Hier een (lange) uitleg van de feiten in het Engels, geleend uit een ander forum. Een van de problemen van het broeikaseffect is dat er veel mensen een mening over hebben zonder er iets over te weten. De 15 stappen hier beneden zijn de basis en onomstreden.
Naar mijn mening valt er pas een discussie te voeren als je onderstaande processen snapt. Het is lang maar het is natuur/scheikunde van het niveau middelbare school.
Why is CO2 the most important greenhouse gas?
1) The earth receives most of its heat from the sun in the visible spectrum (the sun is a black body emitter with a surface temperature of 5778K). At the orbit of the Earth, the intensity of the sun is 1350W/m^2. This varies slightly with the earth's orbital parameters, therefore we get Milankovich cycles (but these are also well understood and bringing them in at this point would not be pedagogical). It also varies with the number of sunspots (they are cooler) --- this is also well understood and in the advanced model but too much to introduce at this point.
2) The amount of heat the Earth absorbs from the sun is thus I_sun=1350W/m^2 times the area that's facing the sun or pi radius^2 ... and we subtract the Earth's albedo (which is 0.33 ... we can leave this as a parameter or a microphysics simulation for later on. People do that too. E.g. when the ice cap melt, the albedo goes down.) So in total I_sun pi r^2 (1-alpha) ... that's about 1000W/m^2.
2) The earth emits this in the infrared band (the earth is also a black body emitter with a surface temperature of 288K). A blackbody emitter radiates via the Stefan-Boltzmann law, so the surface of the earth (goes out in all directions) or 4 pi r^2 times sigma*T^4, where T is the Earth's surface temperature, and sigma is the Stefan-Boltzmann constant which is 5.67e-8 in SI units (I'll keep everything in SI). I_earth = 4pi r^2 sigma T^4
3) There's an energy balance between the two so that ingoing energy from the sun matches outgoing energy from the earth. So I_sun = I_earth. If this is not in balance, the earth would either heat up or cool down until it is satisfied because if you heat up an object (like the earth) then it will start emitting infrared until it's in balance. This happens at the equilibrium temperature. We can solve for that, so
I_sun pi r^2 (1-alpha) = 4pi r^2 sigma T^4 => T^4 = (1-alpha) I_sun / (4 sigma) ... Everybody has all the numbers, so please calculate.
You should all get 251.3K for the Earth's surface temperature.
This is high school level, so everybody reading along should be able to get the same number I did.
No, don't just trust me. Calculate and verify.
Now, you'll notice a one thing. This result is much lower than the actual observed surface temperature of 288K. Why is that? It's because I haven't added greenhouse gases yet. Fourier noticed the same thing back in 1826 which caused him to postulate the greenhouse affect.
Currently our model has no atmosphere, but it does account for energy balance.
4) Now lets add an atmosphere to see the greenhouse effect. The greenhouse effect works because the atm (greenhouse) doesn't stop visible light (it's transparent to visual wavelenghs) but it attenuates/stops/reduces infrared. You can see through glass with your eyes but it stops heat so you can't feel it on your skin. Try it. The key point here is that radiation comes in at visible wavelength. Gets absorbed ... and tries to leave at a much longer wave lengths where it gets blocked.
This is how greenhouses work. Basic physics.
I'll do a simple slab model (aka a one-zone model).
Instead of just the Earth and the Sun. We'll have Earth, Sun, and atmosphere (which you can think of as a piece of glass---made out of air), so we need to keep track of where the radiation goes and leaves from all three of them. Fourier understood this almost 200 years ago.
As before, ultimately, what comes in eventually goes out once a temperature equilibrium is reached.
* All radiation from the sun (visible) goes directly through the atmosphere to the surface. That was I_sun (1-alpha) pi r^2.
* All the radiation from the Earth (infrared) goes up and gets absorbed in the atmosphere (because it's opaque to IR). That was 4pi r^2 sigma T^4.
* Half of the radiation (also infrared) from the atmosphere is radiated back down I_atm_down and half is radiated up I_atm_up.
How does this add up?
What goes into the atmosphere equals what comes out: 4pi r^2 sigma T_earth^4 = I_atm_down + I_atm_up or because I_atm_up = I_atm_down and both are 4pi r^2 sigma T_atm^4 (think of the atmosphere as a hollow sphere with the Earth in the center that radiates in both directions, we get sigma T_earth^4 = 2 sigma T_atm^4
What goes into the ground equals what comes up. The ground is receiving visible light from the sun and IR from the atm, so
4pi r^2 sigma T_Earth^4 = pi r^2 I_sun (1-alpha) + 4pi r^2 sigma T_atm^4
What enters the atm+earth system from the sun goes out from the atm (via IR), so I_atm_up= 4pi r^2 sigma T_atm^4 = I_sun pi r^2 (1-alpha)
Now, lets calculate T_earth in the slab-model.
sigma T_atm^4 = I_sun (1-alpha) / 4 and we insert that in sigma T_earth^4 = 2 sigma T_atm^4 = 2 I_sun (1-alpha) / 4, so T_earth = 298K.
That's 47 degrees higher. Cf 251K wo atm and 288K measured. Not bad for something that can be calculated on the back of a napkin.
Anyone who has followed along so far now understands the greenhouse effect at a level of the science community at the time Andrew Jackson was president or at the level at which high school students should be able to in current times. This is basically highschool physics and if I didn't have to type it down, I could sketch it out in 5 minutes on a black board.
If you made thus far you now understand why the Earth is neither colder than Hoth nor warmer than Vulcan.
Again, don't trust me, verify, using HS level science.
However, even this crude level is far more sophisticated that anything that happens in the comment space when uninformed laymen talk about climate change. This makes me sad and this is why I urge people to either read a book or get out of the kitchen when the adults are cooking. Real models are much more sophisticated. The ones I worked with to model surface/atmospheres on neutron stars and white dwarf stars had hundreds of zones detailing the transport between each of them in far greater detail including how the gas could diffuse and react chemically. Modern climate models are much more sophisticated still.
5) But all I've shown so far is why red-herring comments about "only a 1% difference" are eye-rolling to someone who understands the physics at this simple level. Try increasing I_sun by 1% and see what effect you get on the surface. Temperature goes up by 0.7C or 1.2F ... which also happens to be around the order at which temperatures have actually increased since we started adding CO2.
Key-point: Difference in the energy balance goes with the fourth root (because Stefan Boltzmann) .. and so because I'm one of those people who can do math in my head, I'll just go ... (1.01)^0.25 * 288K = 288.7K