Molecular Mechanics of the Greenhouse Effect

Vincent J. Curtis

14 Nov 21

Despite this imposing title, the greenhouse effect is most easily understood by looking at it from the molecular level.

When the earth cools at night, the surface of the earth emits infra-red radiation in a broad spectrum that closely follows what’s called in physics blackbody radiation.  The greenhouse effect occurs when atmospheric gases absorb some of this radiation and convert it to heat.  The primary greenhouse gases are water vapour and carbon dioxide, with ozone playing a role in the upper atmosphere.  Methane and nitrous oxide are minor greenhouse gases.  The mechanism of the greenhouse effect is basically the same for all of them.

These gases absorb infra-red light in certain portions of the spectrum.  Carbon dioxide, for instance, absorbs infra-red light in a narrow band around 15 micron wavelength.  When a molecule absorbs a photon of infra-red light it is kicked from its so-called ground vibrational state into an excited vibrational state.  When in an excited vibrational state, one of two things can happen: either the molecule emits a photon in a random direction and falls back to its ground state, or it collides with another molecule and transfers kinetic energy to that other molecule while it falls back into its ground vibrational state.  The second possibility is the essence of the greenhouse effect: infra-red radiation is converted into thermal energy.  That now faster moving second molecule is how heat is expressed in a gas.

Typically, the CO2 molecule will transfer energy to either a nitrogen or oxygen molecule, giving them a thermal-kinetic “kick.”  Suppose all the energy that could be captured at 15 microns was already being captured and converted into thermal energy.  What would be the effect of adding more capturing molecules?  The answer is that those additional capturing molecules wouldn’t be busy because all the infra-red energy available to be captured is already being captured and converted into thermal energy in nitrogen and oxygen.  If the criminal is already being caught, adding more cops to that arrest team isn’t going to result in the capture of more than that one criminal.  In the case of CO2, maximum greenhouse effect is reached at between 50 and 100 ppm concentration in the atmosphere.

The earth has only so much energy to capture in the infra-red, and if all of that is already being captured, adding more arresting agents won’t increase the amount of energy arrested.  Hence, adding more CO2 and methane to the atmosphere will not result in global warming or climate change because the amount of CO2 and methane already present in the atmosphere is already capturing all there is to be captured at their respective wavelengths.  Over the night, the thermal and infra-red energy of the lower atmosphere is transferred into the upper atmosphere and is finally radiated into outer space as infra-red radiation.  The greenhouse effect slows, but cannot stop, the transfer of energy from the earth to outer space in the form of infra-red radiation.

Ultimately, the amount of energy the earth absorbs during the day has to be emitted at night, or else the earth would warm.  This is a very closely maintained energy balance because even a slight imbalance would rapidly result in either heating or cooling until the situation stabilized at a new temperature.

Rate of heat transfer is proportional to the difference in temperature, so if the earth got warmer or cooler the rate of heat transfer would increase or decrease until a new stable temperature was reached.  All the while, the amount of solar radiation received by the earth remains the same.  If the earth radiates more energy than the sun is putting in, the earth will cool and the rate slow until the rates in and out balance at a new, lower temperature.  If the earth radiates less energy than the sun puts in, the earth will warm and the rate speed up until the balance is re-established at a new, higher temperature.  Keep in mind that the insulating effects of CO2 and methane are already at a maximum.  This is why it’s hard for the earth’s atmosphere to experience a thermal runaway.

I’m not going to try to explain now why so many reputations have been staked and so many billions of dollars spent hyping the alleged danger of allowing CO2 and methane concentrations in the atmosphere to rise.  One word will suffice for now: politics.  Scientists are human too.

COP26 was a failure by the standards of the climate fanatics.  Climate change has become a religion for many and they can’t abide by failure.  Hopefully, there’s enough sense in the world to save its economy from destruction by the nihilism of the climate change religion.

The ultimate message is that the world is in no danger from mankind-induced climate change.  Adding more CO2 and methane to the atmosphere isn’t going to harm the planet.

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