Methane sources
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Methane Sources: A Comprehensive Overview
Introduction to Methane as a Greenhouse Gas
Methane (CH4) is a potent greenhouse gas, contributing significantly to global warming and climate change. It is responsible for approximately 20% of the warming induced by long-lived greenhouse gases since pre-industrial times1 2. Methane's impact on atmospheric chemistry is profound, affecting levels of ozone, water vapor, and hydroxyl radicals2 3.
Natural Sources of Methane
Wetlands and Geological Seepage
Natural wetlands are a major source of methane emissions. These emissions have been linked to the observed rise in global methane levels post-20061. Geological methane emissions, including onshore hydrocarbon macro-seeps, submarine seeps, and geothermal manifestations, also contribute significantly to the atmospheric methane budget4. The isotopic signature of geological methane is distinct and helps in identifying its sources4.
Microbial Methanogenesis
Microbial methanogenesis, occurring in anaerobic environments such as wetlands and swamps, is another critical natural source of methane. This process involves the reduction of CO2 or fermentation pathways, with the latter being more prevalent in recent sediments3 8. Microbial methane oxidation, both aerobic and anaerobic, plays a role in limiting methane release from these environments3.
Anthropogenic Sources of Methane
Agriculture and Livestock
Agriculture, particularly enteric fermentation in livestock, is the largest anthropogenic source of methane emissions. Manure management and rice paddies also contribute significantly9. The agricultural sector's impact on methane emissions has been substantial, especially with the rise in human activities since the 1700s2.
Fossil Fuels and Industrial Activities
Fossil fuel extraction, including natural gas and petroleum systems, is a major source of methane emissions. Uncombusted losses from natural gas infrastructure, coal mining, and oil production are significant contributors5 6. The use of ethane as a tracer has been effective in identifying methane emissions from these sources7.
Waste Management
Landfills and waste treatment facilities are notable sources of methane emissions. The decomposition of organic waste under anaerobic conditions leads to significant methane release9. Effective waste management strategies are crucial for mitigating these emissions.
Historical Trends and Variability
Pre-Industrial and Modern Trends
Methane levels have varied significantly over the past millennia, influenced by both natural climate variability and human activities. Ice core data reveal pronounced centennial-scale variations in methane isotopic composition, correlating with events such as the Medieval Climate Anomaly and the Little Ice Age10. Since the 1700s, human activities have more than doubled methane emissions, leading to a 2-3 fold increase in atmospheric concentrations2.
Recent Decadal Changes
The stabilization of methane levels between 1999 and 2006 can be attributed to decreasing fossil fuel emissions and stable microbial emissions. However, the renewed rise in methane levels post-2006 is likely due to increased emissions from natural wetlands and fossil fuels1. The uncertainties in emission trends highlight the need for improved data and modeling approaches.
Conclusion
Methane emissions arise from a complex interplay of natural and anthropogenic sources. Understanding these sources and their contributions is crucial for developing effective mitigation strategies. Continued research and advanced measurement techniques are essential for accurately quantifying methane emissions and addressing their impact on global climate change.
Sources and full results
Most relevant research papers on this topic
Three decades of global methane sources and sinks
Decreased fossil fuel emissions and stable microbial emissions may have stabilized methane levels between 1999 and 2006, while a rise in natural wetland emissions and fossil fuel emissions likely caused the renewed increase in global methane levels after 2006.
Highly CitedAtmospheric methane and global change
Human activities have significantly increased atmospheric methane levels, posing concerns for atmospheric chemistry and climate change.
Highly CitedBiogeochemical aspects of atmospheric methane
Atmospheric methane production is influenced by microbial and thermogenic factors, with uncertainties in source and sink sizes, and its impact on climate system is significant.
Highly CitedGridded maps of geological methane emissions and their isotopic signature
This study presents the first global gridded maps of geological methane sources, revealing that the highest emissions are in the Northern Hemisphere, North America, the Caspian region, Europe, and the East Siberian Arctic Shelf.
Highly CitedAttributing Atmospheric Methane to Anthropogenic Emission Sources.
New analytical methods and chemical mass balance methods can improve the identification and quantification of methane emission sources, reducing uncertainty in emissions estimates.
On the sources of methane to the Los Angeles atmosphere.
Most methane emissions in Los Angeles are attributed to uncombusted losses from the natural gas system, but other sources like natural gas seeps and petroleum production also contribute.
Highly CitedDemonstration of an ethane spectrometer for methane source identification.
Ethane-Mini spectrometers can accurately identify methane source types, aiding in emissions studies in the oil and natural gas sector.
Highly CitedMultiple origins of methane in the Earth
Methane's origins in the Earth's crust are predominantly biogenic, but it can also form through inorganic reactions and geothermal processes.
Highly CitedSources and mitigation of methane emissions by sectors: A critical review
The agricultural sector is the largest source of methane emissions, followed by energy, waste, and industry.
Highly CitedNatural and anthropogenic variations in methane sources during the past two millennia
Centennial-scale variations in methane isotope ratios between 100 BC and 1600 can be linked to changes in pyrogenic and biogenic sources, and climate variability and human population changes.
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