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(CO2).
- The Natural Methane Cycle
- The Impact of Human Activities
The Natural Methane Cycle
Methane (CH4) is generated naturally by bacteria that break down organic matter, it is found in the guts of termites and other animals and in natural gas deposits. Methane (CH4) remains in the atmosphere for about 12 years. This is less time than most other long life greenhouse gases.
Sources of methane (CH4) include wetlands such as peatland, the gut of certain animals and the decay of organic wastes. Methane (CH4) is removed from the atmosphere through natural processes.
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 (CH4). 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 (CH4) 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 atmospheric concentration of methane has increased from between 600-700 ppb in pre-industrial times (1780), to 1774 ppb in 2005. The level of Methane (CH4) in the atmosphere has therefore almost trebled since pre-industrial levels. In recent years the increase in atmospheric methane levels has reduced.
The reduction in Methane (CH4) 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 if the energy replaced would have been derived from fossil fuels.