Climate-Greenhouse Effect

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• Climate-Greenhouse Effect

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Greenhouse
Glass, the material that greenhouse is made of,
1) transmit 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 reradiated back to earth.

The gases in the atmosphere that act like glass
in a greenhouse are called greenhouse gases.
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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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Enhanced greenhouse effect
When concentrations of greenhouse gases increase,
more infrared radiation is returned toward the
earth and the surface temperature rises.
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What makes a gas greenhouse gas?

• Able to absorb infrared light
• Must have molecular vibration(s)
• This excludes monoatomic gases as greenhouse
  gases. (That is why argon, the third most
  abundant atmospheric constituents is transparent
  to infrared irradiation)
• The molecular vibrations must be non-symmetric,
  i.e. infrared active
• Homonuclear diatomic molecules only have
  symmetric vibrations. Thats why N2, O2 are not
  greenhouse gases.

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What are the major greenhouse gases?

• H2O
• CO2
• CH4
• N2O
• O3
• CFCs
• SF6

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Absorption of terrestrial radiation by H2O and CO2
Atmospheric window 8000-12000nm
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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-live 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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CFC-11 and CFC-12 are effective infrared absorber
The absorption spectra of CFC-11 and CFC-12
coincides with the atmospheric window
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Comparison of different greenhouse gases
CO2 CH4 CFC-11 CFC-12 N2O
Concentration Preindustrial (lt1800) Current ppm 280 370 ppm 0.8 1.74 ppt 0 268 ppt 0 484 ppb 288 314
Atmospheric lifetime (yr) 50-100 10 45 130 114
Per molecule of radiative forcing relative to CO2 1 23 4,000 15,800 296
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Are human beings causing increases in greenhouse
gases?
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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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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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Nitrous oxide (N2O)
Rate of increase 0.25/year Use of fertilizer
increases both nitrification and denitrification
? increase N2O production
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Sources and sinks of N2O

• Sources
• denitrification process for energy production by
  anaerobic bacteria.
• Nitrification process (NH4? NO3-)
• Fertilizer use
• Biomass burning
• Combustion
• Unknown sources
• Sink Photolysis in the stratosphere

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CFC-11
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Sources and sinks of CFCs

• Sources
• No natural sources
• Synthetic chemicals
• Sink Photolysis in the stratosphere.

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Is the earth getting warmer?
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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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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

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Is the temperature rise due to human
activities?Or is it part of the natural
variation?
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When greenhouse gases, aerosols, and changes in
solar irradiance are used as inputs into general
circulation models, predicted temperatures are
very close to those observed.
When greenhouse gases are the only input,
predicted temperature are higher than those
observed.
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The state of climate change science

• The Earths natural greenhouse effect is required
  to support life on earth.
• Aerosol particles are important in formation of
  clouds.
• Human activities are contributing to increases in
  greenhouse gases and aerosol loading.
• The Earths surface has warmed during the last
  century and is projected to continue warming.