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)
Astro 2037 Spring 07, Lecture 16
Water, Carbon Dioxide, Methane and Other Molecules Have
Strong Absorption Bands in the Infrared for Absorbing Infrared
Photons
10 m
20 m
The greenhouse effect on Earth is SELF – REGULATING !
Carbonate – Silicate Cycle ( Self- regulating mechanism )
Temperature Increases
More Water Vapor (moisture)
in the atmosphere
Increase in Rainfall and runoff
Increased
weathering
More CO2 removed from
atmosphere
Temperature drops due to
reduced greenhouse effect
Less Water Vapor
in the atmosphere
Decrease in the
amount of rainfall
Less CO2 removed
because of reduced
weathering
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
Limestone
rocks
• The cycle is about
400,000 years
• The CO2 cycle acts as a
thermostat
• If the earth warms up
slightly, carbona