Amazon methane budget derived from multi-year airborne observations highlights regional variations in emissions

AbstractAtmospheric methane concentrations were nearly constant between 1999 and 2006, but have been rising since by an average of ~8 ppb per year. Increases in wetland emissions, the largest natural global methane source, may be partly responsible for this rise. The scarcity of in situ atmospheric methane observations in tropical regions may be one source of large disparities between top-down and bottom-up estimates. Here we present 590 lower-troposphere vertical profiles of methane concentration from four sites across Amazonia between 2010 and 2018. We find that Amazonia emits 46.2 ± 10.3 Tg of methane per year (~8% of global emissions) with no temporal trend. Based on carbon monoxide, 17% of the sources are from biomass burning with the remainder (83%) attributable mainly to wetlands. Northwest-central Amazon emissions are nearly aseasonal, consistent with weak precipitation seasonality, while southern emissions are strongly seasonal linked to soil water seasonality. We also find a distinct east-west contrast with large fluxes in the northeast, the cause of which is currently unclear.

Download Full-text

Assessment of the theoretical limit in instrumental detectability of Arctic methane sources using <sup>13</sup>C atmospheric signal

10.5194/acp-2018-1217 ◽

2018 ◽

Author(s):

Thibaud Thonat ◽

Marielle Saunois ◽

Isabelle Pison ◽

Antoine Berchet ◽

Thomas Hocking ◽

...

Keyword(s):

Transport Model ◽

The Arctic ◽

Atmospheric Methane ◽

Chemistry Transport Model ◽

Isotopic Signatures ◽

Arctic Regions ◽

Methane Budget ◽

Source Signal ◽

Methane Source ◽

Global Emissions

Abstract. Despite their modest 4 % magnitude compared to global emissions, Arctic methane sources are key elements in closing the global atmospheric methane budget, due to high uncertainties in their quantification and to their strong climate sensitivity. Recent efforts brought together bottom-up quantification approaches (inventories, process-based models) and regional observations of methane concentrations through inverse modelling to better estimate the Arctic methane sources, but the relatively small number of available observations in Arctic regions leaves gaps in fully understanding the drivers and distributions of the different types of methane sources present in the Arctic. Observations of methane isotope ratios could bring new insights on methane processes with increasingly affordable and accurate instruments. Here, we present the source signal that could be observed from methane isotopic measurements if high-resolution observations were available, and thus what requirements should be fulfilled in future instrument deployments in terms of accuracy in order to constrain different emission categories. This theoretical study uses the regional chemistry-transport model CHIMERE driven by different scenarios of isotopic signatures for each regional methane source mix. It is found that if the current network of methane monitoring sites is equipped with instruments measuring the isotopic signal continuously, only sites that are significantly influenced by emission sources could differentiate regional emissions from the background with a reasonable level of confidence. Nevertheless, we show that the detection of individual Arctic sources requires daily accuracies of

Download Full-text

On the role of trend and variability in the hydroxyl radical (OH) in the global methane budget

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-13011-2020 ◽

2020 ◽

Vol 20 (21) ◽

pp. 13011-13022

Author(s):

Yuanhong Zhao ◽

Marielle Saunois ◽

Philippe Bousquet ◽

Xin Lin ◽

Antoine Berchet ◽

...

Keyword(s):

Hydroxyl Radical ◽

El Niño ◽

Climate Model ◽

El Nino ◽

Interannual Variations ◽

Atmospheric Methane ◽

Tropical Regions ◽

Ch4 Emissions ◽

Methane Budget

Abstract. Decadal trends and interannual variations in the hydroxyl radical (OH), while poorly constrained at present, are critical for understanding the observed evolution of atmospheric methane (CH4). Through analyzing the OH fields simulated by the model ensemble of the Chemistry–Climate Model Initiative (CCMI), we find (1) the negative OH anomalies during the El Niño years mainly corresponding to the enhanced carbon monoxide (CO) emissions from biomass burning and (2) a positive OH trend during 1980–2010 dominated by the elevated primary production and the reduced loss of OH due to decreasing CO after 2000. Both two-box model inversions and variational 4D inversions suggest that ignoring the negative anomaly of OH during the El Niño years leads to a large overestimation of the increase in global CH4 emissions by up to 10 ± 3 Tg yr−1 to match the observed CH4 increase over these years. Not accounting for the increasing OH trends given by the CCMI models leads to an underestimation of the CH4 emission increase by 23 ± 9 Tg yr−1 from 1986 to 2010. The variational-inversion-estimated CH4 emissions show that the tropical regions contribute most to the uncertainties related to OH. This study highlights the significant impact of climate and chemical feedbacks related to OH on the top-down estimates of the global CH4 budget.

Download Full-text

δ 13 C methane source signatures from tropical wetland and rice field emissions

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2020.0449 ◽

2021 ◽

Vol 380 (2215) ◽

Author(s):

James L. France ◽

Rebecca E. Fisher ◽

David Lowry ◽

Grant Allen ◽

Marcos F. Andrade ◽

...

Keyword(s):

Rice Field ◽

Ambient Air ◽

Atmospheric Methane ◽

Isotopic Signatures ◽

Methane Budget ◽

Significant Seasonal Variation ◽

Methane Source ◽

Wetland Extent ◽

Term Monitoring

The atmospheric methane (CH 4 ) burden is rising sharply, but the causes are still not well understood. One factor of uncertainty is the importance of tropical CH 4 emissions into the global mix. Isotopic signatures of major sources remain poorly constrained, despite their usefulness in constraining the global methane budget. Here, a collection of new δ 13 C CH 4 signatures is presented for a range of tropical wetlands and rice fields determined from air samples collected during campaigns from 2016 to 2020. Long-term monitoring of δ 13 C CH 4 in ambient air has been conducted at the Chacaltaya observatory, Bolivia and Southern Botswana. Both long-term records are dominated by biogenic CH 4 sources, with isotopic signatures expected from wetland sources. From the longer-term Bolivian record, a seasonal isotopic shift is observed corresponding to wetland extent suggesting that there is input of relatively isotopically light CH 4 to the atmosphere during periods of reduced wetland extent. This new data expands the geographical extent and range of measurements of tropical wetland and rice δ 13 C CH 4 sources and hints at significant seasonal variation in tropical wetland δ 13 C CH 4 signatures which may be important to capture in future global and regional models. This article is part of a discussion meeting issue ‘Rising methane: is warming feeding warming? (part 2)’.

Download Full-text

Investigation of the global methane budget over 1980–2017 using GFDL-AM4.1

10.5194/acp-2019-529 ◽

2019 ◽

Cited By ~ 1

Author(s):

Jian He ◽

Vaishali Naik ◽

Larry W. Horowitz ◽

Ed Dlugokencky ◽

Kirk Thoning

Keyword(s):

Atmospheric Chemistry ◽

Latitudinal Gradient ◽

Methane Emissions ◽

Anthropogenic Emissions ◽

Atmospheric Methane ◽

Recent Past ◽

Methane Budget ◽

Global Trend ◽

Emission Changes ◽

Global Emissions

Abstract. Changes in atmospheric methane abundance have implications for both chemistry and climate as methane is both a strong greenhouse gas and an important precursor for tropospheric ozone. A better understanding of the drivers of trends and variability in methane abundance over the recent past is therefore critical for building confidence in projections of future methane levels. In this work, the representation of methane in the atmospheric chemistry model AM4.1 is improved by optimizing total methane emissions (to an annual mean of 576 ± 32 Tg yr−1) to match surface observations over 1980–2017. The simulations with optimized global emissions are in general able to capture the observed global trend, variability, seasonal cycle, and latitudinal gradient of methane. Simulations with different emission adjustments suggest that increases in methane sources (mainly from energy and waste sectors) balanced by increases in methane sinks (mainly due to increases in OH levels) lead to methane stabilization (with an imbalance of 5 Tg yr−1) during 1999–2006, and that increases in methane sources combined with little change in sinks (despite small decreases in OH levels) during 2007–2012 lead to renewed methane growth (with an imbalance of 14 Tg yr−1 for 2007–2017). Compared to 1999–2006, both methane emissions and sinks are greater (by 31 Tg yr−1 and 22 Tg yr−1, respectively) during 2007–2017. Our results also indicate that the energy sector is more likely a major contributor to the methane renewed growth after 2006 than wetland, as increases in wetland emissions alone are not able to explain the renewed methane growth with constant anthropogenic emissions. In addition, a significant increase in wetland emissions would be required starting in 2006, if anthropogenic emissions declined, for wetland emissions to drive renewed growth in methane, which is a less likely scenario. Simulations with varying OH levels indicate that 1 % change in OH levels could lead to an annual mean of ~ 4 Tg yr−1 difference in the optimized emissions and 0.08 year difference in the estimated tropospheric methane lifetime. Continued increases in methane emissions along with decreases in tropospheric OH concentrations during 2008–2015 prolong methane lifetime and therefore amplify the response of methane concentrations to emission changes. Uncertainties still exist in the partitioning of emissions among individual sources and regions.

Download Full-text

Centennial evolution of the atmospheric methane budget: what do the carbon isotopes tell us?

Atmospheric Chemistry and Physics ◽

10.5194/acp-7-2119-2007 ◽

2007 ◽

Vol 7 (8) ◽

pp. 2119-2139 ◽

Cited By ~ 55

Author(s):

K. R. Lassey ◽

D. M. Etheridge ◽

D. C. Lowe ◽

A. M. Smith ◽

D. F. Ferretti

Keyword(s):

Nuclear Power ◽

Isotope Composition ◽

Mixing Ratio ◽

Atmospheric Methane ◽

Global Budget ◽

Polar Ice ◽

Direct Production ◽

Methane Budget ◽

Atmospheric Data ◽

Methane Source

Abstract. Little is known about how the methane source inventory and sinks have evolved over recent centuries. New and detailed records of methane mixing ratio and isotopic composition (12CH4, 13CH4 and 14CH4) from analyses of air trapped in polar ice and firn can enhance this knowledge. We use existing bottom-up constructions of the source history, including "EDGAR"-based constructions, as inputs to a model of the evolving global budget for methane and for its carbon isotope composition through the 20th century. By matching such budgets to atmospheric data, we examine the constraints imposed by isotope information on those budget evolutions. Reconciling both 12CH4 and 13CH4 budgets with EDGAR-based source histories requires a combination of: a greater proportion of emissions from biomass burning and/or of fossil methane than EDGAR constructions suggest; a greater contribution from natural such emissions than is commonly supposed; and/or a significant role for active chlorine or other highly-fractionating tropospheric sink as has been independently proposed. Examining a companion budget evolution for 14CH4 exposes uncertainties in inferring the fossil-methane source from atmospheric 14CH4 data. Specifically, methane evolution during the nuclear era is sensitive to the cycling dynamics of "bomb 14C" (originating from atmospheric weapons tests) through the biosphere. In addition, since ca. 1970, direct production and release of 14CH4 from nuclear-power facilities is influential but poorly quantified. Atmospheric 14CH4 determinations in the nuclear era have the potential to better characterize both biospheric carbon cycling, from photosynthesis to methane synthesis, and the nuclear-power source.

Download Full-text

Termites Facilitate Methane Oxidation and Shape the Methanotrophic Community

Applied and Environmental Microbiology ◽

10.1128/aem.02785-13 ◽

2013 ◽

Vol 79 (23) ◽

pp. 7234-7240 ◽

Cited By ~ 24

Author(s):

Adrian Ho ◽

Hans Erens ◽

Basile Bazirake Mujinya ◽

Pascal Boeckx ◽

Geert Baert ◽

...

Keyword(s):

Methane Oxidation ◽

Type I ◽

Atmospheric Methane ◽

Nest Area ◽

Active Nest ◽

Content Type ◽

Reference Soil ◽

Methane Budget ◽

Species Analysis

ABSTRACTTermite-derived methane contributes 3 to 4% to the total methane budget globally. Termites are not known to harbor methane-oxidizing microorganisms (methanotrophs). However, a considerable fraction of the methane produced can be consumed by methanotrophs that inhabit the mound material, yet the methanotroph ecology in these environments is virtually unknown. The potential for methane oxidation was determined using slurry incubations under conditions with high (12%) andin situ(∼0.004%) methane concentrations through a vertical profile of a termite (Macrotermes falciger) mound and a reference soil. Interestingly, the mound material showed higher methanotrophic activity. The methanotroph community structure was determined by means of apmoA-based diagnostic microarray. Although the methanotrophs in the mound were derived from populations in the reference soil, it appears that termite activity selected for a distinct community. Applying an indicator species analysis revealed that putative atmospheric methane oxidizers (high-indicator-value probes specific for the JR3 cluster) were indicative of the active nest area, whereas methanotrophs belonging to both type I and type II were indicative of the reference soil. We conclude that termites modify their environment, resulting in higher methane oxidation and selecting and/or enriching for a distinct methanotroph population.

Download Full-text

Investigation of the global methane budget over 1980–2017 using GFDL-AM4.1

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-805-2020 ◽

2020 ◽

Vol 20 (2) ◽

pp. 805-827 ◽

Cited By ~ 3

Author(s):

Jian He ◽

Vaishali Naik ◽

Larry W. Horowitz ◽

Ed Dlugokencky ◽

Kirk Thoning

Keyword(s):

Atmospheric Chemistry ◽

Latitudinal Gradient ◽

Sharp Decrease ◽

Methane Emissions ◽

Anthropogenic Sources ◽

Anthropogenic Emissions ◽

Atmospheric Methane ◽

Methane Budget ◽

Emission Changes ◽

Global Emissions

Abstract. Changes in atmospheric methane abundance have implications for both chemistry and climate as methane is both a strong greenhouse gas and an important precursor for tropospheric ozone. A better understanding of the drivers of trends and variability in methane abundance over the recent past is therefore critical for building confidence in projections of future methane levels. In this work, the representation of methane in the atmospheric chemistry model AM4.1 is improved by optimizing total methane emissions (to an annual mean of 580±34 Tg yr−1) to match surface observations over 1980–2017. The simulations with optimized global emissions are in general able to capture the observed trend, variability, seasonal cycle, and latitudinal gradient of methane. Simulations with different emission adjustments suggest that increases in methane emissions (mainly from agriculture, energy, and waste sectors) balanced by increases in methane sinks (mainly due to increases in OH levels) lead to methane stabilization (with an imbalance of 5 Tg yr−1) during 1999–2006 and that increases in methane emissions (mainly from agriculture, energy, and waste sectors) combined with little change in sinks (despite small decreases in OH levels) during 2007–2012 lead to renewed growth in methane (with an imbalance of 14 Tg yr−1 for 2007–2017). Compared to 1999–2006, both methane emissions and sinks are greater (by 31 and 22 Tg yr−1, respectively) during 2007–2017. Our tagged tracer analysis indicates that anthropogenic sources (such as agriculture, energy, and waste sectors) are more likely major contributors to the renewed growth in methane after 2006. A sharp increase in wetland emissions (a likely scenario) with a concomitant sharp decrease in anthropogenic emissions (a less likely scenario), would be required starting in 2006 to drive the methane growth by wetland tracer. Simulations with varying OH levels indicate that a 1 % change in OH levels could lead to an annual mean difference of ∼4 Tg yr−1 in the optimized emissions and a 0.08-year difference in the estimated tropospheric methane lifetime. Continued increases in methane emissions along with decreases in tropospheric OH concentrations during 2008–2015 prolong methane's lifetime and therefore amplify the response of methane concentrations to emission changes. Uncertainties still exist in the partitioning of emissions among individual sources and regions.

Download Full-text

Centennial evolution of the atmospheric methane budget: what do the carbon isotopes tell us?

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-6-4995-2006 ◽

2006 ◽

Vol 6 (3) ◽

pp. 4995-5038 ◽

Cited By ~ 2

Author(s):

K. R. Lassey ◽

D. M. Etheridge ◽

D. C. Lowe ◽

A. M. Smith ◽

D. F. Ferretti

Keyword(s):

Nuclear Power ◽

Isotope Composition ◽

Mixing Ratio ◽

Atmospheric Methane ◽

Global Budget ◽

Polar Ice ◽

Direct Production ◽

Methane Budget ◽

Atmospheric Data ◽

Methane Source

Abstract. Little is known about how the methane source inventory and sinks have evolved over recent centuries. New and detailed records of methane mixing ratio and isotopic composition (12CH4, 13CH4 and 14CH4) from analyses of air trapped in polar ice and firn can enhance this knowledge. We use existing bottom-up constructions of the source history, including ''EDGAR''-based constructions, to assemble a model of the evolving global budget for methane and for its carbon isotope composition through the 20th century. By matching such budgets to atmospheric data, we examine the constraints imposed by isotope information on those budget evolutions. Balancing both 12CH4 and 13CH4 budgets requires participation by a highly-fractionating atmospheric sink such as active chlorine (removing at least 10 Tg yr-1), which has been proposed independently. Examining a companion budget evolution for 14CH4 exposes uncertainties in inferring the fossil-methane source from atmospheric 14CH4 data. Specifically, methane evolution during the nuclear era is sensitive to the cycling dynamics of ''bomb 14C'' (originating from atmospheric weapons tests) through the biosphere. In addition, since ca 1970, direct production and release of 14CH4 from nuclear-power facilities is influential but poorly quantified. Atmospheric 14CH4 determinations in the nuclear era have the potential to better characterize biospheric carbon cycling and to better quantify the ill-determined nuclear-power source.

Download Full-text

On the role of trend and variability of hydroxyl radical (OH) in the global methane budget

10.5194/acp-2020-308 ◽

2020 ◽

Cited By ~ 1

Author(s):

Yuanhong Zhao ◽

Marielle Saunois ◽

Philippe Bousquet ◽

Xin Lin ◽

Antoine Berchet ◽

...

Keyword(s):

Hydroxyl Radical ◽

El Niño ◽

Climate Model ◽

El Nino ◽

Interannual Variations ◽

Atmospheric Methane ◽

Tropical Regions ◽

Ch4 Emissions ◽

Methane Budget

Abstract. Decadal trends and interannual variations in the hydroxyl radical (OH), while poorly constrained at present, are critical for understanding the observed evolution of atmospheric methane (CH4). Through analyzing the OH fields simulated by the model ensemble of the Chemistry–Climate Model Initiative (CCMI), we find (1) the negative OH anomalies during the El Niño years mainly corresponding to the enhanced carbon monoxide (CO) emissions from biomass burning and (2) a positive OH trend during 1980–2010 dominated by the elevated primary production and the reduced loss of OH due to decreasing CO after 2000. Both two-box model inversions and variational 4D inversions suggest that ignoring the negative anomaly of OH during the El Niño years leads to a large overestimation of the increase in global CH4 emissions by up to 10 Tg yr−1 to match the observed CH4 increase over these years. Not accounting for the increasing OH trends given by the CCMI models leads to an underestimation of the CH4 emission increase by ~ 23 Tg yr−1 from 1986 to 2010. The variational inversion estimated CH4 emissions show that the tropical regions contribute most to the uncertainties related to OH. This study highlights the significant impact of climate and chemical feedbacks related to OH on the top-down estimates of the global CH4 budget.

Download Full-text