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Announcements

Announcements. OUTLINE OF YOUR PAPER IS DUE ONE WEEK FROM TODAY! If you have not signed up for a topic (and have chosen one of us as your mentor), do so immediately! 15% of your final grade is based on the midterm, which is the first draft of your paper – DUE OCTOBER 23 !!. Climate Change.

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Announcements

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  1. Announcements • OUTLINE OF YOUR PAPER IS DUE ONE WEEK FROM TODAY! • If you have not signed up for a topic (and have chosen one of us as your mentor), do so immediately! 15% of your final grade is based on the midterm, which is the first draft of your paper – DUE OCTOBER 23!!

  2. Climate Change 3rd “Cosmology” physics lecture PHYS120

  3. The climate seems to be changing: IPCC Report 4 Nov 2007 Extension of the Arctic Ice Cap

  4. Most of this is not really controversial (anymore) + AAAS, APS, NAS, AMS,… 1917 2005 Pedersen Glacier (Alaska)

  5. At the same time, CO2 has increased due to human activity ice core record “Keeling Curve”

  6. Is there a connection? But: Correlation ≠ Causation What does Physics tell us?

  7. Energy Content of the Atmosphere Source: Insolation Sinks IR outgoing radiation All directions, day and night Depends on T => Equilibrium Influenced by clouds, gases… Heating of land surface Heating of oceans Melting and Evaporation last 3 ultimately feed back into atmosphere • Total of radiation from the sun: 1,366 W/m2 (const±0.1%) • Incoming flux minus reflected flux (Albedo ≈ 30%) • Dayside only; cos(q-qZenith) • Heat from radioactive decays in Earths mantle is minimal • Other sources are miniscule If “in” > “out”: Energy content increases. Possible consequences are temperature increase, increase in water vapor, more wind, …

  8. Possible Effects of Human Activity Albedo IR emission Direct: CO2 Methane Other gases, particulates Indirect: Cloud cover water vapor gases escaping permafrost Possible Effects OUTSIDE of Human Activity: • Volcano eruptions • Variations of solar output (small) • non-human influences on cloud formation (e.g. cosmic radiation?) • Secular changes in Earth’s orbit(correlation between orbit and tilt of axis; possible effects of galactic dust clouds;…)=> Ice Ages! • Direct: • Land use • Particulates in air and on the ground (“dark ice”) • Indirect: • Cloud cover • Snow cover, glaciers Hugely complicated, coupled system. Requires highly sophisticated climate models to understand. We’ll look into only ONE aspect…

  9. Thermal IR Radiation • Main terrestrial sources: surface, atmosphere • wave lengths 5-50 µm • Emission intensity ~ T4 • Local Thermal Equilibrium: molecules absorb IR => excited rotational/vibrational states => collisions redistribute energy => gas warms • Complicated layering of temperatures in the atmosphere depending onabsorption and emission

  10. Absorption at specific frequencies (lines) with hn = DE (energy levels in molecules BUT Doppler broadening (T) and collisional broadening (r) increase absorption “window” -> hence even increase beyond “saturated” CO2 density leads to increased absorption 15 µm

  11. Possible Scenarios

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