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OK, let me change my question to:

Some random person told me that the parts of the spectrum that are absorbed by CH4 are already absorbed by H2O, which is way more prevalent, so the CH4 doesn't matter much.

Is that true/valid/scientific?






Nearer the top of the atmosphere, the concentration of H2O is much less, and the argument breaks down, because it’s the top layers that radiate to space. Lower in the troposphere, photons are being absorbed and re-radiated, but not escaping.

In general, this stuff is complicated, and it’s easy for people using “motivated reasoning” to come up with the answer they want. Lots of comments reflecting such misinformation appear on HN — it’s frustrating.

So, listening to random people isn’t such a good idea. Much better to read a report from people who study this stuff, like: https://nca2018.globalchange.gov/, which I recommend to technically interested nonspecialists.

(I eat lunch with one of the co-authors of the technical paper in Nature linked to the OP, the press release is: https://www.jpl.nasa.gov/news/news.php?feature=7535, paper is: https://www.nature.com/articles/s41586-019-1720-3)


Thank you for a simple, intellectual answer.

Obviously I am not taking in information without skepticism, otherwise I would not have asked the question.

But if I can't read something like that and refute it, then obviously I don't understand the issue very well. The best way to remedy that is to ask (not ignorant silence), so I'm a bit disappointed with the other replies who ridiculed me for asking.


Without a lot of background (some mix of grad school, regular interaction with experts at conferences, reading journal publications) you will be easily misled by motivated reasoning, which is everywhere in this domain. People spend their careers on this stuff. Undergrad physics, chemistry, and earth science is not enough.

Resources like the overview report I linked are critical.




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