My very limited understanding of the subject is that the heat from the sun goes through the atomosphere and then it just kinda bounces between the atomosphere and the earth. Increased greenhouse gasses lead to increased “bounceback”. But shouldn’t increased greenhouse gasses also reduce the heat that enters the system in the first place?
Apologies for any confusion caused by being on mobile and not speaking English as a native language.
In: Biology
Think about the inside of a car on a sunny day, its hotter in there than the outside right? Shouldn’t the the glass reflect all the heat back out instead of trapping it in the car?
Rule 7
[https://commons.wikimedia.org/wiki/File:Solar_Spectrum.png](https://commons.wikimedia.org/wiki/File:Solar_Spectrum.png)
This is the sun spectrum, meaning what are the different wavelenght the Sun emit. You can also see how much the atmosphere absorb or reflect back to space. The Sun mostly emit in visible light, but you can see the different gases absorb and reflect specific wavelenght.
You can see that CO2 absorb and reflect basically nothing, because the incoming light have very little photon at the specific wavlenght that interact with CO2.
There is phenomenon called thermal radiation. ALL matter emit radiation at a specific wavelenght depending on their temperature. If you look at your oven heating element it’s glowing reddish, a fire glow yellow/orange at the center where it’s hotter, then go to reddish on the outside where it’s colder, and most matter around us is cold enough to emit radiation in infrared. As most of the incoming heat is in visible light, but most of the heat the earth send back to space is in infrared, which CO2 will in part absorb and reflect.
* Energy from the sun enters as light.
* Light passes through the gases very easily.
* Light hits something on Earth and gets converted to heat
* The gases are good at trapping the heat.
The rays coming from the sun have a short wavelength which makes it easy for them to go through the atmosphere. When those hit the earth, they are partly converted to infra red heat rays which have a long wavelength thus making it harder to not hit a greenhouse gas molecule in the Atmosphere
You can think of it like throwing small and big balls against a net. Most of the smaller ones will easily fit through the holes, but the big ones have a great chance of hitting a strings of the net.
The energy coming in from the sun is at a wavelength that passes through those greenhouse gasses. The heat the earth tries to radiate out to space is at a different wavelength, which bounces off of them. The effect really is very much like a greenhouse in that regard. It captures and retains heat. The greenhouse gasses are like the glass on a greenhouse.
heat isn’t just heat, and greenhouse gasses care about what kind of light is holding that heat.
When the sun is blasting us with energy it comes in as more or less even distribution of electromagnetic waves, including visible light and ultra-violet light. Greenhouse gasses tend to be transparent to those higher frequencies of light and just pass it right trough uninterrupted.
However the earth is mostly radiating heat out via infrared light. Greenhouse gasses are *not* transparent to that, and will try to absorb that radiation. This causes the”bounceback”.
Essentially the gasses form a one-way mirror. It will let the high-energy light pass trough from the sun, but doesn’t allow the lower-energy infrared radiation to pass back out from the other side.
I think most people have covered the main answer to your question, which is that the wavelength changes. The only nitpick I have with many explanations is that greenhouse gases don’t “reflect” heat back to Earth. Rather, they absorb it. Those molecules of water vapor, methane, CO2, etc., are warmed up by IR radiation, warming the atmosphere. They can then also radiate the energy themselves but that is not the same as reflecting, which is part of the reason some say that “greenhouse effect” is not a completely accurate name. Such radiated heat goes in all directions, including a portion of it that still ends up radiating in to space.
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