Greenhouse Gases

I. History of the Earth's Atmosphere (Fig 1)

II. Composition of Today's Atmosphere

  1. major gases in the atmosphere (troposphere) N2 and O2
  2. many other gases at very low concentration (Table 1, Fig 2)

III. Greenhouse Gases

  1. definition: absorb solar radiation (Fig 3)
  2. H2O, O3, CO2, N2O, CH4, CFC's, (SF6)
  3. low concentration but very high efficiency absorbing long-wave radiation
  4. absorption of solar radiation as a function of wavelength (Fig 4)
  5. individual gases and their green house potential (Table 2)
    1. water vapor is the most important greenhouse gas, contributes >80% of (natural) greenhouse warming
    2. if it were not for the green house gases, the mean annual temperature on Earth would drop from 15oC to -20oC

IV. Basic Characteristics of Green House Gases (Table 3)

  1. CO2
    1. anthropogenic sources: burning of fossil fuel and deforestation
    2. expected to double by the end of the next century
    3. increase in atmosphere is only half as high as expected; rest goes into ocean and bioshere? ('missing sink') (Fig 5)
  2. CH4 - anthropogenic sources: rice paddies, cattle, fossil fuels, biomass burning, solid waste
  3. N2O - anthopogenic sources: fertilizers, land use concersion
  4. O3 - anthopogenic sources: hydrocarbons and NOx (troposphere)
  5. CFCs - anthopogenic sources: refrigerants, aerosols, industrial processes
  6. H2O - not too well understood
  7. Relative contributions to the anthopogenic greenhouse effect (Fig 6)

V. Human Impacts on the Global Atmosphere Over the Past Few Centuries

  1. Rates of increase of individual greenhouse gases (Fig 7) (Fig 8)
  2. Mauna Loa CO2 record (Fig 9)
    1. one of the most important environmental monitoring efforts
    2. Mauna Loa, Hawai, US Weather Bureau research station far away from CO2 sources (Fig 10)
    3. record started in 1958, until present
      1. seasonal variations (5ppm)
      2. overall increase (1980s): 0.5%/y
    4. record can be extended into the past by using the ice core archive: CO2 increased from 1700 to today from 280ppm to 360ppm
  3. Methane record
    1. atmospheric methane levels have been reconstructed from ice cores (Fig 7)
      1. overall increase (1980s): 0.9%/year
      2. increased from 1700 to today from 790ppb to 1709ppb
  4. increase of greenhouse gases will most likely cause climate change
  5. it is not easy to estimate the extent of global warming because of feedback mechanisms
    1. increased temperature would result in more water vapor content of the atmosphere (warming, postive feedback) but also in more clouds (cooling, negative feedback)
    2. general circulation models predict a temperature rise from 1990 to 2100 of 2 to 5 degrees C

Text by Martin Stute.