Intuitively, the GHGs makes the atmosphere a little like a one-way "blanket", allowing some energy through (at optical and UV frequencies), but making it harder for the infrared radiation to get back out again.
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In more detail, the temperature of the Earth+atmosphere system isn't changed by GHGs (since the absorptivity and thus emissivity isn't changed, and ignoring the role of water vapour in setting emissivity). But the ground temperature may well be.
That sounds pretty plausible to me. I'll want to think on it. It may help explain something else I've been confused about, which is that I've read that the altitude of GHGs in the atmosphere matters.
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Just linking to your other tweet, to collect everything before Twitter's multithreading makes a mess:https://twitter.com/PESimeon/status/1096989969225154560 …
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Summing up further: do a Stefan-Boltzmann calculation with the combined Earth+atmosphere system. This _isn't_ changed by the GHGs. But then you can construct some simple model of atmospheric heating based on GHG absoption which lets you infer the ground temperature.
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And I totally buy that that will be determined by the concentration of GHGs, probably in quite an interesting way, possibly dependent quite a bit on the variation of density with altitude (not just overall concentration).
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Thanks again
@PESimeon - I'll want to work through the details, but it seems very likely you've pointed out the source of my confusion.
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I've read it before. But I'll read it again with
@PESimeon's comment in mind, and may well now see how to clear up the confusion I had with the emissivity and Stefan-Boltzmann law.
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