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"So what can possibly cause warming is only the effect of the difference in temperatures between the CO2 gas and the surface. Which should only be significant in higher altitudes. Which have much less CO2 because it is heavier." My understanding is that CO2 being heavier results in it having lower concentration only at very high altitudes, which are irrelevant for CO2-caused warming. At the relevant altitudes, it's well mixed due to winds. In the basic mechanism as I understand it, what's relevant is the altitude at which a photon emitted by CO2 is likely to escape to space, rather than being reabsorbed by another CO2 molecule. If CO2 concentration is increased, this altitude goes up, to where CO2 concentration is the same as before. At higher altitudes, the temperature is lower, so emission is from a colder gas, which means less energy is emitted. This isn't a stable situation, however, since the amount of energy coming in is the same as before. Equilibrium is restored when the whole atmosphere heats up a bit, so the temperature at the altitude where photons escape to space is the same as before. Understanding this makes the discussion about positive feedback from water vapour seem more iffy. Warming is supposed to increase H2O in the atmosphere, which is a greenhouse gas, indeed, the one with most effect. But all that matters is the amount of H2O at the altitude where photons are emitted to space. What happens at that altitude seems like a very complex question, so one is really back to trusting the simulations, which as you say don't seem all that trustworthy. Disclaimer: Not really a physicist. |