Anthropogenic Sources of Atmospheric Methane
The atmosphere has always contained the Greenhouse Gas methane. Along with carbon
dioxide, nitrous oxide, and water vapor, methane helps to create the natural greenhouse effect.
These gases trap some of the sun's energy and keep the Earth at a warm enough temperature
to sustain life. If the occurrence of any of these gases in the atmosphere is increased, the
natural greenhouse effect will intensify and further warm the Earth. Due to man's activities, the
amount of atmospheric methane has more than doubled since pre-industrial times. It could
double again by the year 2050. Today, 60 to 70% of methane releases come from human-
Pie chart of Greenhouse Gases
The Effect of Methane on Global Warming
Methane is the second largest contributor to potential global warming (carbon dioxide being the
first). Methane is an extremely powerful greenhouse gas, and it increases the greenhouse effect
in two ways. Firstly, it absorbs infrared radiation well, making it twenty times more effective at
trapping heat in the atmosphere than carbon dioxide. Secondly, increased amounts of methane
increases the amount of water vapor in the stratosphere, further trapping heat. Another
characteristic of methane relative to global warming is its staying power: the methane released
today could still trap heat more than a decade from now. Its concentration in the atmosphere is
The largest source of methane emissions in the United States are landfills. Landfill gas, which is
mainly composed of methane and carbon dioxide, is the result of the anaerobic decomposition of
biodegradable organic wastes. This process begins usually within 10 to 50 days after the arrival of
the waste in the landfill. The majority of methane generated by a landfill occurs within 30 years of its
completion, though it can continue for 60 years or more. Landfills account for 36% of
anthropogenic methane emissions in this country, and between 20 to 40% of global
Another large source of atmospheric methane is enteric fermentation in domestic livestock.
During an animal's process of digestion, methane is produced through this process in which
microbes that live in the animal's digestive systems break down the feed consumed by the animal.
The methane is then emitted when the animal belches or flagellates. Cows flagellate about a half
pound of methane per day. The animals with the highest levels of methane emissions are called
ruminants. Ruminants include cattle, buffalo, sheep, and goats. They are given this name
because they have a rumen, or large fore-stomach, in which methane-producing fermentation
occurs. This fermentation process is what enables ruminant animals to eat coarse material such
as grasses and straws which...