Global Warming: or Thermal Management on the Big Spaceship

1. Global Warming: or Thermal Management on the Big Spaceship Lecture #22 Space concepts

2. The Big Spaceship

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

4. Blackbody Radiation Curve

5. Black Body Radiation Curve

6. 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 ,  >1 for real surfaces • =5.76x 10 –8 Wm –2 K-4 • ( Stefan-Boltzmann constant)

7. Solar Spectrum

8. 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

9. Kirkhoff’s Law • Energy balance Poynting’s theorem

10. Radiant equilbrium Planetary radiance Sunlight Infrared Energy arrives at visible frequencies and is radiated at infrared frequencies Gaussian surface

11. Radiation Equibrium

12. Heat Transport Thermal Conduction: Heat transport from hot to cold Heat flows downhill

13. Thermal Conduction Heat flows downhill

14. 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.

15. Molecular Thermal Transport Downward flux of enthalpy h= cpT Net flux  Upward flux of enthalpy h= cpT

16. 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.

17. Radiation Thermal Transport Downward flux of energy E= cp (T’)T’ p Net flux Upward flux of enthalpy E= cp(T)T

18. Thermal Photon Diffusivity Diffusivity is lowered by increased CO2!!

19. Greenhouse Effect

20. about 5×10^-22 m^2 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

23. Reflected Sunlight Emitted Thermal

24. Thermal Emission CO2 emission and absorption band

25. 25% increase CO2 levels in the atmosphere

26. Oxygen levels

27. Icecaps are melting

28. UK government data

29. NOAA Satellites

30. Solar Radiance

32. 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

33. 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

34. 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