Does it seem strange to you that the smartest kids in the class, the kids that can explain the quantum mechanics supporting the greenhouse gas effect, can’t adequately explain how Long Wave Infrared Radiation (LWIR) and CO2 can warm the earth? This Video made by TEDEd does a phenomenal job explaining the quantum mechanics involved, but then they forget to mention the most important metrics.
Here are the important facts they failed to mention:
- CO2 only absorbs LWIR of 2.7, 4.3, and 15 Microns.
- Earth emits LWIR around 10 Microns
- The only LWIR spectrum applicable to CO2 and the Greenhouse Gas Effect is 15 Microns
- 10 Microns has a blackbody temperature of about room temperature of 64°F/18°C
- 15 Microns has a blackbody temperature of about -112°F/-80°C
How does LWIR convert to thermal radiation? Molecular Vibrations
666 cm-1 wavenumber is 15 microns and is associated with the “bending” of the CO2 molecules. The 2.7 and 4.3 Micron absorption bands are related to the stretching and are not involved in the atmospheric absorption.
This graphic shows the absorption spectrum of CO2, which is transparent to incoming visible radiation (0.4 to 0.8 microns)
What makes a potent Greenhouse Gas is a “permanent dipole” or bend. CO2 doesn’t have a bend, unlike the extremely potent Greenhouse Gas H2O.
Because CO2 doesn’t have a Permanent Dipole, it only absorbs the three above mentioned wavelengths, allowing it to absorb only a small amount of radiation.
LWIR of 15 Microns gets absorbed by a CO2 molecule, kicking the CO2 Molecule’s electrons into a higher energy state, causing them to bend back and forth. This movement is thermal energy, the LWIR electromagnetic radiation is changed in form into kinetic energy which can be measured with a thermometer. (Remember, Energy can be neither created or destroyed, it can only be changed in form)
In the video, it claimed that the CO2 molecule radiated LWIR back to earth and warms the earth. That isn’t the Greenhouse Gas Effect, and LWIR of 15 microns won’t even warm ice. The Greenhouse Gas Effect is the thermalization of the LWIR causing warming of the surrounding atmosphere.
Why CO2 isn’t significant is because it is a trace gas. CO2 is 410 parts per million or 4.1 parts per 10,000, or 0.00041 or 0.041% of the atmosphere. If you look at a 100,000 seat stadium, with each person representing a molecule in the atmosphere, CO2 would represent 41 people. If 41 people suddenly went into epileptic seizures, would their kinetic energy be able to significantly alter the kinetic energy of the other 999,959 people in the stadium? Absolutely not. Being only 0.041% of the atmosphere, its impact is greatly diffused to basically nothing.
More importantly, the energy associated with 15 Microns isn’t even warm enough to melt ice. Ice emits LWIR of a shorter wavelength than 15 Microns.
In Conclusion, 1 out of every 2500 molecules vibrating at an energy level consistent with -112°F/-80°C isn’t going to warm anything to any significant amount.
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