VII. Climate Change Blackbody model Windows and saturation Feedbacks Aerosols.
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Transcript of VII. Climate Change Blackbody model Windows and saturation Feedbacks Aerosols.
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VII. Climate Change
Blackbody modelWindows and saturationFeedbacksAerosols
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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 SB Tearth
4
SB is Stefan-Boltzmann constant
Tearth = 255 K ignores clouds and greenhouse gases
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Energy Balance beyond Blackbody
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Earth’s IR Emissions
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Energy Balance beyond Blackbody
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CO2
Concentration increasing, seasonal variationAbsorptions are nearly saturated
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Saturation
Strong CO2 absorptions almost saturated.Window regions between strong absorbances:
Activity: model greenhouse gases X and Ya) Consider [Y] = 2.5 x 1013 molecules cm-3
at 1 in IR, Y = 1 x 10-19 cm2 molecule-1 What is A(1), the absorbance at 1 ?
b) Add [X] = 2.5 x 1011 molecules cm-3
at 1 in IR, X = 4 x 10-18 cm2 molecule-1
at 2 in IR, X = 1 x 10-18 cm2 molecule-1
What is the total A(1) and what is A(2) ?
c) Does the addition of X reduce heat emission more at 1 or 2?
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Global mean radiative forcing of climatefor year 2000 relative to 1750 (IPCC)
Human Affects on Radiation Budget
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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)
t
t
t
dttIRFAGWP
etIRFtIRF
0
/
)(
)0()(
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Greenhouse Gases
Global Warming Potential (w/respect to CO2)
(dimensionless)
t
t
tCO
t
t
ti
t
t
CO
t
t
i
dtetIRF
dtetIRF
dttIRF
dttIRF
iGWPCO
i
0
/2
0
/
0
2
0
2)0(
)0(
)(
)(
)(
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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)