Consider a simple model in which Earth’s surface temperature is uniform and remains constant. In order to maintain therm

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Consider a simple model in which Earth’s surface
temperature is uniform and remains constant. In order to maintain
thermal equilibrium, Earth must radiate energy to space just as
quickly as it absorbs radiation.
Q1) Sunlight strikes the Earth at a rate of 1.74 x 1017
W, but only 70% of that energy is absorbed by the planet. (The rest
is reflected back to space.) Given Earth’s radius and assuming the
planet has an emissivity of 1, what should be Earth’s equilibrium
surface temperature?
A. 245 K (–28°C) B. 255 K (–18°C) C. 265 K (–8°C)
D. 275 K (+2°C)
Q2) Instead, Earth’s average surface temperature is 288
K (+15°C) due to greenhouse gases in the atmosphere that warm the
planet by trapping radiation. What is Earth’s effective emissivity
in this simple model?
A. 0.6 C. 0.8 B. 0.7 D.
0.9
Q3) If Earth could not radiate away the energy it
absorbs from the Sun, its temperature would increase dramatically.
Assume all of the energy absorbed by Earth were deposited in
Earth’s oceans which contain 1.4 x 1021 kg of water. How long would
it take the average temperature of the oceans to rise by
2°C?