OK, you have all seen the question before BUT let's make the challenge a little different this time. I want you to use the Feynman Method ! You have to explain it simply, preferably just text but one or 2 sketch diagrams may be OK (no complicated graphs with multiple colours please) and I am going to limit you to 150 words. Who fancies the challenge - make sure you don't leave out any of the important physics. This question is asking for an explanation of how something works. I am not interested in experimental evidence or proof, just a clear explanation that you can chat about to someone to help explain the physics behind it in as simple terms as possible. Like if your mate down the pub says, OK, tell me how this works then.
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1$\begingroup$ I don't think that this is the right venue for artificially constrained challenges like this. If someone can answer this well in 150 words with a sketch diagram, then the place to post that answer is the existing question on this topic. Splitting every question into sub-questions restricted to different answer styles is going to make information harder to find, not easier. $\endgroup$– PontCommented Apr 14, 2017 at 10:01
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1$\begingroup$ I don't think the 'experiment' question is a duplicate of this one, but I can't find a better duplicate (Such a 'basic' questions has not been asked?). This answer explains it well in a little under 250 words and a picture. $\endgroup$– Jan DoggenCommented Apr 14, 2017 at 11:32
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1$\begingroup$ @JanDoggen Maybe you're right: the questions are a little different. On the other hand, most of the answers to the earlier question are broader than the question (since they have to explain why lab experiments aren't the whole story) and would also work well as answers to this one. But I still maintain that arbitrary restrictions on answer format have no place here. It would also be fun to explain radiative forcing in iambic pentameter or interpretative dance, but that choice of medium belongs in the answer, not the question. If the restrictions are edited out I'll retract my close vote. $\endgroup$– PontCommented Apr 14, 2017 at 19:22
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$\begingroup$ How can a trace amount of arsenic possibly be bad for me. It's a scam I tell ya. A scam. $\endgroup$– userLTKCommented Apr 14, 2017 at 21:15
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1$\begingroup$ Feynman wrote: “Is no one inspired by our present picture of the universe? Our poets do not write about it; our artists do not try to portray this remarkable thing. The value of science remains unsung by singers: you are reduced to hearing not a song or poem, but an evening lecture about it.” I don't see anything silly about explaining science in poetry or dance, and I don't think he did either. I don't object at all to answers which impose formal constraints on themselves, but, once more: I don't think it's helpful for a Stack Exchange question to impose formal constraints on the answers. $\endgroup$– PontCommented Apr 16, 2017 at 21:55
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The answer can be explained very simply. The Oxygen and Nitrogen (the non trace gases) are mostly transparent to thermal wavelength of light that leave Earth's surface. CO2 in the air, can be compared to colored dye in water. It's not too difficult to imagine that water with 280 ppm red dye might be visibly lighter than water with 400 ppm of the same dye. The real answer is somewhat more complex as you need to look at different bands in the IR spectrum that get reflected by different trace gases, but that's the gist.
55 words under. :-)
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$\begingroup$ And you didn't use the words temperature or heat once ! Mind you I like the use of the dye analogy. Of course if 999,600 ppm are transparent then 99.96% of the thermal radiation passes straight through your "dye". $\endgroup$– user7733Commented Apr 16, 2017 at 20:27
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2$\begingroup$ @user7733 No, it doesn't. A couple of drops of ink make a glass of water completely opaque, even if it's still 99% water. $\endgroup$– gerrit ♦Commented Apr 18, 2017 at 13:56
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1$\begingroup$ @user7733 you wanted 150 words or less. I came in under 100. (pats self on back). Scientists knew about the behavior of thermal radiation and greenhouse gas for decades, but assumed that circulation would undo any CO2 effect, that and no significant observed effect, so nobody took it seriously for a long time. It took super-computers and a whole lot of measurements to work out better estimates. The true answer to your question needs more than 150 words. The short answer is that a trace gas is enough because the non trace gasses are largely unable to absorb thermal radiation. $\endgroup$– userLTKCommented Apr 18, 2017 at 20:43