VII. Climate Change Blackbody model Windows and saturation Feedbacks Aerosols

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# VII. Climate Change Blackbody model Windows and saturation Feedbacks Aerosols - PowerPoint PPT Presentation

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

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

### Energy Balance beyond Blackbody

CO2

Concentration increasing, seasonal variation

Absorptions are nearly saturated

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

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

Greenhouse Gases

See Coursepack Section E Table 3

Seinfeld and Pandis Figures 21.17-19

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

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

Greenhouse Gases

Global Warming Potential (w/respect to CO2)

(dimensionless)

Key Points