I have a doubts about how $\small\mathsf{CO_2}$ absorbs an re-emits infra red (IR) radiation.

Let's imagine an only-$\small\mathsf{CO_2}$ atmosphere. In this case, a large amount of 15 $\small\mathsf{\mu{m}}$ radiation that the soil emits will be absorbed.

Will the temperature of this only-$\small\mathsf{CO_2}$ atmosphere increase? I think so, but in this case the atmosphere would not be able to re-emit IR in the 15 $\small\mathsf{\mu{m}}$ band but would emit black body radiation that depends on the temperature reached by absorbing 15 $\small\mathsf{\mu{m}}$ IR.

To sum up, does $\small\mathsf{CO_2}$ act as a mirror and reflect 15 $\small\mathsf{\mu{m}}$ IR or does it absorb this wavelength and transform it into heat and then emits it like a black body? What is $\small\mathsf{CO_2}$ albedo to 15 $\small\mathsf{\mu{m}}$ wavelength?

  • $\begingroup$ If the amount of CO2 doesn't change there should not be any temperature change due to greenhouse effect. Surface temperature will be higher than for a planet with different or no atmosphere but if CO2 is not changing it should be at equilibrium. Important to note that it is high in the atmosphere, where IR can pass out to space that is most significant for greenhouse effect. Convection driven air circulation carrying warm air to that altitude, where it can radiate to space, is an essential component. $\endgroup$
    – Ken Fabian
    Dec 18 '19 at 5:13
  • $\begingroup$ The doubt here is if CO2 absorb the IR energy and warm the only-CO2 atmosphere and it warm the soil with black body radiation or if CO2 reflects IR energy at same wavelenght and soil is re-warmed and then warm the surrounding air by conduction. $\endgroup$
    – J.Arranz
    Dec 18 '19 at 23:53
  • 1
    $\begingroup$ The atmosphere will reach an equilibrium temperature as described in How is the mechanism of greenhouse gases interacting with IR radiation? $\endgroup$ Dec 21 '19 at 20:19

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