So what I’m reading is that these gas absorb the light from the sun and keeps it trapped on the earth.
What I don’t get is how is it letting the light and heat in from the sun in, but not the light and heat reflected from the Earth out? If it’s a barrier, shouldn’t it block both ways? If it’s not a barrier, how is it trapping the heat?
In: 950
Others made a good point about different types of radiation, which is true and a very important aspect of the greenhouse effect.
In addition, it’s also not so much a barrier as a filter or a sieve. If you look at it as a sieve than it isn’t really all that weird that it lets in more than it lets out. Let’s say 80% passes the sieve and 20% is filtered out. In that case 80% of sunlight comes into the earth, passing the sieve once. Going out it passes the sieve again and 20% is filtered out again, so only 64% leaves the earth.
To add to others good answers, we *can* do the opposite with materials designed to emit wavelengths transparent to our atmosphere. [Here is a cool video on making it](https://youtu.be/N3bJnKmeNJY)
The light and the heat are two different things. The atmosphere is transparent enough for the light to get through because photons simply pass through it mostly.
But heat is essentially the energy of molecules in a fluid bouncing/colliding and generally moving. So for heat to leave the system, all that energy has to make its way out of the outer atmosphere. This is why that is more difficult
Comes in as visible light which passes through the atmosphere no problem and then is radiated out as infrared which doesn’t travel through the atmosphere as well.
Oversimplification.
Basically, Regular sunlight/energy is going from Space to Earth, where it’s reflected, then back to Space.
What happens with greenhouse gases, like carbon dioxide, chlorofluorocarbons, nitrous oxides, etc, is the bigger molecules interact with the sun’s energy and slow down the transfer back into space.
The longer the energy spends in the atmosphere the more the atmosphere heats up. If the concentration of greenhouse gases get high enough it basically traps the energy indefinitely.
Infrared radiation is a form of radiation “created” by the Earth in reaction to receiving radiation from the Sun and it is this radiation which is reflected back to the surface of the Earth causing the rise in temperature. https://youtu.be/_vFRSAs9DiY
The light from the sun that heats the earth up (visible light) is different from the light the earth emits to cool down (infrared light). GHGs are opaque to infrared light but not opaque to visible light. They slow down cooling but let the earth heat up at the same rate
How well light transmits through a material depends on the wave length of light. Light from the sun has a peak intensity in the visible range, which transmits through the atmosphere fairly well. Once that light hits earth, it is largely absorbed and transformed into heat which radiates away through longer infrared wavelengths. It is these infrared wave links that greenhouse, gases absorb, thus trapping the energy
Imagine that barrier as having two different surfaces, one of them is more reflective than the other, lets say a sunray hits the ozone layer 40% of that makes it through and hits the ground, then the ground reflects it and it bounces up again this time only 40% of that 40% actually makes it out, creating a cumulative effect, look up how a greenhouse works
Sunlight that comes in is largely in the visible spectrum of light.
The earth radiates heat out as light in the infrared spectrum.
Greenhouse gasses absorb a lot of infrared light, but little to no light in the visible spectrum, creating a one way mirror for heat. (methane for instance is completely transparent to our eyes, but is pitch black through an IR-camera)
Latest Answers