Causes of Climate Change - Climate Resilient Agriculture for Ensuring Food Security - page 23

Fig. 2.5 The carbon cycle

enteric fermentation is attributed primarily to an
increase in the cattle population, both beef and
dairy cattle, and to increase in the swine
population.
Methane is also emitted from landfi lls and
other waste dumps. If the waste is put into an
incinerator or burnt in the open, carbon dioxide is
emitted. Methane is also emitted during the pro-
cess of oil drilling, coal mining, and also from
leaking gas pipelines (due to accidents and poor
maintenance of sites).
Methane rose from a preindustrial atmo-
spheric concentration of around 700 parts per
billion by volume (ppbv) to about 1,789 ppbv by
2007.
Methane has 25 times the GWP of carbon
dioxide and is therefore 25 CO 2 e. It is released
from the digestive systems of ruminant live-
stock by a process known as enteric fermenta-
tion and from manures and slurries. Similar to
nitrous oxide, it is not possible to eliminate
methane production from agriculture, but
emissions can be reduced through improved
livestock health, breed selection, and careful
modifi cations to the diet and methods of manure
storage and application. Increased production
effi ciency will mean that less methane is emit-
ted per unit of production so careful manage-

ment to optimize production will also help
reduce emissions.
Ruminant animals (such as sheep and cattle)
emit methane as a by-product of digesting feed.
In 2008, this contributed 55 Mt of CO 2 e to
Australia's national Kyoto accounts, correspond-
ing to 9.6 % of Australia's total greenhouse gas
emissions and the largest component of agricul-
tural emissions. The contribution is defi ned by
the total number of animals and the emission rate
per animal, which, in turn, is controlled by the
animal's diet and management. Methane produc-
tion by these animals represents lost energy that
would otherwise be directed towards animal
growth.
In ruminant animals, methane is produced as a
by-product of the digestion of feed in the rumen
under anaerobic condition. Methane emission is
related to the composition of animal diet (grass,
legume, grain, and concentrates) and the propor-
tion of different feeds (e.g., soluble residue,
hemicelluloses, and cellulose content). Mitigation
of methane emitted from livestock is approached
most effectively by strategies that reduce feed
input per unit of product output. Nutritional,
genetic, and management strategies to improve
feed effi ciency increase the rate of product (milk,
meat) output per animal. Because most CH 4 is