4 ms·

That why we look at the "global warming potential" [1]. But even with a time horizon of 100 years, methane is still 30 times potent than CO2. How can it be irr

by revax 7y ago

That why we look at the "global warming potential" [1]. But even with a time horizon of 100 years, methane is still 30 times potent than CO2. How can it be irrelevant? [1] https://en.wikipedia.org/wiki/Global_warming_potential https://en.wikipedia.org/wiki/Global_warming_potential

Merrill 7y ago
The numerator integral must decline rapidly as a function of TH unless the radiative efficiency is a strong function of time, which seems unlikely. Most of the actual warming effect of a methane release would occur in the first three decades, after which there would be a long tail of slight warming. Methane is not irrelevant, but "global warming potential" seems to obscure the actual time varying nature of the relative impacts. Methane is actually a much stronger greenhouse gas than carbon dioxide in the short run and less strong in the long run that global warming potential would indicate.
MikeSchurman 7y ago
30 times more potent for a similar mass. But we emit far far more CO2 than methane. To know if it's important you'd need to know by how much.
- revax 7y ago
  Well, methane is one the reasons why livestock and paddy fields emit so much greenhouse gases. These two examples are not insignificant.
  - jessaustin 7y ago
    Significance is almost beside the point. Any methane "emitted" by livestock is already present in the carbon cycle: cows eat grass which is made of atmospheric carbon. It isn't sensible to compare that to carbon from fossil fuels. This "methane is worse" proposition was used to argue that livestock production is as bad as burning fossil fuels, but of course that completely falls apart if the main problem with methane is the carbon dioxide into which it degrades. That carbon dioxide may have been methane for the last 12 years, but immediately before that it was grass and immediately before that it was the same existing carbon dioxide that it is again now. There isn't something magical about a cow's gut that somehow multiplies carbon levels.
    - hansbo 7y ago
      This has always been my thought as well, and I have never gotten a good explanation as to why it's wrong. If anyone has one I would love to hear it.
      - KirinDave 7y ago
        It was explained to me as: "even if an activity is carbon neutral, if it increases the net free atmospheric carbon it can have a negative effect." The areas we devote to cattle raising are increasing (often at the cost of carbon fixing native flora). So the amount of free methane and carbon are on the rise just by nature of human expansion. I'm not sure that is the whole story, but I always found that explanation helpful for questions like, "Why can't we switch to using charcoal based local power if its carbon neutral?"
    - revax 7y ago
      You are right saying that the carbon cycle is a closed cycle, there is no net change over time in carbon dioxide concentrations (as you are not using fossile fuels or burying grass). But during the 12 years lifespan of methane you will have considerably more radiative forcing.
    - newscracker 7y ago
      > Any methane "emitted" by livestock is already present in the carbon cycle: cows eat grass which is made of atmospheric carbon. It isn't sensible to compare that to carbon from fossil fuels. Considering that: a. most cows in today’s world don’t eat grass, or rather, they eat a lot more soy, corn and other foods grown for them b. the feed for the cows is grown using conventional methods to keep costs under control, which also implies using fertilizers that are produced from fossil fuels (also add the fossil fuels used in the transport of feed as well as the animals) I don’t understand how your entire argument holds true. Seems like there are gaps in your model of the world.
      - revax 7y ago
        With a traditional grazing system he's right. You don't need any fertilizers, cows will just eat grass. Of course you can't feed billions of people with it nor you will be able to eat meat every day. But even if you are carbon neutral over time, the methane released will still have a negative effect as it trap more energy than CO2. https://www.nzagrc.org.nz/faq-1,listing,464,how-do-livestock-affect-the-carbon-cycle.html https://www.nzagrc.org.nz/faq-1,listing,464,how-do-livestock...

by revax 7y ago

Merrill 7y ago

The numerator integral must decline rapidly as a function of TH unless the radiative efficiency is a strong function of time, which seems unlikely. Most of the actual warming effect of a methane release would occur in the first three decades, after which there would be a long tail of slight warming. Methane is not irrelevant, but "global warming potential" seems to obscure the actual time varying nature of the relative impacts. Methane is actually a much stronger greenhouse gas than carbon dioxide in the short run and less strong in the long run that global warming potential would indicate.

MikeSchurman 7y ago

30 times more potent for a similar mass. But we emit far far more CO2 than methane. To know if it's important you'd need to know by how much.

revax 7y ago
Well, methane is one the reasons why livestock and paddy fields emit so much greenhouse gases. These two examples are not insignificant.
- jessaustin 7y ago
  Significance is almost beside the point. Any methane "emitted" by livestock is already present in the carbon cycle: cows eat grass which is made of atmospheric carbon. It isn't sensible to compare that to carbon from fossil fuels. This "methane is worse" proposition was used to argue that livestock production is as bad as burning fossil fuels, but of course that completely falls apart if the main problem with methane is the carbon dioxide into which it degrades. That carbon dioxide may have been methane for the last 12 years, but immediately before that it was grass and immediately before that it was the same existing carbon dioxide that it is again now. There isn't something magical about a cow's gut that somehow multiplies carbon levels.
  - hansbo 7y ago
    This has always been my thought as well, and I have never gotten a good explanation as to why it's wrong. If anyone has one I would love to hear it.
    - KirinDave 7y ago
      It was explained to me as: "even if an activity is carbon neutral, if it increases the net free atmospheric carbon it can have a negative effect." The areas we devote to cattle raising are increasing (often at the cost of carbon fixing native flora). So the amount of free methane and carbon are on the rise just by nature of human expansion. I'm not sure that is the whole story, but I always found that explanation helpful for questions like, "Why can't we switch to using charcoal based local power if its carbon neutral?"
  - revax 7y ago
    You are right saying that the carbon cycle is a closed cycle, there is no net change over time in carbon dioxide concentrations (as you are not using fossile fuels or burying grass). But during the 12 years lifespan of methane you will have considerably more radiative forcing.
  - newscracker 7y ago
    > Any methane "emitted" by livestock is already present in the carbon cycle: cows eat grass which is made of atmospheric carbon. It isn't sensible to compare that to carbon from fossil fuels. Considering that: a. most cows in today’s world don’t eat grass, or rather, they eat a lot more soy, corn and other foods grown for them b. the feed for the cows is grown using conventional methods to keep costs under control, which also implies using fertilizers that are produced from fossil fuels (also add the fossil fuels used in the transport of feed as well as the animals) I don’t understand how your entire argument holds true. Seems like there are gaps in your model of the world.
    - revax 7y ago
      With a traditional grazing system he's right. You don't need any fertilizers, cows will just eat grass. Of course you can't feed billions of people with it nor you will be able to eat meat every day. But even if you are carbon neutral over time, the methane released will still have a negative effect as it trap more energy than CO2. https://www.nzagrc.org.nz/faq-1,listing,464,how-do-livestock-affect-the-carbon-cycle.html https://www.nzagrc.org.nz/faq-1,listing,464,how-do-livestock...