Corrected EES 108 Class 06

# Corrected EES 108 Class 06 - Temperature of Earth Steady...

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Temperature of Earth Steady temperature: Heat in must balance heat out Heat = Intensity × Area Heat in:  – Intensity = Solar constant × (1- Albedo) Does not depend on earth’s temperature Area: sun only shines on half the planet Heat out:  – Intensity from Stefan-Boltzmann – Intensity =  σ T 4 Area: longwave radiation from the whole planet T adjusts until heat in = heat out

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Earth’s equilibrium temperature Energy balance: Heat in = Heat out Heat in = absorbed sunlight Solar constant × Area × (1 – Albedo) Heat out = infrared radiation σ T 4  × Area S 0  (1– A ) = 4 σ T 4 After a little algebra… 4 0 4 ) 1 ( σ S A T - = Don’t worry about  memorizing this equation Helpful hint: To take a fourth root on  your calculator, just press  the square root key twice! S 0  = solar constant A = albedo
Earth, Mars, Venus Earth Mars Venus Solar Constant 1370 W/m 2 590 W/m 2 2610 W/m 2 Albedo 0.30 0.22 0.75 Calculated  Temperature 255 K 0°F 217 K -70°F 232 K -40°F Actual Surface  Temperature 288 K 59°F 220 K -64°F 730 K 850°F

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Earth, Mars, Venus Comments Venus has 280,000 times as much CO 2  as Earth  does. Mars has only 6% as much air as Earth does; CO 2   but no water vapor Earth Mars Venus Solar Constant 1370 W/m 2 590 W/m 2 2610 W/m 2 Albedo 0.30 0.22 0.75 Radiative  Temperature 255 K 217 K 232 K Greenhouse  Warming 33 K 3 K 498 K Surface  Temperature 288 K 220 K 730 K
Sahara Mediterranean Antarctic Seen from space,  earth’s average  infrared emission

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## This note was uploaded on 04/09/2008 for the course HIST 101 taught by Professor Guliver during the Spring '08 term at Vanderbilt.

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Corrected EES 108 Class 06 - Temperature of Earth Steady...

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