Copied off stack exchange...
The real fact is that all of the atmosphere is principally heated by thermal conduction and convection - heating the atmosphere by absorbing infrared radiation is negligible.
Water vapour is accepted to be about 1% of a normal atmosphere. At the Earth's surface the mass of a cubic metre of air is about 1.205 kg. As we go up in the atmosphere pressure decreases and thus so does the mass of air per cubic metre.
At 1% water vapour concentration by volume or about 1.5% by weight there are about 19 grams per cubic metre at sea level - significantly less at higher altitudes. Kiehl & Trenberth claim greenhouse gases produce "backradiation" of 324 Watts / square metre.
A watt is equivalent to a Newton metre per second. A newton is a mass of 1 kilogram accelerated by gravity - 9.8 metres per second.
Hence 324 Watts per square metre is equivalent to 324 Newton metres per second.
324 Newtons is 33 kg subjected to gravity's acceleration.
If anyone can explain to me how a mere 12 grams of water vapour in every cubic metre of normal air at sea level can produce that sort of energy I would feel much enlightened - I simply say it is impossible without furnace like temperatures.
As for Carbon Dioxide at 0.04% by volume which is 0.06% by weight it constitutes approximately 0.732 grams per cubic metre - again significantly less at high altitudes as it is heavier than air.
By similar logic if any one can explain how such an insignificant mass of Carbon Dioxide can produce any detectable quantity of radiation I would feel much enlightened !!
As data from the Moon orbiting satellites a heated surface radiating to space cools at a very slow rate.
True the Moon can become very cold on the night side but that lunar night lasts 354 Earth hours and the surface cools about 290 degrees during that 354 hours - less than a degree per hour.
At that rate the dark side of the Earth would "cool" less than 12 degrees before the Sun rose again.
It is the period of rotation of the Earth that is significant into determining how much the Earth cools.
It is the power of the Solar radiation that determines the maximum daytime temperature.
The atmosphere and oceans reduce the temperature the Solar radiation is capable of causing and there is simple proof in that the Moon's surfaces are heated to over the boiling point of water whilst the Earth never approaches those extremes except when conduction/convection is suppressed or prevented entirely.
Finally do you really believe that although Nitrogen and Oxygen do not significantly absorb Infrared radiation they do not radiate Infrared radiation ?
A well known fact of physics is that everything that has a temperature above absolute zero radiates electromagnetic radiation !
At ambient air temperatures well established physics, Wien's law, predicts that the intensity of the emitted electromagnetic radiation is at a peak well within the Infrared radiation wavelength band.
Almost all of the electromagnetic radiation in the atmosphere is coming from Nitrogen and Oxygen which constitute about 99% of the atmosphere.
The only way Nitrogen and Oxygen would not constitute the vast bulk of this atmospheric radiation is if they were at absolute zero and all the warmth you feel came from 19 grams per cubic metre water vapour and 0.732 grams per cubic metre CO2.
I think that proposition is absurd !