Download Atmosphere www.AssignmentPoint.com The atmosphere is one of

Atmosphere
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The atmosphere is one of the Earth's major carbon reservoirs and an
important
component
of
the
global
carbon
cycle,
holding
approximately 720 gigatons of carbon. Atmospheric carbon plays an
important role in the greenhouse effect. The most important carbon
compound in this respect is the gas carbon dioxide (CO2). Although it
is a small percentage of the atmosphere (approximately 0.04% on a
molar basis), it plays a vital role in retaining heat in the atmosphere
and thus in the greenhouse effect. Other gases with effects on the
climate containing carbon in the atmosphere are methane and
chlorofluorocarbons (the latter is entirely anthropogenic). Emissions
by humans in the past 200 years have almost doubled the amount
carbon dioxide in the atmosphere.
Methane (CH4) is one of the more potent greenhouse gases and is
mainly produced by the digestion or decay of biological organisms. It
is considered the second most important greenhouse gas, yet the
methane cycle in the atmosphere is currently only poorly understood.
The amount of methane produced and absorbed yearly varies widely.
Large stores of methane can be found in the form of methane ice
under permafrost and on continental shelves. Additional methane is
produced by the anaerobic decay of organic material and is produced
in organisms' digestive tracts, soil, etc. Natural methane production
accounts 10-30% of global methane sources.
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Anthropogenic methane is produced in various ways, e.g. by raising
cattle or through the decay of trash in landfills. It is also produced by
several industrial sources, including the mining and distribution of
fossil fuels. More than 70% of atmospheric methane comes from
biogenic sources. Methane levels have risen gradually since the onset
of the industrial era, from ~700 ppb in 1750 to ~1775 ppb in 2005.
Methane can be removed from the atmosphere through a reaction of
the photochemically produced hydroxyl free radical (OH). It can also
leave the atmosphere by entering the stratosphere, where it is
destroyed, or by being absorbed into soil sinks. Because methane
reacts fairly quickly with other compounds, it does not stay in the
atmosphere as long as many other greenhouse gases, e.g. carbon
dioxide. It has an atmospheric lifetime of about eight years. This
keeps the concentration of methane in the atmosphere relatively low
and is the reason that it currently plays a secondary role in the
greenhouse effect to carbon dioxide, despite the fact that it produces a
much more powerful greenhouse effect per volume.
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