Study Note - Climate Change – Methane by Sector

Methane (CH4) is a natural atmospheric gas that contributes to the greenhouse effect, and is far more effective than carbon dioxide at absorbing long-wave radiation. The recent increase in methane concentrations in the atmosphere is causing concern as it is a by-product of both energy consumption and agricultural activity.

A large proportion of the methane increase may be the result of anaerobic decomposition of the organic matter associated with rice paddy cultivation, as well as the digestive processes of animals such as cattle.

Along with rising human populations over the past two centuries, the amount of land given over to rice cultivation and animal grazing has led to a rise in methane concentrations, currently rising at a rate of about 1 per cent per year (compared with 0.48 per cent for carbon dioxide).

A lot of methane is stored on the sea bed as a gas hydrate, which is formed under conditions of very high pressure and low temperature. As temperatures rise due to climate change, this could add another source of methane to the atmosphere, as it has been estimated that about 10,000 gigatonnes of carbon as methane are stored on the sea bed.

Methane accounts for approximately 18% of the anthropomorphic greenhouse gas emissions, and not all of the methane emitted comes from agricultural sources, though that is by far the biggest contributor:

Source: Smithson et al, 2008, Fundamentals of the Physical Environment, Routledge.