Ozone

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Radiation balance for Earth (bare Earth model)
Solar Insolation Iinput 1350 W/m2

• Iin flux of solar energy directed at Earth
• Total surface area of Earth that emits IR light
  4pr2
• BUT surface of Earth directed at Sun to receive
  light pr2
• Fraction of incident radiation fully reflected
  (albedo a) 30
• Accounting for these
• Input flux Fin (W) Iin(1-a)pr2earth (rearth
  6.37 x 106 m)
• Output flux Fout (W) Iout (4pr2earth)
• Treat Earth as a blackbody
• Blackbodies radiate energy by the
  Stefan-Boltzmann law I esT4
• where s 5.7 x 10-8 W/m2-K4

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Bare Earth model
For Iin 236 W/m2 (Earth), then Tearth
255K (236 W/m2 is the solar insolation constant)
BUT average Earths surface T 288K (15C) ?
some heat is trapped NATURAL GREENHOUSE EFFECT
WARMS EARTH BY 33K ATMOSPHERE FUNCTIONS AS AN
INSULATOR
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Bare rock model, no atmosphere
Bare rock atmosphere
l 10,000 nm
l 500 nm
What happens when we add the atmosphere into the
model?
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Solar energy transfer is mediated by water
evaporation, movement, condensation, and
release of latent heat
adiabatic expansion in a convection
column (-6.5C/km w/ water condensation lapse
rate) DHcond mitigates lapse rate
The lapse rate helps to modulate the greenhouse
effect (radiative-convective equilibrium)
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Radiation balance for Earth
100 units corresponds to 54.4 x 1020 kJ/yr
Albedo of reflected radiation from
Earths surface varies widely from 2-90
Global albedo of 30 reflection by clouds
reflection by atmosphere reflection from
Earth surface Absorbed by Earth (heating Earth)
44 Absorbed by atmosphere (heating atmosphere)
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Radiation balance for Earth
Heat balance on the atmosphere
Influx of solar energy minus reflection

• Maintain energy balance 70 of input solar
  energy (that is not reflected)
• must be radiated out (at IR wavelengths)
• Because of the greenhouse effect, more energy is
  in circulation in the
• outgoing IR absorbing gases (H2O, CO2, etc)
  reradiate in all directions
• (Earth emits 115 units heat balance requires
  70 units output)

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THE BASIS FOR THE GREENHOUSE EFFECT LIES IN
INFRARED SPECTROSCOPY
Possible different quantized electron
transitions are shown by vertical
arrows Within each electronic state, there
are closely spaced vibrational states with
energy differences in the infrared
range Within each vibrational state there are
closely spaced rotational states with energy
differences in the microwave range
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Vibrational spectroscopy Bonds can be thought of
as springs connected to two masses The
stiffness of the spring is the force constant
of the bond The lowest energy position is the
equilibrium bond distance moving the atoms
closer together or farther apart increases the
energy.

• O2, N2 and Ar are unable to absorb IR light
• argon is monatomic and has no bond stretching or
  angle stretching frequencies
• absorption requires a change in dipole moment
  (O2, N2 lack a dipole)
• Heteronuclear diatomic gases (CO, NO) have a
  dipole, but are present at
• too-low concentration to influence greenhouse
  heating

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Infrared absorptions for H2O and CO2
667 cm-1
2350 cm-1
X
X
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Effect of greenhouse gases on Earths IR emissions
300
280
atmospheric window (no absorbing gases)
near tropopause (coldest light)
saturated at center of band
for methane, some absorption, but not saturated
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atmospheric window
corresponds to 667 cm-1
Effect of CO2 is that much of the outgoing IR
centered around l 15 mm gets absorbed and
reradiated. The incremental effect is small for
each additional CO2, because much of that
outgoing radiation is already absorbed
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Effects of progressive CO2 addition to the
Earths IR emissions
No CO2
10 ppm CO2
1000 ppm CO2
100 ppm CO2
Response of IR emission to CO2 is not
linear instead it is logarithmic (incremental
decrease is proportional to the amount already
there)
-doubling of CO2 concentration, in any range,
decreases Iout by the same amount
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Atmosphere with no CO2
Addition of greenhouse gas (CO2)
Radiation balance reestablished by increasing
temperature on the ground
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Model-dependent temperature sensitivity to CO2
increase
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Other greenhouse gases CFCs, methane, nitrous
oxide
?
Radiative forcing per molecule
The atmospheric window where much of the
reradiated IR is not absorbed is between
about 8 13 mm. CFCs and CFC replacements,
unfortunately, absorb in this window Relative
global warming efficiency relates to (i)
persistence (ii) extent to which there is
already much absorbance in a particular window

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Long-term fate of atmospheric CO2 following a
large release from fossil fuel burning
Climatic Change 90, 283-297 (2008)