3 ms·
I feel like I'm being gaslighted. In advanced physical chemistry we took IR spectroscopy of methane and CO2 and CO2 definitely had much, much more absorption t
by dnautics 5y ago
I feel like I'm being gaslighted. In advanced physical chemistry we took IR spectroscopy of methane and CO2 and CO2 definitely had much, much more absorption than methane on account of the dipole difference between Carbon and oxygen (IR absorption depends on stretching modes between atoms of different electronegativity, carbon is very close to methane). At the time, it was explained to us young chemistry students that methane was more potent GHG because it lasted in the air longer (CO2 is scrubbed by plants).
Am I missing something? How can methane be a more potent GHG if it has lower IR absorption AND a shorter lifespan?
Edit: found spectra here (not the data that i took, obviously):
https://wattsupwiththat.files.wordpress.com/2014/04/methane_absorption_spectra.png?w=720 https://wattsupwiththat.files.wordpress.com/2014/04/methane_...
CO2 has a big fat band that blows out the absorption at 4.5 um in a region untouched by water (and one that is overwhelmed by water); methane has two spiky bands both of which are partially occluded by water.
- mongol 5y agoCould it be something like how it is distributed in the atmosphere?
- dnautics 5y agoI'm curious and hoping someone can explain it to me
- adrianN 5y agoI'm just guessing: a) We don't have enough water in the atmosphere that the overlap with Methane meaningfully reduces net absorption, b) in the bands Methane absorbs there is more radiation available to absorb than in the CO2 band. If both are true that would explain the bigger effect of Methane.
- agilebodyshoppe 5y agothe greenhouse effect is about internal reflections basically. its the same effect that makes cloth appear darker when its wet even though water is basically colorless. greenhouse gases bend light slightly, making it more likely that a light ray will hit the ground multiple times.
- dnautics 5y agoThis is a wrong answer if I've ever heard one.
- agilebodyshoppe 5y agoseems like ive misunderstood this since i was a child. thank you for allowing me to embarrass myself in a safe environment.
- dnautics 5y agoIt's ok! Not all of us are atmospheric chemists! I certainly am not one.... Hence my lack of understanding.
- quantum_magpie 5y agoFor the most part, the CO2 absorption bands are already saturated -- increasing CO2 concentration has much less effect on transmission spectrum than that for methane.