Atmospheric methane

Atmospheric methane is the methane present in Earth's atmosphere. Atmospheric methane concentrations are of interest because it is one of the most potent greenhouse gases in Earth's atmosphere. Atmospheric methane is rising.Emissions and Sinks: 1990–2015 report We believe the preponderance of evidence indicates shale gas has a larger GHG footprint than conventional gas, considered over any time scale. The GHG footprint of shale gas also exceeds that of oil or coal when considered at decadal time scales, We find greenhouse gas emissions from agriculture and fossil fuel extraction and processing (i.e., oil and/or natural gas) are likely a factor of two or greater than cited in existing studies. Atmospheric methane is the methane present in Earth's atmosphere. Atmospheric methane concentrations are of interest because it is one of the most potent greenhouse gases in Earth's atmosphere. Atmospheric methane is rising. The 20-year global warming potential of methane is 84. That is, over a 20-year period, it traps 84 times more heat per mass unit than carbon dioxide and 32 times the effect when accounting for aerosol interactions. Global methane concentrations rose from 722 parts per billion (ppb) in pre-industrial times to 1866 ppb by 2019, an increase by a factor of 2.5 and the highest value in at least 800,000 years. Its concentration is higher in the Northern Hemisphere since most sources (both natural and human) are located on land and the Northern Hemisphere has more land mass. The concentrations vary seasonally, with, for example, a minimum in the northern tropics during April−May mainly due to removal by the hydroxyl radical. Early in the Earth's history carbon dioxide and methane likely produced a greenhouse effect. The carbon dioxide would have been produced by volcanoes and the methane by early microbes. During this time, Earth's earliest life appeared. These first, ancient bacteria added to the methane concentration by converting hydrogen and carbon dioxide into methane and water. Oxygen did not become a major part of the atmosphere until photosynthetic organisms evolved later in Earth's history. With no oxygen, methane stayed in the atmosphere longer and at higher concentrations than it does today. The known sources of methane are predominantly located near the Earth's surface. In combination with vertical atmospheric motions and methane's relatively long lifetime, methane is considered to be a well-mixed gas. In other words, the concentration of methane is taken to be constant with respect to height within the troposphere. The dominant sink of methane in the troposphere is reaction with hydroxyl radicals that are formed by reaction of singlet oxygen atoms with water vapor. Methane is also present in the stratosphere, where methane's concentration decreases with height. Methane in the Earth's atmosphere is a strong greenhouse gas with a global warming potential (GWP) 104 times greater than CO2 in a 20-year time frame; methane is not as persistent a gas as CO2 and tails off to about GWP of 28 for a 100-year time frame. This means that a methane emission will have 28 times the impact on temperature of a carbon dioxide emission of the same mass over the following 100 years. Methane has a large effect but for a relatively brief period, having an estimated lifetime of 9.1 years in the atmosphere, whereas carbon dioxide has a small effect for a long period, having an estimated lifetime of over 100 years. The globally averaged concentration of methane in Earth's atmosphere increased by about 150 percent from 722 ± 25 ppb in 1750 to 1803.2 ± 1.2 ppb in 2011. As of 2011, methane contributed radiative forcing of 0.48 ± 0.05 Wm−2 , or about 17% of the total radiative forcing from all of the long-lived and globally mixed greenhouse gases. According to NOAA, the atmospheric methane concentration has continued to increase since 2011 to an average global concentration of 1850.5 ppb as of July 2018. The balance between sources and sinks of methane is not yet fully understood. The IPCC Working Group I stated in chapter 2 of the Fourth Assessment Report that there are 'large uncertainties in the current bottom-up estimates of components of the global source', and the balance between sources and sinks is not yet well known. The most important sink in the methane cycle is reaction with the hydroxyl radical, which is produced photochemically in the atmosphere. Production of this radical is not fully understood and has a large effect on atmospheric concentrations. This uncertainty is exemplified by observations that have shown between the year 2000 and 2006 increases in atmospheric concentration of methane ceased, for reasons still being investigated. Various sources give the following values for methane emissions: Any process that results in the production of methane and its release into the atmosphere can be considered a 'source.' The two main processes that are responsible for methane production occur as a result of microorganisms anaerobically converting organic compounds into methane.