The%20Greenhouse%20Effect

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The Greenhouse Effect

• Good or Bad?

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Global Climate History
Geologic evidence clearly indicates relative
long-term climate stability that has allowed
liquid H2O to exist for most of geologic history.
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Earths Atmosphere
77 N2, 21 O2, 1 Ar, trace gases (CO2, CH4,
H2O)
Absorbs incoming solar radiation and warms the
planet. Important component of global climate.
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Without atmosphere, average Earth temperatures
would be a cool 17C!!
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Natural Greenhouse effect
The natural greenhouse effect causes the mean
temperature of the Earth's surface to be about
33oC warmer than it would be if natural
greenhouse gases were not present.
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Greenhouse
Glass, the material that greenhouse is made of,
1) transmits short-wavelength visible light, 2)
absorbs and redirects the longer wavelengths of
energy. These two aspects make the greenhouse
warmer than outside air temperature.
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Greenhouse effect of the atmosphere

• Light from the sun includes the entire visible
  region and smaller portions of the adjacent UV
  and infrared regions.
• Sunlight penetrates the atmosphere and warms the
  Earths surface.
• Longer wavelength infrared radiation is radiated
  from the earths surface.
• A considerable amount of the outgoing IR
  radiation is absorbed by gases in the atmosphere
  and re-radiated back to Earth.

The gases in the atmosphere that act like glass
in a greenhouse are called greenhouse gases.
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Greenhouse Effect Global Warming

• The greenhouse effect global warming are not
  the same thing.
• Global warming refers to a rise in the
  temperature of the surface of the earth
• An increase in the concentration of greenhouse
  gases leads to an increase in the the magnitude
  of the greenhouse effect. (Called enhanced
  greenhouse effect)
• This results in global warming

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Enhanced greenhouse effect
When concentrations of greenhouse gases increase,
more infrared radiation is returned towards the
Earth. ? The surface temperature rises.
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Climate Change vs. Variability
Climate variability is natural.
Even in a stable climate regime, there will
always be some variation (wet/dry years,
warm/cold years) A year with completely average
or normal climate conditions is rare
The challenge for scientists is to determine
whether any increase/decrease in precipitation,
temperature, frequency of storms, sea level, etc.
is due to climate variability or climate change.
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The Last Ice Age
30 of the land surface was covered by ice (only
10 is covered today)
Northern Idaho was covered by 1 km thick ice
sheet
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Selected Greenhouse Gases

• Carbon Dioxide (CO2)
• Source Fossil fuel burning, deforestation
• Anthropogenic increase 30
• Average atmospheric residence time 500 years
• Methane (CH4)
• Source Rice cultivation, cattle sheep
  ranching, decay from landfills, mining
• Anthropogenic increase 145
• Average atmospheric residence time 7-10 years
• Nitrous oxide (N2O)
• Source Industry and agriculture (fertilizers)
• Anthropogenic increase 15
• Average atmospheric residence time 140-190 years

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What determines the contribution of a greenhouse
gas to global warming?

• Concentrations
• H2O and CO2 are the two biggest contributors to
  the atmospheric warming because of their higher
  concentrations.
• Lifetime
• The longer-lived a gas is, the higher the
  contribution. e.g. N2O contribution gt CH4
• Effectiveness as an infrared absorber
• For example, CFC-11 and CFC-12

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CO2 Concentrations at Mauna Loa, Hawaii
The average atmospheric CO2 concentrations
observed at Muana Loa, Hawaii increased
approximately 40 ppmv between 1958 and 1995. The
small fluctuations in the curve are seasonal
variations due primarily to the withdrawal and
production of carbon dioxide by terrestrial life.
Notice that minimum values occur during the
northern hemisphere summers (when global
photosynthetic activity is greatest) and maximum
values occur six months later.
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The concentration of greenhouse gases,
particularly CO2, is important global climate
regulation
What regulates the amount of CO2??
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The Earths Climate System - very complex!!
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Sources and sinks of CO2

• Sources
• Natural respiration of vegetation and soil
  detritus
• Man-made Fossil fuel combustion, deforestation
• Sinks
• slow exchange of carbon between surface waters
  and deep layers of ocean.
• (Seawater is alkaline while CO2 is acidic ? The
  oceans are a vast reservoir of CO2).

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Methane
Rate of increase 0.9 annually
Atmospheric methane has increased steadily to
present day levels this increase is highly
correlated with human population growth and with
related activities, including agricultural
practices.
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Sources and sinks of methane

• Sources
• Natural end-product of the metabolism from an
  anaerobic bacteria, methanogen.
• Natural wetlands, enteric fermentation (wild
  animals), termites, biomass burning, ocean/fresh
  water
• Man-made rice paddies, gas drilling and
  transmission, landfills, coal mining, biomass
  burning, enteric fermentation (domestic animals)
• Sink OH CH4? CH3. H2O

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Temperature over the past one century
The global air temperature at the Earth's surface
has increased about 0.5oC during the past
century.
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Temperature over the past 1000 years
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Short-Term Climate Change

• Climate change over short time scales (lt1,000,000
  years)
• Related to complex, poorly understand
  interactions between atmosphere, hydrosphere, and
  lithosphere

WARM
COLD
Possible Causes

1. Orbital Parameters of the Earth
2. Changes in Atmospheric Composition
3. Changes in Ocean Circulation
4. Sunspot Activity
5. Changes in Reflectivity (albedo)

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Recent Global Warming
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Consequences of global warming

• Sea level rise
• Beach erosion
• Coastal wetland loss
• Loss of low-lying territories
• Water resources change
• Precipitation pattern shift
• Increases instances of heavy precipitation
• New burdens on water capture, storage and
  distribution system to be expected.
• Effects on agriculture
• Changes in the length of growing season
• Growth of undesirable plant species

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Consequences of global warming (Continued)

• Effects on air quality
• Increase in reaction rates and concentrations of
  certain atmospheric species? increase in O3 in
  urban areas
• More droughts? widespread forest fire? worsen air
  quality
• Change in how pollutants are dispersed.
• Impacts on human health
• Changes in patterns of sickness and death.
• Respiratory problems affected by air quality
  change
• Biodiversity
• Some species may grow too quick and overshoot
  their reproductive period (e.g. reef corals)
• Forest could be devastated if the rate of climate
  change outpaced the rate at which forest species
  could migrate.
• Change in the pattern of ocean current