Here we have a well-known graphic about the Global Energy Flow:
Let's just repeat and explain the facts: (all figures approximately in watts/m²)
1. Incoming global shortwave radiation: 340
- Reflected by clouds, atmosphere and surface 100 (Note: surface reflection is only 23 of the general budget,6.7%)
- Absorbed by atmosphere: 80
-Remaining 160 w/m² absorbed by the surface.
2. Now how to get rid of the surface heat:
- Transported into the atmosphere by thermal convection: 20
- Transported into the atmosphere by evaporation: 80
- Surface radiation through the atmospheric window
(these IR waves are not trapped by greenhouse gases): 40
- Remaining Surface Radiation 360 minus Back Radiation from the greenhouse gases 340:
Rest 20, wich are absorbed from the atmosphere.
-All of the 160 w/m² which heated up the surface, are now in the atmosphere.
3. Now we have in the atmosphere 75 from the incoming sunlight, 20 from convection, 85 from evaporation in total 200 which is radiated from the Greenhouse Gases towards open space. (or 240 together with the 40 which escaped through the Atmospheric Window.
Only 20 w/m² are radiated towards the atmosphere and are hopping like Pingpong balls between the greenhouse molecules. But as the outer space is about -270 centigrades (There is nearly nil Back Radiation from the space, except the sun), and as the distance between the molecules in the upper layer of the atmosphere is steadily growing with the distance from the surface, most of the heat will be radiated into the space.
So, what would happen, if we had no Greenhouse Gases?
In the contrary, O and N molecules cannot absorb nor radiate heat. But they can collect heat from other molecules and the earth surface through contact. This is why the air is a such a good insulator. Bu the heat, once trapped, cannot radiate, and the molecules stay hot. To cool down, they need the help from greenhouse gases.
Now we look at our Earth Surface, heated up with 160 w/m². 80 we get into the atmosphere trough evaporation, 20 through thermal convection. No greenhouse gases in the air, except water vapour. 40 will vanish through the Atmospheric window, and 20 don't go into the atmosphere but straight into space, as there are no disturbing GG.
Now we have a problem: There are 100 w/m² in the atmosphere, and they can't escape. No help from the GG. So the temperature will climb up to the hottest tempeartures on Earth, about 60°. The poles will melt, and we will be boiled. Thank God, we have the greenhouse gases! They don't heat up, they mostly cool.
Okay, there is something wrong with my model, as water vapour is also a greenhouse gas, and it can help in cooling a bit. But it will not help with all the 100w/m². Even some Watts are dangerous. Why? look at the graphic: There is mentioned a 0.6 or 0.9 w/m² net absorbed energy, which is't released from the surface. Which means even this small amount is considered as dangerous as it will remain in the atmosphere and heat it up. But we have to handle 100 w/m²!
Now we come to our first question: What will happen, when the green house gases are growing together with the Radiative Backforcing?
Only 20 w/m² will go through the atmospheric pingpong, all others have their own way. At the moment I have no good numbers, which amount of CO2 will increase the backforcing by 1 watt. But just lets get the picture: 1/8 (160 w/m² surface heating : 20 radiation into the atmosphere) of each additional Watt has to go through the greenhouse gases, the rest has other ways to come into the atmosphere or to the space.
But even this slightly hotter surface means:
1. More heat causes more evaporation, ergo more heat transport.
2.More heat causes more thermal convection, ergo more heat transport.
3. More heat causes more radiation, ergo more heat transport into space or the atmosphere.
4. Hotter atmosphere means more temperature difference to the space, ergo more heat radiation from the Greenhouse gases going there.
5. More heat causes more vapour in the air, ergo more clouds, which are reflecting incoming sunligth.
6. More GG in the atmosphere means more heat transport on the outer edge of the atmosphere to the space due to more heat collecting and emitting GG molecules.
7. What has not yet been discussed are the phases of heating and cooling. The model acts like a flat earth with all processes going on at the same time, wich is not true. Directly below the sun (e.g. on the equator) the incoming radiation is 1300+ w/m², wheras on the poles it is near to nil. There are cold and warm regions (where cold or warm winds can transport heat). Heating up during the day is followed by many hours for sufficient cooling. (in the dessert a boiling day can be followed by a real cold night) When it is hot, the outgoing radiation is much stronger than the backradiation, helping to get rid of the excess heat quickly. Also thermal convection during heat is much stronger.
Seems there are a lot of thermostatic functions here on our Earth to keep the climate in good shape. Seven physically well known effects seem more than sufficient to regulate the Earths climate. So from a theoretical point of view increased Greenhouse Gases seem not to be the big problem.
It's fair to add one possible obstacle: Some scientists believe that increased water vapour (=greenhouse Gas) in the atmosphere will lead to more radiative backforcing, which will increase the greenhouse effect. This is a not yet approved theory. In reality, steady expotentially rising CO2 has neither caused higher temperatures nor more water vapour during the last 17 years. The opposite cold be: More clouds (which reflect sunrays) through more vapour. One study (I have to look for the data) observes regularely clouds during hot hours in the tropics, which will exactly avoid overheating, when necessary.
So far my theory. I encourage to countercheck everything.