5 ms·

I don't think it's that complicated. Start with water vapor - moisture evaporates from the ocean, lakes, soil, vegetation. On average such a water molecule st

I don't think it's that complicated. Start with water vapor - moisture evaporates from the ocean, lakes, soil, vegetation. On average such a water molecule stays in the atmosphere for 4-10 days - because water condenses as rain, unlike methane or carbon dioxide. Water vapor increase accounts for about 2/3 of the immediate global warming effect, but is controlled by temperature, which is in turn controlled by the CO2 and CH4 in the atmosphere. Hence we can think of water vapor in the atmosphere as a feedback to the CO2/CH4 forcing. This is not too difficult for people to understand. The fact that methane is a reactive gas, i.e. CH4 + O2 -> CO2 over time (OH just being an intermediate), means it gets converted to CO2, accounting for the relatively short 10-year lifetime. CO2 + OH/O2 does nothing, so we can expect a longer lifetime. The notion that CO2 lifetime in the atmosphere is 100 years is perhaps a bit more complicated, as it involves ocean uptake and things like that, but it's all fairly straightforward. The gas/oil/coal sector might want people to believe that passing gas in a closed room won't eventually create a stink, but it's the same general concept.

boringg 5y ago
I agree I don't think it's that complicated but when you have a regulatory industry surrounding complex science with politicians weighing in it can get very tricky. I refer to climate deniers/paid advocacy groups and mud rakers who constantly try and trip up progress by trying to bring sow doubt through poking holes in the argument or nitpicking small issues.
lstodd 5y ago
You forgot the albedo effect of the clouds. On both sides - top and bottom. This has not ever been modelled to my knowledge. And it is very complicated.
- quantum_magpie 5y ago
  Albedo is included in every single atmospheric model.
  - lstodd 5y ago
    Cloud albedo? Its effects depending on surface temps? Cloud cover changes wrt local climate change? Do you have any sources for that?
s1artibartfast 5y ago
>I don't think it's that complicated The complicated part that I have spent many hours trying to understand is how more CO2 increases the greenhouse effect if the the frequencies it absorbs are already 100% absorbed. If current CO2 PPM absorbs 100% of the IR it can interact with, why does X+1 PPM have positive forcing? The feedback loop is already maxed out? If I shine a flashlight at a concrete wall, it doesn't matter if I make the wall thicker.
- NumberWangMan 5y ago
  > The complicated part that I have spent many hours trying to understand is how more CO2 increases the greenhouse effect if the the frequencies it absorbs are already 100% absorbed. I'm curious where you're getting the figure that the relevant frequencies are 100% absorbed, I didn't think it was that high, but I'm far from an expert on this. I don't think you can ever get to 100%, just arbitrarily close -- there's always the chance that a given photon will get lucky and escape without hitting any CO2 molecule. But I think that if every IR molecule that was radiated from earth hit a CO2 molecule, what would happen after that first absorption would matter. The photon would get re-radiated with an equal chance to go in any direction. If it goes up, great, it escapes into space -- but the more CO2, the more of a chance that it gets absorbed again and re-radiated back down. So it's not a concrete wall, it's like a field of gopher holes with gophers that will take any golf ball that falls into their hole and chuck it out randomly. Even if the field is dense enough that you can't roll a golf ball directly across it without going into at least one hole, if you increase the density of gopher holes more, it still lowers the chance that the ball will make it to the other side. *edit - This article[1] I just found goes more into the math, it helped clarify it a bit for me. [1] https://www.geoexpro.com/articles/2022/04/recent-advances-in-climate-change-research-part-xiv-the-doom-of-a-photon-on-a-random-walk https://www.geoexpro.com/articles/2022/04/recent-advances-in...
  - s1artibartfast 5y ago
    >I'm curious where you're getting the figure that the relevant frequencies are 100% absorbed, I didn't think it was that high, but I'm far from an expert on this. Last time I researched this I saw various estimates that IR in the CO2 absorptions bands only makes it 10-25 meters before it 99% of it is absorbed by CO2. Your link gives and average distance of 2.6m for IR in the CO2 absorption band. >Assume that [C]=400 ppm. The mean free path becomes 2.646m so that N=3024. The probability of returning to the Earth becomes p(1)=0.9997. A photon with frequency or wavenumber near the centre of the absorption band is virtually certain to make the return to Earth. If the CO2 concentration is doubled, the probability doesn’t change much; it becomes p(1)=0.9998. Any CO2 increase has minor effect on the photons in the center of the absorption band. This part of the band is ‘saturated’. The website and other papers I have read seem to argue that it is not the majority of photons in the center of the emission and absorption band, but a much smaller number of off band photons in the "wings" that matter for the greenhouse effect. When I have tried to read about how this works, I get bogged down by the complexity of the science, and a lot of different arguments from the climate skeptic community which I don't have the foundational understanding to reject. They say that the shoulder theory is bunk because it ignores interactions between CO2 and other molecules. Instead of photons bouncing from CO2 to CO2, they say that the CO2 passes the energy off to nitrogen and oxygen. I don't really give too much weight to the climate skeptic criticism, but I do have to acknowledge that greenhouse effect is a lot more complicated than taught in grade school and there is still a lot of active research using extremely simplified models trying to model how it works from first principles with a lot of exclusions and assumptions. like the paper cited in the link you shared from 2012. Thank you for sharing the link, I will take some time to try to read and digest it.
alar44 5y ago

boringg 5y ago

I agree I don't think it's that complicated but when you have a regulatory industry surrounding complex science with politicians weighing in it can get very tricky. I refer to climate deniers/paid advocacy groups and mud rakers who constantly try and trip up progress by trying to bring sow doubt through poking holes in the argument or nitpicking small issues.

lstodd 5y ago

You forgot the albedo effect of the clouds. On both sides - top and bottom. This has not ever been modelled to my knowledge. And it is very complicated.

quantum_magpie 5y ago
Albedo is included in every single atmospheric model.
- lstodd 5y ago
  Cloud albedo? Its effects depending on surface temps? Cloud cover changes wrt local climate change? Do you have any sources for that?

s1artibartfast 5y ago

>I don't think it's that complicated The complicated part that I have spent many hours trying to understand is how more CO2 increases the greenhouse effect if the the frequencies it absorbs are already 100% absorbed. If current CO2 PPM absorbs 100% of the IR it can interact with, why does X+1 PPM have positive forcing? The feedback loop is already maxed out? If I shine a flashlight at a concrete wall, it doesn't matter if I make the wall thicker.

NumberWangMan 5y ago
> The complicated part that I have spent many hours trying to understand is how more CO2 increases the greenhouse effect if the the frequencies it absorbs are already 100% absorbed. I'm curious where you're getting the figure that the relevant frequencies are 100% absorbed, I didn't think it was that high, but I'm far from an expert on this. I don't think you can ever get to 100%, just arbitrarily close -- there's always the chance that a given photon will get lucky and escape without hitting any CO2 molecule. But I think that if every IR molecule that was radiated from earth hit a CO2 molecule, what would happen after that first absorption would matter. The photon would get re-radiated with an equal chance to go in any direction. If it goes up, great, it escapes into space -- but the more CO2, the more of a chance that it gets absorbed again and re-radiated back down. So it's not a concrete wall, it's like a field of gopher holes with gophers that will take any golf ball that falls into their hole and chuck it out randomly. Even if the field is dense enough that you can't roll a golf ball directly across it without going into at least one hole, if you increase the density of gopher holes more, it still lowers the chance that the ball will make it to the other side. *edit - This article[1] I just found goes more into the math, it helped clarify it a bit for me. [1] https://www.geoexpro.com/articles/2022/04/recent-advances-in-climate-change-research-part-xiv-the-doom-of-a-photon-on-a-random-walk https://www.geoexpro.com/articles/2022/04/recent-advances-in...
- s1artibartfast 5y ago
  >I'm curious where you're getting the figure that the relevant frequencies are 100% absorbed, I didn't think it was that high, but I'm far from an expert on this. Last time I researched this I saw various estimates that IR in the CO2 absorptions bands only makes it 10-25 meters before it 99% of it is absorbed by CO2. Your link gives and average distance of 2.6m for IR in the CO2 absorption band. >Assume that [C]=400 ppm. The mean free path becomes 2.646m so that N=3024. The probability of returning to the Earth becomes p(1)=0.9997. A photon with frequency or wavenumber near the centre of the absorption band is virtually certain to make the return to Earth. If the CO2 concentration is doubled, the probability doesn’t change much; it becomes p(1)=0.9998. Any CO2 increase has minor effect on the photons in the center of the absorption band. This part of the band is ‘saturated’. The website and other papers I have read seem to argue that it is not the majority of photons in the center of the emission and absorption band, but a much smaller number of off band photons in the "wings" that matter for the greenhouse effect. When I have tried to read about how this works, I get bogged down by the complexity of the science, and a lot of different arguments from the climate skeptic community which I don't have the foundational understanding to reject. They say that the shoulder theory is bunk because it ignores interactions between CO2 and other molecules. Instead of photons bouncing from CO2 to CO2, they say that the CO2 passes the energy off to nitrogen and oxygen. I don't really give too much weight to the climate skeptic criticism, but I do have to acknowledge that greenhouse effect is a lot more complicated than taught in grade school and there is still a lot of active research using extremely simplified models trying to model how it works from first principles with a lot of exclusions and assumptions. like the paper cited in the link you shared from 2012. Thank you for sharing the link, I will take some time to try to read and digest it.

alar44 5y ago