Global production of methane

Ratering S. and Conrad R. (1998) Effects of short-term drainage and aeration on the production of methane in submerged rice soil. Global Change Biol. 4, 397—407. 

What has changed in the last few hundred years is the additional release of carbon dioxide by human activities. Fossil fuels burned to run cars and trucks, heat homes and businesses, and power factories are responsible for about 98% of carbon dioxide emissions, 24% of methane emissions, and 18% of nitrous oxide emissions. Increased agriculture, deforestation, landfills, industrial production, and mining also contribute a significant share of emissions (5). For example, in 1997, the United States emitted about one-fifth of total global greenhouse gases. 

Liquefied petroleum gas (LPG) was used as fuel for the first time in the USA in 1912. Under the general term natural gas liquids (NGL), 60% of global LPG originates as a fraction separated from methane during the production of oil and gas the remaining 40% are generated as a by-product from the fractionated distillation of crude oil in refineries. Liquefied petroleum gas is a mixture of propane and butane, with the mixing ratio dependent on the country and season. 

Aselmann 1, Crutzen PJ. 1989. Global distribution of natural fresh-water wetlands and rice paddies their net primary productivity, seasonality and possible methane emissions. Journal of Atmospheric Chemistry 8 307-358. 

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