Wieso ist Helium kein Klimagas?

Helium has a weak cooling effect because it increases the thermal conductivity of the air due to its low weight (and consequently high speed). As a result, heat is better transported from the warm ground to the cold heights (and to radiation). In this respect, helium is actually a slightly cooling climate gas. But it’s not a greenhouse gas.

The oscillation of a molecule can absorb heat radiation only when the dipole moment of the molecule changes during the oscillation. Since helium does not form bindings, there can be no vibration in trivial manner and there can also be no vibration at which its dipole moment changes.

Also in the case of 2-atomic molecules such as N2, O2, H2, Cl2 … which consist of two identical atoms, there can be no vibration that can absorb IR light (and re-emitulate). It looks different from NO and CO. These are actually weak greenhouse gases.

But the greenhouse gasses are just starting with 3-atomy gases. There are so-called bending vibrations. This is an oscillation in which the binding does not submerge or expands, but displaced. You’ve got a strong feather fixed at one end. It is much easier to push the other end a little to the side than to press the spring together. This is also the case with the bending vibrations. These absorb very easily heat radiation.

CO2 is, by the way, a special case because of its linearity in the basic state. As a result, it not only reproduces radiation of the frequency which it previously absorbed, but also in smaller frequencies, and this preferably directed into the same direction, into which previously absorbed IR photon was directed. And its IR-active vibrations can also be excited by collision with other gas molecules. Unfortunately, the whole situation is much more complicated than the mainstream of climate research wants to make us believe.