Evolution of Earths Greenhouse Effect Jeffrey T. Kiehl National Center for Atmospheric Research 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? Greenhouse Effect F TOA G = - F TOA Wm -2 g = /F TOA Greenhouse Effect (Energy) Greenhouse Efficiency Greenhouse Effect: G or g Convolves a number of relevant climatic variables: Temperature Water Vapor Clouds Trace Gases {CO 2, CH 4, } 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 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 ( ) Ammann et al. Obs. Collins(2003) = 17,002 Wm -2 S = S 0 (1- p )/4 = F= 185 Wm -2 G = 16,817 Wm -2 g = 92 Venus Earth = 402 Wm -2 F = 239 Wm -2 G = 163 Wm -2 g = 1.7 = 133 Wm -2 Mars S = S 0 (1- p )/4 = F= 123 Wm -2 G = 10 Wm -2 g = 1.1 Whither the Future? FALL 2003 AGU SESSION on Evolution of Earths Greenhouse