bayesian variational optimization algorithm to optimize parameters of VPRM coupled to the CHIMERE chemistry transport model and which involves a preliminary transformation of the input XCO2 data that reduces the impact of the CHIMERE boundary conditions on inversion results. We investigated the potential of our inversion system by applying it to a European region (that includes, in particular, the EU countries and the UK) for the warm season (May–September) of 2021. The inversion of the OCO-2 observations resulted in a major (more than threefold) reduction of the prior uncertainty in the regional NEE estimate. The posterior NEE estimate agrees with independent estimates provided by the CarbonTracker Europe High-Resolution (CTE-HR) system and the ensemble of the v10 OCO-2 model intercomparison (MIP) global inversions. We also found that the inversion improves the agreement of our simulations of XCO2 with retrievals from the Total Carbon Column Observing Network (TCCON). Our sensitivity test experiments using synthetic XCO2 data indicate that the posterior NEE estimate would remain reliable even if the actual regional CO2 fluxes drastically differed from their prior values. Furthermore, the posterior NEE estimate is found to be robust to strong biases and random uncertainties in the CHIMERE boundary conditions. Overall, this study suggests that our approach offers a reliable and relatively simple way to derive robust estimates of CO2 ecosystem fluxes from satellite XCO2 observations while enhancing the applicability of VPRM in regions where eddy covariance measurements of CO2 fluxes are scarce. [ABSTRACT FROM AUTHOR]

Peatlands play an important role in global carbon cycling, as they act as a natural sink of carbon dioxide (CO 2) or as a source of methane (CH 4). The influence of microtopography (lawns and hummock-hollow complexes) in the biogeochemical dynamics of dissolved organic and inorganic carbon (DOC and DIC) and dissolved CH 4 and CO 2 is generally miss-considered. Southernmost Patagonia has huge areas of pristine peatlands, which are still in a largely natural state with scarce anthropogenic influence. In this study we provide foundational insights into the dynamics of greenhouse gasses (GHGs) and DOC in Sphagnum dominated peatlands of Southern Patagonia, assessing the impact of microtopography on these dynamics. The stocks of dissolved GHGs and DOC in hummock-hollows complex and lawns were analysed at three depths (25, 50, and 75 cm) in four ombrotrophic peatbogs. CH 4 , N 2 O and CO 2 fluxes, net ecosystem exchange (NEE) and gross primary productivity (GPP) were also studied. CO 2 and CH 4 fluxes were strongly affected by microtopography. Hummock-hollows showed higher CO 2 fluxes, and temperature and radiation were the main drivers for respiration and GPP, respectively. In addition, in this microtopography, higher DOC concentrations were observed at the top depth. In contrast, lawns acted as a source of CH 4 , with higher emission rates and high dissolved GHGs concentration throughout the depth profile. [ABSTRACT FROM AUTHOR]

Seagrass meadows are effective sinks of atmospheric carbon dioxide (CO2). However, there is little insight on how methane (CH4) emissions may potentially offset carbon sequestration in seagrass meadows. Here, we resolve diel and seasonal dynamics of CH4 and CO2 water‐air fluxes over a cold‐temperate Zostera marina seagrass meadow using high‐resolution timeseries observations in seawater. CH4 was emitted from the seagrass‐dominated coastal bay year‐round to atmosphere with CH4 fluxes ranging from 0.2 to 2.6 μmol m−2 d−1. These fluxes are at the lower end of earlier estimates based mostly on short‐term (i.e., 1 day) observations. The 13‐fold seasonal fluctuations in CH4 emissions were greater than the 6‐fold diel fluctuation. Radon observations imply that dissolved CH4 was primarily originated from sediment porewater. The main fate of CH4 in the water was outgassing to the atmosphere via wind forcing. Oxygen and temperature partially controlled dissolved CH4 seasonal dynamics. There was an annual average uptake of CO2 from the atmosphere (−0.9 ± 1.5 mmol m−2 d−1) driven by enhanced photosynthesis in the spring and summer. The CO2‐equivalent CH4 outgassing (0.5 ± 0.6 g CO2 eq m−2 yr−1) offsets only 0.8% of the sediment carbon accumulation in this cold‐temperate Z. marina meadows over a 20‐year time horizon. The CO2‐equivalent CH4 flux was 6% of the average annual CO2 uptake. Hence, CH4 emissions from this cold‐temperate seagrass meadow acted as a minor offset to carbon sequestration. Plain Language Summary: Natural carbon sinks help to partially mitigate climate change. Highly productive seagrass beds in coastal areas are natural sinks storing carbon in sediment for thousands of years. However, seagrass meadows also release the potent greenhouse gas methane, potentially counteracting some of the carbon sink. Methane assessments in seagrass meadows are scarce and have been conducted mostly in warm climates over short timescales. Here, we measure air‐sea methane emissions from a seagrass‐dominated ecosystem in a cold climate using continuous measurements over diel and seasonal timescales. Methane emissions were lower than global averages and had larger seasonal than diel variability. Winds, oxygen, and temperature influenced dissolved methane dynamics. The methane released from the seagrass reduced <1% of the climate benefit of carbon storage in sediments over a year. Hence, seagrass meadow preservation in cold climates remains crucial for carbon sequestration, contributing to climate change mitigation efforts. Key Points: Seasonal fluctuations in CH4 emissions were greater than diel variationCH4 emissions counteracted about 6% of the average annual CO2 water‐air uptake over a seagrass meadowSeagrass ecosystem CH4 emissions offset about 1% of sediment carbon sequestration [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive review of building lifecycle carbon emissions (CEBL) and reduction approaches, analyzing over 300 recent publications and engaging in in-depth discussion of more than 100 key studies. The review systematically examines CO2 emissions across all stages of a building's lifecycle, from material production and transportation to construction, operation, demolition, and material recycling. While existing research highlights the significance of operational energy efficiency, this review reveals critical research gaps in quantifying transportation emissions, accounting for on-site equipment emissions during construction, and addressing the unique characteristics of non-residential buildings. Furthermore, the paper underscores the urgent need for improved construction waste management practices, especially in developing countries where landfilling remains prevalent. For the building carbon reduction approaches, promising building carbon emission reduction approaches include leveraging carbon dioxide sinks, implementing integrated energy systems, integrating building-integrated photovoltaics (BIPV), and enacting effective policy interventions are separately discussed. By revealing data and theoretical limitations within current research, this review calls for more integrated and context-specific approaches to CEBL assessment, paving the way for a more sustainable built environment. [ABSTRACT FROM AUTHOR]

Large stocks of soil carbon (C) and nitrogen (N) in northern permafrost soils are vulnerable to remobilization under climate change. However, there are large uncertainties in present‐day greenhouse gas (GHG) budgets. We compare bottom‐up (data‐driven upscaling and process‐based models) and top‐down (atmospheric inversion models) budgets of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) as well as lateral fluxes of C and N across the region over 2000–2020. Bottom‐up approaches estimate higher land‐to‐atmosphere fluxes for all GHGs. Both bottom‐up and top‐down approaches show a sink of CO2 in natural ecosystems (bottom‐up: −29 (−709, 455), top‐down: −587 (−862, −312) Tg CO2‐C yr−1) and sources of CH4 (bottom‐up: 38 (22, 53), top‐down: 15 (11, 18) Tg CH4‐C yr−1) and N2O (bottom‐up: 0.7 (0.1, 1.3), top‐down: 0.09 (−0.19, 0.37) Tg N2O‐N yr−1). The combined global warming potential of all three gases (GWP‐100) cannot be distinguished from neutral. Over shorter timescales (GWP‐20), the region is a net GHG source because CH4 dominates the total forcing. The net CO2 sink in Boreal forests and wetlands is largely offset by fires and inland water CO2 emissions as well as CH4 emissions from wetlands and inland waters, with a smaller contribution from N2O emissions. Priorities for future research include the representation of inland waters in process‐based models and the compilation of process‐model ensembles for CH4 and N2O. Discrepancies between bottom‐up and top‐down methods call for analyses of how prior flux ensembles impact inversion budgets, more and well‐distributed in situ GHG measurements and improved resolution in upscaling techniques. Plain Language Summary: The northern permafrost region covers large areas and stores very large amounts of carbon and nitrogen in soils and sediments. With climate change, there is concern that thawing permafrost will release greenhouse gases into the atmosphere, shifting the region from long‐term cooling of the global climate to a net warming effect. In this study, we used different techniques to assess the greenhouse gas budgets of carbon dioxide, methane and nitrous oxide for the time period 2000‒2020. We find that the region is a net sink of carbon dioxide, mainly in boreal forests and wetlands, while carbon dioxide is emitted from inland waters and fires affecting both forest and tundra. Lakes and wetlands are strong sources of methane, which contributes to warm the climate significantly, especially over shorter timescales. Nitrous oxide is emitted at low rates across the region, with a relatively limited impact on climate. In summary, the climate warming from the northern permafrost region is likely close to neutral when calculated over a 100 years time window, but it warms the climate when calculated over a 20 years time window. Key Points: The northern terrestrial permafrost region was a weak annual CO2 sink and stable source of CH4 and N2O during the time period 2000–2020The global warming potential is indistinguishable from neutral over a 100 years time period but a net source of warming over a 20 year periodBottom‐up and top‐down methods yield different magnitudes of estimates that cannot be fully reconciled [ABSTRACT FROM AUTHOR]

The Northeast Greenland Shelf is a region currently considered to be an annual net sink of carbon dioxide (CO2) from the atmosphere. Water from the Northeast Greenland Shelf is advected to the formation regions of North Atlantic Deep Water; therefore, any carbon stored in the region may be retained in the global oceans on the timescales of the thermohaline circulation. We present the most extensive study of carbon chemistry on the Northeast Greenland Shelf to date, made possible by opportunistic sampling due to a sudden decrease in the sea ice concentration in late-August and September 2017. These are the first full-depth measurements of total alkalinity and dissolved inorganic carbon at latitudes between 75 and 79° N, with additional data collected in the region of the Northeast Water Polynya and outside of Young Sound. We find that surface mixed-layer concentrations are variable and (for many stations) higher than the interpolated atmospheric concentration for the region during the sampling period. Below the surface mixed layer, CO2 concentrations increase linearly with decreasing apparent oxygen utilisation. The mixed layer deepens during the study period; this is associated with apparent changes in CO2 uptake. The Northeast Greenland Shelf is a hydrologically complex region with many processes influencing the carbonate system at smaller scales than our sampling density. The scatter in the dataset represents more than mere outliers, and the lack of relationship between the outliers and any measured variable indicates a strong influence of a currently undescribed (set of) variable(s) and/or process(es) at the sampled scales. These data were collected during a time of radically low sea ice concentrations for the region and may be an indication of future conditions. As they indicate the potential of the region to act as a seasonal source of CO2 to the atmosphere, this may modify our current estimate of the region as a strong annual net sink that is relatively protected from the immediate influence of atmospheric warming and climate change. [ABSTRACT FROM AUTHOR]

An understanding of how boreal forest composition responds to global environmental changes is an important challenge to predicting the future global carbon balance. Boreal forests are the most significant sink for atmospheric carbon dioxide; however, their sequestration capacity is highly sensitive to ongoing climate changes. The combination of the hydrothermal conditions of a territory strongly regulates its biogeochemical processes. The carbon fluxes in boreal forests are strongly mediated by the ground vegetation cover, composed of mosses (mesic) and lichens (xeric). Despite the concurrence of xeric and mesic vegetation types, their responses to climate variations varies significantly. Soil emission is an informative indicator of ecosystem functioning. In this study, we focused on the soil CO2 dynamics during frost-free seasons with different precipitation regimes in the xeric and mesic boreal ecosystems of Central Siberia. Seasonal measurements of soil CO2 emissions were conducted during frost-free seasons using the dynamic chamber method. Our findings reveal that the precipitation regimes of each year may control the seasonal soil emission dynamics. The soil moisture is the most important driver of emissions growth in the water-limited lichen pine forest (R2adj. = 18%). The soil temperature plays the largest role in the feather moss pine forest during the dry (R2adj. = 31%) seasons, and in the lichen pine forest during the wet (R2adj. = 41%) seasons. The cumulative efflux for the xeric and mesic sites is mostly related to the hydrothermal conditions, and not to the differences in ground vegetation cover. During the dry seasons, on average, the soil CO2 emissions are 45% lower than during the wet seasons for both sites. These findings emphasize the need for estimating and including the hydrothermal characteristics of the growing season for detailed emission assessments. [ABSTRACT FROM AUTHOR]

In the framework of the RECCAP2 initiative, we present the greenhouse gas (GHG) and carbon (C) budget of Europe. For the decade of the 2010s, we present a bottom‐up (BU) estimate of GHG net‐emissions of 3.9 Pg CO2‐eq. yr−1 (using a global warming potential on a 100 years horizon), which are largely dominated by fossil fuel emissions. In this decade, terrestrial ecosystems acted as a net GHG sink of 0.9 Pg CO2‐eq. yr−1, dominated by a CO2 sink that was partially counterbalanced by net emissions of CH4 and N2O. For CH4 and N2O, we find good agreement between BU and top‐down (TD) estimates from atmospheric inversions. However, our BU land CO2 sink is significantly higher than the TD estimates. We further show that decadal averages of GHG net‐emissions have declined by 1.2 Pg CO2‐eq. yr−1 since the 1990s, mainly due to a reduction in fossil fuel emissions. In addition, based on both data driven BU and TD estimates, we also find that the land CO2 sink has weakened over the past two decades. A large part of the European CO2 and C sinks is located in Northern Europe. At the same time, we find a decreasing trend in sink strength in Scandinavia, which can be attributed to an increase in forest management intensity. These are partly offset by increasing CO2 sinks in parts of Eastern Europe and Northern Spain, attributed in part to land use change. Extensive regions of high CH4 and N2O emissions are mainly attributed to agricultural activities and are found in Belgium, the Netherlands and the southern UK. We further analyzed interannual variability in the GHG budgets. The drought year of 2003 shows the highest net‐emissions of CO2 and of all GHGs combined. Plain Language Summary: We have synthesized the European budgets of carbon and the greenhouse gases (GHG) carbon dioxide, methane and nitrous oxide. This synthesis includes estimates of direct emissions from fossil fuel burning, industrial production, waste management and agriculture, as well as of sources and sinks in the terrestrial biosphere. Summing up the sources and sinks of the three GHGs, we estimate for the decade of the 2010s an average annual net‐emission of 3.9 billion tons of carbon dioxide equivalents. These net‐emissions are dominated by carbon dioxide from fossil fuel emissions (4.1 billion tons of carbon dioxide). In contrast, the terrestrial biosphere acts as a net sink of carbon dioxide, the effect of which is only partly counterbalanced by net emissions of methane and nitrous oxide. The net‐effect of the terrestrial biosphere's GHG budget is a sink of 0.9 billion tons of carbon dioxide equivalents per year. Over the last three decades, European GHG emissions have declined by 1.2 billion tons carbon dioxide equivalents per year, mainly due to reductions in fossil fuel emissions. However, the sink capacity of the terrestrial biosphere has diminished since the 2000s. Key Points: We provide a bottom‐up estimate of CO2, CH4, N2O emissions of 3.9 Pg CO2‐eq. yr−1 over Europe, 2010–2019Terrestrial ecosystems acted as a greenhouse gas net sink of 0.9 Pg CO2‐eq. yr−1, dominated by CO2 sinkNet‐greenhouse gas emissions decreased by ∼1/4 since the 1990s, but land carbon sink is weakening since the 2000s [ABSTRACT FROM AUTHOR]

The terrestrial biosphere plays a major role in the global carbon cycle, and there is a recognized need for regularly updated estimates of land‐atmosphere exchange at regional and global scales. An international ensemble of Dynamic Global Vegetation Models (DGVMs), known as the "Trends and drivers of the regional scale terrestrial sources and sinks of carbon dioxide" (TRENDY) project, quantifies land biophysical exchange processes and biogeochemistry cycles in support of the annual Global Carbon Budget assessments and the REgional Carbon Cycle Assessment and Processes, phase 2 project. DGVMs use a common protocol and set of driving data sets. A set of factorial simulations allows attribution of spatio‐temporal changes in land surface processes to three primary global change drivers: changes in atmospheric CO2, climate change and variability, and Land Use and Land Cover Changes (LULCC). Here, we describe the TRENDY project, benchmark DGVM performance using remote‐sensing and other observational data, and present results for the contemporary period. Simulation results show a large global carbon sink in natural vegetation over 2012–2021, attributed to the CO2 fertilization effect (3.8 ± 0.8 PgC/yr) and climate (−0.58 ± 0.54 PgC/yr). Forests and semi‐arid ecosystems contribute approximately equally to the mean and trend in the natural land sink, and semi‐arid ecosystems continue to dominate interannual variability. The natural sink is offset by net emissions from LULCC (−1.6 ± 0.5 PgC/yr), with a net land sink of 1.7 ± 0.6 PgC/yr. Despite the largest gross fluxes being in the tropics, the largest net land‐atmosphere exchange is simulated in the extratropical regions. Plain Language Summary: Around one third of human‐induced CO2 emissions are absorbed by land ecosystems and thus act to mitigate climate change. It is essential to understand the processes, ecosystems and regions responsible for this natural carbon sink, to inform on the efficiency of the sinks into the future. These sinks are susceptible to year‐to‐year variation in response to climate variations and extremes. At the same time deforestation and other forms of land management are changing the land surface, which overall adds significantly to the human‐induced CO2 emissions. There is a need to regularly update our estimate of land carbon dynamics to aid global stock takes for the Paris agreement to avoid dangerous climate change. Here we present an international initiative that on an annual basis assesses "Trends and drivers of the regional scale terrestrial sources and sinks of carbon dioxide" (TRENDY) using computer models of the land carbon cycle. We quantify the land sink during the contemporary period (2012–2021), and attribute to processes, mainly the large opposing effects of CO2 fertilization enhancing plant productivity and land‐use change. Forests and semi‐arid ecosystems are largely responsible for the mean and trend in the land sink, with the latter most important for its year‐to‐year variation. Key Points: We quantify and attribute land carbon dynamics to underlying processes at regional scales, contributing bottom‐up estimates to RECCAP‐2Models simulate a contemporary net land sink of 1.7 ± 0.6 PgC/yr, with large opposing effects of CO2 fertilization and land‐use changeDespite the largest gross fluxes being in the tropics, the largest net land‐atmosphere exchange is simulated in the extratropical regions [ABSTRACT FROM AUTHOR]

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The marine subsurface is a long-term sink of atmospheric carbon dioxide with significant implications for climate on geologic timescales. Subsurface microbial cells can either enhance or reduce carbon sequestration in the subsurface, depending on their metabolic lifestyle. However, the activity of subsurface microbes is rarely measured. Here, we used nanoscale secondary ion mass spectrometry (nanoSIMS) to quantify anabolic activity in 3,203 individual cells from the thermally altered deep subsurface in the Guaymas Basin, Mexico (3-75 m below the seafloor, 0-14°C). We observed that a large majority of cells were active (83%-100%), although the rates of biomass generation were low, suggesting cellular maintenance rather than doubling. Mean single-cell activity decreased with increasing sediment depth and temperature and was most strongly correlated with porewater sulfate concentrations. Intracommunity heterogeneity in microbial activity decreased with increasing sediment depth and age. Using a dual-isotope labeling approach, we determined that all active cells analyzed were heterotrophic, deriving the majority of their cellular carbon from organic sources. However, we also detected inorganic carbon assimilation in these heterotrophic cells, likely via processes such as anaplerosis, and determined that inorganic carbon contributes at least 5% of the total biomass carbon in heterotrophs in this community. Our results demonstrate that the deep marine biosphere at Guaymas Basin is largely active and contributes to subsurface carbon cycling primarily by not only assimilating organic carbon but also fixing inorganic carbon. Heterotrophic assimilation of inorganic carbon may be a small yet significant and widespread underappreciated source of labile carbon in the global subsurface. [ABSTRACT FROM AUTHOR]

Restoration of mangrove forests has garnered increasing global prominence as a nature‐based solution for carbon (C) sequestration. However, it was unclear whether the radiation forcing induced by methane (CH4) emissions and albedo changes during mangrove restoration processes can offset the cooling effect resulting from the net carbon dioxide (CO2) uptake. In this study, we measured the CO2, CH4, and albedo during 2020–2022 using an open‐path eddy covariance system in an 8‐year restored mangrove ecosystem afforested in Zhejiang Province, China. Their integrated global warming potentials (GWPs) were calculated to assess the climatic impact of mangrove restoration. The results showed that the restored mangroves functioned as a CO2 sink and a CH4 source, with annual values of −656.75 to −465.41 and 5.54 to 9.07 g C m−2 yr−1, respectively. The albedo varied slightly with a range of 0.11–0.13. The integrated GWPs of CO2, CH4, and albedo were −1,354.00 and −1,875.70 g CO2‐eq m−2 yr−1 over the 20‐ and 100‐year time horizons, respectively. The negative values indicated that the mangrove restoration had a net cooling effect, mainly due to CO2 uptake. The warming effects caused by CH4 emissions and albedo changes had the potential to partially offset CO2 uptake by 12.55%–36.51% and 0.08%–0.42%, respectively. Random forest analysis showed that photosynthetically active radiation (PAR) was the dominant driver on integrated GWPs with feature importance values of 0.34. Our results revealed that the cooling benefit of 8‐year restored mangroves remained significant, even when it was partially offset by CH4 emissions and albedo changes. Plain Language Summary: Restored mangrove ecosystems have great potential to mitigate climate change and expand natural carbon sinks. They have climate benefits by sequestering atmospheric carbon dioxide, but these benefits could be offset by methane emissions and albedo changes during mangrove restoration processes. Currently, long‐term measurements of these carbon fluxes and albedo in mangrove restoration are lacking. Based on 3‐year flux tower measurements, we examined these fluxes in 8‐year restored mangrove wetlands, located in the estuary of the Aojiang River in southeastern China. The mangrove restoration acted as a carbon dioxide sink and a methane source, and the albedo of the ecosystem exhibited slight variations of 0.11–0.13. The global warming potentials of these carbon fluxes and albedo were calculated to evaluate the climatic effect of mangrove restoration. The results showed that the cooling effect of carbon dioxide uptake was dominant in the restored mangrove ecosystem, partially offset by positive radiative forcing from methane emissions and albedo changes. Mangrove restoration resulted in a net cooling contribution to the climate, despite only 8 years of restoration. Key Points: Mangrove restoration acted as a CO2 sink and a CH4 source from 2020 to 2022Integrated GWPs of CO2, CH4, and albedo showed a net cooling effect in restored mangroves and were mainly driven by CO2 uptakeRandom forest algorithm showed that PAR was the most important driver of the integrated GWPs in the restored mangrove ecosystem [ABSTRACT FROM AUTHOR]

Tidewater glaciers are highly vulnerable to climate change due to warming from both atmospheric and seawater sources. Most tidewater glaciers are rapidly retreating, but little is known about how glacial melting modifies coastal biogeochemical cycles. Here, we investigate carbonate and nutrient dynamics and fluxes in an expanding proglacial tidal lagoon connected to Europe's largest glacier in Iceland (Vatnajökull). The lagoon N:P:Si ratios (2:1:30) imply a system deficient in nitrogen. The large variations in the freshwater endmembers highlighted the complexity of resolving sources and transformations. The lagoon acted as a sink of dissolved inorganic carbon (DIC). Floating chamber incubations revealed a CO2 uptake of 26 ± 15 mmol m−2 d−1. Lagoon waters near the glacier had a 170% higher CO2 uptake than near the lagoon mouth, likely driven by primary production stimulated by nitrogen‐rich bottom water upwelling. The lateral DIC and total alkalinity (TA) flux rates (outwelling) from the lagoon to the ocean were −1.5 ± 0.1 (export to ocean) and 23 ± 5 mmol m−2 d−1 (import into the lagoon) respectively. All samples were undersaturated with respect to aragonite due to glacial meltwater dilution of TA and CO2 uptake. This implies dilution of oceanic alkalinity, lowering the nearshore buffering capacity against ocean acidification. Plain Language Summary: Marine terminating glaciers are rapidly retreating and releasing freshwater, sediments, carbon, and nutrients to the ocean. We investigated glacier‐ocean exchange in a climate change hotspot in Iceland. The glacier‐fed lagoon was a sink of atmospheric carbon dioxide with greater uptake close to the glacier where primary production is enhanced. Nutrients, dissolved inorganic and organic carbon were exported from the glacier‐fed lagoon to the ocean. Substantial amounts of dissolved inorganic carbon were consumed within the estuarine lagoon prior to exchange with the ocean. Glacier meltwater diluted alkalinity and acidified the lagoon, contributing to local ocean acidification. We emphasize the need to resolve carbon transformations and transport at the land‐ocean interface in areas impacted by glaciers. Key Points: The tidewater glacier enhanced CO2 uptake within the lagoonEstuarine transformations within the lagoon modify carbon and nutrient transport to the coastal oceanGlacial meltwater diluted lagoon alkalinity and enhanced local ocean acidification [ABSTRACT FROM AUTHOR]

Urban environments play a significant role in global carbon emissions and sequestration, necessitating a comprehensive understanding of their spatial distribution. This study presents a micro‐scale spatial modeling framework to elucidate the complex interplay between CO2 sources and sinks within urban settings. Utilizing advanced geospatial analysis, remote sensing data, and geographically weighted regression (GWR) modeling techniques, we provide a detailed characterization of emission patterns and identify the spatial distribution of carbon dioxide sequestration. Employing the bottom‐up method and geographic information system techniques, we quantified carbon dioxide emissions in Isfahan City, Iran, attributing 81.68% to stationary combustion sources (residential, commercial, industrial, and power plant sectors) and 18.32% to mobile combustion sources (road‐rail transportation, and non‐road transportation [agricultural machinery]). To model carbon sequestration, we calculated tree biomass using allometric equations and estimated carbon sequestration per tree unit. Subsequently, we employed GWR to map the spatial distribution of carbon deposition across the city. The results revealed an annual carbon sequestration capacity of 7,704 tons, equivalent to storing 28,275 tons of CO2. Our findings highlight the substantial contribution of urban areas to greenhouse gas emissions and the potential of urban green spaces to mitigate these emissions. The spatial modeling framework developed in this study provides a valuable tool for urban planners to optimize carbon management strategies and promote sustainable urban development. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Peatlands store organic carbon available for decomposition and transfer to neighboring water bodies, which can ultimately generate carbon dioxide (CO2) and methane (CH4) emissions. The objective of this study was to clarify the biogeochemical functioning of open-water peatland pools and their influence on carbon budgets at the ecosystem and global scale. Continuously operated automated equipment and monthly manual measurements were used to describe the CO2 and CH4 dynamics in boreal ombrotrophic peatland pools and porewater (Québec, Canada) over the growing seasons 2019 and 2020. The peat porewater stable carbon isotope ratios (δ13C) for both CO2 (median δ13C-CO2: -3.8‰) and CH4 (median δ13C-CH4: -64.30‰) suggested that hydrogenotrophic methanogenesis was the predominant degradation pathway in peat. Open-water pools were supersaturated in CO2 and CH4 and received most of these dissolved carbon greenhouse gases (C-GHG) from peat porewater input. Throughout the growing season, higher CO2 concentrations and fluxes in pools were measured when the water table was low--suggesting a steady release of CO2 from deep peat porewater. Higher CH4 ebullition and diffusion occurred in August when bottom water and peat temperatures were the highest. While this study demonstrates that peatland pools are chimneys of CO2 and CH4 stored in peat, it also shows that the C-GHG concentrations and flux rates in peat pools are comparable to other aquatic systems of the same size. Although peatlands are often considered uniform entities, our study highlights their biogeochemical heterogeneity, which, if considered, substantially influences their net carbon balance with the atmosphere. [ABSTRACT FROM AUTHOR]

Significant progress in permafrost carbon science made over the past decades include the identification of vast permafrost carbon stocks, the development of new pan‐Arctic permafrost maps, an increase in terrestrial measurement sites for CO2 and methane fluxes, and important factors affecting carbon cycling, including vegetation changes, periods of soil freezing and thawing, wildfire, and other disturbance events. Process‐based modeling studies now include key elements of permafrost carbon cycling and advances in statistical modeling and inverse modeling enhance understanding of permafrost region C budgets. By combining existing data syntheses and model outputs, the permafrost region is likely a wetland methane source and small terrestrial ecosystem CO2 sink with lower net CO2 uptake toward higher latitudes, excluding wildfire emissions. For 2002–2014, the strongest CO2 sink was located in western Canada (median: −52 g C m−2 y−1) and smallest sinks in Alaska, Canadian tundra, and Siberian tundra (medians: −5 to −9 g C m−2 y−1). Eurasian regions had the largest median wetland methane fluxes (16–18 g CH4 m−2 y−1). Quantifying the regional scale carbon balance remains challenging because of high spatial and temporal variability and relatively low density of observations. More accurate permafrost region carbon fluxes require: (a) the development of better maps characterizing wetlands and dynamics of vegetation and disturbances, including abrupt permafrost thaw; (b) the establishment of new year‐round CO2 and methane flux sites in underrepresented areas; and (c) improved models that better represent important permafrost carbon cycle dynamics, including non‐growing season emissions and disturbance effects. Plain Language Summary: Climate change and the consequent thawing of permafrost threatens to transform the permafrost region from a carbon sink into a carbon source, posing a challenge to global climate goals. Numerous studies over the past decades have identified important factors affecting carbon cycling, including vegetation changes, periods of soil freezing and thawing, wildfire, and other disturbance events. Overall, studies show high wetland methane emissions and a small net carbon dioxide sink strength over the terrestrial permafrost region but results differ among modeling and upscaling approaches. Continued and coordinated efforts among field, modeling, and remote sensing communities are needed to integrate new knowledge from observations to modeling and predictions and finally to policy. Key Points: Rapid warming of northern permafrost region threatens ecosystems, soil carbon stocks, and global climate targetsLong‐term observations show importance of disturbance and cold season periods but are unable to detect spatiotemporal trends in C fluxCombined modeling and syntheses show the permafrost region is a small terrestrial CO2 sink with large spatial variability and net CH4 source [ABSTRACT FROM AUTHOR]

The Northeast Greenland shelf carbon system is largely undescribed with the exception of the region associated with the Northeast Water Polynya. We describe the carbon system and the dominant processes affecting it in the region between 24 August and 25 September 2017. During this period the shelf was largely sea ice free and although the north shelf was a carbon dioxide sink, the rest of the shelf and slope acted as both source and sink. This is in contrast to the common perception for this 5 Arctic outflow shelf region as a CO2 sink during the ice-free season. In the southern end of our sampling area, and particularly along the slope, low values of TA can lead to the shelf being a strong carbon dioxide source to the atmosphere. We hypothesize on the possible causes for this low TA [ABSTRACT FROM AUTHOR]

[Display omitted] As one of the world's largest emitters of greenhouse gases, China has set itself the ambitious goal of achieving carbon peaking and carbon neutrality. Therefore, it is crucial to quantify the magnitude and trend of sources and sinks of atmospheric carbon dioxide (CO 2), and to monitor China's progress toward these goals. Using state-of-the-art datasets and models, this study comprehensively estimated the anthropogenic CO 2 emissions from energy, industrial processes and product use, and waste along with natural sources and sinks of CO 2 for all of China during 1980–2021. To recognize the differences among various methods of estimating greenhouse emissions, the estimates are compared with China's National Greenhouse Gas Inventories (NGHGIs) for 1994, 2005, 2010, 2012, and 2014. Anthropogenic CO 2 emissions in China have increased by 7.39 times from 1980 to 12.77 Gt CO 2 a−1 in 2021. While benefiting from ecological projects (e.g., Three Norths Shelter Forest System Project), the land carbon sink in China has reached 1.65 Gt CO 2 a−1 averaged through 2010–2021, which is almost 15.81 times that of the carbon sink in the 1980s. On average, China's terrestrial ecosystems offset 14.69% ± 2.49% of anthropogenic CO 2 emissions through 2010–2021. Two provincial-level administrative regions of China, Xizang and Qinghai, have achieved carbon neutrality according to our estimates, but nearly half of the administrative regions of China have terrestrial carbon sink offsets of less than 10% of anthropogenic CO 2 emissions. This study indicated a high level of consistency between NGHGIs and various datasets used for estimating fossil CO 2 emissions, but found notable differences for land carbon sinks. Future estimates of the terrestrial carbon sinks of NGHGIs urgently need to be verified with process-based models which integrate the comprehensive carbon cycle processes. [ABSTRACT FROM AUTHOR]

Perennial bioenergy crops are a key tool in decarbonizing global energy systems, but to ensure the efficient use of land resources, it is essential that yields and crop longevity are maximized. Remedial shallow surface tillage is being explored in commercial Miscanthus plantations as an approach to reinvigorate older crops and to rectify poor establishment, improving yields. There are posited links, however, between tillage and losses in soil carbon (C) via increased ecosystem C fluxes to the atmosphere. As Miscanthus is utilized as an energy crop, changes in field C fluxes need to be assessed as part of the C balance of the crop. Here, for the first time, we quantify the C impacts of remedial tillage at a mature commercial Miscanthus plantation in Lincolnshire, United Kingdom. Net ecosystem C production based on eddy covariance flux observations and exported yield totalled 12.16 Mg C ha−1 over the 4.6 year period after tillage, showing the site functioned as a net sink for atmospheric carbon dioxide (CO2). There was no indication of negative tillage induced impacts on soil C stocks, with no difference 3 years post tillage in the surface (0–30 cm) or deep (0–70 cm) soil C stocks between the tilled Miscanthus field and an adjacent paired untilled Miscanthus field. Comparison to historic samples showed surface soil C stocks increased by 11.16 ± 3.91 Mg C ha−1 between pre (October 2011) and post tillage sampling (November 2016). Within the period of the study, however, the tillage did not result in the increased yields necessary to "pay back" the tillage induced yield loss. Rather the crop was effectively re‐established, with progressive yield increases over the study period, mirroring expectations of newly planted sites. The overall impacts of remedial tillage will depend therefore, on the longer‐term impacts on crop longevity and yields. [ABSTRACT FROM AUTHOR]

The coastal ocean contributes to regulating atmospheric greenhouse gas concentrations by taking up carbon dioxide (CO2) and releasing nitrous oxide (N2O) and methane (CH4). In this second phase of the Regional Carbon Cycle Assessment and Processes (RECCAP2), we quantify global coastal ocean fluxes of CO2, N2O and CH4 using an ensemble of global gap‐filled observation‐based products and ocean biogeochemical models. The global coastal ocean is a net sink of CO2 in both observational products and models, but the magnitude of the median net global coastal uptake is ∼60% larger in models (−0.72 vs. −0.44 PgC year−1, 1998–2018, coastal ocean extending to 300 km offshore or 1,000 m isobath with area of 77 million km2). We attribute most of this model‐product difference to the seasonality in sea surface CO2 partial pressure at mid‐ and high‐latitudes, where models simulate stronger winter CO2 uptake. The coastal ocean CO2 sink has increased in the past decades but the available time‐resolving observation‐based products and models show large discrepancies in the magnitude of this increase. The global coastal ocean is a major source of N2O (+0.70 PgCO2‐e year−1 in observational product and +0.54 PgCO2‐e year−1 in model median) and CH4 (+0.21 PgCO2‐e year−1 in observational product), which offsets a substantial proportion of the coastal CO2 uptake in the net radiative balance (30%–60% in CO2‐equivalents), highlighting the importance of considering the three greenhouse gases when examining the influence of the coastal ocean on climate. Plain Language Summary: The coastal ocean regulates greenhouse gases. It acts as a sink of carbon dioxide (CO2) but also releases nitrous oxide (N2O) and methane (CH4) into the atmosphere. This synthesis contributes to the second phase of the Regional Carbon Cycle Assessment and Processes (RECCAP2) and provides a comprehensive view of the coastal air‐sea fluxes of these three greenhouse gases at the global scale. We use a multi‐faceted approach combining gap‐filled observation‐based products and ocean biogeochemical models. We show that the global coastal ocean is a net sink of CO2 in both observational products and models, but the coastal uptake of CO2 is ∼60% larger in models than in observation‐based products due to model‐product differences in seasonality. The coastal CO2 sink is strengthening but the magnitude of this strengthening is poorly constrained. We also find that the coastal emissions of N2O and CH4 counteract a substantial part of the effect of coastal CO2 uptake in the atmospheric radiative balance (by 30%–60% in CO2‐equivalents), highlighting the need to consider these three gases together to understand the influence of the coastal ocean on climate. Key Points: We synthesize air‐sea fluxes of CO2, nitrous oxide and methane in the global coastal ocean using observation‐based products and ocean modelsThe coastal ocean CO2 sink is 60% larger in ocean models than in observation‐based products due to systematic differences in seasonalityCoastal nitrous oxide and methane emissions offset 30%–60% of the CO2 coastal uptake in the net radiative balance [ABSTRACT FROM AUTHOR]

The oceans act as major carbon dioxide sinks, greatly influencing global climate. Knowing how these sinks evolve would advance our understanding of climate dynamics. We construct a conceptual box model for the oceans to predict the temporal and spatial evolution of CO 2 of each ocean, and the time-evolution of their salinities. Surface currents, deep water flows, freshwater influx, and major fluvial contributions are considered, as also the effect of changing temperature with time. We uncover the strongest carbon uptake to be from the Southern Ocean, followed by the Atlantic. The North Atlantic evolves into the most saline ocean with time and increasing temperatures. The Amazon River is found to have significant effects on CO 2 sequestration trends. An alternative flow scenario of the Amazon is investigated, giving interesting insights into the global climate in the Miocene epoch. [ABSTRACT FROM AUTHOR]

Carbon Integration methods help identify the appropriate allocation of captured carbon dioxide (CO2) streams into CO2-using sinks, and are especially useful when a number of CO2 sink options are present simultaneously. The method helps identify CO2 allocation scenarios when subjected to an emission target on the CO2 overall network. Many carbon dioxide sink options are costly, and more often than not, require a high purity carbon dioxide source to satisfy the sink demand. Hence, it is imperative to effectively incorporate treatment units in such networks, to obtain high-purity CO2 streams. In fact, it has been previously reported in many studies that the most expensive step in Carbon Capture, Utilization and Sequestration (CCUS) is the treatment system. As a result, this paper focuses on reassessing the performance of carbon integration networks using a more rigorous cost model for the treatment design stage. The effect of utilizing different treatment operating conditions on the overall cost of the treatment stage of CO2 (before allocation) is first captured using a detailed cost model. Subsequently, this information is then fed into a network design problem that involves a CO2 source-sink allocation network problem, and different CO2 net capture targets within the network. For this, an enhanced treatment model that captures all necessary treatment design parameters has been utilized alongside the original model. The original carbon integration formulation has been adopted from previous work. Many of the cost items have been lumped into single parameters in the original formulation, and lack the necessary depth required to carry out the necessary investigations for this work. Hence, the treatment model introduced in this paper is more rigorous, as it accounts for important technical performance constraints on the system to be assessed. Utilizing a more detailed cost model was found to be very helpful in understanding several effects of varying parameters on the overall source-sink allocations, when subjected to different CO2 net emission reduction targets. The cost of the carbon network increases when the solvent temperatures are increased. However, there was a noticeable linear trend at lower temperatures compared to higher temperatures, where the increase became non-linear. Furthermore, it was discovered that for net capture targets of 20% and 25%, no revenue from carbon storage could be generated beyond a solvent temperature of 25 °C. Additionally, the optimal diameter of the treatment column was more responsive to changes in solvent temperature for cases with low net capture targets (below 10%), while its sensitivity decreased for higher capture targets (above 10%). [ABSTRACT FROM AUTHOR]

The quasi-two-dimensional mean effective concentration fields and mean effective fields of methane and carbon dioxide sources and sinks in the region of the Kara and Barents seas are analyzed. The fields were retrieved using the instrumental and computational atmospheric fluid-location technology (passive remote sensing using wind) based on measurements of the surface concentrations on the island of Belyi during the summer months of 2016 and 2017. The concept of the emission and uptake flux disbalance index is introduced, which quantitatively characterizes a degree of the impact of the regional greenhouse gas sources and sinks on the climate system. Estimates of the index are performed for two greenhouse gases for the region of the Barents and Kara seas, which was an emitter of methane (the flux disbalance index is 2.15 and 1.61, respectively) and a sink of carbon dioxide (0.75 and 0.92, respectively), in the summers of 2016 and 2017. [ABSTRACT FROM AUTHOR]

The northwest Atlantic Ocean is an important sink for carbon dioxide produced by anthropogenic activities. However the strong seasonal variability in the surface waters paired with the sparse and summer biased observations of ocean carbon makes it difficult to capture a full picture of its temporal variations throughout the water column. We aim to improve the estimation of temporal trends of dissolved inorganic carbon (DIC) due to anthropogenic sources using a new statistical approach: a time series generalization of the extended multiple linear regression (eMLR) method. Anthropogenic increase of northwest Atlantic DIC in the surface waters is hard to quantify due to the strong, natural seasonal variations of DIC. We address this by separating DIC into its seasonal, natural and anthropogenic components. Ocean carbon data is often collected in the summer, creating a summer bias, however using monthly averaged data made our results less susceptible to the strong summer bias in the available data. Variations in waters below 1000m have usually been analyzed on decadal time scales, but our monthly analysis showed the anthropogenic carbon component had a sudden change in 2000 from stationary to an increasing trend at the same rate as the waters above. All depths layers had similar rates of anthropogenic increase of ∼0.57µmol kg−1 year−1, and our uncertainty levels are smaller than with eMLR results. Integration throughout the water column (0–3,500 m) gives an anthropogenic carbon storage rate of 1.37 ± 0.57 mol m−2 year−1, which is consistent with other published estimates. Plain Language Summary: We need to measure the ocean sink for the CO2 emitted by industrialized societies, and it is particularly important for the northwest Atlantic Ocean. The rate of carbon increase is often overshadowed by natural and seasonal variability. We introduce new statistical approaches to better estimate the rate of anthropogenic carbon that has accumulated due to human activities. Ocean carbon data is often collected in the summer, creating a summer bias, however using monthly averaged data made our results less susceptible to the strong summer bias in the available data. From 1993 to 2015 in the northwest Atlantic Ocean, anthropogenic carbon increased at ∼0.57 μmol kg−1 year−1 within all depth‐layers. Integration of results throughout the water column (0–3,500 m) gives an anthropogenic carbon storage rate of 1.37 ± 0.57 mol m−2 year−1. Key Points: A time series generalization of the extended multiple linear regression (eMLR) method is developed to produce monthly estimates with uncertainties of anthropogenic ocean carbonThe rate of anthropogenic carbon increase in northwest Atlantic is roughly the same for all depth layers, at 0.57 µmol/kg/yearOur method produces estimates of anthropogenic carbon increase that are comparable to those from eMLR, but with smaller uncertainties [ABSTRACT FROM AUTHOR]

The Southern Ocean is among the largest contemporary sinks of atmospheric carbon dioxide on our planet; however, remoteness, harsh weather and other circumstances have led to an undersampling of the ocean basin, compared with its northern hemispheric counterparts. While novel data interpolation methods can in part compensate for such data sparsity, recent studies raised awareness that we have hit a wall of unavoidable uncertainties in air–sea CO2 flux reconstructions. Here, we present results from autonomous observing campaigns using a novel platform to observe remote ocean regions: sailboats. Sailboats are at present a free of charge environmentally friendly platform that recurrently pass remote ocean regions during round-the-globe racing events. During the past 5 years, we collected >350 000 measurements of the sea surface partial pressure of CO2 (p CO2) around the globe including the Southern Ocean throughout an Antarctic circumnavigation during the Vendée Globe racing event. Our analysis demonstrates that the sailboat tracks pass regions where large uncertainty in the air–sea CO2 flux reconstruction prevails, with regional oversaturation or undersaturation of the sea surface p CO2. Sailboat races provide an independent cross-calibration platform for autonomous measurement devices, such as Argo floats, ultimately strengthening the entire Southern Ocean observing system. This article is part of a discussion meeting issue 'Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities'. [ABSTRACT FROM AUTHOR]

High-mountain ecosystems are experiencing the acute effects of climate change, most visibly through glacier recession and the greening of the terrestrial environment. The streams draining these landscapes are affected by these shifts, integrating hydrologic, geologic, and biological signals across the catchment. We examined the organic and inorganic carbon dynamics of streams in four Alpine catchments in Switzerland to assess how glacier loss and vegetation expansion are affecting the carbon cycle of these high-mountain ecosystems. We find that the organic carbon concentration and fluorescence properties associated with humic-like compounds increase with vegetation cover within a catchment, demonstrating the increasing importance of allochthonous dissolved organic carbon sources following glacier retreat. Meanwhile, streams transitioned from carbon dioxide sinks to sources with decreasing glacier coverage and increased vegetation coverage, with chemical weathering and soil respiration likely determining the balance. Periods of sink behavior were also observed in non-glaciated streams, possibly indicating that the chemical consumption of carbon dioxide could be more common in high-mountain, minimally vegetated catchments than previously known. Together, these results demonstrate the dramatic shifts in carbon dynamics of high-mountain streams following glacier recession, with significant changes to both the organic and inorganic carbon cycles. The clear link between the terrestrial and aquatic zones further emphasizes the coupled dynamics with which all hydrologic and biogeochemical changes in these ecosystems should be considered, including the carbon sink or source potential of montane ecosystems. [ABSTRACT FROM AUTHOR]

Unconventional shale petroleum systems, owing to their petroleum generation and storage properties have gained tremendous exploitation and research interest in recent years. Moreover, their emergence as potential atmospheric carbon dioxide sinks has further warranted a detailed examination of their multiple properties. Laboratory geochemical screening and geomechanical investigations provide valuable information for classifying these reservoirs. Although some guidelines exist for conducting such analyses, the analytical methods and sampling techniques applied do influence the quality of the derived measurements. For laboratory geochemical screening using the Rock-Eval technique, various factors including sample grain size, type of kerogen, sample quantity, and nature of S2 and S4 curves, all substantially influence the quality of the data generated. In this work, we summarize the different factors that influence the data generated from Rock-Eval analysis and recommend a method that involves optimization of sample weight and sizes for the generation of reliable geochemical data. A new emerging technology in the field of organic petrography for the simultaneous characterization of organic and inorganic phases in shales has also been discussed. Once source-rock potential of the shale formation is ascertained, the next step is a selection of suitable target shale reservoir zones, and designing successful hydraulic fracturing programs for the exploitation of the reservoir. For this purpose, detailed knowledge of geomechanical properties is essential. However, the quantity of intact shale-core samples recovered from coring operations is typically insufficient for reliably analyzing geomechanical properties by applying the established standards. A comparison is made between the uniaxial compressive strength and Young's modulus measurements on shale specimens of different length-to-diameter ratios. It reveals that specimens smaller than the recommended standard exhibit unacceptable variations in the values of strength and elastic parameters they generate. To overcome this, it is justified to use alternative techniques suited to the small sample sizes typically recovered in borehole shale cores. For instance, a punching tool and nanoindentation, which require small sample sizes, can both be used to reliably analyze geomechanical properties in circumstances where larger shale samples are not available from borehole zones of interest. Research highlights: Sample handling and preparation is critical for producing reliable data from geochemical and geomechanical screening measurements of shales. Sample weight and sizes have significant influence on the quality of the geochemical data generated using Rock-Eval technique. Optical-electron correlative microscopy- a new tool for shale heterogeneity study Critical evaluation of the generated pyrograms is necessary before accepting the Rock-Eval measurements. The limited shale core sample availability issues can be mitigated using techniques like punching-tool and nano-indentation which are specifically tailored for small samples. [ABSTRACT FROM AUTHOR]

Land is both a source and a sink of carbon dioxide (CO2), the chief greenhouse gas. Through sustainable land management (SLM), it can capture extra CO2 and store it as carbon in vegetation and soil. SLM can also reduce CO2 emissions from the land. Thus, SLM is viewed as the key land-based solution for climate change mitigation. Yet, SLM also provides effective climate change (CC) adaptation practices—such as agroforestry, mulching and water harvesting—which confer resilience, and simultaneously help secure production. This is especially valuable for land users in sub-Saharan Africa (SSA) who depend on rainfed agriculture. They are amongst the poorest on Earth and the most vulnerable to CC impacts, despite their minimal carbon footprint. The World Overview of Conservation Approaches and Technologies (WOCAT) manages the Global SLM Database: this holds a rich and ever-growing collection of SLM practices. Analysis of the database for rainfed SSA sheds light on which SLM technologies are effective in CC adaptation, and how well they cope with changing rainfall and temperature. Both "mechanisms" and "attributes" are explored, yielding new insights. This perspective paper showcases current developments in the field, and summarizes future directions for SLM as a CC adaptation solution for land users in SSA. [ABSTRACT FROM AUTHOR]

Soil carbon flux rates are a crucial metric of carbon cycling that contribute to calculating an ecosystem's carbon budget, and thus whether it is a source or sink of atmospheric carbon dioxide. However, soil carbon flux datasets are frequently low‐resolution across either space or time, limiting our abilities to identify small‐scale ecological contexts that influence soil carbon dynamics. Existing datasets are distributed unevenly, with some soil carbon‐rich regions (like tropical grasslands) significantly understudied. We developed an autonomous, inexpensive, do‐it‐yourself (DIY) soil carbon flux chamber (a "fluxbot") and data processing software. We deployed a distributed array of 12 fluxbots in a long‐term experiment in a central Kenyan savanna where it has been logistically impossible to collect high‐resolution soil carbon flux data. With this array we collected over 10,000 individual flux estimates over almost two months, spanning the end of a dry season and the start of a wet season. With our successful deployment in situ, we demonstrate the potential for low‐cost, autonomous, DIY sensors in improving resolution of soil carbon flux datasets (particularly in under‐studied or logistically challenging systems). If implemented widely, such an improvement in data collection capacities could improve our understanding of ecological and climatic drivers of soil carbon flux dynamics on the local to global scale. Plain Language Summary: Soil carbon flux, the rate at which carbon dioxide is exchanged between soil and the atmosphere, is a key feature of an ecosystem's carbon budget. However, measuring soil carbon flux rates at spatial and temporal scales that capture global ecosystems' ecological heterogeneity is extremely difficult due to the logistical constraints of manual data collection and high costs of commercial sensor systems. As such, many existing soil carbon flux datasets do not have the resolution necessary to identify small‐scale ecological patterns in carbon dynamics, and datasets are distributed unevenly across easy‐to‐monitor ecosystems globally. We developed an inexpensive, robotic, autonomous soil carbon flux chamber that collects hourly data for as long as it is deployed. We built and deployed an array of 12 sensors in an ecologically complex central Kenyan savanna ecosystem. We collected almost two months of hourly data consisting of over 10,000 soil carbon flux measurements, the largest and most high‐resolution dataset collected in this system. Wider adoption of such open‐access chambers could result in the collection of highly resolved soil carbon flux datasets in understudied systems worldwide, and greater understanding of the ecological contexts that mediate soil carbon flux. Key Points: We developed an autonomous soil carbon flux chamber ("fluxbot") to improve data collection resolution and extentWe prioritized low price and accessibility to enable the capture of small‐scale ecological heterogeneityWe distributed a fluxbot array in a large community ecology experiment to test their ability to capture complexity [ABSTRACT FROM AUTHOR]

The Australian continent contributes substantially to the year-to-year variability of the global terrestrial carbon dioxide (CO2) sink. However, the scarcity of in situ observations in remote areas prevents the deciphering of processes that force the CO2 flux variability. In this study, by examining atmospheric CO2 measurements from satellites in the period 2009–2018, we find recurrent end-of-dry-season CO2 pulses over the Australian continent. These pulses largely control the year-to-year variability of Australia’s CO2 balance. They cause two to three times larger seasonal variations compared with previous top-down inversions and bottom-up estimates. The pulses occur shortly after the onset of rainfall and are driven by enhanced soil respiration preceding photosynthetic uptake in Australia’s semiarid regions. The suggested continental-scale relevance of soil-rewetting processes has substantial implications for our understanding and modeling of global climate–carbon cycle feedbacks. [ABSTRACT FROM AUTHOR]

The climate crisis and rising demand for critical minerals necessitate the development of novel carbon dioxide removal and ore processing technologies. Microbial processes can be harnessed to recover metals from and store carbon dioxide within mine tailings to transform the mining industry for a greener and more sustainable future. Historically thought of as waste, mine tailings are an underutilized source of metals and carbon dioxide sink. This Perspective outlines how microbes can be used to help the mining industry transition to a more sustainable future. [ABSTRACT FROM AUTHOR]

In this study, the carbon dioxide (CO 2) system on the continental shelf of the southwestern part of Peter the Great Bay (PGB), Sea of Japan was investigated during the autumn of 2015. During this season, the PGB represents an ocean-dominated shelf interaction system as the source of nutrients on the shelf is the subsurface part of the Sea of Japan. Weak seasonal upwelling occurred during the study period (October 20–23, 2015), forming a two-layer water structure on the shelf with a sharp pycnocline. The upper warm layer (12–15 °C) is characterized by nutrient depletion and supersaturation of dissolved oxygen concentrations (apparent oxygen utilization (AOU) < 0), and it simultaneously acts as a sink to atmospheric carbon dioxide (p CO 2 < p CO 2atm). The layer beneath the pycnocline is characterized by low temperatures (2–5 °C) and a high concentration of nutrients; it exhibits an oxygen deficit (AOU>0) and an excess of carbon dioxide (p CO 2 > p CO 2atm). Nitrate concentrations in the near-bottom layer of the waters suggest that these waters upwelled to the PGB shelf at depths of 200–300 m in the open Japan-East Sea. We observed a high intensity of photosynthesis corresponding to the pycnocline zone, with chlorophyll a concentration exceeding 10 mg/m3, which was attributed to the phytoplankton bloom. The estimated primary production in the euphotic layer of the southwestern part of PGB is up to 4.98 gC m−2 day−1. Based on the dissolved inorganic carbon (DIC)/nutrient ratio in the subsurface waters of the northwestern Sea of Japan, the shelf becomes a sink for atmospheric carbon dioxide after upwelling. Owing to the heating of surface waters during summer, the PGB acts as a source of CO 2 to the atmosphere. • Observations from October 2015 indicate weak upwelling of water from the Sea of Japan onto the PGB shelf. • Upwelling caused high phytoplankton production turning surface waters into a sink for atmospheric carbon dioxide. • Comparison of data from summer 2014 with fall 2015 suggest that seasonal heating makes PGB a source of CO2 in summer. [ABSTRACT FROM AUTHOR]

Chemical weathering over geological timescales acts as a source or sink of atmospheric carbon dioxide (CO 2), while influencing long-term redox cycling and atmospheric oxygen (O 2) at Earth's surface. There is a growing recognition that the oxidative weathering of rock organic carbon (OC petro) can release more CO 2 than is locally drawn down by silicate weathering, and may vary due to changes in erosion and climate. The element rhenium (Re) has emerged as a proxy to track the oxidative weathering of OC petro , yet uncertainties in its application remain namely that we lack a systematic assessment of the comparative mobility of Re and OC petro during sedimentary rock weathering. Here we measure Re and OC petro loss across gradients in rock weathering at 9 global sites, spanning a range of initial OC petro values from ∼0.2 % to >10 %. We use titanium to account for volume changes during weathering and assess Re and OC petro loss alongside major elements that reflect silicate (Na, Mg), carbonate (Ca, Mg) and sulfide (S) weathering. Across the dataset, Re loss is correlated with OC petro loss but not with loss of any other major element. Across the weathering profiles, the average molar ratio of OC petro to Re loss was 0.84 ± 0.15, with 8 out of 9 sites having a ratio >0.74. At one site (Marcellus Shale), the average ratio was lower at 0.58 ± 0.11. The excess loss of Re matches expectations that, typically, between ∼0 and 20 % of the Re liberated by sedimentary rock weathering derives from silicate or sulfide phases, while some OC petro may be physically or chemically protected from weathering. Overall, our measurements provide validation for the Re proxy of OC petro oxidation and allow future work to further improve our knowledge of regional and global-scale rates of this important source of CO 2 in the geochemical carbon cycle. [ABSTRACT FROM AUTHOR]

• Methane (CH 4) flux was mainly controlled by water temperature from half-hourly to monthly timescales. • CH 4 flux was negatively correlated with carbon dioxide (CO 2) flux, and positively related to the ecosystem gross primary production and respiration. • The fraction of vegetation cover had great positive impact on CH 4 emission, and large fraction of vegetation cover in southwest sector led to CH 4 emission 'hotspots'. Wetlands are the primary natural source of methane (CH 4) emissions to the atmosphere, however, the quantification of wetland CH 4 flux and net carbon budgets remains uncertain due to limited measurements and large variability across different types of wetlands. Based on continuous measurements using the eddy covariance (EC) technique over a "floating blanket" wetland in southwest China for a period of over three years (2018–2021), we examined the temporal variations of CH 4 flux and its environmental controls on different temporal scales. The results showed that this wetland acted as a sink for carbon dioxide (CO 2) while simultaneously serving as a source for CH 4. The annual CO 2 uptake and CH 4 emission was 155.9–221.2 g C-CO 2 m−2 yr−1 and 44.6–56.9 g C-CH 4 m−2 yr−1 during 2019–2021, respectively. The annual total carbon budget varied from -176.6 g C m−2 yr−1 to -99.0 g C m−2 yr−1. From half-hourly to monthly timescales, CH 4 flux was mainly controlled by water temperature with a positive correlation. There was a negative correlation between CH 4 flux and CO 2 flux, and the importance of CO 2 flux to CH 4 flux increased as the timescale extended. CH 4 flux exhibited a significant positive correlation with the ecosystem gross primary production (GPP) and respiration (Re) on daily and monthly timescales. In addition, the fraction of vegetation cover had a positive impact on CH 4 emissions. There was a significant variation in the fraction of vegetation cover with wind direction. The southwestern wind sector had the highest fraction of vegetation cover compared to other sectors, leading to the formation of the CH 4 emission hotspot. The cumulative CH 4 emissions in the southwestern wind sector were also higher than those in other sectors, accounting for around 58.13% of the annual total CH 4 emissions, while the cumulative CH 4 emissions in other wind sectors accounted for 5.21%–21.50%. [ABSTRACT FROM AUTHOR]

Mangrove forests represent important sources of methane, partly thwarting their ecosystem function as an efficient atmospheric carbon dioxide sink. Many studies have focused on the spatial and temporal variability of methane emissions from mangrove ecosystems, yet little is known about the microbial and physical controls on the release of biogenic methane from tidally influenced mangrove sediments. Here, we show that aerobic methane oxidation is a key microbial process that effectively reduces methane emissions from mangrove sediments. We further demonstrate clear links between the tidal cycle and fluctuations in methane fluxes, with contrasting methane emission rates under different tidal amplitudes. Our data suggest that both the microbial methane oxidation activity and pressure-induced advective transport modulated methane fluxes in the mangrove sediments. Methane oxidation activity is limited by the availability of oxygen in the surface sediments, which in turn is controlled by tidal dynamics, further highlighting the interactive physico-biogeochemical controls on biological methane fluxes. Although we found some molecular evidence for anaerobic methanotrophs in the deeper sediments, anaerobic methane oxidation seems to play only a minor role in the mangrove sediments, with potential rates being two orders of magnitude lower than those of aerobic methane oxidation. Our findings confirmed the importance of surface sediments as biological barrier for methane. Specifically, when sediments were exposed to the air, methane consumption increased by ∼227%, and the methane flux was reduced by ∼62%, compared to inundated conditions. Our data demonstrate how tides can orchestrate the daily rhythm of methane consumption and production within mangrove sediments, thus explaining the temporal variability of methane emissions in the tidally influenced coastal mangrove systems. [Display omitted] • Methane emissions from a coastal mangrove varied with tidal cycle and amplitude. • Sediment methane consumption increased by ∼227%, and methane flux was reduced by ∼62%, under air exposure during low tide. • Both microbial processes and tidal dynamics modulate methane flux during inundation. • Aerobic methane oxidation rates were two orders of magnitude higher than AOM rates. [ABSTRACT FROM AUTHOR]

Forests contribute to climate change mitigation by retaining carbon in their biomass, providing the renewable resource for wood-based products, bioenergy, and the substitution of materials with a bigger ecological footprint. Whether or not forest management is carbon neutral is a matter of discussion that is compromised by unclear terminology. It is claimed that unmanaged forests hold higher carbon stocks in the biomass and therefore contribute more to the mitigation of climate change. Particularly critical is the appraisal of bioenergy from wood. Based on Austrian data we demonstrate that forest management has been sustainable for at least several decades and that the business-as-usual management with a focus on timber production and bioenergy mainly as side-stream of timber processing does not introduce additional carbon dioxide (CO 2) to the atmosphere, but removes it. With annual harvest rates consistently lower than the annual timber increment and a vital timber processing industry the forests and the wood products have been a sink of greenhouse gases that have compensated for on average 14 % of the Austrian greenhouse-gas (GHG) emissions between 1990 and 2022. We critically assess concepts that classify forest management operations as non‑carbon-neutral and conclude that the narrative is only valid in regions with unsustainable forest management and deforestation. The storage of carbon in the biomass and in wood products, the generation of bioenergy mainly from a side stream of timber processing, and the substitution of non-wood products represent a consistent sink of carbon dioxide. We also conclude that frequently used baselines of unmanaged forests as comparison to managed forests are based on unfounded assumptions of forest ecosystem dynamics, insufficiently accounting for tree mortality and disturbances. We support the business-as-usual forest management as carbon neutral and recognize the need for active forest management to implement adaptive measures to successfully cope with climate change impacts, and to supply society with a renewable resource of small GHG footprint. • Carbon neutrality is scrutinized against field data instead of theoretical constructs • Carbon neutrality and sustainable forest managment is feasible even when management intensities are increased. • Forests are no permanent sink for greenhouse gases. [ABSTRACT FROM AUTHOR]

Steppe ecosystems, occupying about 8% of the terrestrial area, are an essential element of the global carbon cycle in the atmosphere–vegetation–soil system. The carbon (C–CO2) balance of natural steppe ecosystems in Russia is estimated based on the geoinformation–analytical method and employing the database of empirically measured values of the net primary production and a climate-driven regression model that makes it possible to estimate the intensity of carbon dioxide flux from soils into the atmosphere. Natural steppes in Russia serve as a significant sink of carbon dioxide from the atmosphere. The average intensity of this carbon flux can be estimated at 231 ± 202 gC/m2 per year. The estimated annual accumulation of carbon dioxide in the natural steppe ecosystems of Russia is 111 ± 97 MtC. According to the estimates, the steppe ecosystems under study provide from 8 to 19% of the atmospheric carbon sink to the terrestrial ecosystems of Russia. [ABSTRACT FROM AUTHOR]

High-mountain ecosystems are experiencing acute effects of climate change, most visibly through glacier recession and the greening of the terrestrial environment. The streams draining these landscapes are affected by these shifts, integrating hydrologic, geologic, and biological signals across the catchment. We examined the organic and inorganic carbon dynamics of streams in four Alpine catchments in Switzerland to assess how glacier loss and vegetation expansion are affecting the carbon cycle of these high mountain ecosystems. We find that organic carbon concentration and fluorescence properties associated with humic-like compounds increase with vegetation cover within a catchment, demonstrating the increasing importance of allochthonous carbon sources following glacier retreat. Meanwhile, streams transitioned from carbon dioxide sinks to sources with decreasing glacier coverage and increased vegetation coverage, with chemical weathering and soil respiration likely determining the balance. Periods of sink behavior were also observed in non-glaciated streams, indicating geochemical consumption of carbon dioxide may be more common in high-mountain, minimally vegetated catchments than previously described. Together, these results demonstrate the dramatic shifts in carbon dynamics of alpine streams following glacier recession, with significant changes to both the organic and inorganic carbon cycles. The clear link between the terrestrial and aquatic zones further emphasizes the coupled dynamics with which all hydrologic and biogeochemical changes in these ecosystems should be considered, including the role of mountain streams in the global carbon cycle. [ABSTRACT FROM AUTHOR]

Peatlands are globally important long‐term sinks of atmospheric carbon dioxide (CO2). However, there is concern that climate change‐mediated drying will reduce gross primary productivity (GPP) and increase ecosystem respiration (ER) making peatlands vulnerable to a weaker carbon sink function and potential net carbon loss. While large and deep peatlands are usually resilient to moderate summer drying, CO2 exchange in shallow Boreal Shield peatlands is likely more sensitive to drying given the reduced groundwater connectivity and water storage potential. To better understand the carbon cycling responses of Boreal Shield peatlands to meteorological conditions, we examined ecohydrological controls on CO2 fluxes using the eddy covariance technique at a shallow peatland during the summer season for 5 years, from 2016–2020. We found lower GPP in dry summer years. Mean summer water table depth (WTD) was found to be significantly correlated with summer total net ecosystem CO2 exchange (R2 = 0.78; p value = 0.046) and GPP (R2 = 0.83; p value = 0.03), where wet summers with a WT close to the peat surface sequestered more than twice the amount of CO2 than dry summers. Our findings suggest that shallow Boreal Shield peatland GPP may be sensitive to climate‐mediated drying as they may switch to a net CO2 source in the summer season when WTDs exceed a critical ecohydrological threshold for a prolonged period of time. Plain Language Summary: Peatlands take in carbon from the atmosphere and store it in the ground as peat, a process that helps to regulate climate change. Peatlands in the Boreal Shield are positioned in bedrock basins. Their water table (WT) is controlled by precipitation, which can trigger water flow over the bedrock between wetland ecosystems. Due to this unique setting, we expected Boreal Shield peatlands to be more sensitive to differences in growing season meteorological conditions from year to year. We used 5 years of carbon dioxide (CO2) exchange measurements between land and atmosphere during the summer season in a Boreal Shield peatland in Ontario, Canada. We found the peatland vegetation took up more CO2 from the atmosphere during summers with more rain which keeps the WT in the peatland closer to the peat surface. The peatland took up less CO2 when the summer was dry. Our findings provide insight into how Boreal Shield peatlands are responding to summer droughts under current climate conditions. Key Points: Summers with higher rainfall (and lower P‐PET) maintain a water table near the peat surface and have greater net carbon dioxide (CO2) uptakeInterannual differences in summer net ecosystem CO2 exchange are attributable to changes in summer gross primary productionShallow Boreal Shield peatlands may switch to a net carbon source in the summer season [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) plays a vital role in the global carbon cycle and is a potential sink for carbon dioxide. Agricultural management practices can support carbon sequestration and, therefore, offer potential removal strategies whilst also improving overall soil quality. Meta-analysis allows one to summarize results from primary articles by calculating an overall effect size and to reveal the source of variation across studies. The number of meta-analyses published in the field of agriculture is continuously rising. At the same time, more and more articles refer to their synthesis work as a meta-analysis, despite applying less than rigorous methodologies. As a result, poor-quality meta-analyses are published and may lead to questionable conclusions and recommendations to scientists, policymakers, and farmers. This study aims at quantitatively analyzing 31 meta-analyses, published between the years of 2005 and 2020, studying the effects of different management practices on SOC. We compiled a set of quality criteria suitable for soil and agricultural sciences by adapting existing meta-analytical guidelines from other disciplines. The set is supported by a scoring scheme that allows for a quantitative analysis. The retrieved meta-analyses were structured according to 11 management categories, such as tillage, cover crops, crop residue management, and biochar application, which allowed us to assess the state of knowledge on these categories. Major deficiencies were found in the use of standard metrics for effect size calculation, independence of effect sizes, standard deviation extraction for each study, and study weighting by the inverse of variance. Only 1 out of 31 SOC meta-analyses, which studied the effects of no tillage/reduced tillage compared with conventional tillage, was found to be of high quality. Therefore, improved meta-analyses on the effects of organic agriculture, biochar, fertilization, or crop diversification on SOC are urgently needed. We conclude that, despite efforts over the last 15 years, the quality of meta-analyses on SOC research is still low. Thus, in order for the scientific community to provide high-quality synthesis work and to make advancements in the sustainable management of agricultural soils, we need to adapt rigorous methodologies of meta-analysis as quickly as possible. [ABSTRACT FROM AUTHOR]

Determining mesopelagic organic carbon budgets is essential to characterize the ocean's role as a carbon dioxide sink. This is because the biological processes observed in the mesopelagic zone are crucial for understanding the biological carbon pump. Yet, field assessments of carbon budgets are often unbalanced with the carbon demand exceeding its supply. This underlines either methodological issues in the budget calculations or incomplete knowledge of the mesopelagic carbon cycling with potentially missing sources. Carbon budgets are built by partitioning the ocean into vertical depth zones. Vertical boundaries are conventionally defined between 200 and 1000 m depth or using various thresholds. Such approaches lack consistent methodology preventing robust comparison of mesopelagic carbon budget from region to region. Here, using a statistical rupture detection method applied to conductivity–temperature–depth (CTD)‐cast variables (fluorescence, O2 concentration, potential temperature, salinity, and density), we aim to provide independent estimates of mesopelagic boundaries. We demonstrate that the so‐determined upper boundary is highly correlated with the knee points of the particulate organic carbon (POC) fluxes estimated by a power law and that over 90% of the POC flux attenuation occurs within our method boundaries. The identified zone therefore corresponds to the most active part of the conventional mesopelagic zone and we name it the "active mesopelagic zone" (AMZ). We find that the depths of the mesopelagic zone depend on the region considered. Our results demonstrate that the mesopelagic carbon budget discrepancy can vary up to four folds depending on the boundaries chosen and hence provide novel grounds to reassess existing and future mesopelagic carbon budgets. [ABSTRACT FROM AUTHOR]

Tidal freshwater forested wetlands (TFFW) provide critical ecosystem services including an essential habitat for a variety of wildlife species and significant carbon sinks for atmospheric carbon dioxide. However, large uncertainties remain concerning the impacts of climate change on the magnitude and variability of carbon fluxes and storage across a range of TFFW. In this study, we developed a process‐driven Tidal Freshwater Wetlands DeNitrification‐DeComposition model (TFW‐DNDC) that has integrated new features, such as soil salinity effects on plant productivity and soil organic matter decomposition to explore carbon dynamics in the TFFW in response to drought‐induced saltwater intrusion. Eight sites along the floodplains of the Waccamaw River (USA) and the Savannah River (USA) were selected to represent the TFFW transition from healthy to moderately and highly salt‐impacted forests, and eventually to oligohaline marshes. The TFW‐DNDC was calibrated and validated using field observed annual litterfall, stem growth, root growth, soil heterotrophic respiration, and soil organic carbon storage. Analyses indicate that plant productivity and soil carbon sequestration in TFFW could change substantially in response to increased soil pore water salinity and reduced soil water table due to drought, but in interactive ways dependent on the river simulated. These responses are variable due to nonlinear relationships between carbon cycling processes and environmental drivers. Plant productivity, plant respiration, soil organic carbon sequestration rate, and storage in the highly salt‐impacted forest sites decreased significantly under drought conditions compared with normal conditions. Considering the high likelihood of healthy and moderately salt‐impacted forests becoming highly salt‐impacted forests under future climate change and sea‐level rise, it is very likely that the TFFW will lose their capacity as carbon sinks without up‐slope migration. [ABSTRACT FROM AUTHOR]

Archean Serpentinised dunite is important not only for understanding the evolution of the ultramafic deposit of magnesium, but also serves as a possible sink material for the carbon dioxide sequestration. Future anti-pollution measures may include sequestering of waste CO2 as magnesite (MgCO3) by processing ultramafic rocks to obtain reactable Mg. For the first time, the Raman spectroscopic investigation of dunite is presented from the Karya, Sargur supracrustals (3Ga) Greenstone Belt. The Raman spectra of the sample reveal abundant presence of serpentine. Polymorphs of serpentine: lizardite, antigorite and chrysotile exhibit typical intense band at 685–692 cm−1 in the Raman spectrum. The Raman peaks in this study also indicates the presence of chromite and magnesite. The lunar dunite 72415, one of the oldest lunar samples of the Mg-suite, contains chromite symplectites indicative of crystallization at 40–50 km rather than at a shallow depth of <1 km, also having a olivine content of about 85%. The present study showed the dunite has about 85% olivine, which is almost identical to the Martian dunite, meteorite Northwest Africa (NWA) 2737 is the second known chassignite, an olivine-rich igneous rock with mineral compositions and isotopic ratios that suggest it formed on Mars. NWA 2737 consists of ∼ 85% vol. The present study on the Karya dunite of Sargur supracrustals (3 Ga) greenstone belt, Western Dharwar Craton Karnataka, indicates a possibility of using this as a terrestrial analogue material for improving the Martian surface mineralogy and occurrence of hydrous minerals and life support system in Mars. [ABSTRACT FROM AUTHOR]

The Global Stocktake (GST), implemented by the Paris Agreement, requires rapid developments in the capabilities to quantify annual greenhouse gas (GHG) emissions and removals consistently from the global to the national scale and improvements to national GHG inventories. In particular, new capabilities are needed for accurate attribution of sources and sinks and their trends to natural and anthropogenic processes. On the one hand, this is still a major challenge as national GHG inventories follow globally harmonized methodologies based on the guidelines established by the Intergovernmental Panel on Climate Change, but these can be implemented differently for individual countries. Moreover, in many countries the capability to systematically produce detailed and annually updated GHG inventories is still lacking. On the other hand, spatially-explicit datasets quantifying sources and sinks of carbon dioxide, methane and nitrous oxide emissions from Earth Observations (EO) are still limited by many sources of uncertainty. While national GHG inventories follow diverse methodologies depending on the availability of activity data in the different countries, the proposed comparison with EO-based estimates can help improve our understanding of the comparability of the estimates published by the different countries. Indeed, EO networks and satellite platforms have seen a massive expansion in the past decade, now covering a wide range of essential climate variables and offering high potential to improve the quantification of global and regional GHG budgets and advance process understanding. Yet, there is no EO data that quantifies greenhouse gas fluxes directly, rather there are observations of variables or proxies that can be transformed into fluxes using models. Here, we report results and lessons from the ESA-CCI RECCAP2 project, whose goal was to engage with National Inventory Agencies to improve understanding about the methods used by each community to estimate sources and sinks of GHGs and to evaluate the potential for satellite and in-situ EO to improve national GHG estimates. Based on this dialogue and recent studies, we discuss the potential of EO approaches to provide estimates of GHG budgets that can be compared with those of national GHG inventories. We outline a roadmap for implementation of an EO carbon-monitoring program that can contribute to the Paris Agreement. [ABSTRACT FROM AUTHOR]