Global Warming: or Thermal Management on the Big Spaceship

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Global Warming or Thermal Management on the Big
Spaceship

• Lecture 22
• Space concepts

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The Big Spaceship
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Agenda

• Planetary temperatures
• Venus
• Earth
• Is Global Warming Real?
• What is driving it?
• A Simple Model
• Solutions

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Blackbody Radiation Curve
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Black Body Radiation Curve
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Blackbody radiation

• If a body absorbs and radiates EM radiation
  perfectly, it is called a blackbody
• It then radiates power by the Stefan Boltzman Law
  W/m2 ??T4
• ?emissivity, 1 for a black body , ? gt1 for real
  surfaces
• ?5.76x 10 8 Wm 2 K-4
• ( Stefan-Boltzmann constant)

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Solar Spectrum
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Space Thermal Radiation problems

• Spacecraft receive and radiate heat by blackbody
  radiation
• They receive radiation in the visible
• .5-micron because the sun is hotter than they
  are ( 10,000K)
• They radiate at much lower temperature 300K
  peak radiation 10microns

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Kirkhoffs Law

• Energy balance Poyntings theorem

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Radiant equilbrium
Planetary radiance
Sunlight
Infrared
Energy arrives at visible frequencies and is
radiated at infrared frequencies
Gaussian surface
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Radiation Equibrium
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Thermal Conduction Heat transport from hot to
cold
Heat flows downhill
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Thermal Conduction
Heat flows downhill
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Molecular Mean Free Path
Mean free path ?
A mean free path is the scale size on which
molecules mix and transport energy, momentum in
a gas.
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Molecular Thermal Transport
Downward flux of enthalpy h cpT
Net flux
?
Upward flux of enthalpy h cpT
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Photon Mean Free Path
photon
molecule
Photon Mean free path ?p
A photon mean free path is the scale size on
which photons of a given wavelength are absorbed
and reradiated and transport energy in a gas.
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Radiation Thermal Transport
Downward flux of energy E cp (T)T
?p
Net flux
Upward flux of enthalpy E cp(T)T
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Thermal Photon Diffusivity
Diffusivity is lowered by increased CO2!!
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Greenhouse Effect
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about 510-22 m2 per molecule 5 x 10-18cm2 3
x1019 cm3 molecles x 300 x10-6 co2 9x10 15 cm3
1/(sig n) 1/(5 x 10 -18 cm2 x 9 x10 15 cm3 )
1 /(.45 x 10-1) 20 cm mean free path at 15
microns
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CO2 levels in the atmosphere
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Oxygen levels
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Icecaps are melting


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UK government data
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NOAA Satellites
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Solar Radiance
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Global Warming and Causes

• Global warming appears to be a fact, temperatures
  are rising especially since 1980
• Solar radiance for the last decade appears flat
  or decreasing
• Volcanic activity , indicating geothermal
  heating, appears flat or decreasing
• Green House gases are rising appearing to
  correlate with warming

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Conclusions

• Global warming appears to be a reality
• Global warming appears principally driven by
  decreased infrared diffusivity in the atmosphere
  due to increased greenhouse gases-other
  explanations do not appear viable
• Global warming, if unchecked, could have very
  negative consequences for the human race

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Solutions

• Humanity must shift from fossil fuels to nuclear
  power and other non-greenhouse producing forms of
  energy.
• France and Japan have converted to 80 nuclear
  Fission it is both possible and practical
• Fusion power , cleaner and safer than Fission ,
  can replace all fossil fuels