Evolution of Earth’s 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

FTOA

< Ts4 >

G = < Ts4> - FTOA Wm-2

g = < Ts4>/FTOA

Greenhouse Effect (Energy)

Greenhouse Efficiency

Greenhouse Effect: G or g Convolves a number of relevant climatic

variables: Temperature Water Vapor Clouds Trace Gases {CO2, CH4, …}

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 (1870-2000)

Ammann et al.

1.0

1.2

1.4

1.6

1.8

2.0

Neoprot Cretaceous Eocene LGM Holocene Present

Greenhouse Effect

Time Period

Obs. Collins(2003)

< Ts4> = 17,002 Wm-2

S = S0(1-p)/4 = F= 185 Wm-2

G = 16,817 Wm-2

g = 92

Venus

Earth

< Ts4> = 402 Wm-2

F = 239 Wm-2

G = 163 Wm-2

g = 1.7

< Ts4> = 133 Wm-2

Mars

S = S0(1-p)/4 = F= 123 Wm-2

G = 10 Wm-2

g = 1.1

Whither the Future?

FALL 2003 AGU SESSIONon

Evolution of Earth’s Greenhouse