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Jovial Monk
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Gas molecules made of three or more atoms are “greenhouse gases” that are partially opaque to infrared radiation. IR has a wavelength a bit longer than light. We know the band of visible light can be subdivided into 7 sub-bands corresponding to the colors red, orange, yellow. . .violet and IR also stretches out over a band of wavelengths.
Radiation can be thought of as little packets of electromagnetic energy called a photon, or you can think of it as a ray but I will use the term photon. Now I will just use CO2 but CH4 and N2O etc works the same way. Let us write CO2 as OCO and the electric charge (density in the electron cloud) is distributed between the CO and the OC dipoles.
In the Relationships board, LarsenC thread the second post describes all this in more detail. Imagine an OCO molecule floating around when it absorbs (gets hit by) a photon at the OC or CO dipole. The OCO molecule is “excited” or made more energetic, spinning/vibrating at a more rapid rate but it cannot hold on to the energy and re-emits the photon a fraction of a second after absorbing it. By this time the dipole that re-emits the photon may be facing any direction and the IR photon can be re-emitted as likely downwards as upwards.
The photon may be absorbed by another and another molecule of one of the GHGs present in the atmosphere. Whatever IR got re-emitted downwards reaches the surface of the globe, strikes a molecule on the surface which is excited but being a solid or liquid strikes adjacent molecules and the energy of the photon is absorbed. The surface just got heated by the amount of the energy of that photon.
Now, you are thinking “this is rubbish, don’t believe it!” but studies of the IR spectrum from the ground show it receives more IR over time while studies from satellites show less IR reaching satellites over time. Over time more and more GHGs are present in the atmosphere, IR photons are absorbed/emitted more and more and more and more IR is absorbed by the surface.
Look at the Harries diagram. It shows that over a period of time less and less IR reaches as high as the satellite (the brightness temperature or blackbody temperature measured as IR brightness) and it even shows the two bands, the OC and the CO of CO2.
Watervapor, which we can write as H–O–H, is a three atom gaseous molecule and so, yup, is a GHG. It is usually called a reinforcer because, unlike CO2, CH4 etc its concentration varies as evaporation-precipitation (rain etc)–evaporation etc. CH4 is relatively shortlived but is much more constant than H2O, taking decades before it is oxidised to other compounds.
The theory and observation fits very well. Only Booby might say the global temperatures are declining but we know they are not. If 2018 is an El Nino year god knows what temperatures we see.
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