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Option C: Energy
C.5 – Environmental Impact:
Global Warming
Greenhouse effect
• Natural greenhouse effect: absorption of
infrared radiation by natural greenhouse
gases (CO2 and H2O vapour) in the
atmosphere warming the earth – if not
surface would be 30K cooler.
• Anthropogenic greenhouse effect: caused by
gases emitted by human activities.
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solar radiation spectrum
natural greenhouse effect
http://www.elmhurst.edu/~chm/vchembook/globalwarmA5.html
Greenhouse Analogy: Energy from the sun
in the form of some ultraviolet and visible
light (short wavelength) passes through the
glass of the greenhouse. As the light strikes
various surfaces in the greenhouse they are
heated. These surfaces in turn re-radiate the
heat in the form of infrared radiation (long
wavelength). However, the IR radiation is
blocked from escaping by the glass. IR is not
able to pass through the glass, hence the
greenhouse air heats up fairly dramatically.
The greenhouse gases have the same property as the glass towards the IR
radiation. Think of the greenhouse gases acting as an invisible glass shield
around the earth.
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∆T 1950 – present day
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Where will it occur primarily?
terminology
• greenhouse effect = the absorbing of
some of the infra-red radiation radiated
from the Earth in the atmosphere which is
then reradiated back to Earth; this results
in…
• global warming = a gradual increase in
planet-wide temperatures
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Global warming: evidence
http://en.wikipedia.org/wiki/Image:Instrumental_Temperature_Record.png
Global warming: Historic CO2 levels
• Ice core from 2874 m depth, 491 000 years old
Thin slice of ice – gas bubbles are dark
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What does ice core data tell us?
Global warming: CO2 emissions
http://www.eia.doe.gov/oiaf/1605/ggccebro/chapter1.html
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Global warming effects (1)
World wide rise in sea levels resulting from:
Partial melting of glaciers and polar ice caps
Thermal expansion of water (as a result of
heating).
Changes in crop yields: some crops will grow
better, other worse.
Global warming effects (2)
• Changes in distribution of commercial crops
• Changes in the distribution of pests and diseasecarrying organisms e.g. malaria.
• More severe weather conditions:
– floods in particular of coastal areas; more severe storms
e.g. monsoon floods in Pakistan 2010
– More severe droughts e.g. 2010 worst drought in
Amazon
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Local effects will differ – why?
Greenhouse factor
• Compares ability of a greenhouse gas to absorb IR
to the same amount of carbon dioxide which has a
factor of 1.
• Example: greenhouse factor of methane is 30 which
means it absorbs as much as 30 molecules of
carbon dioxide or 1 molecule of methane absorbs
30 times more as 1 molecule of carbon dioxide.
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Greenhouse gases: H2O
• Sources:
–Human: combustion of hydrocarbons
–Natural: evaporation
• Relative effect: 0.1 - Least effective in trapping
radiation but is most abundant.
greenhouse gas: CO2
• Sources:
– Human: burning fossil fuels and wood, forest fires,
burning waste
– Natural: respiration, decay of organic matter, natural
forest fires
• Relative effect: Most important greenhouse gas (50%
contribution) because of its great abundance (second
largest after water vapour) and the large range of
wavelengths over which it absorbs IR.
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Greenhouse gases: CH4
• Sources:
– Human: cattle farming, rice paddies (wet soil means any
organic matter in it is decomposed without oxygen) ,
petroleum and natural gas production.
– Natural: digestive tracts of ruminants, cattle, bogs or
marshes, bacterial fermentation – when organic matter
is decomposed anaerobically, methane gas is produced.
• Relative effect: 30 - Low abundance in atmosphere but it
is more effective in absorbing infrared radiation, however,
its atmospheric lifespan in the atmosphere is short.
Greenhouse gases: N2O
• Sources:
– Human: use of nitrogen based fertilizers
– Natural: bacterial action
• Relative effect: 160 - Very effective in absorbing
radiation, fairly long atmospheric life.
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Greenhouse gases: CFCs
• Sources:
– Human: refrigerators, air- conditioning, aerosols
in spraying cans, foaming agents
– Natural: none!!!!
• Relative effect: 10 000 – 25 000 - Very effective in
absorbing radiation, long atmospheric life but low
abundance.
Greenhouse gases: SF6
• Human source: electrical
insulators
• Greenhouse effect: 24 000
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Greenhouse gases
Ocean Acidification:
CO2 + H2O H2CO3
• CO2 released into the
atmosphere combines
with water according
the equation above,
leading to ocean
acidification.
• The inhibits shell
growth in animals and
causes reproductive
issues in fish.
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Global Dimming
• The release of
particulates into the
atmosphere from
incomplete combustion
of fossil fuel use blocks
light.
• This can lead to a
reduction in global
temperatures, although
with consequences.
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Strategies for Reducing CO2 Levels
• Increased energy
efficiency
• Reduced dependence
on carbon-based fuels
• Capture and storage of
carbon from fossil fuels.
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• Increased energy
efficiency
• Reduced dependence
on carbon-based fuels
• Capture and storage of
carbon from fossil fuels.
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