Mary Presnail, Samantha Linman
Emily, Brenna
Josh, Megan
Paul, Jason Kopp
ESPM 3000
Greenhouse Gas Feedback Mechanisms
There are a number of feedback processes important to Earth’s climate system.
One important feedback process is the greenhouse gas feedback mechanism. This paper
will discuss what a greenhouse gas feedback is, how it works and lastly how it relates to
climate sensitivity.
In order to define greenhouse gas feedback, first we must define positive
feedback. Positive feedback is a phenomenon that occurs, which creates effects that
increase the occurrence of said phenomenon. In the case of green house gasses one
example might be: Carbon dioxide in the atmosphere warms air temperatures, which in
turn melts polar ice caps. The melting ice releases CO2, which traps more heat and
increases atmospheric temperatures.
The Atmosphere is composed of a number of different gasses; 78% Nitrogen and
20% Oxygen, water vapor and other gasses make up the remainder of the atmosphere.
Some of these gasses have the ability to absorb long wave radiation (heat) that is
reflected from the surface of the earth. The trapping of this heat is important the
temperature regulation of the earth, without it, all life on earth would die. However,
humans are greatly increasing the amount of heat trapping greenhouse gasses, which are
trapping more heat than necessary around the earth.
The greenhouse gases are comprised of carbon dioxide, methane,
chlorofluorocarbons, hydrofluorocarbons, ozone, nitrous oxide and water vapor. As
concentrations of the above greenhouse gases increase within the atmosphere and
warming results, a positive feedback loop involving water vapor begins to evolve.
Warming temperatures result in increased temperatures of streams, rivers, lakes, and
oceans. In turn, these bodies of water begin an accelerated evaporation process which
results in increased levels of water vapor within the atmosphere. Water vapor acts as
greenhouse gas, reflecting escaping infrared radiation back toward the earth’s surface.
Although its reflective strength is relatively weak compared to other greenhouse gases, its
concentration in the atmosphere is much larger at about 1%. So, as the world warms as a
result of other greenhouse gases, increased evaporation occurs resulting in increased
concentrations of water vapor which, in turn, adds to the warming cycle. Because the
additional water vapor exasperates the already existing warming trend, the result is a
positive feedback loop.
While water vapor accounts for the largest percent of the greenhouse gases, CO2
accounts for the largest effect, as a percentage, on the Earth’s radiative balance. CO2 is
released into the atmosphere by human contributions, but there are also naturally
occurring sources. Some of the human contributions are the burning of fossil fuels, the
reduction of the worlds’ forests and population growth. Naturally occurring CO2 comes
from the ocean, volcanic activity, fires, and biological respiration.
“Many non-CO2 greenhouse gases are far more effective than CO2 at
contributing to the radiative forcing. For example, the absorption strength of heavily
fluorinated molecules can be 10,000 times that of CO2. CO2 has a dominant radiative
forcing only because the increase in its atmospheric concentration has been so largearound 100 ppm since preindustrial times. Methane, by contrast has increased by only
1ppm” (Shine, Sturges 2007).
Methane is a greenhouse gas that is 20 times more potent than Carbon Monoxide.
Methane is released naturally into the atmosphere from ocean deposits during periods of
warming and from other sources throughout ecosystems (ex. animal gases). It is also
released from pig slurry, cattle slurry, and livestock manure within livestock production
which contributes a significant amount of global CH4 to the atmosphere. Methane
increases temperatures in the atmosphere which then leads to additional methane being
release. This is another positive feedback loop linked to greenhouse gas feedback.
These positive feedback mechanisms are directly related to climate sensitivity.
There is an increasing concentration of greenhouse gases (such as water vapor, CO2, and
Methane) in the Earth’s atmosphere and they have the potential to change the global
climate dramatically. Many anthropogenic activities, such as burning fossil fuels are
modifying the composition of the global atmosphere. The sensitivity of the climate
system to human perturbations over the next century will be determined by a combination
of feedbacks such as the greenhouse gas feedback mechanism that amplify or dampen the
direct radiative effects of increasing concentrations of greenhouse gases.
The Earth’s climate is extremely sensitive and by altering the greenhouse gas
feedback mechanism, we may be causing irreversible harm to it. Some of the problems
associated with increased greenhouse gas emissions are increase to the ice albedo effect,
decreased ecosystem diversity, loss of habitat, rising sea levels, and so on.
One of the most pronounced feedback mechanisms that relate to climate
sensitivity and global climate change is the greenhouse gas feedback mechanism. This is
a positive feedback mechanism which creates effects that increase the occurrence gases in
the atmosphere. In recent decades greenhouse gases have increased in the atmosphere
due to natural and anthropogenic sources. This, in turn, causes changes to the global
climate.
Literature Cited:
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Henson, Robert. The Rough Guide to Climate Change. Strand, London. Rough Guides
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