Summary
Highlights
Methane (CH4), also known as natural gas, is a significant greenhouse gas whose atmospheric concentration is rising. Its residence time is about 12 years. While a methane molecule is 70 times more potent than carbon dioxide in trapping heat in the short term, its long-term effect is about 20 times due to its shorter lifespan. However, continuous addition of methane to the atmosphere creates a substantial problem.
Dedicated satellites now monitor global methane emissions, though data interpretation is still evolving. Natural gas is primarily methane, and while burning it converts it to less potent carbon dioxide, leaks release pure methane directly into the atmosphere. Leaks from gas wells, pipelines, and processing plants account for roughly 20% of atmospheric methane. Regions like Russia and North America, especially the Permian Basin in West Texas, show significant methane plumes from such leaks.
Methane, earning its moniker 'marsh gas,' forms when vegetation decays in the absence of oxygen, typically underwater. Wetlands are a major natural source. Furthermore, the thawing of permafrost in the Arctic, caused by global warming, is releasing vast amounts of methane from previously frozen plant material. These Arctic lakes are estimated to eventually release more than 10 times the current atmospheric methane.
Man-made reservoirs also contribute to methane emissions. When valleys are flooded to create dams, submerged vegetation decays without oxygen, generating methane. Although a smaller percentage, it amounts to approximately 30 million tons of methane annually, with significant concentrations observed in areas like Northern California and the Pacific Northwest.
Landfills, particularly those containing food waste, are another major man-made source of methane. Globally, about 2.5 billion tons of food are wasted yearly, much of which ends up in landfills. The decomposition of organic matter in low-oxygen landfill environments produces massive methane plumes, such as one observed over an Iranian landfill. Californian law now mandates the separation and proper treatment of organic waste to mitigate this.
Cattle are the largest man-made source, contributing about 25% of all atmospheric methane. As herbivores, their digestive systems break down vegetation in an anaerobic environment, producing methane released through burps and farts. The immense global population of cattle maintained by humans makes this a significant issue, as evidenced by large methane plumes over cattle feedlots in California.
Overall, approximately 65% of atmospheric methane is anthropogenic. Other significant greenhouse gases include nitrous oxide, primarily from farming practices like manure and fertilizer use. Freon, though banned for manufacturing in 1995 due to ozone depletion, is also a potent greenhouse gas, being 2,000 times more powerful than carbon dioxide with a residence time of around 100 years. Its atmospheric concentration has been decreasing since 2003, making it less of a concern currently.