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

CC BY-SA 4.0
2021-10-28T17:39:13.347Z
You ca find [explanations](https://www.google.com/search?channel=fs&client=ubuntu&q=Do+greenhouse+gases+absorb++photons) with various degrees of simplification.
Keith McClary
CC BY-SA 4.0
2021-10-28T19:37:40.480Z
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.
AtmosphericPrisonEscape
CC BY-SA 4.0
2021-10-30T10:39:22.693Z
Note that CO2 IR absorption and emission are independent processes, the former is not a condition for the latter.
Poutnik
CC BY-SA 4.0
2021-11-05T15:01:24.857Z
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](https://physics.stackexchange.com/). 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](https://en.wikipedia.org/wiki/Airglow)?
Matt Hall
CC BY-SA 4.0
2021-11-06T01:44:04.743Z
@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.
AtmosphericPrisonEscape
<climate-change><geophysics><climate><climatology><solar-terrestrial-physics>
Do greenhouse gases absorb and re-emit photons or reflect them diffusely? Or both? (CO2, CH4, H2O, N20, HFC-134a, etc.)
Kurt Hikes
# Do greenhouse gases absorb and re-emit photons or reflect them diffusely? Or both? (CO2, CH4, H2O, N20, HFC-134a, etc.)

(Asked by: username_0 on 2021-10-28)

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....

**Tags:** climate-change, geophysics, climate, climatology, solar-terrestrial-physics

> **Comments:**
> **username_1**: You ca find [explanations](https://www.google.com/search?channel=fs&client=ubuntu&q=Do+greenhouse+gases+absorb++photons) with various degrees of simplification.  
> **username_2**: 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.  
> **username_3**: Note that CO2 IR absorption and emission are independent processes, the former is not a condition for the latter.  
> **username_4**: 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](https://physics.stackexchange.com/). 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](https://en.wikipedia.org/wiki/Airglow)?  
> **username_2**: @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.  

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