The average Earth surface temperature without its atmosphere would be 255 K. Why?
(a) At that temperature, the emission rate of radiation from Earth would just balance the absorption rate of radiation from the Sun.
(b) The emission of Earth radiation is from a sphere of area $4 \pi R_{\text { Earth }},$ whereas the absorption of radiation from the Sun is from an area $\pi R_{\text { Earth }}$ .
(c) Earth’s cross section would be significantly reduced be- cause of the lack of the atmosphere.
(d) Answers a and b are correct.
(e) Answers a, b, and c contribute about equally to this temperature calculation.