4 ms·

Where did you get that? Every link I've ever seen indicates that the half-life is 7-9 years. Regardless of what the half-life is, what you say is true about th

by zasz 10y ago

Where did you get that? Every link I've ever seen indicates that the half-life is 7-9 years. Regardless of what the half-life is, what you say is true about the concentration of methane. It is so much better at trapping heat than carbon dioxide, though, that even over a 100 year time frame, it will warm the earth 34 times more than carbon dioxide would. (https://www.epa.gov/ghgemissions/understanding-global-warming-potentials https://www.epa.gov/ghgemissions/understanding-global-warmin...)

Retric 10y ago
CO2 concentrations went from 280,000 to ~404,000ppb CH4 concentrations went from 700 to 1,850. So if you use 34x that 1,000ppb is only 39,000 vs 124,000 meaning it's significantly less important overall contribution. It would need to reach ~4,347ppb to cause as much impact as CO2 has which is in nobody's projections that I have seen. PS: "Methane has a large effect (24 times as strong as carbon dioxide per unit mole) for a brief period (having an estimated lifetime of 8.9±0.6 years in the atmosphere)" https://en.wikipedia.org/wiki/Atmospheric_methane https://en.wikipedia.org/wiki/Atmospheric_methane So, if it's lifetime is ~8.3-9.5 years it's half life is around 1/2 that. However, I have also seen a lot of other numbers tossed around and most people want to make it seem much more important even if it's been rising very slowly.
- zasz 10y ago
  Okay, the half-life of methane is 7-9 years. Not the lifetime. The 34x potential I gave is for methane over a hundred years. https://en.wikipedia.org/wiki/Global_warming_potential https://en.wikipedia.org/wiki/Global_warming_potential It's incredibly potent stuff, so much that despite the relatively quick breakdown, an initial mass of methane will have a warming effect that is 20-35x that of an equivalent mass of carbon dioxide over a century. GWP numbers take the brief half-life of methane into account when calculated. You're making the mistake of looking at the absolute quantity of methane and short half-life, and thinking that it couldn't possibly have much of an effect. Well, people have already run the numbers, and it can have a huge effect. Current rates of methane leaks from mining natural gas could very well offset the benefits of moving away from coal: http://blog.nature.org/science/2016/06/24/natural-gas-coal-leak-rate-energy-climate/ http://blog.nature.org/science/2016/06/24/natural-gas-coal-l... Methane's very bad news, even in small quantities.
  - Retric 10y ago
    The risk is from 100s's of Gigatons which is a extremely massive quantity. How much of that is going to be liberated and how soon has a massive impact on estimates. Anyway, your first link says " In the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, methane has a lifetime of 12.4 years" (If that's X ln(2) for half life it's 8.6 years) "This means that a methane emission will have 28 times the impact on temperature of a carbon dioxide emission of the same mass over the following 100 years." https://en.wikipedia.org/wiki/Atmospheric_methane https://en.wikipedia.org/wiki/Atmospheric_methane PS: As to small quantities, we are talking about billions of tons of a gas.
    - zasz 10y ago
      The point of everything I have said is that it would take only a small quantity of methane, relatively speaking, to make a significant contribution to global warming. You don't need to emit as much methane as would match all the warming caused by current levels of CO2. Even an extra tenth of a degree is bad news. Every tenth of a degree shaves off a decade from the time we have to fix our planet. Any significant source of greenhouse gases.

by zasz 10y ago

Retric 10y ago

CO2 concentrations went from 280,000 to ~404,000ppb CH4 concentrations went from 700 to 1,850. So if you use 34x that 1,000ppb is only 39,000 vs 124,000 meaning it's significantly less important overall contribution. It would need to reach ~4,347ppb to cause as much impact as CO2 has which is in nobody's projections that I have seen. PS: "Methane has a large effect (24 times as strong as carbon dioxide per unit mole) for a brief period (having an estimated lifetime of 8.9±0.6 years in the atmosphere)" https://en.wikipedia.org/wiki/Atmospheric_methane https://en.wikipedia.org/wiki/Atmospheric_methane So, if it's lifetime is ~8.3-9.5 years it's half life is around 1/2 that. However, I have also seen a lot of other numbers tossed around and most people want to make it seem much more important even if it's been rising very slowly.

zasz 10y ago
Okay, the half-life of methane is 7-9 years. Not the lifetime. The 34x potential I gave is for methane over a hundred years. https://en.wikipedia.org/wiki/Global_warming_potential https://en.wikipedia.org/wiki/Global_warming_potential It's incredibly potent stuff, so much that despite the relatively quick breakdown, an initial mass of methane will have a warming effect that is 20-35x that of an equivalent mass of carbon dioxide over a century. GWP numbers take the brief half-life of methane into account when calculated. You're making the mistake of looking at the absolute quantity of methane and short half-life, and thinking that it couldn't possibly have much of an effect. Well, people have already run the numbers, and it can have a huge effect. Current rates of methane leaks from mining natural gas could very well offset the benefits of moving away from coal: http://blog.nature.org/science/2016/06/24/natural-gas-coal-leak-rate-energy-climate/ http://blog.nature.org/science/2016/06/24/natural-gas-coal-l... Methane's very bad news, even in small quantities.
- Retric 10y ago
  The risk is from 100s's of Gigatons which is a extremely massive quantity. How much of that is going to be liberated and how soon has a massive impact on estimates. Anyway, your first link says " In the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, methane has a lifetime of 12.4 years" (If that's X ln(2) for half life it's 8.6 years) "This means that a methane emission will have 28 times the impact on temperature of a carbon dioxide emission of the same mass over the following 100 years." https://en.wikipedia.org/wiki/Atmospheric_methane https://en.wikipedia.org/wiki/Atmospheric_methane PS: As to small quantities, we are talking about billions of tons of a gas.
  - zasz 10y ago
    The point of everything I have said is that it would take only a small quantity of methane, relatively speaking, to make a significant contribution to global warming. You don't need to emit as much methane as would match all the warming caused by current levels of CO2. Even an extra tenth of a degree is bad news. Every tenth of a degree shaves off a decade from the time we have to fix our planet. Any significant source of greenhouse gases.