How does the atmospheric Greenhouse Effect work?

Much has been written about the greenhouse effect and many comparisons have been made. However, much of this is misleading or even wrong.
The greenhouse effect is caused by the fact that with increasing CO₂ a slightly increasing proportion of infrared radiation is emitted from the upper, cold layers of the earth’s atmosphere (i.e. the stratosphere) into space.
 The facts are complicated in detail, which is why it is so easy to scare people with exaggerations, distortions or lies. Here I would like to describe the basics of the atmospheric greenhouse effect, in which CO₂ plays an important role, in a
physically correct way and without formulas.

Viewed from space, the temperature balance of the Earth’s surface and atmosphere is determined by

• irradiation of short-wave, largely visible sunlight and through
• Radiation of long-wave invisible infrared radiation.

If the energy content of the incoming radiation is equal to the energy content of the outgoing radiation, there is an equilibrium and the average temperature of the earth remains constant. Warming always takes place when either the radiation decreases or the irradiation increases, until equilibrium is restored.

Infrared radiation is the only way the Earth can emit energy (heat) into space. It is therefore necessary to understand how the mechanisms of infrared radiation work.

The mechanisms of infrared radiation into space

There are only 2 ways in which the Earth can release energy into space:

• The molecules of the earth’s surface or the sea surface emit infrared waves at ground temperature (average 15°C = 288 K).
• The molecules of the so-called greenhouse gases, mainly water vapor and CO₂ (to a much lesser extent methane and some other gases), emit infrared waves from the atmosphere at the temperature prevailing in their environment. The other gases in the atmosphere, such as oxygen or nitrogen, are unable to emit significant amounts of infrared radiation.
  CO₂ differs from water vapor in that it is only active in a small wavelength range. On the other hand, the proportion of water vapor molecules in the atmosphere decreases very quickly from an altitude of 5 km because the water vapor condenses back into clouds when it cools down and then rains down. We can see that from this: In an airplane at an altitude of 10 km, we are always above the clouds. And there is virtually no water vapor above the clouds. However,
  CO₂ is evenly mixed with other gases, primarily oxygen and nitrogen, right up to the highest layers of the atmosphere.

CO₂ and water vapor are therefore like two competing handball teams, one of which (the water vapor) is only allowed to run up to the halfway line and the other (CO₂ ) can only move within a narrow longitudinal strip of the playing field. This narrow longitudinal strip becomes a little wider when the “CO₂ team” gets more players (more CO₂ ). The goal is the same for both teams (space) and stretches across the entire width of the pitch. As long as the ball is still far away from the goal, another player catches it rather than it entering the goal. This other player passes the ball back in a random direction. The closer the players are, the quicker the ball is caught and played back. The closer the ball gets to the goal, the further apart the players stand. This means that it is easier for the ball to get between the players and into the goal.

As long as there are other greenhouse gas molecules in the vicinity, the infrared radiation cannot reach outer space (the other molecules are too close together); it is collected again by the other molecules and emitted by them. Specifically, the infrared radiation in the lower atmosphere only has a range of around 25m until it is intercepted again by another greenhouse gas molecule, usually a water molecule or CO₂ . The thinner the greenhouse gases (fewer players) in the atmosphere become with increasing altitude, the more likely it is that the infrared radiation will reach space.

From this we can conclude that there are in principle 3 layers from which infrared radiation reaches space:

• When the air is dry and without clouds, there is a part of the infrared called the “atmospheric window” that radiates directly from the ground into space (this is when there are no or very few water vapor players in the field),

• between 2 and 8 km altitude, on average at 5 km altitude, is the upper edge of the clouds, from where the water vapor molecules of the clouds emit a large proportion of the infrared radiation into space at an average of 255 K = -18°C
• the proportion of infrared radiation in the wavelength range around 15 micrometers (the narrow strip of the playing field) is transported by CO₂ into the high cold layers of the stratosphere, from where it is emitted into space at around 220 K = -53°C.

This leads to a competitive situation as to whether a water molecule can radiate directly or whether its infrared radiation is still intercepted by a CO₂ molecule and transmitted to the heights of the stratosphere.

The greenhouse effect

How does a growing CO₂ concentration lead to reduced energy radiation into space and thus to warming?

It is important to know that the radiated energy decreases sharply with decreasing air temperature and that the temperature decreases with increasing altitude. If the CO₂ concentration increases over time, the wavelength range in which the CO₂ is “responsible” for radiation becomes a little wider (the narrow strip of the playing field). This means that a small part of the infrared radiation that would otherwise be emitted by the water vapor at 255 K is now emitted by the CO₂ at 220 K, i.e. with significantly lower energy. As a consequence, this means that the energy of the total radiation is slightly reduced – the radiation from sunlight, which is assumed to be constant, therefore predominates and a warming effect occurs.

However, the effect is not as great as it is usually portrayed in the media:
Since the beginning of industrialization, the earth’s infrared radiation has decreased by just 2 watts/sqm
 with a 50%
increase in CO₂ concentration from 280 ppm to 420 ppm. With an average radiation of 240 watts/sqm, that is¹ only just under 1% in 170 years.
We now know the first possibility of how the balance mentioned at the beginning is disturbed by a change in radiation. But so far only to a very small extent.

The effects of changes in irradiation are greater than the greenhouse effect

The second way of disturbing the balance is through changes in irradiation.
The fluctuations in irradiation caused by changing cloud cover are up to 100 times greater than the aforementioned 2 W/sqm (which owners of photovoltaic systems can confirm), which can be attributed to the greenhouse effect. Looking at Germany, according to the German Weather Service, the number of hours of sunshine in Germany has been increasing by 1.5% per decade for 70 years². In other words, in less than 10 years, the effect has been greater than that of the greenhouse effect in 170 years. For a more precise numerical comparison, both measurement data to be compared must be available in the relevant period: In the period of the last 40 years, there was 6 times the warming due to the increase in hours of sunshine in Germany compared to the greenhouse effect. The changes in solar radiation are therefore responsible for global warming to a far greater extent than the changes in CO₂ concentration.

This describes and classifies the generally known positive greenhouse effect. There is therefore no reason to use the greenhouse effect to justify fear and panic. And there is an urgent need for research, the media and politicians to look into the influence and causes of the increasing hours of sunshine. An initial, more detailed analysis of the data from the German Weather Service shows that the changes in hours of sunshine in Germany explain 90% of the monthly temperatures over the last 70 years and that the greenhouse effect in Germany has no statistically significant influence.

One important phenomenon is still missing: in the Antarctic, the increase in CO₂ concentration leads to cooling, which is known as the negative greenhouse effect.

The negative greenhouse effect in the Antarctic

There is a peculiar effect when we look at the one area of the earth where the earth’s surface is at times even colder than the 220 K at which the infrared radiation of CO₂ is emitted into space: In the Antarctic, where temperatures below -60°C (=213 K) are not uncommon, we actually find a negative greenhouse effect.
In other words, where cooling occurs as the CO₂ concentration increases.
As the CO₂ concentration
increases, the proportion of infrared radiation from the CO₂ increases as usual. However, at 220 K, the CO₂ layer is now warmer than the surface of the Antarctic. This means that more heat is dissipated from the CO₂ in the atmosphere than from the Earth’s surface below.
 In other words: In the Antarctic, the increase in CO₂ concentration means that heat dissipation into space is increased, and it is therefore getting colder there, not warmer.

1. Reason for the 240 W/sqm: https://www.zamg.ac.at/cms/de/klima/informationsportal-klimawandel/klimasystem/umsetzungen/energiebilanz-der-erde ︎
2. Calculation: 10*168h/72 years = 23 h/decade => (23h/decade)/1544h = 1.5%/decade ︎