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To mitigate methane emission from urban natural gas distribution systems, it is crucial to understand local leak rates and occurrence rates. To explore urban methane emissions in cities outside the U.S., where significant emissions were found previously, mobile measurements were performed in 12 cities across eight countries. The surveyed cities range from medium size, like Groningen, NL, to large size, like Toronto, CA, and London, UK. Furthermore, this survey spanned across European regions from Barcelona, ES, to Bucharest, RO. The joint analysis of all data allows us to focus on general emission behavior for cities with different infrastructure and environmental conditions. We find that all cities have a spectrum of small, medium, and large methane sources in their domain. The emission rates found follow a heavy-tailed distribution, and the top 10% of emitters account for 60-80% of total emissions, which implies that strategic repair planning could help reduce emissions quickly. Furthermore, we compare our findings with inventory estimates for urban natural gas-related methane emissions from this sector in Europe. While cities with larger reported emissions were found to generally also have larger observed emissions, we find clear discrepancies between observation-based and inventory-based emission estimates for our 12 cities.

Atmospheric methane (CH4) continues to increase, but there are multiple anthropogenic source categories that can be targeted for cost-effective emissions reduction. Cities emit CH4 to the atmosphere from a mixture of anthropogenic CH4 sources, which include, but are not limited to, fugitive emissions from natural gas distribution systems, wastewater treatment facilities, waste-and rainwater networks, and landfills. Therefore, to target mitigation measures, it is important to locate and quantify local urban emissions to prioritize mitigation opportunities in large cities. Using mobile measurement techniques, we located street-level CH4 leak indications, measured flux rates, and determined potential source origins (using carbon and hydrogen stable isotopic composition along with ethane: CH4 ratios) of CH4 in Bucharest, Romania. We found 969 confirmed CH4 leak indication locations, where the maximum mole fraction elevation (above background) was 38.3 ppm (mean = 0.9 ppm ± 0.1 ppm s.e.; n = 2482). Individual leak indicator fluxes, derived using a previously established empirical relation, ranged up to around 15 metric tons CH4 yr-1 (mean = 0.8 metric tons yr-1 ± 0.05, s.e.; n = 969). The total estimated city emission rate is 1832 tons CH4 yr-1 (min = 1577 t yr-1 and max = 2113 t yr-1). More than half (58%–63%) of the CH4 elevations were attributed to biogenic wastewater, mostly from venting storm grates and manholes connecting to sewer pipelines. Hydrogen isotopic composition of CH4 and ethane:methane ratios were the most useful tracers of CH4 sources, due to similarities in carbon isotope ratios between wastewater gas and natural gas. The annual city-wide CH4 emission estimate of Bucharest exceeded emissions of Hamburg, Germany by 76% and Paris, France by 90%.

Removing methane from the air is possible, but do the costs outweigh the benefits? This note explores the question of whether removing methane from the atmosphere is justifiable. Destruction of methane by oxidation to CO2 eliminates 97% of the warming impact on a 100-yr time scale. Methane can be oxidized by a variety of methods including thermal or ultraviolet photocatalysis and various processes of physical, chemical or biological oxidizers. Each removal method has energy costs (with the risk of causing embedded CO2 emission that cancel the global warming gain), but in specific circumstances, including settings where air with high methane is habitually present, removal may be competitive with direct efforts to cut fugitive methane leaks. In all cases however, great care must be taken to ensure that the destruction has a net positive impact on the total global warming, and that the resources required would not be better used for stopping the methane from being emitted.

The methane emissions from the Hungarian Pannonian Basin are not well qualified, due to a lack of measurements of CH4 mole fraction and δ13CCH4 in the air. This study reports methane measurements in air samples from Hungary, placing them in the context of regional and global background data, to investigate the inputs to the methane burden in Central Europe. CH4 mole fraction and δ13CCH4 from the Hungarian tall tower station, Hegyhátsál, and additional data from Mace Head (Ireland) and Zeppelin (Svalbard) are used with back-trajectory modeling to identify central European source areas and their seasonal variation between the summer vegetation and winter heating periods. Methane measurements in air masses sampled in the European interior, have significantly higher maxima and seasonal amplitudes than at the Mace Head and Zeppelin European background sites. The mean CH4 mole fraction value is about 80 ppb higher than the comparable marine background, and values above 2000 ppb were frequently observed between February 2013 and December 2015. The mean δ13CCH4 value -47.5±0.3 ‰ (2σ) was comparable to values at all three monitoring sites, but specific pollution events were detected at Hegyhátsál. Concentration weighted trajectory modeling, meteorological parameters, stable carbon isotopic composition (δ13CCH4), and Miller-Tans analysis show that the main factors influencing CH4 at the Hegyhátsál, apart from diurnal and seasonal changes in the Planetary Boundary Layer, are emissions from residential heating and industrial CH4 emissions during the winter.

Biological oxidation of methane in landfill cover material can be calculated from the carbon isotopic signature (δ13CCH4) of emitted CH4. Enhanced microbial consumption of methane in the aerobic portion of the landfill cover is indicated by a shift to heavier (less depleted) isotopic values in the residual methane emitted to air. This study was conducted at four landfill sites in southwest England. Measurement of CH4 using a mobile vehicle mounted instrument at the four sites was coupled with Flexfoil bag sampling of ambient air for high-precision isotope analysis. Gas well collection systems were sampled to estimate landfill oxidised proportion. Closed or active status, seasonal variation, cap stripping and site closure impact on landfill isotopic signature were also assessed. The δ13CCH4 values ranged from −60 to −54‰, with an average value of −57 ± 2‰. Methane emissions from active cells are more depleted in 13C than closed sites. Methane oxidation, estimated from the isotope fractionation, ranged from 2.6 to 38.2%, with mean values of 9.5% for active and 16.2% for closed landfills, indicating that oxidised proportion is highly site specific.

Sharks are iconic and ecologically important predators found in every ocean. Because of their ecological role as predators, some considered apex predators, and concern over the stability of their populations due to direct and indirect overfishing, there has been an increasing amount of work focussed on shark conservation, and other elasmobranchs such as skates and rays, around the world. Here we discuss many aspects of current shark science and conservation and the path to the future of shark conservation in the Northeastern and Eastern Central Pacific. We explore their roles in ecosystems as keystone species; the conservation measures and laws in place at the international, national, regional and local level; the conservation status of sharks and rays in the region, fisheries for sharks in the Northcentral Pacific specifically those that target juveniles and the implications to shark conservation; a conservation success story: the recovery of Great White Sharks in the Northeast Pacific; public perceptions of sharks and the roles zoos and aquariums play in shark conservation; and the path to the future of shark conservation that requires bold partnerships, local stakeholders and innovative measures.

The rising number of operational biogas plants in the UK brings a new emissions category to consider for methane monitoring, quantification and reduction. Minimising methane losses from biogas plants to the atmosphere is critical not only because of their contribution of methane to global warming but also with respect to the sustainability of renewable energy production. Mobile greenhouse gas surveys were conducted to detect plumes of methane emissions from the biogas plants in southern England that varied in their size, waste feed input materials and biogas utilization. Gaussian plume modelling was used to estimate total emissions of methane from ten biogas plants based on repeat passes through the plumes. Methane emission rates ranged from 0.1 to 58.7 kg CH4 hr-1, and the percentage of losses relative to the calculated production rate varied between 0.02 and 8.1%. The average emission rate was 15.9 kg CH4 hr-1, and the average loss was 3.7%. In general, methane emission rates from smaller farm biogas plants were higher than from larger food waste biogas plants. We also suggest that biogas methane emissions may account for between 0.4 and 3.8%, with an average being 1.9% of the total methane emissions in the UK excluding the sewage sludge biogas plants.

Emissions of methane from combustion sources are typically distinguished by being enriched in 13C and 2H, causing a large isotopic shift to atmospheric methane δ13C and δD measurements downwind of fires.The isotopic composition of the plant material being burnt has a strong effect on the isotopic composition of methane, with combustion of C4 plant material producing methane more enriched in 13C than C3 plant combustion. Characterisation of the bulk isotopic signature of methane emitted from large areas of biomass burning is required to improve our ability to use isotopes in global models and ascertain the extent to which fire emissions influence interannual variations in the methane budget.Two approaches have been used to collect air samples from large areas of biomass burning for isotopic characterisation of methane emitted from the fires. In campaigns in Senegal, Uganda, Zambia and Finland, the UK’s FAAM research aircraft flew through fire plumes and onboard measurement of methane concentration allowed targeted sampling within the plumes. This work was carried out as part of the NERC highlight Global Methane Budget project (MOYA). Ground based sampling downwind of fires around Sydney, New South Wales in late 2019/early 2020 has allowed isotopic characterisation of those plumes. All air samples were measured by isotope ratio mass spectrometry at Royal Holloway University of London and Keeling plots used to identify source signatures, e.g. δ13C for fires in Senegal in March 2017 was -28.5 ± 0,8 , typical of C3 burning.In this work we compare the isotopic signatures of methane from burning in these particular regions and discuss the extent to which the regional variability of the isotopic composition of fire emissions should be taken into account in global models using isotopes to constrain the global methane budget.

One of the case study sites for the Climate and Clean Air Coalition (CCAC) Methane Science Studies is the coal seam gas (CSG) field in the Surat Basin, Queensland, Australia, where there are over 6000 CSG wells and associated gas and water processing infrastructure. Previous bottom-up estimates suggest that the major source of methane in the region is cattle, not CSG (Katestone, 2018, Luhar et al. 2018).In September 2018, an airborne measurement campaign was undertaken to provide a top-down estimate of regional methane emissions. Modelling of the airborne methane mole fraction data has produced a defensible total methane emissions estimate. However, there are challenges with proportioning the top-down estimates provided by the airborne data, because of adjacent sources with similar d13C-CH4 isotopic chemistry, rapid mixing of adjacent sources and substantial dilution of the plumes at the airborne measurement sampling height. We present how we will overcome these challenges.At each gas production well, tens of thousands of litres of water are produced daily in association with the methane extracted from the coal measures. This water is stored in ponds and is also used as a water supply for cattle feedlots, which are located throughout and adjacent to the CSG wells and processing facilities. Power stations are also located within the CSG field. This arrangement makes it challenging to obtain clean top-down estimates of the emissions from CSG production. Quantifying methane emissions associated with CSG production is further complicated by numerous other sources of methane in the region immediately adjacent to the CSG field. These sources include grazing cattle, abattoirs, more power production facilities, coal mines, wetlands, natural gas seeps, and small urban centres with associated sewage treatment plants and landfills. Grab bag air samples were collected at each of these sources and analysed for d13C-CH4, d13C-CO2 and dD-CH4.The airborne measurement campaign was u

This report presents the results and interpretation for Phase 5 of an integrated environmental monitoring programme that is being undertaken around two proposed shale gas sites in England – Preston New Road, Lancashire and Kirby Misperton, North Yorkshire. The report should be read in conjunction with previous reports freely available through the project website1 . These provide additional background to the project, presentation of earlier results and the rationale for establishment of the different elements of the monitoring programme.

Environmental monitoring plays a key role in risk assessment and management of industrial operations where there is the potential for the release of contaminants to the environment (i.e. air and water) or for structural damage (i.e. seismicity). The shale-gas industry is one such industry. It is also new to the UK and so specific environmental regulation and other controls have been introduced only recently. Associated with this is a need to carry out monitoring to demonstrate that the management measures to minimise the risk to the environment are being effective. While much of the monitoring required is common to other industries and potentially polluting activities, there are a number of requirements specific to shale gas and to what is a new and undeveloped industry. This report presents recommendations for environmental monitoring associated with shale-gas activities and in particular the monitoring required to inform risk assessment and establish the pre-existing environmental conditions at a site and surrounding area. This baseline monitoring is essential to provide robust data and criteria for detecting any future adverse environmental changes caused by the shale-gas operations. Monitoring is therefore required throughout the lifecycle of a shale gas operation. During this lifecycle, the objectives of the monitoring will change, from baseline characterisation to operational and post-operational monitoring. Monitoring requirements will also change. This report focusses on good practice in baseline monitoring and places it in the context of the longer-term environmental monitoring programme, recognising the need to transition from the baseline condition and to establish criteria for detecting any changes within the regulatory framework. The core suite of environmental monitoring activities currently required to support regulatory compliance, i.e. meet environmental and other permit conditions, encompasses monitoring of seismicity, water quality (groundwater an

The Greenland ice sheet is one of the largest contributors to global mean sea-level rise today and is expected to continue to lose mass as the Arctic continues to warm. The two predominant mass loss mechanisms are increased surface meltwater run-off and mass loss associated with the retreat of marine-terminating outlet glaciers. In this paper we use a large ensemble of Greenland ice sheet models forced by output from a representative subset of the Coupled Model Intercomparison Project (CMIP5) global climate models to project ice sheet changes and sea-level rise contributions over the 21st century. The simulations are part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). We estimate the sea-level contribution together with uncertainties due to future climate forcing, ice sheet model formulations and ocean forcing for the two greenhouse gas concentration scenarios RCP8.5 and RCP2.6. The results indicate that the Greenland ice sheet will continue to lose mass in both scenarios until 2100, with contributions of 90±50 and 32±17 mm to sea-level rise for RCP8.5 and RCP2.6, respectively. The largest mass loss is expected from the south-west of Greenland, which is governed by surface mass balance changes, continuing what is already observed today. Because the contributions are calculated against an unforced control experiment, these numbers do not include any committed mass loss, i.e. mass loss that would occur over the coming century if the climate forcing remained constant. Under RCP8.5 forcing, ice sheet model uncertainty explains an ensemble spread of 40 mm, while climate model uncertainty and ocean forcing uncertainty account for a spread of 36 and 19 mm, respectively. Apart from those formally derived uncertainty ranges, the largest gap in our knowledge is about the physical understanding and implementation of the calving process, i.e. the interaction of the ice sheet with the ocean.