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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
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

Climate Change

3rd “Cosmology” physics lecture PHYS120

the climate seems to be changing
The climate seems to be changing:

IPCC Report 4 Nov 2007

Extension of the Arctic Ice Cap

most of this is not really controversial anymore
Most of this is not really controversial (anymore)

+ AAAS, APS, NAS, AMS,…

1917

2005

Pedersen Glacier (Alaska)

is there a connection
Is there a connection?

But: Correlation ≠ Causation

What does Physics tell us?

energy content of the atmosphere
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, …

possible effects of human activity
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…

thermal ir radiation
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
slide10

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