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causes of the greenhouse effect

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					Astro 2037 Spring 07, Lecture 16

Greenhouse Effect Causes Temperature Increase on both Earth and Venus




   Greenhouse Effect: the trapping of infrared radiation by a planet’s
   atmosphere (mainly by CO2 and H2O absorption and re-radiation)
Water, Carbon Dioxide, Methane and Other Molecules Have
Strong Absorption Bands in the Infrared for Absorbing Infrared
Photons




                                        20 m 10 m
The greenhouse effect on Earth is SELF – REGULATING !
      Carbonate – Silicate Cycle ( Self- regulating mechanism )


Temperature Increases              More Water Vapor (moisture)
                                        in the atmosphere


 Less CO2 removed
                                  Increase in Rainfall and runoff
 because of reduced
    weathering                                        Increased
                                                      weathering
                                     More CO2 removed from
  Decrease in the
                                           atmosphere
 amount of rainfall


 Less Water Vapor                      Temperature drops due to
 in the atmosphere                     reduced greenhouse effect
Comparisons of Actual Temperatures and “No Greenhouse”
Temperatures for Venus, Earth, and Mars
Runaway Greenhouse Effect Causes Venus to be Extremely Hot
                     (Inhabitable!)
 • Proximity of Venus to the Sun and large amounts of CO2 causes the global
 temperature to be higher than Earth. Water is vaporized and absorbs additional
 solar radiation to further increase its temperature. Eventually, all of water
 becomes vaporized. This phenomenon is called a Runaway Greenhouse
 effect
 • Water vapor rises high enough to be broken apart (photo-dissociated) by high
 energy ultraviolet radiation from the sun




The hydrogen atoms would escape from the planet’s gravitation field since
they have so little mass, while the heavier oxygen atoms would remain behind.
Illustration of how to turn the Earth into Venus by placing it at at
the Venus’s distance, the runaway greenhouse effect causes the
oceans to evaporate completely
 On Earth, CO2 content in the air is regulated by the Carbon
 Dioxide Cycle (the carbonate-silicate cycle, or the inorganic
 carbon cycle) to avoid runaway Greenhouse effect


                                               • The cycle is about
                                               400,000 years
                                               • The CO2 cycle acts as a
                                               thermostat
                                               • If the earth warms up
                                               slightly, carbonate minerals
                                               form in the oceans at a
                                               more rapid rate and takes
                                               away more CO2

Limestone
rocks
The Boundary of the Sun’s Habitable Zone Today
Global Temperature Increase may Cause a Runaway Greenhouse
Effect!

				
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