Methane Decay in atmosphere 4

[Roger.Bryenton]

Hello Engineers, Help Needed on Methane Decay ... Thx
I am researching climate change, and with Covid and a few years, seems foggier that usual. However, from what I can determine, methane, CH4 has a half-life of about 7 years. That means it decays at about 10% per year. The concentration in the atmosphere is slowly increasing. If in year one, the rate of decline is 10%, then it would take about 10% to maintain the roughly constant concentration. Now, what about the CH4 that is there from the year before? It will decline about 9% in its second year.

If I sum the total of declines over, say 21 years, its down to 25% so the overall decline is 75%, correct?


Here's another description. In a dynamic atmospheric model of methane decay to CO2, methane's half life of 7 years means it decays into CO2 at 10%, declining, per year. Thus in order to maintain to roughly steady amount of 1920 parts per billion, in year 1 it will decline 10%. In year 2 it declines about another 9%, year 3 about 8% etc. This assumes it is not constantly refreshed, to maintain the constant concentration.

How much is required each year to stay constant? My mind is a bit foggy after several bouts with Covid, however the answer is germain to our planet's health. 10% new methane a year is a huge flow, and methane's warming effect during year 1 is about 120 times as bad as CO2.

THUS, the first year's decay at 10% is a huge amount. What about the dynamics of the continuing decay from the "2 year old" methane? Doesn't it also have to be replaced in order to maintain a constant methane concentration? Similarly with the 3 year old methane, etc? If it were a "stock" or fixed volume, it would decay to 50% over 7 years.

BUT it holds constant concentration, ie it is a "flow", dynamic, being constantly refreshed while simultaneously decaying at 10% per year. One part of the brain says it is a 10% "refreshment flow",annually while another part of the brain says "account for all the decay, constantly, which approximates, over 14 years, to be 75% decline, which would me an unimaginable massive flow of new methane annually.

What % of the methane concentration is needed to maintain a steady concentration, please? IF it's only 10% per year, what about the decay in year 2, 3 etc? How is that accounted for. Thank you VERY much. Roger

 

[dik]

Shvet... Drop the subject, your comments are neither appreciated nor helpful.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Roger.Bryenton]

Interesting discourse. Thank you all, very much.

The decay of methane is a huge aspect of climate change, thus the chemistry and decay critical. At about 10% per year, this is a HUGE methane flow, just to replace that amount, every year. The growth (rate of increase) of methane is around 1% per year, so if the decay rate changes 1%, that entirely doubles or reduces to nothing, the growth rate. It's really sensitive. Yes, the methane and permafrost are important aspects, as are, potentially, hydro reservoirs, forest fires, slash burning.

Global warming is chemistry related, and why I very much appreciate your folks' input.

Re Global Warming and CH4 : Comparative Heating Effects.
Paul Balcombe et all determined the short-term ( less than 10 years - the half-life of methane) global warming potential (GWP) for methane, of up to 120 times that of CO2. If we take the concentration of CH4 vs CO2 times their GWP we get comparative warming contributions:
CH4 - 1920 part per billion of CH4 = 1.9ppm. 1.9 x GWP of 120 = 228 "warming units"
CO2 - 420 ppm x 1 (GWP) = 420 "warming units". TOTAL = 648 "warming units".
CONCLUSION - CH4 is 35% of our global warming. You read it first here! You helped this conclusion, thank you, and it's frightening. We MUST reduce CH4, because it's short term effect means we can reduce warming immediately.
Reducing CO2 that lasts decades or more, just stops us from getting warmer while methane reduction avoids warming.

I wonder if this is part of why a 100 year time frame has been used, to mask the short-term effect of methane?

I hope none of you are offended by my conclusion, and I'd love to be wrong. If you can counter my math or conclusion, that's what peer review is about, isn't it? If you are interested, I am planning a "peer reviewed" paper for publication and I'd like to acknowledge the input and support of Eng-tips. It's a great forum for learning and sharing.

Again, thank you for this opportunity. Cheers, Roger Bryenton

 

[georgeverghese]

Aside from the chemical mechanics of methane decomposition, this study report says, in its conclusion:-

"methane molecules give a low contribution to an observed increase of the global temperature of our planet. The contribution of other trace gases is also negligible."

https://www.auburn.edu/cosam/departments/physics/iramp/11_2/smirnov_zhilyaev.pdf

Must confess I am a long way from understanding much of the theory used

 

[dik]

That's contrary to most information I've encountered about methane...

"Methane (CH4) is a greenhouse gas that is much stronger than carbon dioxide (CO2), 34 times stronger if compared over a 100-year period. While concentrations of methane in the atmosphere are about 200 times lower than carbon dioxide, methane was responsible for 60% of the equivalent radiative forcing caused by carbon dioxide since the onset of the Industrial Revolution. Methane’s presence in the atmosphere can also affect the abundance of other greenhouse gases, such as ozone (O3), water vapor (H2O), and carbon dioxide."

https://eos.org/editors-vox/methane-climate-change-and-our-uncertain-future

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik