Methane (CH4) is a powerful greenhouse gas, a compound in Earth’s atmosphere that traps heat. Its presence contributes to the warming of the planet. Human activities significantly increase the concentration of methane in the atmosphere. This article explores the primary ways in which human endeavors release methane, influencing global climate patterns.
Methane’s Role as a Greenhouse Gas
Methane is a potent greenhouse gas, meaning it is highly effective at absorbing infrared radiation and trapping heat in the atmosphere. Its impact on warming the planet is much stronger than carbon dioxide (CO2) on a per-molecule basis over a shorter timeframe. While methane has a relatively short atmospheric lifespan, typically around 7 to 12 years, its Global Warming Potential (GWP) is significantly higher than CO2. Over a 100-year period, methane’s GWP is estimated to be about 27–30 times greater than CO2, and over a 20-year period, it is about 81–83 times greater.
Natural processes, such as the decomposition of organic matter in wetlands, also release methane, accounting for approximately 40% of total methane emissions. However, the term “anthropogenic” refers specifically to emissions originating from human activities, which are responsible for an estimated 60% of today’s methane emissions. These human-driven sources have dramatically increased atmospheric methane concentrations since the pre-industrial era, with levels more than doubling over the past 200 years.
Energy Production and Distribution
The extraction, processing, and transportation of fossil fuels represent a major anthropogenic source of methane emissions, accounting for about 35% of global anthropogenic methane emissions. Natural gas, composed primarily of methane, can escape into the atmosphere at various points throughout its supply chain, including wells, pipelines, and processing plants. These unintentional releases are known as fugitive emissions.
During oil and gas extraction, methane is also released through venting and flaring. Venting involves the direct release of methane into the atmosphere, often occurring when gas is produced alongside oil and there are no facilities to capture or transport it. Flaring, on the other hand, burns off excess gas, converting most of the methane into carbon dioxide, though some methane can still escape uncombusted. Coal mining operations also release methane, known as coal seam methane, which is trapped within coal deposits and escapes into the atmosphere during mining activities.
Agricultural Practices
Agricultural activities are another substantial contributor to anthropogenic methane emissions, accounting for approximately 40% of global anthropogenic methane emissions. Enteric fermentation in livestock, particularly ruminant animals like cattle, sheep, goats, and buffalo, is a primary source. Microbes in their digestive tracts, specifically in the rumen, decompose and ferment food, producing methane as a byproduct that is then released through burping. This process can result in a loss of 2–12% of a ruminant’s energy intake as methane.
Manure management practices also contribute to methane emissions, especially when animal waste is stored in anaerobic conditions. For example, large quantities of manure collected in lagoons or pits without oxygen undergo decomposition, leading to the production and release of methane. Liquid manure management systems, in particular, tend to create anaerobic conditions that increase methane production. Rice cultivation is another agricultural source, as flooded paddy fields create anaerobic conditions in the soil. Organic matter in the soil decomposes without oxygen, leading to methane production. Rice paddies contribute about 10–12% of global methane emissions.
Waste Management and Other Sources
Waste management facilities, particularly municipal solid waste landfills, are significant emitters of methane. When organic waste, such as food scraps, decomposes in landfills without oxygen, it generates landfill gas, which is typically about 50% methane. Food waste, due to its rapid decay, contributes more methane emissions from landfills than any other material.
Wastewater treatment also contributes to methane emissions, primarily through the anaerobic digestion of organic matter in sewage. Methane can be generated in wastewater collection systems and at treatment plants where anaerobic conditions prevail. Other anthropogenic sources include certain industrial processes, such as ammonia fertilizer production, which can release methane, and biomass burning, like forest fires and the burning of agricultural residues.
References
1. EPA. Understanding Global Warming Potentials. https://www.epa.gov/ghgemissions/understanding-global-warming-potentials
2. US EPA. Methane Emissions. https://www.epa.gov/gmi/methane-emissions