ATMOSPHERIC CHANGE: the Greenhouse Effect

CHRONOLOGICAL SCALE
109 106 103 102 10 YR
    ATMOSPHERE 1.2. 3.4. 5 6 6? 6
GEOGRAPHICAL SCALE
  Local  Regional  Global 
    ATMOSPHERE 1 2 3 4 5 6
numbers refere to notes, below


THE CARBON CYCLE



1. EVOLUTION OF THE EARTH'S ATMOSPHERE:

2. GEOLOGIC TIME SCALE


PHANEROZOIC CO2 AND CLIMATE

Anomalously warm climate during the Cretaceous may have resulted from rapid sea floor spreading, decreased carbonate in sediments and increased CO2 in the atmosphere (Berner et al. 1983)


Geologic record of ocean storm intensity (storm bed [tempestite] thickness) indicates greater storminess during Cretaceous and late Paleozoic CO2 maxima (Brandt, 1990)

TERTIARY COOLING
    - Oceanic Feedback

Reduced atm. CO2 produces initial cooling
  • Tertiary cooling reduced polar water temperatures (~0°C) so that N.Pacific chemically stratified (fresh over saline)
  • N. & Equat. Pacific surface fresh, N.Atlantic saline after closing of Bolivar Trench
  • CO2 and OM accumulate below pycnocline, reducing atm. CO2 cooling 2.7 Ma (Sigman et al., 2004)
    precip


  • 3. PALEOCENE-EOCENE THERMAL MAXIMUM (PETM)

    8-10 °C warming
    CO2 8 x modern (2600 ppmv)
    Tertiary Climate
    (Zachos et al., 2004)
  • Expulsion of 1200 to 2500 Gt of CH4 from deep-ocean gas hydrates (Dickens et al., 1995, 1997) Triggered by hydrothermal sea-floor vents in North Sea (Svensen et al., 2004)
  • Absorption of CH4 results results in acidification of oceans, dissolution of ocean carbonates, and release of additional 2000 Gt of CO2 to atm.

  • Oligocene Cooling

    Lower atm. CO2 makes glaciations stable.
    (even during high insolation periods)

    4. late-MIOCENE 1 x modern atm. CO2

    Low atmospheric CO2 (ca. 300-320 ppmv) may have been reached ca. 7 Ma,
    when C4 plant gained competitive advantage over C3 plants,
    increasing δ 13C



    5. PLEISTOCENE-HOLOCENE ATMOSPHERIC CO2 CHANGE


    THE GREENHOUSE EFFECT

    Without Atmospheric absorption of re-radiated longwave radiation, the global temperature would be -17.3 oC (32 oC colder)

    Rasool and deBergh (1970) GOLDILOCKS PARADOX Venus, too hot for liquid water, vapor lost into space, CO2 retained in atmosphere, temperature 450 oC. Earth cool enough for precipitation: active carbon cycle (erosion, weathering, biological activity). Mars too cold for liquid water, weak carbon cycle,CO2 lost to space.

    Certain gasses (e.g., CO2 CH3) effect the amount of energy absorbed in the atmosphere

      The Sun's energy received as shortwave radiation
      • energy = cT4
      • wavelength = cT-4

      30% of sun's energy reflected back into space
      The 70% absorbed is radiated back into space as longwave radiation.

    Water vapor absorbs much longwave radiation except a WINDOW from 600 - 1300 cm-1.

    CO2, O3, CH4, N2O absorb at these wavelengths closing the window


    Cumulative effect of other greenhouse gasses is to more than
    double CO2's warming (Schneider, 1989)
    6. The 20th Century Greenhouse Effect: Greenhouse effect makes Earth habitable,
    but how much temperature change would rusult from 0.3% to 0.6% or 1.2% atm. CO2 ?
    1. Documented CO2 increase in atmosphere
    2. However, calculations from burning of fossil fuels and land clearance indicate that CO2 increase should be twice as great.
    3. Is there Meteorological Evidence for warming?
      Jones et al. (1986) document a global increase in world temperature since 1910.
    4. Potential Effects
    5. Predicting the Effects


    Climate Atmospheric Readings

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