Methane emissions

Résumé

Increasing methane emissions are a major contributor to the rising concentration of greenhouse gases in Earth's atmosphere, and are responsible for up to one-third of near-term global heating. During 2019, about 60% (360 million tons) of methane released globally was from human activities, while natural sources contributed about 40% (230 million tons). Reducing methane emissions by capturing and utilizing the gas can produce simultaneous environmental and economic benefits. Since the Industrial Revolution, concentrations of methane in the atmosphere have more than doubled, and about 20 percent of the warming the planet has experienced can be attributed to the gas. About one-third (33%) of anthropogenic emissions are from gas release during the extraction and delivery of fossil fuels; mostly due to gas venting and gas leaks from both active fossil fuel infrastructure and orphan wells. Russia is the world's top methane emitter from oil a

Source officielle

https://en.wikipedia.org/wiki/Methane_emissions

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Methane oxidation pathways in Lake La Cruz

Corinne Jegge

Even though lakes only occupy a small percentage of Earth's surface, they represent a natural source of methane, contributing substantially to methane emissions and ultimately to global warming. There is extensive evidence that methane emissions from lakes are mitigated by its oxidation. However, many uncertainties concerning biotic controls on methane release from lakes remain, especially in zones where oxygen is depleted and other electron acceptors might be important. In this study, biological methane oxidation was investigated in the water column of Lake La Cruz, a small karstic lake located in Central Eastern Spain near the city of Cuenca. Permanent stratification and unusually high concentrations of dissolved iron(II) make this lake ideal for studying methane oxidation in the absence of oxygen, particularly the possibility of this process coupled to iron reduction. The physical and chemical properties of Lake La Cruz were investigated, including the presence of methane and possible electron acceptors. Incubation experiments with 13C-methane were carried out to measure methane oxidation rates, test possible electron acceptors and other coupled processes. Highest methane oxidation rates were measured at the oxic-anoxic boundary, where aerobic oxidation dominated. Moreover, the aerobic pathway also seemed relevant below the oxycline, likely triggered by in-situ production of oxygen via photosynthesis. Evidence suggests that nitrate, nitrite and iron also function as electron acceptors for methane oxidation, whereas manganese and sulfate are unlikely oxidants. Methane oxidation coupled to denitrification seemed to proceed in close vicinity to aerobic methane oxidation and was likely limited by nitrate/nitrite availability and competition with denitrifiers. Iron mediated methane oxidation only appeared relevant in lower parts of the lake where both oxygen and nitrate were depleted. Though known aerobic methanotrophs were present and appeared to mediate methane oxidation to some degree, the involvement of unknown groups of aerobic and also anaerobic methane-oxidizers is probable. Methane emissions to the atmosphere are effectively mitigated by a seemingly complex interplay of aerobic and anaerobic processes in Lake La Cruz.

2015

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ENERGY STORAGE: LIQUID CH4 AND CO2 NETWORK INTEGRATION

Charles-Thomas Stern

In this project, we will study the energy storage with liquid methane linked to a CO2 network that provides heat for district heating. The generated methane enters an hybrid cycle composed of a solid oxide fuel cell and turbines to generate electricity. The goal of this project is to determine the global eciency of the system but also to optimize it with the help of softwares like Belsim Vali and Osmose. In addition, we determine its cost. At the end, we compare the global system with an equivalent one without the CO2 network integration.

2014

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Recent analyses of ice core methane concentrations suggested that methane emissions from wetlands were the primary driver for prehistoric changes in atmospheric methane. However, these interpretations conflict as to the location of wetlands, magnitude of emissions, and the environmental controls on methane oxidation. The flux of other reactive trace gases to the atmosphere also controls apparent atmospheric methane concentrations because these compounds compete for the hydroxyl radical (OH), which is the primary atmospheric sink for methane. In a series of linked biosphere-atmosphere chemistry-climate modeling experiments, we simulate the methane and biogenic volatile organic compound emissions from the terrestrial biosphere from the Last Glacial Maximum (LGM) to the present. Using a state-of-the-art chemistry-climate model, we simulate the atmospheric concentrations of methane, OH, and other reactive trace gas species. Over the past 21,000 years, methane emissions from wetlands increased slightly to the end of the Pleistocene but then decreased again, reaching levels at the preindustrial Holocene that were similar to the LGM. Global wetland area decreased by 14% from LGM to the preindustrial time. Emissions of biogenic volatile organic compounds (BVOCs), however, nearly doubled over the same period of time. Atmospheric OH burdens and methane concentrations were affected by this major change in BVOC emissions, with methane lifetimes increasing by more than 2 years from LGM to the present. We simulate a change in methane concentration of ∼385 ppb, accounting for 88% of the ∼440 ppb increase in methane concentrations observed in ice cores. Thus glacial-interglacial changes in atmospheric methane concentrations would have been modulated by BVOC emissions. In addition, the increase in atmospheric methane concentrations since the mid-Holocene is partly caused in our results by the increases in anthropogenic methane emissions over this period. While the interplay between BVOC and wetland methane emissions since the LGM cannot explain the entire record of ice core methane concentrations, consideration of BVOC source dynamics is central to understanding ice core methane. Rapid changes in atmospheric methane concentrations, also observed in ice cores, require further study.

2006

Chargement

2006

Methane oxidation pathways in Lake La Cruz

Corinne Jegge

2015