1. Global Warming and the Venus Greenhouse Effect
11 October 2017

2. Venus: Global warming gone bad

3. Earth & Venus: Sister planets?
Mass
5x1024 kg
6x1024 kg
a (semi-major axis)
0.7 AU
1 AU
T at surface
~750 K
~300 K
P at surface
~90 atm
~1 atm
atm composition
N2 and H2O clouds
CO2 and H2SO4 clouds
What is the boiling Temp of water?

4. Terrestrial Planet Atmospheres
Table 10.1
Terrestrial Planet Atmospheres
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5. How do we know Venus’s surface temperature?

6. How do we know Venus’s surface temperature?
low energy
long wavelength
“redder”
cold
high energy
short wavelength
“bluer”
hot

7. How do we know Venus’s surface temperature?
the Sun emits light here. T=6000 K
Earth emits light here. T=300 K
Venus emits light here. T=750

8. Wavelength of light (in the infrared)
How do we know what the clouds are made of?
Spectrum of planet with no atmosphere
Amount of light observed above the atmosphere
Wavelength of light (in the infrared)

9. How do we know what the clouds are made of?
Spectrum of planet with no atmosphere
Spectrum of planet with atmosphere
Amount of light observed above the atmosphere
Amount of light observed above the atmosphere
Wavelength at which a molecule in the atmosphere absorbs light
Wavelength of light (in the infrared)
Wavelength of light (in the infrared)

10. How do we know what the clouds are made of?
(Infrared light)

14. Two views: Venus atmosphere Figure 10.31
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16. Table 10.2
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17. Figure 10.18
Climate change causes
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18. Figure
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19. Figure
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20. Figure
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21. Figure 10.21
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22. Figure 10.37
Global warming since 1880
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23. CO2 over last 800,000 years Figure 10.38
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24. Figure 10.39
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25. Pink: Melting ice in Greenland!
Figure 10.41
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Pink: Melting ice in Greenland!

26. How did Venus get so hot?
Remember - all gases absorb light at specific wavelengths.
“Greenhouse” gases (like carbon dioxide, water and methane) like to absorb in the infrared wavelengths.
Planets emit light at infrared wavelengths (same as human bodies).
Conclusion? “Greenhouse” gases don’t lett the heat from the planet escape.

27. A planet with no atmosphere
How did Venus get so hot?
A planet with no atmosphere
Solar radiation comes in
Planetary radiation goes out
Planetary surface

28. A planet with an atmosphere
How did Venus get so hot?
A planet with an atmosphere
Solar radiation comes in
The greenhouse gases reradiate. Some of the energy goes towards the surface.
Planetary radiation goes out, but gets absorbed
Greenhouse gases
Planetary surface

29. How do greenhouse gases get into the atmosphere?
Water: evaporation
CO2: vaporization of rocks, release from traps, vaporization of biotic material (like fossil fuels), respiration
Methane: release from traps, biology (bacteria, cows, rice)

30. Venus is an example of a “runaway greenhouse”.
greenhouse gases heat the surface of the planet
rocks and water vaporize and release greenhouse gases
Why was Venus hot in the first place?

31. Earth was also a “runaway greenhouse” at one point!
greenhouse gases heat the surface of the planet
rocks and water vaporize and release greenhouse gases

32. Why did the Earth cool, but Venus stay so hot?

33. Figure 10.32
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34. Why did the Earth cool, but Venus stay so hot?
Ideas: Oceans?
Biology?
It probably has to do with water, but why the Earth has water and Venus doesn’t is not well understood. It MAY be that water allowed plate tectonics to occur, and when the oceanic plates subduct, they take CO2 with them.

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36. The Surface of Venus
Venus’s surface can’t be viewed in visible light. The atmosphere absorbs most visible light.
Radio light reaches the surface.

37. Venus’s surface was mapped with RADAR.
RADAR instrument
surface
RADAR instruments can map topography.

38. Venus’s surface was mapped with RADAR.
RADAR instrument
smooth surface
rough surface
RADAR instruments can determine roughness.

39. Venus’s surface was mapped with RADAR.
RADAR instrument
Reflective surface
Absorptive surface
RADAR instruments can determine reflectivity.

40. Venus’s has few small craters. Why?
Venus’s has few large craters. Why?

41. Venus’s has few small craters. Why?
Venus has a dense atmosphere.
Venus’s has few large craters. Why?
Venus’s surface is ‘young’.

42. How are craters on Venus different from craters on other bodies?
the moon
Venus

43. Venus’s surface is covered with volcanic features.
How can you tell impact craters from volcanic calderas?
What does the brightness mean in these images?

44. Venus’s surface is covered with volcanic features.
Few craters have been altered by lava.
What does this mean?
If lava lies over an existing crater, then the crater came first.

46. Venus: Take-away messages
Venus’s bulk properties (mass, size, distance from sun) are similar to Earth.
However, Venus’s atmosphere has a lot of CO2 and therefore its surface is very hot.
Exactly why Venus and Earth evolved in different ways is not well understood, but is probably related to water.
Volcanism is an important process on its surface, but may not have been active recently.
Venus’s entire surface is ‘young’, so some global resurfacing event occurred.