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Evolution of Earth’s Greenhouse Effect

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Evolution of Earth’s Greenhouse Effect

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  1. Evolution of Earth’s Greenhouse Effect Jeffrey T. Kiehl National Center for Atmospheric Research

  2. Outline • What is the Greenhouse Effect? • Forcings over Geologic Time • Sources to Estimate Greenhouse Effect • Evolution of Greenhouse Effect • Comparison to Neighboring Planets • Whither the Greenhouse Effect?

  3. Greenhouse Effect FTOA <s Ts4 >

  4. Greenhouse Effect (Energy) G = <s Ts4> - FTOA Wm-2 Greenhouse Efficiency g = <s Ts4>/FTOA

  5. Greenhouse Effect: G or g • Convolves a number of relevant climatic variables: • Temperature • Water Vapor • Clouds • Trace Gases {CO2, CH4, …}

  6. Forcings over Geologic Time • Solar Insolation • Luminosity • Interplanetary Dust? • Milankovitch S(t,) • Atmospheric Composition • Carbon Dioxide & Methane • Volcanic Aerosols • Paleogeography • Orography • Positions of Continents • Ocean Basins • Ocean Bathymetry

  7. Sources of Greenhouse Effect • Neoproterozoic (~600 MYA) • Pavlov and Kiehl, Chandler & Sohl • Cretaceous (~70 MYA) • Otto-Bliesner et al. • Eocene (~55 MYA) • Huber and Sloan • Last Glacial Maximum (~18,000 y b.p.) • Otto-Bliesner et al. • Holocene (~3,500 y b.p.) • Otto-Bliesner et al. • Modern (1870-2000) • Ammann et al.

  8. Obs. Collins(2003)

  9. Venus <s Ts4> = 17,002 Wm-2 S = S0(1-ap)/4 = F= 185 Wm-2 G = 16,817 Wm-2 g = 92

  10. Earth <s Ts4> = 402 Wm-2 F = 239 Wm-2 G = 163 Wm-2 g = 1.7

  11. Mars <s Ts4> = 133 Wm-2 S = S0(1-ap)/4 = F= 123 Wm-2 G = 10 Wm-2 g = 1.1

  12. Whither the Future?

  13. FALL 2003 AGU SESSION on Evolution of Earth’s Greenhouse