Methane

Methane (CH₄) is the second most important greenhouse gas. Even though it occurs in much lower concentrations than carbon dioxide (CO₂), molecule for molecule it produces approximately 21 times as much warming as carbon dioxide.

The Natural Methane Cycle

Methane is generated naturally by bacteria that break down organic matter. Sources of methane include natural gas deposits, wetlands such as peatland, the gut of certain animals such as cows and termites, and the decay of organic wastes. Methane remains in the atmosphere for about 12 years, less time than most other greenhouse gases.

Methane is removed from the atmosphere through natural processes.

Cow

The manure produced by cows naturally releases methane into the atmosphere.Companies can then take this manure and flush it into a tank or tented lagoon, where the manure can decompose and the methane gas bubbles off.

© The Irish Times

Cow
© The Irish Times

Cow

© The Irish Times

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The Impact of Human Activities

An increase in livestock farming and rice growing, which is in reponse to an increased global population and changing demand for food, has led to an increase in atmospheric methane. Other sources are the extraction of fossil fuels, landfill sites and the burning of biomass. In addition there is increasing concern about the levels of methane that may be released to the atmosphere due to the melting of the northern latitude permafrost regions that currently lock up and store vast quantities of methane preventing it from reaching the atmosphere.

The mean atmospheric concentration of methane has increased from between 600-700 ppb (parts per billion) in pre-industrial times (pre-1750), to 1800 ppb in 2013. The level of methane in the atmosphere has therefore almost trebled since pre-industrial levels. In recent years the rate of increase in atmospheric methane levels has slowed.

The reduction in methane emissions is due to reduced leakage of natural gas and better management of landfill sites. The move to utilise organic waste for bio-energy is considered to be a win-win for actions on climate change as the energy replaced would have been derived from fossil fuels.

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