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 Greenhouse
Gases |
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The greenhouse
gases include the commonly known carbon dioxide (CO2),
nitrous oxide (N2O),
methane (CH4),
chlorofluorocarbons (CFC), and etc. The greenhouse effect
has been occurring ever since the beginning of the Earth,
and is present on other planets, Venus, for example. The
presence of greenhouse gases not only warms the surface of
our planet, they also lower the temperature difference
between night and day.
Compared to
carbon dioxide, the other greenhouse gases cause more
greenhouse effect per molecule. Methane is 21 times as
powerful, nitrous oxide is 206 times, while CFCs are tens of
thousands times more powerful. However, carbon dioxide is
present in much greater amounts, so the amount of greenhouse
effect caused is much greater. Another characteristic of
greenhouse gases is that they usually have extremely long
life spans, 50~200 years for carbon dioxide, 12~17 years for
methane, 120 years for nitrous oxide, and 102 years for
CFCs. Once these gases enter the atmosphere, they are
usually impossible to recapture, and only the natural
process of degradation can make them disappear. Because of
their long life span, greenhouse gases cause long lasting
and global influences. Even if humans stop emitting these
man made greenhouse gases right now, the amount accumulated
after the Industrial Revolution will continue to affect the
Earth's climate. Figure
drawn by: Ben
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Carbon dioxide
emitted by cars
Figure
from:
Lingnan University http://www.ln.edu.hk/
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The atmosphere is like a filter
which can control the amount of energy exchanged between the
Earth, the sun, and space. Some gases in the atmosphere
allow short wave-length radiation to shine on the surface of
the earth as light, and absorb the long wave-length
radiation reflected by the surface. These energy retaining
gases are what we call greenhouse gases. The main ones are:
Carbon
dioxide (CO2)- Because of large amounts of coal, oil, and
natural gas usage, the global carbon dioxide amount is
increasing by 6 billion tons per year.
CFCs- Major
types are CFC-11, CFC-12, and CFC-113. They are used in air
conditioner coolants and aerosol sprays. These compounds are
also the major cause of the destruction of the ozone layer.
Methane (CH4
)- Formed from decaying materials or fermentation, and
incomplete combustion of materials. Mainly comes from
livestock, motor vehicles, and power plants.
Nitrous
Oxide (N2O)- Formed from the burning of fossil fuels,
microorganisms, and the decomposition of chemical
fertilizers.
Ozone (O3)-
Comes from pollution, like nitrogen oxides and hydrocarbons
produced by motor vehicles and power plants. These gases are
converted through photochemical reactions to ozone. |
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Over deforestation
Abundant mining for coal, oil, natural gases, and other
fossil fuels
Figure
from:
Lingnan University http://www.ln.edu.hk/
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The greenhouse gases include the commonly
known carbon dioxide (CO2), nitrous oxide (N2O),
methane (CH4),
chlorofluorocarbons (CFC), and etc. The greenhouse effect
has been occurring since the beginning of the Earth, and is
present on other planets, Venus, for example. The presence
of greenhouse gases not only warms the surface of our
planet, they also lower the temperature difference between
night and day.
Compared to carbon dioxide, the other
greenhouse gases cause more greenhouse effect per molecule,
methane is 21 times as powerful, nitrous oxide is 206 times,
while CFCs are tens of thousands times more powerful.
However, carbon dioxide is present in much greater amounts,
so the amount of greenhouse effect caused is much greater.
Another characteristic of greenhouse gases is that they
usually have extremely long life spans, 50~200 years for
carbon dioxide, 12~17 years for methane, 120 years for
nitrous oxide, and 102 years for CFCs. Once these gases
enter the atmosphere, they are usually impossible to
recapture, only the natural process of degradation can make
them disappear. Because of their long life span, greenhouse
gases cause long lasting and global influences. Even if
humans stopped emitting these man made greenhouse gases, the
amount accumulated after the Industrial Revolution will
continue to affect the Earth's climate. |
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Human
activities produce excessive amounts of greenhouse gases
Figure
from:: Lingnan
University http://www.ln.edu.hk/ |
Currently, the greenhouse gases
are still increasing in amount. Starting from 1994, carbon
dioxide increases about 0.4% a year, and has a concentration
of 358ppm; methane increases 0.6% a year, concentration
1.7ppm; nitrous oxide increases 0.25% a year, concentration
0.31ppm. CFC-11 has a concentration of around 368ppm, and
CFC-12 has a concentration of around 480ppm. From the figure
we can see that the amount of the greenhouse effect caused
by CFCs are the most, thousands of time more than carbon
dioxide per unit weight. We can also see that carbon dioxide
contributes to about 55% of the greenhouse effect, the most
of all greenhouse gases. From the figure we can see that for
the past 40 years, the greenhouse gases have caused the
temperature to rise.
The increase in the amount of
atmospheric carbon dioxide is caused mainly by two sources:
burning of fossil fuels and deforestation. Fossil fuels
cause more carbon dioxide of the two. In 1992, the world
carbon dioxide amount emitted was around 8 billion tons
(calculated by carbon equivalent). |
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Figure:
Environmental Protection Adminstration
Executive Yuan, R.O.C.
http://www.epa.gov.tw/
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