Also, would it matter if a particular type of greenhouse gas molecule reflected rather than absorbed and then re-emitted light? Would its GWP be higher or lower?

Perhaps this is more of a pure physics question than an applied physics, Earth-science one, but I am very curious....

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    $\begingroup$ You ca find explanations with various degrees of simplification. $\endgroup$ Oct 28 '21 at 17:39
  • $\begingroup$ There are two fundamentally different processes in radiation transport, that can provide opacity: absorption and scattering of photons. What is classically called the Greenhouse effect is purely due to the absorption optical depth being > 1 to infrared photons. $\endgroup$ Oct 28 '21 at 19:37
  • $\begingroup$ Note that CO2 IR absorption and emission are independent processes, the former is not a condition for the latter. $\endgroup$
    – Poutnik
    Oct 30 '21 at 10:39
  • $\begingroup$ This question seems to be about the mechanism of absorption and reflection of photons by gases and I think you'll get better answers on Physics SE. That said, my understanding is that reflection is the same as absorption and emission, whether by a mirror or anything else. In other words, reflectors and scatterers don't 'bounce' photons, they absorb and emit. But you also might be thinking of the emission of new IR photons because of the gas's temperature, or maybe airglow? $\endgroup$
    – kwinkunks
    Nov 5 '21 at 15:01
  • $\begingroup$ @kwinkunks You are fundamentally wrong with this comment. Absorption and scattering fundamentally originate in the real and imaginary parts of the refractive index of a material and are hence unrelated. $\endgroup$ Nov 6 '21 at 1:44

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