This digression article is needed to avoid comment threads being derailed by the basics again and again. I can send commenters here and move comments here.
Many people who don’t understand atmospheric physics dispute the basic idea that adding CO2 to the atmosphere increases the surface temperature of the planet. The idea is known by the imperfect name, “the greenhouse effect”.
There isn’t a simple conceptual idea that we can put in someone’s head to explain why the greenhouse effect is real. Too bad.
Plenty of people try to explain it to the general public. However, give too brief an explanation and you miss out important details.
Ah ha, these idiots don’t understand this subject, look at their lack of attention to detail. It’s much more complicated than that!
Give too long an explanation and no one outside the field can understand it.
Too long and boring. Too nebulous. Too much maths. Give me a simple demonstration of why this is true.
Maybe try basket weaving instead. Or go into politics. Or journalism.
There are some basic ideas that together are used to prove the “greenhouse effect”.
The temperature of the atmosphere decreases as you go up in altitude. Everyone seems familiar with this point.
Gases absorb radiation at various wavelengths, depending on the gas in question. The higher the concentration of the gas, the more the absorption.
Gases emit radiation at various wavelengths. The higher the temperature of the gas, the more the emission. The higher the concentration of the gas, the more the emission.
If we take the temperature profile of the atmosphere as a given, we can write down equations using points 2 and 3. This wasn’t invented by climate scientists. Famous names from history and Nobel prize winners came up with this stuff a long time ago.
It’s in all the textbooks that cover this level of detail. There isn’t an alternative set of equations.
I’ve explained the derivation of the equations in Understanding Atmospheric Radiation and the “Greenhouse” Effect – Part Six – The Equations.
It’s very boring and tedious, and if you don’t have a maths or hard science background you won’t follow it.
Emission and absorption of radiation are not fanciful or unproven ideas. The equations are used in cosmology for working out, for example, the temperatures of gas and dust clouds. The equations are used in satellite observations of the earth, for example, in measuring ocean temperatures and atmospheric humidity. They are solid.
We have spectroscopic measurements of the absorption lines of CO2, water vapor, methane, and other gases. They aren’t some fanciful idea either. The Journal of Quantitative Spectroscopy & Radiative Transfer contains the tedious details in the reference below.
Here’s an example of radiation vs wavelength. We’re comparing the calculation from the physics I’ve just outlined with observations from a satellite. The gap is artificial to make it easier to see the comparison, the lines match:
The big “bite” in the middle is the effect of CO2 - reducing radiation emitted to space. If there was no CO2 this “bite” wouldn’t exist. Radiation to space would increase, meaning the planet would cool down.
It’s just lines on a page, so ignore it if you like. Maybe someone just made it up.
And the equations of absorption and emission, used by countless disciplines, they are probably made up as well.
Over to the enlightened ones.
Further Reading
Here are some references from the old blog, explaining these ideas in more detail:
The “Greenhouse” Effect Explained in Simple Terms – summarizing the effect, attempting to “make it simple but not too simple” with many links to other articles
Theory and Experiment – Atmospheric Radiation – real values of total flux and spectra compared with the theory
Visualizing Atmospheric Radiation - a series
References
The HITRAN 2008 molecular spectroscopic database, by L.S. Rothman et al, Journal of Quantitative Spectroscopy & Radiative Transfer (2009)
Sure, the Greenhouse effect of CO2 is real, but to assume that the effect continues indefinitely is unwarranted. If your corn gowns to 6 ft in 3 months, it doesn't mean it will grow to 12 ft in 6 months. The 14-16 micron band is already totally absorbed at well below the present 400ppm.
Since the band width is determined by the 15mm spike and the Doppler effect, doubling CO2 makes no difference.
Why do activists shy away from experiments to prove their Hypothesis? Perhaps they are not confident of the outcome.
Refer: NASA Technical Memorandum 103957 Appendices E and F. Lord, 1992
Robert Hissey wrote at https://scienceofdoom.substack.com/p/natural-variability-attribution-and-a70/comments#comment-17367039 and I'm helping our host move the conversation here:
"My statements apply only to the 14-16 micron band. Photons in this band have been shown to never reach space. That is, the absorbance by CO2 and transference to heat in the atmosphere vastly outweighs the occasional re-emittance of a photon of that wavelength."
Frank: Photons in this band are emitted to space by our planet all the time. Experimentally we observed them from space continuously. However the photons that are reaching space are not the ones that are emitted by the surface. They are emitted from 10 km above the surface or 20 km above the surface. At 15 km above the surface, we are above 90% of the atmosphere and the mean free path between emission increases 10-fold for photons absorbed by CO2 and far more for photons absorbed by water vapor since the atmosphere gets much drier with altitude.
Your use of the phrase "re-emittance" suggests a possible misunderstanding. Absorbing a photon of thermal IR radiation produces an excited vibrational, rotational or a combinations of vibrational+ rotational excited states. (That is why the 15 um line for CO2 can be resolved into dozens of nearby lines under some conditions). The excited vibrational state has a half-life of about 1 second and collisions occur about 10^9 times a second near the surface, though not every collision is capable of relaxing an excited state. Therefore re-emission of an absorbed photon from the excited state that produced it is not a significant process in the troposphere and lower stratosphere where all the important absorption and emission appear. The energy from the excited state end up increasing the velocity of the colliding gas molecules, increasing their temperature. This process is sometimes called "thermalization".
Essentially all of the excited states that emit photons are created by "collisional excitation". Collisional excitation produces a Boltzmann distribution of energy among all possible excited states (with exp(-E/kT) fewer molecules with in an energy state E above ground state. When deriving Planck Law (and the Schwarzschild equation) we assume a Boltzmann distribution of energy states. Therefore Planck's Law has mathematics that ensures that it needs to be at least 1000 degK to emit a significant number of visible photons, but the atmosphere and surface emit "thermal IR photons" at 190-310 degK. When a Boltzmann distribution of excited states exists (and energy is being exchanged by collisions much faster than by photons of any other process), we say the atmosphere is in "local thermodynamic equilibrium". (This does not mean emission and absorption are in equilibrium). Normally we need to heat something to several thousand degK to get it to emit a significant amount of visible light, but we have invented some devised that allow us to create a lot of excited states without collisional excitation, where a Boltzmann distribution of energy states does not exist and visible light can be emitted without high temperature. LED, lasers, fluorescent light bulbs and microwave ovens are devices that create a non-Boltzmann distribution with far more excited states than normal.