Methane emissions from Amazonian Rivers and their contribution to the global methane budget

For the first time to our knowledge, we report here methane emissions by plant communities in alpine ecosystems in the Qinghai–Tibet Plateau. This has been achieved through long-term field observations from June 2003 to July 2006 using a closed chamber technique. Strong methane emission at the rate of 26.2±1.2 and 7.8±1.1 μg CH 4 m −2 h −1 was observed for a grass community in a Kobresia humilis meadow and a Potentilla fruticosa meadow, respectively. A shrub community in the Potentilla meadow consumed atmospheric methane at the rate of 5.8±1.3 μg CH 4 m −2 h −1 on a regional basis; plants from alpine meadows contribute at least 0.13 Tg CH 4 yr −1 in the Tibetan Plateau. This finding has important implications with regard to the regional methane budget and species-level difference should be considered when assessing methane emissions by plants.

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Sensitivity of the recent methane budget to LMDz sub-grid scale physical parameterizations

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-11853-2015 ◽

2015 ◽

Vol 15 (8) ◽

pp. 11853-11888

Author(s):

R. Locatelli ◽

P. Bousquet ◽

M. Saunois ◽

F. Chevallier ◽

C. Cressot

Keyword(s):

Satellite Data ◽

Transport Model ◽

Deep Convection ◽

Chemical Transport ◽

Global Scale ◽

Methane Emissions ◽

Inverse Modelling ◽

Chemical Transport Model ◽

Methane Budget ◽

Physical Parameterizations

Abstract. With the densification of surface observing networks and the development of remote sensing of greenhouse gases from space, estimations of methane (CH4) sources and sinks by inverse modelling face new challenges. Indeed, the chemical transport model used to link the flux space with the mixing ratio space must be able to represent these different types of constraints for providing consistent flux estimations. Here we quantify the impact of sub-grid scale physical parameterization errors on the global methane budget inferred by inverse modelling using the same inversion set-up but different physical parameterizations within one chemical-transport model. Two different schemes for vertical diffusion, two others for deep convection, and one additional for thermals in the planetary boundary layer are tested. Different atmospheric methane datasets are used as constraints (surface observations or satellite retrievals). At the global scale, methane emissions differ, on average, from 4.1 Tg CH4 per year due to the use of different sub-grid scale parameterizations. Inversions using satellite total-column retrieved by GOSAT satellite are less impacted, at the global scale, by errors in physical parameterizations. Focusing on large-scale atmospheric transport, we show that inversions using the deep convection scheme of Emanuel (1991) derive smaller interhemispheric gradient in methane emissions. At regional scale, the use of different sub-grid scale parameterizations induces uncertainties ranging from 1.2 (2.7%) to 9.4% (14.2%) of methane emissions in Africa and Eurasia Boreal respectively when using only surface measurements from the background (extended) surface network. When using only satellite data, we show that the small biases found in inversions using GOSAT-CH4 data and a coarser version of the transport model were actually masking a poor representation of the stratosphere–troposphere gradient in the model. Improving the stratosphere–troposphere gradient reveals a larger bias in GOSAT-CH4 satellite data, which largely amplifies inconsistencies between surface and satellite inversions. A simple bias correction is proposed. The results of this work provide the level of confidence one can have for recent methane inversions relatively to physical parameterizations included in chemical-transport models.

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Quantifying the contribution of regional methane emissions to the global methane budget between 2008 and 2018 using the TOMCAT chemical transport model

10.5194/egusphere-egu21-6104 ◽

2021 ◽

Author(s):

Emily Dowd ◽

Christopher Wilson ◽

Martyn Chipperfield ◽

Manuel Gloor

Keyword(s):

Carbon Dioxide ◽

Land Surface ◽

Fossil Fuels ◽

Fossil Fuel ◽

Transport Model ◽

Chemical Transport ◽

Methane Emissions ◽

Anthropogenic Sources ◽

Chemical Transport Model ◽

Methane Budget

Methane (CH4) is the second most important atmospheric greenhouse gas after carbon dioxide. Global concentrations of CH4 have been rising in the last decade and our understanding of what is driving the increase remains incomplete. Natural sources, such as wetlands, contribute to the uncertainty of the methane budget. However, anthropogenic sources, such as fossil fuels, present an opportunity to mitigate the human contribution to climate change on a relatively short timescale, since CH4 has a much shorter lifetime than carbon dioxide. Therefore, it is important to know the relative contributions of these sources in different regions.We have investigated the inter-annual variation (IAV) and rising trend of CH4 concentrations using a global 3-D chemical transport model, TOMCAT. We independently tagged several regional natural and anthropogenic CH4 tracers in TOMCAT to identify their contribution to the atmospheric CH4 concentrations over the period 2009 &#8211; 2018. The tagged regions were selected based on the land surface types and the predominant flux sector within each region and include subcontinental regions, such as tropical South America, boreal regions and anthropogenic regions such as Europe. We used surface CH4 fluxes derived from a previous TOMCAT-based atmospheric inversion study (Wilson et al., 2020). These atmospheric inversions were constrained by satellite and surface flask observations of CH4, giving optimised monthly estimates for fossil fuel and non-fossil fuel emissions on a 5.6&#176; horizontal grid. During the study period, the total optimised CH4 flux grew from 552 Tg/yr to 593 Tg/yr. This increase in emissions, particularly in the tropics, contributed to the increase in atmospheric CH4 concentrations and added to the imbalance in the CH4 budget. We will use the results of the regional tagged tracers to quantify the contribution of regional methane emissions at surface observation sites, and to quantify the contributions of the natural and anthropogenic emissions from the tagged regions to the IAV and the rising methane concentrations.Wilson, C., Chipperfield, M. P., Gloor, M., Parker, R. J., Boesch, H., McNorton, J., Gatti, L. V., Miller, J. B., Basso, L. S., and Monks, S. A.: Large and increasing methane emissions from Eastern Amazonia derived from satellite data, 2010&#8211;2018, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2020-1136, in review, 2020.

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Assessing methane emissions for northern peatlands in ORCHIDEE-PEAT revision 7020

10.5194/gmd-2021-280 ◽

2021 ◽

Author(s):

Elodie Salmon ◽

Fabrice Jégou ◽

Bertrand Guenet ◽

Line Jourdain ◽

Chunjing Qiu ◽

...

Keyword(s):

Methane Production ◽

Land Surface ◽

Soil Depth ◽

Land Surface Model ◽

Methane Emissions ◽

Surface Model ◽

Model Parameters ◽

Methane Budget ◽

Northern Peatlands ◽

Over The Top

Abstract. In the global methane budget, the largest natural source is attributed to wetlands that encompass all ecosystems composed of waterlogged or inundated ground, capable of methane production. Among them, northern peatlands that store large amounts of soil organic carbon have been functioning, since the end of the last glaciation period, as long-term sources of methane (CH4) and are one of the most significant methane sources among wetlands. To reduce global methane budget uncertainties, it is of significance to understand processes driving methane production and fluxes in northern peatlands. A methane model that features methane production and transport by plants, ebullition process and diffusion in soil, oxidation to CO2 and CH4 fluxes to the atmosphere has been embedded in the ORCHIDEE-PEAT land surface model which includes an explicit representation of northern peatlands. This model, ORCHIDEE-PCH4 was calibrated and evaluated on 14 peatland sites distributed on both Eurasian and American continents in the northern boreal and temperate regions. Data assimilation approaches were employed to optimized parameters at each site and at all sites simultaneously. Results show that, in ORCHIDEE-PCH4, methanogenesis is sensitive to temperature and substrate availability over the top 75 cm of soil depth. Methane emissions estimated using single site optimization (SSO) of model parameters are underestimated by 9 g CH4 m−2 year−1 on average (i.e. 50 % higher than the site average of yearly methane emissions). While using the multi-sites optimization (MSO), methane emissions are overestimated by 5 g CH4 m−2 year−1 on average across all investigated sites (i.e. 37 % lower than the site average of yearly methane emissions).

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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.

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Isotopic Insights into Methane Production and Emission in Diverse Amazonian Peatlands

10.5194/egusphere-egu2020-12960 ◽

2020 ◽

Author(s):

Alison Hoyt ◽

Hinsby Cadillo-Quiroz ◽

Xiaomei Xu ◽

Margaret Torn ◽

Arturo Bazán Pacaya ◽

...

Keyword(s):

Carbon Source ◽

Methane Emissions ◽

Nutrient Inputs ◽

Tropical Regions ◽

Hydrogenotrophic Methanogenesis ◽

Peatland Hydrology ◽

Methane Budget ◽

Tropical Peatlands ◽

Acetoclastic Methanogenesis ◽

Future Work

Tropical peatlands have the potential to be significant sources of methane (CH4) to the atmosphere but their contribution to the global methane budget remains uncertain. Although much prior work has focused in Southeast Asia, other tropical regions, such as the Congo and the Amazon, have a much wider diversity of peatlands with more variable CH4 emissions. Our work aims to better understand CH4 production and emissions in these diverse peatlands, and how they are controlled by hydrology, geochemistry and vegetation. Using stable isotope and radiocarbon measurements, we assess the production pathway for methanogenesis and its carbon source at sites across the Pastaza-Mara&#241;on basin in Peru. As the largest peatland complex in the Amazon, this region is home to many peatland types, from palm swamps to open peatlands to pole forests. We find clear links between site geochemistry, hydrology, and CH4 production. In rain-fed ombrotrophic sites (pH 3-4), we observe low emissions and highly depleted &#948;13CH4 values (as low as -100&#8240;). The lack of external nutrients and acidic conditions likely limit methanogenesis, and hydrogenotrophic methanogenesis dominates. In more minerotrophic sites (pH 5-6), more enriched methane (-75 to -60&#8240;) suggests a contribution from acetoclastic methanogenesis. Emissions rates are also higher, likely fueled by external nutrient inputs from seasonal flooding. Across sites, modern, vegetation-derived inputs are the dominant carbon source for methanogenesis, with a limited contribution from old peat carbon in some ombrotrophic sites. The strong relationships we observe between peatland hydrology, vegetation, geochemistry and methane emissions will enable future work to upscale methane emissions across the region.

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Monitoring Global Tropospheric OH Concentrations using Satellite Observations of Atmospheric Methane

10.5194/acp-2018-467 ◽

2018 ◽

Author(s):

Yuzhong Zhang ◽

Daniel J. Jacob ◽

Joannes D. Maasakkers ◽

Melissa P. Sulprizio ◽

Jian-Xiong Sheng ◽

...

Keyword(s):

Methane Emissions ◽

Satellite Observations ◽

Atmospheric Methane ◽

Replacement Method ◽

Methyl Chloroform ◽

Methane Budget ◽

Interhemispheric Difference ◽

Shortwave Infrared ◽

Observing System Simulation Experiment ◽

Better Than

Abstract. The hydroxyl radical (OH) is the main tropospheric oxidant and is the largest sink for atmospheric methane. The global abundance of OH has been monitored for the past decades with the methyl chloroform (CH3CCl3) proxy. This approach is becoming ineffective as atmospheric CH3CCl3 concentrations decline. Here we propose that satellite observations of atmospheric methane in the shortwave infrared (SWIR) and thermal infrared (TIR) can provide an effective replacement method. The premise is that the atmospheric signature of the methane sink from oxidation by OH is distinct from that of methane emissions. We evaluate this method in an observing system simulation experiment (OSSE) framework using synthetic SWIR and TIR satellite observations representative of the TROPOMI and CrIS instruments, respectively. The synthetic observations are interpreted with a Bayesian inverse analysis optimizing both gridded methane emissions and global OH concentrations with detailed error accounting, including errors in meteorological fields and in OH distributions. We find that the satellite observations can constrain the global tropospheric OH concentrations with a precision better than 1 % and an accuracy of about 3 % for SWIR and 7 % for TIR. The inversion can successfully separate contributions from methane emissions and OH concentrations to the methane budget and its trend. We also show that satellite methane observations can constrain the interhemispheric difference in OH. The main limitation to the accuracy is uncertainty in the spatial and seasonal distribution of OH.

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Bipolar carbon and hydrogen isotope constraints on the Holocene methane budget

Biogeosciences ◽

10.5194/bg-15-7155-2018 ◽

2018 ◽

Vol 15 (23) ◽

pp. 7155-7175 ◽

Cited By ~ 7

Author(s):

Jonas Beck ◽

Michael Bock ◽

Jochen Schmitt ◽

Barbara Seth ◽

Thomas Blunier ◽

...

Keyword(s):

Southern Hemisphere ◽

Northern Hemisphere ◽

Methane Concentration ◽

Methane Emissions ◽

Anthropogenic Influence ◽

The Holocene ◽

Ch4 Emissions ◽

Methane Budget ◽

Natural Emissions ◽

Concentration Evolution

Abstract. Atmospheric methane concentration shows a well-known decrease over the first half of the Holocene following the Northern Hemisphere summer insolation before it started to increase again to preindustrial values. There is a debate about what caused this change in the methane concentration evolution, in particular, whether an early anthropogenic influence or natural emissions led to the reversal of the atmospheric CH4 concentration evolution. Here, we present new methane concentration and stable hydrogen and carbon isotope data measured on ice core samples from both Greenland and Antarctica over the Holocene. With the help of a two-box model and the full suite of CH4 parameters, the new data allow us to quantify the total methane emissions in the Northern Hemisphere and Southern Hemisphere separately as well as their stable isotopic signatures, while interpretation of isotopic records of only one hemisphere may lead to erroneous conclusions. For the first half of the Holocene our results indicate an asynchronous decrease in Northern Hemisphere and Southern Hemisphere CH4 emissions by more than 30 Tg CH4 yr−1 in total, accompanied by a drop in the northern carbon isotopic source signature of about −3 ‰. This cannot be explained by a change in the source mix alone but requires shifts in the isotopic signature of the sources themselves caused by changes in the precursor material for the methane production. In the second half of the Holocene, global CH4 emissions increased by about 30 Tg CH4 yr−1, while preindustrial isotopic emission signatures remained more or less constant. However, our results show that this early increase in methane emissions took place in the Southern Hemisphere, while Northern Hemisphere emissions started to increase only about 2000 years ago. Accordingly, natural emissions in the southern tropics appear to be the main cause of the CH4 increase starting 5000 years before present, not supporting an early anthropogenic influence on the global methane budget by East Asian land use changes.

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Sensitivity of the recent methane budget to LMDz sub-grid-scale physical parameterizations

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-9765-2015 ◽

2015 ◽

Vol 15 (17) ◽

pp. 9765-9780 ◽

Cited By ~ 21

Author(s):

R. Locatelli ◽

P. Bousquet ◽

M. Saunois ◽

F. Chevallier ◽

C. Cressot

Keyword(s):

Inverse Modeling ◽

Transport Model ◽

Atmospheric Transport ◽

Deep Convection ◽

Regional Scale ◽

Global Scale ◽

Methane Emissions ◽

Data Sets ◽

Methane Budget ◽

Physical Parameterizations

Abstract. With the densification of surface observing networks and the development of remote sensing of greenhouse gases from space, estimations of methane (CH4) sources and sinks by inverse modeling are gaining additional constraining data but facing new challenges. The chemical transport model (CTM) linking the flux space to methane mixing ratio space must be able to represent these different types of atmospheric constraints for providing consistent flux estimations. Here we quantify the impact of sub-grid-scale physical parameterization errors on the global methane budget inferred by inverse modeling. We use the same inversion setup but different physical parameterizations within one CTM. Two different schemes for vertical diffusion, two others for deep convection, and one additional for thermals in the planetary boundary layer (PBL) are tested. Different atmospheric methane data sets are used as constraints (surface observations or satellite retrievals). At the global scale, methane emissions differ, on average, from 4.1 Tg CH4 per year due to the use of different sub-grid-scale parameterizations. Inversions using satellite total-column mixing ratios retrieved by GOSAT are less impacted, at the global scale, by errors in physical parameterizations. Focusing on large-scale atmospheric transport, we show that inversions using the deep convection scheme of Emanuel (1991) derive smaller interhemispheric gradients in methane emissions, indicating a slower interhemispheric exchange. At regional scale, the use of different sub-grid-scale parameterizations induces uncertainties ranging from 1.2 % (2.7 %) to 9.4 % (14.2 %) of methane emissions when using only surface measurements from a background (or an extended) surface network. Moreover, spatial distribution of methane emissions at regional scale can be very different, depending on both the physical parameterizations used for the modeling of the atmospheric transport and the observation data sets used to constrain the inverse system. When using only satellite data from GOSAT, we show that the small biases found in inversions using a coarser version of the transport model are actually masking a poor representation of the stratosphere–troposphere methane gradient in the model. Improving the stratosphere–troposphere gradient reveals a larger bias in GOSAT CH4 satellite data, which largely amplifies inconsistencies between the surface and satellite inversions. A simple bias correction is proposed. The results of this work provide the level of confidence one can have for recent methane inversions relative to physical parameterizations included in CTMs.

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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.

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