The best way to argue for the science, and against the climate alarmists is to simply go back to the basic physics of the greenhouse gas effect (GHG) and how CO2 contributes to it. Stated simply, the GHG effect is the trapping/absorbing of outgoing infrared (IR) radiation by various greenhouse gasses in the atmosphere. These molecules then either thermalize the energy by turning it into kinetic energy or re-radiating the energy in all directions to be absorbed by other molecules.
The key steps are:
- High energy visible radiation warms the earth and oceans
- The warmed earth radiate IR radiation
- GHGs absorb the outgoing IR and either thermalize or re-radiate the energy
- This process acts to slow the cooling of the radiating body, much like insulation slows the cooling of a home
- At no time does the GHG effect warm the atmosphere above the temperature of the radiating body. The GHG effect does not ever add energy to the system, it only helps contain some of the existing energy
The introductory graphic above identifies the contributions each GHG contributes to the entire GHG effect. The bottom part of the graph demonstrates the IR radiation absorbed by the entire atmosphere, which is a summation of all the GHGs listed above it. The IR absorption spectrum of H2O is almost indistinguishable from the total absorption of atmosphere and is why H2O is by far the most significant GHG. The entire contribution of CO2 is to absorb 3 very narrow bands of IR at 2.7, 4.3 and 15 microns. In reality, the only wavelength applicable to the GHG effect is the peak out at 15 microns. 15 microns, by the way, is very low energy and consistent with a blackbody of temperature -80º C.
What makes a GHG is it’s molecular structure. Molecules with a “bipole” are strong GHGs, molecules that don’t have a bipole are considered weak GHGs. Here is a link to help understand the concept; Understanding the DiPole.
DiPole Key Points:
- Bent molecules have a permanent bipole, H20 is bent
- Linear molecules have no permanent bipole, CO2 is linear
- “Bending” of a molecule is easy, and low energy
- Compressing and stretching a molecule is hard, and higher energy
This graphic explains how CO2’s IR spectrum is created. The bending of CO2 at 15 microns is it’s only defined contribution to the GHG effect. That comment is worth repeating; The bending of CO2 at 15 microns is it’s only defined contribution to the GHG effect. Any claim of CO2 caused climate change must be explained through that mechanism.
This graphic provides an understanding of the molecule motions that cause the IR peaks. The center bending is what causes the IR absorption spike at 15 microns/wavenumber 667. That simple weak-energy bending is all CO2 contributes to the GHG effect, that is it. Every claim that identifies CO2 as the cause, must explain how weak-energy bending and the resulting IR absorption/radiation of 15 microns resulted in the observed climate change/global warming/extreme weather. Once again, that weak-energy bending is the only defined mechanism by which CO2 can affect climate change, the only one.
Taking a closer look at CO2, this chart is a linear CO2 absorption chart. It highlights the weak-energy of the 15 micron IR band. The absorption band at 4.7 microns is of much higher energy, but is outside the IR spectrum emitted by the earth, and does not play a part in the GHG effect.
This is a logarithmic chart of CO2’s IR spectrum.
It is worth reviewing that the earth emits radiation at a peak 9.8 to 10 microns, which is consistent with 18º C, or basically room temperature.
Taking a closer look at H2O’s IR spectrum reveals a much more potent GHG, absorbing the much higher-energy/shorter-wavelengths. This is the linear H2O spectrum.
This is H2O logarithmic IR Spectrum. H2O simply absorbs across the entire IR spectrum, with its main and densest peaks in the high-energy end. This is the IR signature of a very potent GHG.
This is a linear chart of H2O and CO2’s IR spectrum. The relevant peaks of CO2 are located at the low-energy end of the spectrum, and H2O is focused on the high-energy end of the IR spectrum.
This is a logarithmic chart of the H2O and CO2’s IR spectrum. The key point is that H2O largely overlaps all of CO2’s spectrum, so in the troposphere, if H2O is present, CO2’s contribution becomes irrelevant. With or without CO2, H2O will absorb the outgoing IR. CO2, however, does not overlap all of H2O’s spectrum, so the absorption at the high-energy end between 5 and 10 microns is dominated by H2O.
The consequence of H2O being the dominant GHG in the warmer IR range is that tropospheric atmospheric temperature is basically controlled by H2O. CO2 is basically irrelevant. That is why using ground based temperatures to measure the impact of CO2 is pure nonsense. Even doubling CO2 has no impact on the lower troposphere at all as these two MODTRAN charts demonstrate.
The other important physical property of CO2 is that it’s IR absorption isn’t linearly related to absorbed energy, it is logarithmically related. That is partially why doubling CO2 in the above graphics had no impact on the energy balance in the troposphere.
The result is that tropospheric atmospheric temperatures and tropospheric water vapor are almost indistinguishable. The same can not be said about CO2, which is a constant 400 ppm all the way up to 80 km.
One last chart defining the relevant physical properties of CO2, and it’s IR absorption spectrum. The oceans are warming. Ocean warming and atmospheric warming are often conflated, and the claim is that atmospheric CO2 is contributing to the warming of the oceans. In reality, visible light is warming the oceans, and the oceans are warming the atmosphere above it. IR between 13 and 18 microns simply doesn’t penetrate or warm water. Atmospheric CO2 can’t be the cause of the warming oceans.
The take home message is that CO2 is a weak GHG that has no permanent dipole, whose main absorption peak is in the cold/weak-energy end of the IR spectrum. If anything CO2 helps to act as a temperature floor for the globe, as it’s main contribution is to thermalize energy consistent with a blackbody temperature of -80º C (-50º C to -110º C). H2O, on the other hand, is a much more potent GHG that totally dominates the temperature of the troposphere. It all boils down to “can CO2, a weak non-dipolar GHG, affect catastrophic climate change through “bending” and the resulting absorption/radiation/thermalization of 15 micron IR (13 to 18 micron range). Once again, that is the only defined mechanism by which CO2 can execute the GHG effect, and affect climate change.