Lecture_14_Global_Energy_Balance

# Lecture_14_Global_Energy_Balance - Earths temperature...

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1 Earth’s temperature • Blackbody radiation • Global Energy Balance Energy absorbed by the earth (light from the sun) = Energy emitted by the earth (infrared) • Global Energy Balance with Albedo • Greenhouse effect • Feedbacks – Ice-albedo feedback (positive) – Water vapor feedback (positive)

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2 Blackbody radiation Energy emitted by an object depends on temperature. Energy Flux [W/m 2 ] = Energy/(Time x Area) = σ T 4 where σ = constant = 5.67x10 -8 W/(m 2 K 4 ) 1 W= 1 Joule/second (Energy/time) T is temperature in K
3 wavelength proportional to 1/T: λ max = 2898/T, where λ is in μ m (10 -6 m)

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4 Object A and B are black spheres of the same size. Object A has a temperature of 2 K, and object B has a temperature of 4K. The rate at which energy is emitted from object B (E B ) is 1. E B = E A x 2 2. E B = E A x 4 3. E B = E A x (4 4 /2 4 ) 4. E B = E A x (2 4 /4 4 )
5 Object A and B are black spheres of the same size. Object A has a temperature of 2 K, and object B has a temperature of 4K. Object A emits electromagnetic radiation with ___________ than object B. 1. Longer wavelengths 2. Higher energy 3. Higher frequency 4. Higher speeds

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6 Object A and C are black spheres of the same temperature. Object A has a radius that is twice that of object C. The rate at which energy is emitted from object A (E A ) is 1. E A = E C x 2 2. E A = E C x 4 3. E A = E C / 2 4. E A = E C / 4
7 Solar radiation = light = “shortwave” radiation Earth radiation = infrared = “longwave” radiation

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8 • Rate at which energy is emitted by the sun [W]
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Lecture_14_Global_Energy_Balance - Earths temperature...

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