Basically. To be clear, it's not that you are worried about getting "the same" heat reflected or otherwise radiated back toward you. (The radiation emitted by y

Basically. To be clear, it's not that you are worried about getting "the same" heat reflected or otherwise radiated back toward you. (The radiation emitted by your roof doesn't appreciably change the radiation incident on your roof from the atmosphere.) It's that if you are passively emitting at some frequency you are necessarily absorbing at that frequency too (by the 2nd law). And you don't want to be absorbing at the frequency where the atmosphere is opaque and hence warm. In contrast, it's fine to be absorbing at the frequency where the atmosphere is transparent, because then you're just exposed to cold outer space.