ATMOSPHERIC CHANGE: the Greenhouse Effect

• Geological Reservoir
  (very slow cycle, 1,000,000 times atmosphere)
  
  75,000,000 tons in carbonates
  5000 tons in fossil fuels
  
• Oceanic Reservoir
  
  600 tons C in Surface Ocean 36,000 tons C in Deep Ocean
• Soil Reservoir
  
  1500 tons soils & peats
• Atmospheric Reservoir
  
  775 tons C in Atmosphere (0.037 % = 370 ppmv)
  
• Biological Reservoir
  
  560 tons biota
• Industrial Age Additions to Atmosphere
  
  5 tons C yr^-1 burning of fossil fuels
  1 ton C yr^-1 plowing the prairie, cutting of tropical forest
  
• Carbon sinks (½ removed from atmosphere)
  
  2 tons C yr^-1 surface ocean
  1 ton C yr^-1 biota + soils
  
• Annual Cycle (Flux to Biota)
  
  122 tons C yr^-1 Oceanic: without circulation, atm. conc. would be 700 ppm.
  100 tons C yr^-1 Terrestrial
  

1. EVOLUTION OF THE EARTH'S ATMOSPHERE:

• SOLAR PARADOX early (3 BY) earth warm, solar irradiance 25-30% less
  
• Sagen and Mullen (1972) CH₄, NH₃ in the primitive atmosphere.
  
• Owen, Chess and Ramanathan (1979) CO₂ conc. 1000X 4 BY
  

  ESTIM. °C	AGE	ATM. CONC.
  85 °C greater	4 Gy	26% CO2	1000 X	1000X atm. concentration before 1.8 Gy disputed by Rye et al. (1995) based on soils siderite, but supported by Ohumoto et all (2004)
  70 °C greater	2 Gy	11% CO2	100 X
  60 °C greater	1 Gy	0.3% CO2	10 X
  0 °C greater	today	0.03% CO2	1 X

2. GEOLOGIC TIME SCALE

• Sources of CO₂:
  
  Outgasing from volcanoes (Budyko, 1977)
  
  → CO₂
  Weathering of carbonate rocks (at surface)
  CaCO₃ + SiO₂ → CaSiO₃ + CO₂
• Sinks for CO₂:
  
  Photosynthesis (and burial) limestones & coal
  CO₂ + H₂O → O₂ + CH₂O
  
  Weathering of silicate rocks (in upper crust)
  
  CaSiO₃ + CO₂ → CaCO₃ + SiO₂
  (and burial)

  Planktonic Calcareous Algae (Ridgwell, Kennedy and Caldeira, 2003)

PHANEROZOIC CO₂ AND CLIMATE

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) (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

5. PLEISTOCENE-HOLOCENE ATMOSPHERIC CO₂ CHANGE

• Ice Core Research (included bubbles)
  
• Atm. CO₂ concentration was low (<200 ppm) during the last glaciation -- higher in early Holocene? (Neftel et al., 1982)
  
• Computer Model driven by CO₂ produces Scandinavian, Siberian and Arctic Ocean ice sheets at CO₂ <250 ppm (Lindstom and MacAyeal, 1989).
  
• Atm. CO₂ concentration in Antarctic Ice closely follows Ocean Core ¹⁸O/¹⁶O curves (& Insolation, & Ice Volume), but not higher in early Holocene
  
• CO₂ sequestration in deep ocean may be governed by Antarctic (polar) ocean stratification.

  Holocene atm. CO2 change (Barnola et al., 1987; Genthon et al., 1987)

  Polar Ocean stratification (Jaccard et al., 2005)

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)

1. Documented CO₂ increase in atmosphere
   
   • increase of CO₂ concentration by 11% since 1958,
     annual cycle of photosynthesis apparent (damped in S. hemisphere)
     
     (Keeling et al., 1989)
   • annual flux largest June at 60^oN
     
   • major sources industrial, major sinks biotic: oceanic, tropical forest
     
   • CO₂ increase since 1880 documented by trapped gas and ¹⁴C anomalies
     
     
2. However, calculations from burning of fossil fuels and land clearance indicate that CO₂ increase should be twice as great.
   
   • increased photosynthesis? LaMarche, 1984 argues for increased growth rate of trees in the White Mountains due to greater CO₂ concentration
     
   • ocean mixed layer? circulation so slow that radiocarbon and fossil fuel inputs not yet in equilibrium with oceanic current circulation (Brewer 1989)
     
3. Is there Meteorological Evidence for warming?
   Jones et al. (1986) document a global increase in world temperature since 1910.
   
   • Due to urban island effects? No, urban centers not included (Jones et al. 1989 ; Karl et al., 1988)
     
   • Other causes? Increased solar irradiance? (Foukal 1990)
     

     Greenhouse vs. Solar: (Crowley, 2000.) (Haigh, 1996.) (Kromer et al., 2004.)

     Historic global temperature change American Institute of Physics
4. Potential Effects
   
   • Sea Level will increase 1-2 m next century,
         has risen 10-20 cm last century (Peltier and Tushingham, 1989)
         primarily increased SST, Alaskan, Andean Glaciers (Rignot et al., 2003)
     
   • Agriculture (crop failures)
     
5. Predicting the Effects
   
   • Models
     
     • Temperature: models agree - increase greatest at poles
       
     • Precipitation: variable results - particularly at mid-latitudes
       
   • Ancient Analogs
     
     • Precambrian, Cretaceous,
       
     • Pliocene (Funder et al., 1985; Valichecko et al. 1993; Miriwaki et al, 1992)
       
     • Early Holocene, Medieval Warm Period, 1920's "dust bowl"