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I finally understand methane lifetimes

climateer.substack.com

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Re: I finally understand methane lifetimes

#41

Post by isoprophlex »

metacritic12 wrote: post #33
dr_dshiv wrote: post #8

So, hydroxide radicals (OH) break down methane (CH4) into carbon dioxide (CO2). This is a good thing for the climate, as a molecule of methane has a much bigger warming effect than CO2. (Although it is odd that the CO2 produced by methane is not counted toward methane’s overall climate impact). There is limited OH in the atmosphere. As a result, more methane “uses up” the OH. That means that increased methane in the…

> There is limited OH in the atmosphere. As a result, more methane “uses up” the OH. > So, why not produce a bunch of OH? Because OH has a half life of less than a second. Hmm. These two statements seem to contradict? If the chemokinetics of OH generation is less than a second, then how can it be used up in the atmosphere? Assuming the <1 second kinetic is correct, there must be a dynamic equilibrium producing it in…

Look at it this way: there's a finite amount of OH radicals being produced each interval of time, which reacts with some CH4 and disappears in the reaction.

You are correct that OH radicals regenerate, but more methane => "breakdown capacity" becomes overwhelmed.

This is known as zeroth order kinetics, similar to alcohol metabolism. Drinking 2 beers = 3 hours until sobriety; 4 beers = 6 hours. Your liver has a fixed capacity, so drinking twice as much doesn't double the metabolic rate.

I'll add that you're also entirely correct: if there's some long lived chemical that catalyzes OH formation, sending that up instead might be a good remedy IMO. If there's no collateral toxicity...

Re: I finally understand methane lifetimes

#42

Post by Robotbeat »

masklinn wrote: post #19
Robotbeat wrote: post #18

Another question I had: what does methane become once it breaks down? It becomes CO2 (a relatively minor greenhouse gas per unit weight, but long-lived) and H2O, right? H2O is no big problem in the lower troposphere. It just rains out. But in the stratosphere… it can stick around for much longer and impact the climate. How much does this matter for methane? I would imagine methane floats up pretty high into the upper…

> It becomes CO2 (a relatively minor greenhouse gas per unit weight, but long-lived) Although it should be noted that 1 tonne methane decays into around 2.5 tonnes of CO2 (I don't remember the exact number but it's around that) and GWP is measured by weight. So even after it's decayed, methane has a higher GWP than CO2. Which is why its GWP remains much higher than CO2 even over extremely long periods: methane has a…

What about the H2O?

Re: I finally understand methane lifetimes

#43

Post by sandworm101 »

>> This has to be a typo, but it’s yet another reminder that – say it with me – you can never trust a number.

No. Never trust an answer to an overly-simplified question. Asking for the lifetime of atmospheric methane is like asking what temperature water boils at. When faced with an overly-simplistic question an intelligent respondent will generally make all sorts of assumptions. I assume he means at sea level. I assume he means on planet earth. I assume he means normal not-heavy water. Answer: 100c. This isn't about trusting answers in the form of simple numbers. Ask an overly-simple question and expect an overly-simple answer. The fault is with the asker.

Re: I finally understand methane lifetimes

#44

Post by dexwiz »

Half lives are a poor term for this; you are really looking for reaction rates, which are dynamic systems. Methane doesn't just disappear, it reacts with something else. A radioactive isotope's decay is relatively self contained, so the half life terminology holds.

A microgram or a kilogram of U-235 will decay at about the same rate, making half life a useful number. Methane reacts with OH, which is sourced from different places. Upper levels of the atmosphere get more UV light, which produces all sorts of radicals to react with. But there are also biological and geological sources for radicals which also contribute to reactions. Sum these reactions together and you get something that can be approximated with a half life, but this assumes constant input of reactants. As we increase our output of Methane this changes the reaction rates in the atmosphere and that half life number changes.

Re: I finally understand methane lifetimes

#45

Post by s1artibartfast »

sandworm101 wrote: post #43

>> This has to be a typo, but it’s yet another reminder that – say it with me – you can never trust a number. No. Never trust an answer to an overly-simplified question. Asking for the lifetime of atmospheric methane is like asking what temperature water boils at. When faced with an overly-simplistic question an intelligent respondent will generally make all sorts of assumptions. I assume he means at sea level. I ass…

It is clearly both. The correct answer to an overly simple question is that it depends. If someone is stating an answer, but leaving off the assumptions, they are doing a disservice

Re: I finally understand methane lifetimes

#47

Post by s1artibartfast »

cwkoss wrote: post #36

If I have a compost pile that's producing methane, is igniting that methane to convert it all into CO2 (regardless of getting any utility from that energy) effectively "net carbon negative" because CO2 has much less climate effect than methane? Kind of weird to think about how burning methane without capturing the energy could be better for the planet that letting it leak into the atmosphere naturally.

The same is true for a lot of chemistry. There are tons of compounds that are poisonous, but if you break down the molecule, it is perfectly safe to eat.

Re: I finally understand methane lifetimes

#49

Post by s1artibartfast »

metacritic12 wrote: post #33
dr_dshiv wrote: post #8

So, hydroxide radicals (OH) break down methane (CH4) into carbon dioxide (CO2). This is a good thing for the climate, as a molecule of methane has a much bigger warming effect than CO2. (Although it is odd that the CO2 produced by methane is not counted toward methane’s overall climate impact). There is limited OH in the atmosphere. As a result, more methane “uses up” the OH. That means that increased methane in the…

> There is limited OH in the atmosphere. As a result, more methane “uses up” the OH. > So, why not produce a bunch of OH? Because OH has a half life of less than a second. Hmm. These two statements seem to contradict? If the chemokinetics of OH generation is less than a second, then how can it be used up in the atmosphere? Assuming the <1 second kinetic is correct, there must be a dynamic equilibrium producing it in…

"consumed" is better than "used up".

In that It is like throwing breadcrumbs to ducks and geese. The more ducks in the pond, the less crumbs the geese will get.

Re: I finally understand methane lifetimes

#50

Post by s1artibartfast »

beders wrote: post #34
alexose wrote: post #21

Earlier quoted context omitted.

There's a group that is advocating for spraying an Iron Salt Aerosol into the atmosphere, which apparently catalyzes the natural decomposition process. I haven't done a deep dive into the subject, but on the surface it seems pretty compelling. https://ironsaltaerosol.com/home/isa_summary

what could possibly go wrong? Let's put iron chloride where it doesn't belong, outside of our control. Haven't we done enough harm yet?

you could say the same about anything. Installing solar or wind power isn't natural part of the environment, and "something" could go wrong, better not do that either.
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