vii climate change blackbody model windows and saturation feedbacks aerosols l.
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VII. Climate Change Blackbody model Windows and saturation Feedbacks Aerosols. Blackbody model. Energy In = Energy Out Energy In = 1368 W/m 2  Earth cross-section  (1-reflectivity) Energy Out = Earth surface Area  s SB  T earth 4 s SB is Stefan-Boltzmann constant

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blackbody model

Blackbody model

Energy In = Energy Out

Energy In = 1368 W/m2  Earth cross-section  (1-reflectivity)

Energy Out = Earth surface Area  sSB Tearth4

sSB is Stefan-Boltzmann constant

Tearth = 255 K ignores clouds and greenhouse gases

slide6
CO2

Concentration increasing, seasonal variation

Absorptions are nearly saturated

saturation

Strong CO2 absorptions almost saturated.

Window regions between strong absorbances:

Activity: model greenhouse gases X and Y

a) Consider [Y] = 2.5 x 1013 molecules cm-3

at l1 in IR, sY = 1 x 10-19 cm2 molecule-1

What is A(l1), the absorbance at l1 ?

b) Add [X] = 2.5 x 1011 molecules cm-3

at l1 in IR, sX = 4 x 10-18 cm2 molecule-1

at l2 in IR, sX = 1 x 10-18 cm2 molecule-1

What is the total A(l1) and what is A(l2)?

c) Does the addition of X reduce heat emission more at l1 or l2?

Saturation

slide8

Human Affects on Radiation Budget

Global mean radiative forcing of climatefor year 2000 relative to 1750 (IPCC)

slide9

Greenhouse Gases

See Coursepack Section E Table 3

Seinfeld and Pandis Figures 21.17-19

Instantaneouse Radiative Forcing (IRF)

of a compound (Watts m-2 kg-1)

Absolute Global Warming Potential (W m-2 kg-1 yr)

slide10

Greenhouse Gases

Global Warming Potential (w/respect to CO2)

(dimensionless)

slide11

Key Points

  • Radiative balance is complicated
  • Greenhouse Gas effect real, global
  • Greenhouse Gas effects not isolated
    • - feedbacks with biosphere
    • - feedback with geosphere
  • Aerosol effects messy, local (temporary)
  • Climatic effects hard to see (weather)