The Faint Young Sun Problem Part 1:CO2 Feedbacks

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The Faint Young Sun ProblemPart 1CO2 Feedbacks
Abiol 574
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Solar Luminosity versus Time
See The Earth System, ed. 2, Fig. 1-12
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Stellar Nucleosynthesis
Wikipedia http//commons.wikimedia.org/wiki/Image
FusionintheSun.png
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Stellar NucleosynthesisNet Reaction
4H ? He energy
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Stellar NucleosynthesisEvolution

• As time goes by, more H is converted into He
• He atoms take up less space than 4 H atoms
• The Suns core contracts and heats up
• This causes the reaction to go faster
• And leads to more energy being produced!

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Solar Luminosity versus Time
See The Earth System, ed. 2, Fig. 1-12
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Ice age (Pleistocene)
Dinosaurs go extinct
Phanerozoic Time
First dinosaurs
Ice age
First vascular plants on land
Ice age
Age of fish
First shelly fossils
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Geologic time
First shelly fossils (Cambrian explosion)
Snowball Earth ice ages
Warm
Rise of atmospheric O2 (Ice age)
Ice age
Warm (?)
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• The Sun was 30 less bright at the time that
  the Solar System first formed
• This would have have caused a significant
  reduction in planetary surface temperatures
• ?Te4 S (1 A)
• 4
• Ts Te ?Tg

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Possible solutions to the FYS problem

• Think back to the planetary energy balance
  equation
• ?Te4 S (1 A)
• 4
• What factors might change?

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Possible solutions to the FYS problem

• Think back to the planetary energy balance
  equation
• ?Te4 S (1 A)
• 4
• Albedo changes? Unlikely..
• Hard to have decreased cloudiness on a warm early
  Earth
• Geothermal heat?
• Too small (0.06 W/m2 vs. 240 W/m2 from absorbed
  sunlight

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Possible solutions to the FYS problem

• An increase in the greenhouse effect is the most
  likely solution
• Ts Te ?Tg
• What greenhouse gases might have been more
  abundant on the early Earth?

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Possible solutions to the FYS problem

• Increasing the greenhouse effect also works
• Ts Te ?Tg
• Possible greenhouse gases
• NH3 Doesnt work (photolyzes rapidly)
• CO2 Works! (supplied by volcanoes)
• CH4 Also works (probably requires life)
• Important to understand climate feedbacks

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The Faint Young Sun Problem
Kasting et al., Scientific American (1988)
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Systems Notation
system component
positive coupling
negative coupling
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Positive Feedback Loops(Destabilizing)
Water vapor feedback
Surface temperature
Atmospheric H2O
()
Greenhouse effect
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The faint young Sun problem
More H2O
Less H2O
Kasting et al., Scientific American (1988)
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Positive feedback loops(destabilizing)
Snow/ice albedo feedback
Surface temperature
Snow and ice cover
()
Planetary albedo
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The Carbonate-Silicate Cycle
(metamorphism)

• Silicate weathering slows down as the Earth
  cools
• ? atmospheric CO2 should build up

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Negative feedback loops(stabilizing)
The carbonate-silicate cycle feedback
Rainfall
Surface temperature
Silicate weathering rate
(-)
Atmospheric CO2
Greenhouse effect
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CO2 vs. time if no other greenhouse gases
(besides H2O)
Snowball Earth events
J. F. Kasting, Science (1993)
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Future Climate Evolution
0 0.4 1.2
1.6
Solar luminosity
Surface temperature/ atmospheric CO2
Kump et al., The Earth System (2002), Fig. 19-1
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Some say the world will end in fire, Some say in
ice. From what I've tasted of desire I hold
with those who favor fire. But if it had to
perish twice, I think I know enough of hate To
say that for destruction ice Is also great And
would suffice. -Robert Frost