Global Greenhouse Gas Budget Research Articles

Sink or source? Methane and carbon dioxide emissions from cryoconite holes, subglacial sediments, and proglacial river runoff during intensive glacier melting on the Tibetan Plateau

High Mountain Asia glaciers are currently ignored in the estimation of global greenhouse gas budgets (e.g., methane (CH4) and carbon dioxide (CO2)). Similar to the Asian Water Tower and Third Pole, the Tibetan Plateau (TP) hosts the largest volume of glaciers outside the polar regions. These glaciers contain large reservoirs of organic carbon that can influence glacial ecosystems under rapid melting. However, no data exist on the current footprint of CH4 and CO2 from glaciers in the TP. Here, we report in situ observations of CH4 and CO2 fluxes for glacial cryoconite holes, subglacial sediments, and proglacial river runoff across the TP. Our results indicate that cryoconite holes and subglacial sediments can accelerate the export of greenhouse gasses during the melting season due to intensive glacier melting. However, to some extent, proglacial river runoff can be a significant sink of atmospheric CO2; this fact was not identified in previous studies. Our findings suggest that variations (source or sink) of greenhouse gasses from TP glacial basins should be considered in regional CH4 and CO2 budgets under climate warming.

Soil greenhouse gas fluxes from a humid tropical forest and differently managed urban parkland in Singapore

Studies of soil greenhouse gas (GHG) fluxes (CO2, CH4 and N2O) from tropical soils are still scarce and the effects of urban green space management on soil GHG fluxes are poorly addressed. In order to establish reliable global GHG budgets, field measurements of soil GHG fluxes from different land uses and management practices in tropical regions are urgently needed. In this study, soil fluxes of CO2, CH4 and N2O were measured over a period of one year, from a forest and an urban parkland in Singapore. At the parkland site, two additional management practices were investigated, namely compost application to urban lawn and the replacement of lawn by legumes. The average CO2 efflux from the forest soil was 0.17 ± 0.01 g C m−2 h−1 and was 30% lower than that of the parkland soil. The forest soil was a CH4 sink (−36.03 ± 8.80 μg C m−2 h−1), while the parkland soil was a source of CH4 (43.79 ± 9.66 μg C m−2 h−1). Both soils were net emitters of N2O, with the forest soil releasing four times more N2O (23.23 ± 5.10 μg N m−2 h−1) than the parkland soil (6.47 ± 2.52 μg N m−2 h−1). During the entire observation period, compost application increased CO2eq by 30% compared with the untreated parkland soil. Shortly after compost addition, CO2 fluxes significantly increased and remained elevated until the end of the experiment. Soil CH4 emissions also increased, but the effect was small compared to CO2 (<1% CO2eq). Compost amendment caused an immediate short-term peak of N2O emissions. However, after the first day, which was characterized by a heavy rain event, the compost effect on N2O production was negligible. Compared to grass cultivation, legume planting resulted in a 20% reduction of CO2eq. This study shows that conserving mature secondary forests and the cultivation of herbaceous legumes on tropical urban soils, where open lawn spaces are not required, can reduce soil GHG emissions.

No effect of warming and watering on soil nitrous oxide fluxes in a temperate sitka spruce forest ecosystem

ABSTRACT Soil fluxes of nitrous oxide (N2O) play an important role in the global greenhouse gas budget. However, the response of soil N2O emissions to climate change in temperate forest plantations is not yet well understood. In this study, we assessed the responses of soil N2O fluxes to experimental warming with or without water addition, using a replicated in situ heating (~2°C above ambient) and water addition (170 mm) experiment in a temperate Sitka spruce plantation forest over the period 2014–2016. We found that seasonal fluxes of N2O during the year were highly variable, ranging from net uptake to net emissions. Seasonal variations in soil N2O fluxes were not correlated with either soil temperature or soil moisture. In addition, none of the individual warming/watering treatments, or their interactions, had significant effects on soil N2O fluxes and N-related soil properties. Overall, our results suggest that despite future increases in temperature, soil N2O emission may remain largely unchanged in many temperate forest ecosystems that are often N-limited.

Greenhouse gas emissions from marine decommissioned hydrocarbon wells: leakage detection, monitoring and mitigation strategies

Hydrocarbon gas emissions from with decommissioned wells are an underreported source of greenhouse gas emissions in oil and gas provinces. The associated emissions may partly counteract efforts to mitigate greenhouse gas emissions from fossil fuel infrastructure. We have developed an approach for assessing methane leakage from marine decommissioned wells based on a combination of existing regional industrial seismic and newly acquired hydroacoustic water column imaging data from the Central North Sea. Here, we present hydroacoustic data which show that 28 out of 43 investigated wells release gas from the seafloor into the water column. This gas release largely depends on the presence of shallow gas accumulations and their distance to the wells. The released gas is likely primarily biogenic methane from shallow sources. In the upper 1,000 m below the seabed, gas migration is likely focused along drilling-induced fractures around the borehole or through non-sealing barriers. Combining available direct measurements for methane release from marine decommissioned wells with our leakage analysis suggests that gas release from investigated decommissioned hydrocarbon wells is a major source of methane in the North Sea (0.9-3.7 [95% confidence interval = 0.7-4.2] kt yr−1 of CH4 for 1,792 wells in the UK sector of the Central North Sea). This means hydrocarbon gas emissions associated with marine hydrocarbon wells are not significant for the global greenhouse gas budget, but have to be considered when compiling regional methane budgets.

Effects of nitrogen deposition and litter layer management on soil CO2, N2O, and CH4 emissions in a subtropical pine forestland

Forestland soils play vital role in regulating global soil greenhouse gas (GHG) budgets, but the interactive effect of the litter layer management and simulated nitrogen (N) deposition on these GHG flux has not been elucidated clearly in subtropical forestland. A field trial was conducted to study these effects by using litter removal method under 0 and 40 kg N ha−1 yr−1 addition in a subtropical forestland in Yingtan, Jiangxi Province, China. Soil CO2 emission was increased by N addition (18–24%) but decreased by litter removal (24–32%). Litter removal significantly (P < 0.05) decreased cumulative N2O emission by 21% in treatments without N addition but only by 10% in treatments with 40 kg N ha−1 yr−1 addition. Moreover, litter-induced N2O emission under elevated N deposition (0.094 kg N2O-N ha−1) was almost the same as without N addition (0.088 kg N2O-N ha−1). Diffusion of atmospheric CH4 into soil was facilitated by litter removal, which increased CH4 uptake by 55%. Given that the increasing trend of atmospheric N deposition in future, which would reduce litterfall in subtropical N-rich forest, the effect of surface litter layer change on soil GHG emissions should be considered in assessing forest GHG budgets and future climate scenario modeling.

Roles of Thermokarst Lakes in a Warming World.

Permafrost covers a quarter of the northern hemisphere land surface and contains twice the amount of carbon that is currently present in the atmosphere. Future climate change is expected to reduce its near-surface cover by over 90% by the end of the 21st century, leading to thermokarst lake formation. Thermokarst lakes are point sources of carbon dioxide and methane which release long-term carbon stocks into the atmosphere, thereby initiating a positive climate feedback potentially contributing up to a 0.39°C rise of surface air temperatures by 2300. This review describes the potential role of thermokarst lakes in a warming world and the microbial mechanisms that underlie their contributions to the global greenhouse gas budget.

Spatial and seasonal variation of methanogenic community in a river-bay system in South China.

River-bay system is a transitional zone connecting land and ocean and an important natural source for methane emission. Methanogens play important roles in the global greenhouse gas budget and carbon cycle since they produce methane. The abundance and community assemblage of methanogens in such a dynamic system are not well understood. Here, we used quantitative PCR and high-throughput sequencing of the mcrA gene to investigate the abundance and community composition of methanogens in the Shenzhen River-Bay system, a typical subtropical river-bay system in Southern of China, during the wet and dry seasons. Results showed that mcrA gene abundance was significantly higher in the sediments of river than those of estuary, and was higher in wet season than dry season. Sequences of mcrA gene were mostly assigned to three orders, including Methanosarcinales, Methanomicrobiales, and Methanobacteriales. Specifically, Methanosarcina, Methanosaeta, and Methanobacterium were the most abundant and ubiquitous genera. Methanogenic communities generally clustered according to habitat (river vs. estuary), and salinity was the major factor driving the methanogenic community assemblage. Furthermore, the indicator groups for two habitats were identified. For example, Methanococcoides, Methanoculleus, and Methanogenium preferentially existed in estuarine sediments, whereas Methanomethylovorans, Methanolinea, Methanoregula, and Methanomassiliicoccales were more abundant in riverine sediments, indicating distinct ecological niches. Overall, these findings reveal the distribution patterns of methanogens and expand our understanding of methanogenic community assemblage in the river-bay system. Key Points • Abundance of methanogens was relatively higher in riverine sediments. • Methanogenic community in estuarine habitat separated from that in riverine habitat. • Salinity played a vital role in regulating methanogenic community assemblage.

Environmental controls on methane fluxes in a cool temperate bog

Peatlands are important ecosystems for understanding global methane (CH4) and greenhouse gas budgets. We evaluated the CH4 emissions from a cool temperate bog in northern Japan and their responses to environmental drivers based on four years of quasi-continuous measurements with the eddy covariance method. The bog acted as a 13 to 19 g C m−2 yr−1 CH4 source. High annual CH4 emissions outweighed the annual carbon dioxide (CO2) sink strength (-223 to -79 g C m−2 yr−1), except in one year, resulting in a net greenhouse gas source at the annual timescale, although greater uncertainties in the annual CO2 budget (14%) than the CH4 budget (5%) caused uncertainties in the greenhouse gas budget. The seasonal variations in the CH4 fluxes were well explained by soil temperatures in the deep layers and the leaf area index of vascular plants. Pressure-driven CH4 emissions were measured at synoptic timescales, indicating high contributions of ebullition emissions. The episodic CH4 emissions during two typhoon events accounted for 5.1% of the annual fluxes in 2018. Nighttime CH4 emissions were greater than daytime emissions during the early growing season, possibly due to the hydrodynamic transport associated with soil temperature instability at night. The annual CH4 emissions were high when the dissolved oxygen concentration at 10 cm was low and the annual CO2 sink was great, suggesting the importance of anaerobic conditions and substrate availability, which facilitate CH4 production and restrict CH4 oxidation. The climate conditions in the study years were within the normal range; thus, further long-term measurements covering a wide range of climatic conditions will be required.

ASSESSING GREENHOUSE GAS EXCHANGE OF AGRICULTURAL CROPS BY FLUX MEASUREMENTS IN THRACE PART OF TURKEY

Agriculture plays an important role in the global greenhouse gas (GHG) budget andits cycle. CO2 is one of the most important greenhouse gases, and plants releaseCO2 into the atmosphere by respiration and sink it by photosynthesis from theatmosphere. In addition, soil has an essential role in this exchange. Unfortunately,studies on the measurement of greenhouse gases above agricultural crops ininternationally accepted methods are not sufficient, especially in developingcountries. Thus, it is a clear need to determine carbon exchange of agriculturalcrops and activities (sink and emission) by taking into consideration of the specificconditions such as climate, crop variety, soil etc. Eddy Covariance (EC) is one ofthe widely used micrometeorological methods in the world for flux measurementstudies. Developments in measurement and analysis by instruments have allowedthis method to be applied more by researchers for the studies on GHG exchange. Inthis research, carbon exchanges (sink and emission) of watermelon grown inAtatürk Soil, Water and Agricultural Meteorology Research Institute located in theThrace part of Turkey, was measured using the Eddy Covariance method. Finally,estimated gas exchange above crops will be presented.

Sustained Antarctic Research: A 21st Century Imperative

The view from the south is, more than ever, dominated by ominous signs of change. Antarctica and the Southern Ocean are intrinsic to the Earth system, and their evolution is intertwined with and influences the course of the Anthropocene. In turn, changes in the Antarctic affect and presage humanity's future. Growing understanding is countering popular beliefs that Antarctica is pristine, stable, isolated, and reliably frozen. An aspirational roadmap for Antarctic science has facilitated research since 2014. A renewed commitment to gathering further knowledge will quicken the pace of understanding of Earth systems and beyond. Progress is already evident, such as addressing uncertainties in the causes and pace of ice loss and global sea-level rise. However, much remains to be learned. As an iconic global “commons,” the rapidity of Antarctic change will provoke further political action. Antarctic research is more vital than ever to a sustainable future for this One Earth.

GOSATの経緯とGOSAT-2への期待─温室効果気体の変動と収支─

GOSATの経緯とGOSAT-2への期待─温室効果気体の変動と収支─

Methane budget of East Asia, 1990–2015: A bottom-up evaluation

The regional budget of methane (CH4) emissions for East Asia, a crucial region in the global greenhouse gas budget, was quantified for 1990–2015 with a bottom-up method based on inventories and emission model simulations. Anthropogenic emissions associated with fossil fuel extraction, industrial activities, waste management, and agricultural activities were derived from the Emission Database for Global Atmospheric Research version 4.3.2 and compared with other inventories. Emissions from natural wetlands and CH4 uptake by upland soil oxidation were estimated using the Vegetation Integrative SImulator for Trace gases (VISIT), a biogeochemical model that considers historical land use and climatic conditions. Emissions from biomass burning and termites were calculated using satellite and land-use data combined with empirical emission factors. The resulting average annual estimated CH4 budget for 2000–2012 indicated that East Asia was a net source of 67.3 Tg CH4 yr−1, of which 88.8% was associated with anthropogenic emissions. The uncertainty (±standard deviation) of this estimate, ±14 Tg CH4 yr−1, stemmed from data and model inconsistencies. The increase of the net flux from 60.2 Tg CH4 yr−1 in 1990 to 78.0 Tg CH4 yr−1 in 2012 was due mainly to increased emissions by the fossil fuel extraction and livestock sectors. Our results showed that CH4 was a crucial component of the regional greenhouse gas budget. A spatial analysis using 0.25° × 0.25° grid cells revealed emission hotspots in urban areas, agricultural areas, and wetlands. These hotspots were surrounded by weak sinks in upland areas. The estimated natural and anthropogenic emissions fell within the range of independent estimates, including top-down estimates from atmospheric inversion models. Such a regional accounting is an effective way to elucidate climatic forcings and to develop mitigation policies. Further studies, however, are required to reduce the uncertainties in the budget.

Blue carbon potential of coastal wetland restoration varies with inundation and rainfall

There is a growing interest in how the management of ‘blue carbon’ sequestered by coastal wetlands can influence global greenhouse gas (GHG) budgets. A promising intervention is through restoring tidal exchange to impounded coastal wetlands for reduced methane (CH4) emissions. We monitored an impounded wetland’s GHG flux (CO2 and CH4) prior to and following tidal reinstatement. We found that biogeochemical responses varied across an elevation gradient. The low elevation zone experienced a greater increase in water level and an associated greater marine transition in the sediment microbial community (16 S rRNA) than the high elevation zone. The low elevation zone’s GHG emissions had a reduced sustained global warming potential of 264 g m−2 yr−1 CO2-e over 100 years, and it increased to 351 g m−2 yr−1 with the removal of extreme rain events. However, emission benefits were achieved through a reduction in CO2 emissions, not CH4 emissions. Overall, the wetland shifted from a prior CH4 sink (−0.07 to −1.74 g C m−2 yr−1) to a variable sink or source depending on the elevation site and rainfall. This highlights the need to consider a wetland’s initial GHG emissions, elevation and future rainfall trends when assessing the efficacy of tidal reinstatement for GHG emission control.

Nitrous oxide emissions from inland waters: Are IPCC estimates too high?

Nitrous oxide (N2 O) emissions from inland waters remain a major source of uncertainty in global greenhouse gas budgets. N2 O emissions are typically estimated using emission factors (EFs), defined as the proportion of the terrestrial nitrogen (N) load to a water body that is emitted as N2 O to the atmosphere. The Intergovernmental Panel on Climate Change (IPCC) has proposed EFs of 0.25% and 0.75%, though studies have suggested that both these values are either too high or too low. In this work, we develop a mechanistic modeling approach to explicitly predict N2 O production and emissions via nitrification and denitrification in rivers, reservoirs and estuaries. In particular, we introduce a water residence time dependence, which kinetically limits the extent of denitrification and nitrification in water bodies. We revise existing spatially explicit estimates of N loads to inland waters to predict both lumped watershed and half-degree grid cell emissions and EFs worldwide, as well as the proportions of these emissions that originate from denitrification and nitrification. We estimate global inland water N2 O emissions of 10.6-19.8GmolNyear-1 (148-277GgNyear-1 ), with reservoirs producing most N2 O per unit area. Our results indicate that IPCC EFs are likely overestimated by up to an order of magnitude, and that achieving the magnitude of the IPCC's EFs is kinetically improbable in most river systems. Denitrification represents the major pathway of N2 O production in river systems, whereas nitrification dominates production in reservoirs and estuaries.

Nitrous oxide emissions from soils under traditional cropland and apple orchard in the semi-arid Loess Plateau of China

The conversions of cropland to forest, or other tree-based systems, are considered to be important processes affecting regional and global greenhouse gas budgets, especially for nitrous oxide (N2O). From April 2007 to March 2009, in the rain-fed semi-arid climate of the Loess Plateau, China, soil N2O emissions were measured using static chambers from a winter wheat field and an apple orchard, which had been established in part of the wheat field 23 years earlier.Annual average N2O emissions from the apple orchard (2.40 kg N2O ha−1yr−1) were 12.15% higher than those in the wheat field (2.14 kg N2O ha−1yr−1). Seasonal rainfall, in combination with higher nitrogen fertilization, had a promoting effect on N2O emissions in the apple orchard compared with the wheat field. The amounts and patterns of summer rainfall and winter snowfall were the principal controllers of seasonal and annual N2O fluxes in these rain-fed semi-arid regions, likely through their influence on soil moisture content. Since there may be a moisture threshold associated with summer rainfall and winter snowfall triggering higher N2O emissions, climatic regimes should be taken into account when assessing the effects of land use on N2O emissions in the Loess Plateau.

Sensitivity of global greenhouse gas budgets to tropospheric ozone pollution mediated by the biosphere

Tropospheric ozone (O3), a harmful secondary air pollutant, can affect the climate via direct radiative forcing and by modifying the radiative forcing of aerosols through its role as an atmospheric oxidant. Moreover, O3 exerts a strong oxidative pressure on the biosphere and indirectly influences the climate by altering the materials and energy exchange between terrestrial ecosystems and the atmosphere. However, the magnitude by which O3 affects the global budgets of greenhouse gases (GHGs: CO2, CH4, and N2O) through altering the land–atmosphere exchange is largely unknown. Here we assess the sensitivity of these budgets to tropospheric O3 pollution based on a meta-analysis of experimental studies on the effects of elevated O3 on GHG exchange between terrestrial ecosystems and the atmosphere. We show that across ecosystems, elevated O3 suppresses N2O emissions and both CH4 emissions and uptake, and has little impact on stimulation of soil CO2 emissions except at relatively high concentrations. Therefore, the soil system would be transformed from a sink into a source of GHGs with O3 levels increasing. The global atmospheric budget of GHGs is sensitive to O3 pollution largely because of the carbon dioxide accumulation resulting from suppressed vegetation carbon uptake; the negative contributions from suppressed CH4 and N2O emissions can offset only ∼10% of CO2 emissions from the soil–vegetation system. Based on empirical data, this work, though with uncertainties, provides the first assessment of sensitivity of global budgets of GHGs to O3 pollution, representing a necessary step towards fully understanding and evaluating O3–climate feedbacks mediated by the biosphere.

Global Biogeographic Analysis of Methanogenic Archaea Identifies Community-Shaping Environmental Factors of Natural Environments.

Methanogenic archaea are important for the global greenhouse gas budget since they produce methane under anoxic conditions in numerous natural environments such as oceans, estuaries, soils, and lakes. Whether and how environmental change will propagate into methanogenic assemblages of natural environments remains largely unknown owing to a poor understanding of global distribution patterns and environmental drivers of this specific group of microorganisms. In this study, we performed a meta-analysis targeting the biogeographic patterns and environmental controls of methanogenic communities using 94 public mcrA gene datasets. We show a global pattern of methanogenic archaea that is more associated with habitat filtering than with geographical dispersal. We identify salinity as the control on methanogenic community composition at global scale whereas pH and temperature are the major controls in non-saline soils and lakes. The importance of salinity for structuring methanogenic community composition is also reflected in the biogeography of methanogenic lineages and the physiological properties of methanogenic isolates. Linking methanogenic alpha-diversity with reported values of methane emission identifies estuaries as the most diverse methanogenic habitats with, however, minor contribution to the global methane budget. With salinity, temperature and pH our study identifies environmental drivers of methanogenic community composition facing drastic changes in many natural environments at the moment. However, consequences of this for the production of methane remain elusive owing to a lack of studies that combine methane production rate with community analysis.

Methane and hydrogen in hyperalkaline groundwaters of the serpentinized Dinaride ophiolite belt, Bosnia and Herzegovina

Methane (CH4) in continental serpentinized peridotites (MSP) has been documented in numerous hyperalkaline (pH > 9) springs and gas seeps worldwide. With a dominantly abiotic origin, MSP is often associated with considerable amounts of hydrogen (H2), produced by serpentinization. Both gases may fuel microbial activity in igneous rocks and may have played roles in the origin of life. MSP is also a natural CH4 source for the atmosphere, not included in the global greenhouse-gas budget, yet. Here we document a new and major case of MSP, in the Dinaride ophiolite belt in Bosnia and Herzegovina. CH4 is dissolved (83–2706 μM) in low temperature (13–30 °C), hyperalkaline (pH 10 to 12.8) waters in six sites, sampled through springs and boreholes. Four sites (Slanac, Vlajići, Kulaši and Lješljani) show CH4 isotopic signatures typical of abiotic MSP (δ13C: −18.5 to −35.7‰; δ2H: −221 to −335.4‰); two sites (Vaićeva and Kiseljak) show a dominantly biotic signature (δ13C: −58.8 and −65.1‰; δ2H: −310.8 and −226.8‰), probably due to mixing with gas from coal-beds adjacent to the ultramafic rocks. H2 concentration is highly variable (up to 348 μM), ethane, propane and butane reach 0.13 vol.% in total, and helium isotopic composition (R/Ra: 0.12 to 0.48) reflects a dominant crustal signature. The Lješljani site features the highest pH (12.8) and CH4 emission (∼9 ton y−1) in peridotite-hosted hyperalkaline groundwater documented so far. Geological and geochemical data converge towards the hypothesis that, as proposed in similar cases, CH4 was mainly generated by Sabatier reaction between H2 (from serpentinization) and CO2 (from C-bearing rocks, in tectonic contact with the ophiolite, or other CO2 sources). CH4-H2-H2O disequilibria and Sabatier reaction constraints suggest that CH4 is not formed in the hyperalkaline water, but in water-free or unsaturated rocks hosting opportune metal catalysts (e.g., chromitites). The amount of methane released to the atmosphere from individual springs is comparable to that of conventional biotic gas seeps/springs in sedimentary basins.

Elevated CO2 and nitrogen addition accelerate net carbon gain in a brackish marsh

Wetlands have an inordinate influence on the global greenhouse gas budget, but how global changes may alter wetland contribution to future greenhouse gas fluxes is poorly understood. We determined the greenhouse gas balance of a tidal marsh exposed to nine years of experimental carbon dioxide (CO2) and nitrogen (N) manipulation. We estimated net carbon (C) gain rates by measuring changes in plant and soil C pools over nine years. In wetland soils that accrete primarily through organic matter inputs, long-term measurements of soil elevation, along with soil C density, provide a robust estimate of net soil C gain. We used net soil C gain along with methane and nitrous oxide fluxes to determine the radiative forcing of the marsh under elevated CO2 and N addition. Nearly all plots exhibited a net gain of C over the study period (up to 203 g C m−2 year−1), and C gain rates were greater with N and CO2 addition. Treatment effects on C gain and methane emissions dominated trends in radiative forcing while nitrous oxide fluxes in all treatments were negligible. Though these soils experience salinities that typically suppress methane emissions, our results suggest that elevated CO2 can stimulate methane emissions, overcoming positive effects of elevated CO2 on C gain, converting brackish marshes that are typically net greenhouse gas sinks into sources. Adding resources, either CO2 or N, will likely increase “blue carbon” accumulation rates in tidal marshes, but importantly, each resource can have distinct influences on the direction of total greenhouse forcing.

Greenhouse gas fluxes from agricultural soils of Kenya and Tanzania

AbstractKnowledge of greenhouse gas (GHG) fluxes in soils is a prerequisite to constrain national, continental, and global GHG budgets. However, data characterizing fluxes from agricultural soils of Africa are markedly limited. We measured carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) fluxes at 10 farmer‐managed sites of six crop types for 1 year in Kenya and Tanzania using static chambers and gas chromatography. Cumulative emissions ranged between 3.5–15.9 Mg CO2‐C ha−1 yr−1, 0.4–3.9 kg N2O‐N ha−1 yr−1, and −1.2–10.1 kg CH4‐C ha−1 yr−1, depending on crop type, environmental conditions, and management. Manure inputs increased CO2 (p = 0.03), but not N2O or CH4, emissions. Soil cultivation had no discernable effect on emissions of any of the three gases. Fluxes of CO2 and N2O were 54–208% greater (p &lt; 0.05) during the wet versus the dry seasons for some, but not all, crop types. The heterogeneity and seasonality of fluxes suggest that the available data describing soil fluxes in Africa, based on measurements of limited duration of only a few crop types and agroecological zones, are inadequate to use as a basis for estimating the impact of agricultural soils on GHG budgets. A targeted effort to understand the magnitude and mechanisms underlying African agricultural soil fluxes is necessary to accurately estimate the influence of this source on the global climate system and for determining mitigation strategies.