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Predominance of methanogens over methanotrophs in rewetted fens characterized by high methane emissions

Rewetting drained peatlands may lead to prolonged emission of the greenhouse gas methane, but the underlying factors are not well described. In this study, we found two rewetted fens with known high methane fluxes had a high ratio of microbial methane producers to methane consumers and a low abundance of methane consumers compared to pristine wetlands. We therefore suggest abundances of methane-cycling microbes as potential indicators for prolonged high methane emissions in rewetted peatlands.

Methane retrieval from MethaneAIR using the CO2 proxy approach: a demonstration for the upcoming MethaneSAT mission

MethaneSAT is an upcoming satellite mission designed to monitor methane emissions from the oil and gas (O&G) industry globally. Here, we present observations from the first flight campaign of MethaneAIR, a MethaneSAT-like instrument mounted on an aircraft. MethaneAIR can map methane with high precision and accuracy over a typically sized oil and gas basin (~200 km2) in a single flight. This paper demonstrates the capability of the upcoming satellite to routinely track global O&G emissions.

Estimating emissions of methane consistent with atmospheric measurements of methane and δ13C of methane

Atmospheric methane (CH4) has been growing steadily since 2007 for reasons that are not well understood. Here we determine sources of methane using a technique informed by atmospheric measurements of CH₄ and its isotopologue 13CH4. Measurements of 13CH4 provide for better separation of microbial, fossil, and fire sources of methane than CH4 measurements alone. Compared to previous assessments such as the Global Carbon Project, we find a larger microbial contribution to the post-2007 increase.

Methane emissions are predominantly responsible for record-breaking atmospheric methane growth rates in 2020 and 2021

Our understanding of recent changes in atmospheric methane has defied explanation. Since 2007, the atmospheric growth of methane has accelerated to record-breaking values in 2020 and 2021. We use satellite observations of methane to show that (1) increasing emissions over the tropics are mostly responsible for these recent atmospheric changes, and (2) changes in the OH sink during the 2020 Covid-19 lockdown can explain up to 34% of changes in atmospheric methane for that year.

Regional variation in the effectiveness of methane-based and land-based climate mitigation options

We model greenhouse gas emission scenarios consistent with limiting global warming to either 1.5 or 2 °C above pre-industrial levels. We quantify the effectiveness of methane emission control and land-based mitigation options regionally. Our results highlight the importance of reducing methane emissions for realistic emission pathways that meet the global warming targets. For land-based mitigation, growing bioenergy crops on existing agricultural land is preferable to replacing forests.

Quantifying methane emissions from the global scale down to point sources using satellite observations of atmospheric methane

We review the capability of satellite observations of atmospheric methane to quantify methane emissions on all scales. We cover retrieval methods, precision requirements, inverse methods for inferring emissions, source detection thresholds, and observations of system completeness. We show that current instruments already enable quantification of regional and national emissions including contributions from large point sources. Coverage and resolution will increase significantly in coming years.

Terrestrial methane emissions from the Last Glacial Maximum to the preindustrial period

We investigate the changes in natural methane emissions between the Last Glacial Maximum and preindustrial periods with a methane-enabled version of MPI-ESM. We consider all natural sources of methane except for emissions from wild animals and geological sources. Changes are dominated by changes in tropical wetland emissions, high-latitude wetlands play a secondary role, and all other natural sources are of minor importance. We explain the changes in ice core methane by methane emissions only.

Autonomous methane seep site monitoring offshore western Svalbard: hourly to seasonal variability and associated oceanographic parameters

Natural sources of atmospheric methane need to be better described and quantified. We present time series from ocean observatories monitoring two seabed methane seep sites in the Arctic. Methane concentration varied considerably on short timescales and seasonal scales. Seeps persisted throughout the year, with increased potential for atmospheric release in winter due to water mixing. The results highlight and constrain uncertainties in current methane estimates from seabed methane seepage.

Highest methane concentrations in an Arctic river linked to local terrestrial inputs

Permafrost thaw releases methane that can be emitted into the atmosphere or transported by Arctic rivers. Methane measurements are lacking in large Arctic river regions. In the Kolyma River (northeast Siberia), we measured dissolved methane to map its distribution with great spatial detail. The river’s edge and river junctions had the highest methane concentrations compared to other river areas. Microbial communities in the river showed that the river’s methane likely is from the adjacent land.

Quantifying the loss of processed natural gas within California’s South Coast Air Basin using long-term measurements of ethane and methane

This paper investigates the cause of the known underestimate of bottom-up inventories of methane in California’s South Coast Air Basin (SoCAB). We use total column measurements of methane, ethane, carbon monoxide, and other trace gases beginning in the late 1980s to calculate emissions and attribute sources of excess methane to the atmosphere. We conclude that more than half of the excess methane to the SoCAB atmosphere is attributable to processed natural gas.

Detectability of Arctic methane sources at six sites performing continuous atmospheric measurements

Atmospheric methane simulations in the Arctic have been made for 2012 and compared to continuous observations at six measurement sites. All methane sources significantly affect the measurements at all stations, at least at the synoptic scale, except for biomass burning. An appropriate modelling framework combined with continuous observations of atmospheric methane enables us to gain knowledge on regional methane sources, including those which are usually poorly represented, such as freshwater.

Global distribution of methane emissions, emission trends, and OH concentrations and trends inferred from an inversion of GOSAT satellite data for 2010–2015

We use 2010–2015 satellite observations of atmospheric methane to improve estimates of methane emissions and their trends, as well as the concentration and trend of tropospheric OH (hydroxyl radical, methane’s main sink). We find overestimates of Chinese coal and Middle East oil/gas emissions in the prior estimate. The 2010–2015 growth in methane is attributed to an increase in emissions from India, China, and areas with large tropical wetlands. The contribution from OH is small in comparison.

Opinion: A research roadmap for exploring atmospheric methane removal via iron salt aerosol

Rapid reduction in atmospheric methane is needed to slow the rate of global warming. Reducing anthropogenic methane emissions is a top priority. However, atmospheric methane is also impacted by rising natural emissions and changing sinks. Studies of possible atmospheric methane removal approaches, such as iron salt aerosols to increase the chlorine radical sink, benefit from a roadmapped approach to understand if there may be viable and socially acceptable ways to decrease future risk.

High-frequency monitoring of anomalous methane point sources with multispectral Sentinel-2 satellite observations

Satellites can detect methane emissions by measuring sunlight reflected from the Earth’s surface and atmosphere. Here we show that the European Space Agency’s Sentinel-2 twin satellites can be used to monitor anomalously large methane point sources around the world, with global coverage every 2–5 days and 20 m spatial resolution. We demonstrate this previously unreported capability through high-frequency Sentinel-2 monitoring of two strong methane point sources in Algeria and Turkmenistan.

Ideas and perspectives: Sea-level change, anaerobic methane oxidation, and the glacial–interglacial phosphorus cycle

A glacial–interglacial methane-fuelled redistribution of reactive phosphorus between the oceanic and sedimentary phosphorus reservoirs can occur in the ocean when falling sea level lowers the pressure on the seafloor, destabilizes methane hydrates, and triggers the dissolution of P-bearing iron oxides. The mass of phosphate potentially mobilizable from the sediment is similar to the size of the current oceanic reservoir. Hence, this process may play a major role in the marine phosphorus cycle.

High-resolution underwater laser spectrometer sensing provides new insights into methane distribution at an Arctic seepage site

Methane seepage from the seafloor west of Svalbard was investigated with a fast-response membrane inlet laser spectrometer. The acquired data were in good agreement with traditional sparse discrete water sampling, subsequent gas chromatography, and with a new 2-D model based on echo-sounder data. However, the acquired high-resolution data revealed unprecedented details of the methane distribution, which highlights the need for high-resolution measurements for future climate studies.

Ideas and perspectives: is shale gas a major driver of recent increase in global atmospheric methane?

Atmospheric methane has risen rapidly since 2008 and has become more depleted in ¹³C, in contrast to the trend towards more ¹³C enrichment in the late 20th century. Many have used this isotopic evidence to infer an increased biogenic source. Here I analyze the ¹³C trend with the consideration that methane from shale gas is somewhat depleted in ¹³C compared to other fossil fuels. I conclude that shale gas may be responsible for a third of the global increase from all sources.

Methane emissions from the Munich Oktoberfest

We demonstrate for the first time that large festivals can be significant methane sources, though they are not included in emission inventories. We combined in situ measurements with a Gaussian plume model to determine the Oktoberfest emissions and show that they are not due solely to human biogenic emissions, but are instead primarily fossil fuel related. Our study provides the foundation to develop reduction policies for such events and new pathways to mitigate fossil fuel methane emissions.

Continuous weekly monitoring of methane emissions from the Permian Basin by inversion of TROPOMI satellite observations

We use TROPOMI satellite observations to quantify weekly methane emissions from the US Permian oil and gas basin from May 2018 to October 2020. We find that Permian emissions are highly variable, with diverse economic and activity drivers. The most important drivers during our study period were new well development and natural gas price. Permian methane intensity averaged 4.6% and decreased by 1% per year.

Ensemble estimates of global wetland methane emissions over 2000–2020

This study assesses global methane emissions from wetlands between 2000 and 2020 using multiple models. We found that wetland emissions increased by 6–7 Tg CH4 yr-1 in the 2010s compared to the 2000s. Rising temperatures primarily drove this increase, while changes in precipitation and CO2 levels also played roles. Our findings highlight the importance of wetlands in the global methane budget and the need for continuous monitoring to understand their impact on climate change.

High-resolution interpolar difference of atmospheric methane around the Last Glacial Maximum

Here we present new high-resolution methane records from the North Greenland Ice Core Project and the European Project for Ice Coring in Antarctica Dronning Maud Land ice cores covering Termination 1, the Last Glacial Maximum, and parts of the last glacial back to 32 000 years before present.

High spatial resolution imaging of methane and other trace gases with the airborne Hyperspectral Thermal Emission Spectrometer (HyTES)

Using data from a new airborne Hyperspectral Thermal Emission Spectrometer (HyTES) instrument, we present a technique for the detection and wide-area mapping of emission plumes of methane and other atmospheric trace gas species over challenging and diverse environmental conditions with high spatial resolution, that permits direct attribution to sources in complex environments.

Methanesulfonic acid (MSA) migration in polar ice: data synthesis and theory

We combine a synthesis of 22 ice core records and a model of soluble impurity transport to investigate the enigmatic, post-depositional migration of methanesulfonic acid in polar ice. Our findings suggest that migration may be universal across coastal regions of Greenland and Antarctica, though it is mitigated at sites with higher accumulation and (or) lower impurity content. Records exhibiting severe migration may still be useful for inferring decadal and lower-frequency climate variability.

The importance of small artificial water bodies as sources of methane emissions in Queensland, Australia

Artificial water bodies are a major source of methane and an important contributor to flooded land greenhouse gas emissions. Past studies focussed on large water supply or hydropower reservoirs with small artificial water bodies (ponds) almost completely ignored. This regional study demonstrated ponds accounted for one-third of flooded land surface area and emitted over 1.6 million t CO₂eq. yr⁻¹(10 % of land use sector emissions). Ponds should be included in regional GHG inventories.

Methanethiol, dimethyl sulfide and acetone over biologically productive waters in the southwest Pacific Ocean

Methanethiol (MeSH) is a reduced sulfur gas originating from phytoplankton, with a global ocean source of ~ 17 % of dimethyl sulfide (DMS). It has been little studied and is rarely observed over the ocean. In this work, MeSH was measured at much higher levels than previously observed (3–36 % of parallel DMS mixing ratios). MeSH could be a significant source of atmospheric sulfur over productive regions of the ocean, but its distribution, and its atmospheric impact, requires more investigation.

Remote sensing of methane leakage from natural gas and petroleum systems revisited

The switch from the use of coal to natural gas or oil for energy generation potentially reduces the impact on global warming due to lower CO ₂ emissions with the same energy content. However, this climate benefit is offset by fugitive methane emissions during the production and distribution process. We quantify emission and leakage rates relative to production for several large production regions based on satellite observations to evaluate the climate footprint of the gas and oil industry.

A compact QCL spectrometer for mobile, high-precision methane sensing aboard drones

We describe a lightweight (2 kg) mid-IR laser spectrometer for airborne, in situ atmospheric methane (CH ₄ ) measurements. The instrument, based on an open-path circular multipass cell, provides fast response (1 Hz) and sub-parts-per-billion precision. It can easily be mounted on a drone, giving access to highly resolved 4D (spatial and temporal) data. The performance was assessed during field deployments involving artificial CH ₄ releases and vertical concentration gradients in the PBL.

Methane emissions due to reservoir flushing: a significant emission pathway?

Biogeosciences
DOI 10.5194/bg-20-4057-2023
25 September 2023

Based on a large dataset of seasonally resolved methane (CH4) pore water concentrations in a reservoir’s sediment, we assess the significance of CH4 emissions due to reservoir flushing. In the studied reservoir, CH4 emissions caused by one flushing operation can represent 7 %–14 % of the annual CH4 emissions and depend on the timing of the flushing operation. In reservoirs with high sediment loadings, regular flushing may substantially contribute to the overall CH4 emissions.

Gaps in network infrastructure limit our understanding of biogenic methane emissions for the United States

To understand the CH4 flux potential of natural ecosystems and agricultural lands in the United States of America, a multi-scale CH4 observation network focused on CH4 flux rates, processes, and scaling methods is required. This can be achieved with a network of ground-based observations that are distributed based on climatic regions and land cover.

Ground-to-UAV, laser-based emissions quantification of methane and acetylene at long standoff distances

Measurements of the emission rate of a gas or gases from point and area sources are important in a range of monitoring applications. We demonstrate a method for rapid quantification of the emission rate of multiple gases using a spatially scannable open-path sensor. The open-path spectrometer measures the total column density of gases between the spectrometer and a retroreflector mounted on an uncrewed aerial vehicle (UAV). By scanning the UAV altitude, we can determine the total gas emissions.

High-resolution spatial patterns and drivers of terrestrial ecosystem carbon dioxide, methane, and nitrous oxide fluxes in the tundra

Arctic greenhouse gas (GHG) fluxes of CO2, CH4, and N2O are important for climate feedbacks. We combined extensive in situ measurements and remote sensing data to develop machine-learning models to predict GHG fluxes at a 2 m resolution across a tundra landscape. The analysis revealed that the system was a net GHG sink and showed widespread CH4 uptake in upland vegetation types, almost surpassing the high wetland CH4 emissions at the landscape scale.

First validation of high-resolution satellite-derived methane emissions from an active gas leak in the UK

We provide the first validation of the satellite-derived emission estimates using surface-based mobile greenhouse gas surveys of an active gas leak detected near Cheltenham, UK. GHGSat’s emission estimates broadly agree with the surface-based mobile survey and steps were taken to fix the leak, highlighting the importance of satellite data in identifying emissions and helping to reduce our human impact on climate change.

Local and regional scale measurements of CH₄, δ¹³CH₄, and C₂H₆ in the Uintah Basin using a mobile stable isotope analyzer

We describe an innovative instrument based on cavity ring down spectroscopy that analyzes the stable isotopes of methane in the ambient atmosphere. This instrument was used to study atmospheric emissions from oil and gas extraction activities in the Uintah Basin in Utah. These measurements suggest that 86 ± 7% of the total emissions in the basin are from natural gas production. The easy field deployment of this instrument can enable similar regional attribution studies across the world.

Evaluating the climate and air quality impacts of short-lived pollutants

This paper presents a summary of the findings of the ECLIPSE EU project. The project has investigated the climate and air quality impacts of short-lived climate pollutants (especially methane, ozone, aerosols) and has designed a global mitigation strategy that maximizes co-benefits between air quality and climate policy. Transient climate model simulations allowed quantifying the impacts on temperature (e.g., reduction in global warming by 0.22K for the decade 2041-2050) and precipitation.

Local- and regional-scale measurements of CH₄, δ¹³CH₄, and C₂H₆ in the Uintah Basin using a mobile stable isotope analyzer

We describe an innovative instrument based on cavity ring-down spectroscopy that analyzes the stable isotopes of methane in the ambient atmosphere. This instrument was used to study atmospheric emissions from oil and gas extraction activities in the Uintah Basin in Utah. These measurements suggest that 85 ± 7% of the total emissions in the basin are from natural gas production. The easy field deployment of this instrument can enable similar regional attribution studies across the world.

A quantitative approach to evaluating the GWP timescale through implicit discount rates

The 100-year GWP is the most widely used metric for comparing the climate impact of different gases such as methane and carbon dioxide. However, there have been recent arguments for the use of different timescales. This paper uses straightforward estimates of future damages to quantitatively determine the appropriate timescale as a function of how society discounts the future and finds that the 100-year timescale is consistent with commonly used discount rates.

Soil greenhouse gas fluxes from tropical coastal wetlands and alternative agricultural land uses

Greenhouse gas emissions were measured and compared from natural coastal wetlands and their converted agricultural lands across annual seasonal cycles in tropical Australia. Ponded pastures emitted ~ 200-fold-higher methane than any other tested land use type, suggesting the highest greenhouse gas mitigation potential and financial incentives by the restoration of ponded pastures to natural coastal wetlands.