I finally understand methane lifetimes | Hacker News Reader

I finally understand methane lifetimes

climateer.substack.com

213 pointsgk181 comments

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 atmosphere results in increased lifetimes of methane. The reason carbon monoxide (CO) has three times the warming potential of CO2 is because CO uses OH, increasing methane!

So, why not produce a bunch of OH? Because OH has a half life of less than a second. Hmm.

However, aerosolized plant terpenes (such as produced by wetlands) are a natural source of OH in the atmosphere.

Interesting. Perhaps this should change the calculation of the carbon credits due to terpene generating biomes (above and beyond the carbon sequestered by the plants). Or, maybe we could mass produce terpenes to clean out atmospheric methane (e.g., after a pipeline leak or something).

Anyone know more?

> the CO2 produced by methane is not counted toward methane’s overall climate impact

It definitely is in some contexts. It's often cited in CO2 equivalent over time. Methane start off to be something like 80 times more potent as a greenhouse gas than CO2. Then as it decays to CO2 its impact is that of CO2 but time has to be accounted for. So for every ton of methane, you can estimate an equivalent CO2 tonnage over then next, say, 50 years.

A quick search for methane co2 equivalent reveals a site claiming methane has 25 times more global warming potential than CO2 over 100 years.

Here is a source explaining why the CO2 produced by methane isn’t counted in estimates of global warming potential. It seems to come down to the different calculations required for anthropogenic sources.

https://ghginstitute.org/2010/07/13/what-is-different-about-...

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?

Seems like we've come far enough to understand that doing nothing and conserving our way out of this problem isn't viable. The time for engineering is upon us.

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.

I think that falls within his qualifier as “under our control”… and also previously tested. I have no dog in the fight, but be honest about what the argument really is.

I guess I don't understand the distinction. Why one is out of our control? Certainly we could stop injecting extra iron into the atmosphere just as easily and dismantling a solar plant.

It seems like a lot of people conflate "out of control" with "I don't understand it".

Ok, releasing the iron compound into the sky we find causes immeasurable amounts of suffering. Go up there and get it back.

You know exactly what the topic is an you are pretending not to - for some reason.

it's interesting folks have interpreted this as a blocking call to effectively do nothing in the face of such uncertainty. To me it was an invitation to begin to engage in second order thinking.

Well they haven't tested any of their assumptions in the field and their atmospheric chemistry cycle diagram has some bullshit reaction mechanisms so it is pretty much shit.

Also the following statement surprisingly lacks any mention of anything related to atmospheric or earth scientists:

>We seek funding for a world-first trial in Australian waters under scientific supervision, in cooperation with the marine biology community and with industries including insurance, fishing, tourism, energy and shipping.

How much money is worth “wasting” to investigate new possible solutions to global warming?

If you look at the “official” plans, they all rely on the emergence of magical new technologies. So we’d better start testing even the less promising approaches. Shotgun strategies are needed.

Of course, at the moment, many are seeking to ban research science in this area because it is viewed as morally dangerous [1].

[1] https://climateandcapitalism.com/2022/01/17/climate-scientis...

In this case, I think people want to ban large-scale deployments of untested, unvalidated technologies with no definitive positive effect and a non-negligible probability of disastrous consequences.

I myself am an atmospheric chemist and no one has banned me from doing scientic research.

Read their letter and paper. They don’t want to ban large scale deployments. They want to ban any deployments, even for small-scale research purposes. This will ensure that all unvalidated technologies remain untested. That’s unfortunate because we all know we can’t decarbonize in time. We need other braking mechanisms and we should be pretty open to experimentation.

If no one is upset with your particular atmospheric research, maybe you aren’t ambitious enough. Just kidding— I’d love to know what you are working on.

"we all know we can’t decarbonize in time"

I guess you mean "we all know that almost no current government has the political courage to do what is necessary so that we decarbonize in time".

Or " we all know that we don't have the fortitude to do to do what is necessary so that we decarbonize in time". => that version is better if governments do what their public opinion is willing to do.

To fight in the WWI and WII, the most advanced economies of those times turned in less than two years into war economies, where more than 50% of the GDP was directed to the war effort.

True for Germany, France, the UK plus, for WWII, the USA, the USSR, Japan.

The Apollo program amounted during the 60s to 4% of the US GDP, just for the political sake of keeping up with the USSR.

If we considered - as we should - the dereliction of climate and the on-going massive reduction of biodiversity as an existential threat, we would act accordingly.

We can decarbonize in time. But we don't want to "look up", e.g. to listen to the Science.

Australia is having huge fires and large floods every year now - but still elect a government in denial of the causes.

In the USA, the natural disasters are rising sharply in frequency and magnitude (current drought in the West, hurricanes etc).

Etc etc.

When it will become unbearable, we will at last act accordingly. The solutions are there already.

There are many breakthroughs (batteries for example, to store surplus of renewables energies so that it can be used at will when necessary). Far many more would occur if we invested money in research and R&D.

We ought not to bet on a hypothetical magic bullet. Not that we shouldn't fund those research. Startups with small odds to succeeded easily raise VC money since a success would offer a huge ROI.

But the trap is to bet the future of the world on a hypothetical magic bullet when the solutions already exist. We just don't want to do what necessary to implement them.

The USA, Canada, Australia for example emit 3 times more CO2 than France per inhabitant. However, the loss of biodiversity is as fast (and maybe higher) in France (which governments do very little to tackle gashouse emissions).

I think you under-estimate how quickly human populations will mentally adjust to "the new normal" and how much suffering we're willing to tolerate, especially if it happens to someone else on the other side of the planet.

I think we agree with each other. I’m not aware even of a plan that would enable timely decarbonization. If you know of one, I’d be interested to read it. But at present, the time targets are completely infeasible. That doesn’t mean amazing progress isn’t being made. For instance, Dubai will be 100% solar powered by 2050. But that’s not fast enough.

Let me know what you think of this article: https://www.nytimes.com/interactive/2022/04/25/magazine/vacl...

> 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 the atmosphere to begin with. In such a case OH is not truly being used up in any real sense. It's whatever that generates OH is being used up, and that can be artificially boosted.

One limiting factor in generating OH is specific wavelengths of light, which is harder to artificially boost

Laser beams. We can only hope that this whole solution is dependent on laser beams :)

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...

There is no such thing as zero-order kinetics in atmospheric chemistry.

But are there pseudo zero order kinetics in atmospheric chemistry? smirks

"consumed" is better than "used up".

In that <1 second, the OH can react with methane or CO. The more CO in the atmosphere, the more likely it will find the OH before the methane.

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

It's because that statement is incredibly wrong. Methane concentrations in atmosphere are 8 orders of magnitude higher than OH. More methane in the atmosphere has exactly 0 effect on OH. And you can't inject OH into atmosphere either because it will react with pretty much anything it comes in contact with.

In this case, annual reaction mass of OH is more important than the concentration at any given time. The concentration of any highly reactive molecule will be very low, but that doesn't tell you how much was created or consumed.

Methane levels don't impact OH levels (it is always consumed immediately). OH generation levels can impact methane levels. CO levels can compete with methane for OH as is it generated.

The short lifespan of an OH radical isn’t an issue if it’s deployed at the site of emission (à la scrubbers). You then don’t need them to last long enough to randomly bump into methane particles in the wild as you’re inducing them in a high-methane concentration environment where you expect them to react before they react with something else and break down.

That’s the moral of the story for all climate control: don’t produce bad stuff, if you have to try to get rid of it as close as possible (temporally and spatially) to the source because once it’s diluted in the atmosphere it becomes insanely more difficult.

Global CO2 levels are at 450 parts per million meaning you need to actively filter 2,222 parts of air to get to one measly CO2 molecule in the wild. It’s horrible inefficient (expensive and slow). But if you don’t produce the CO2 or if you tackle it right then and there at the site of production where it is at much higher concentrations, you still have a chance.

I remember someone pointing out that (1) there is a very large amount of advocacy based around going to the Great Pacific Garbage Patch and harvesting microplastic particles there; and (2) this is a colossally stupid idea, because there is almost no plastic in the Great Pacific Garbage Patch. It's a a part of the ocean where the level of plastic is higher than usual. But it's still a part of the ocean.

If you want to filter plastic out of the ocean, you want to filter it out of the input stream, where it's concentrated, not out of the end product of diluting the input stream with the entire ocean.

Interestingly, the wikipedia article on the Patch is headlined by a disclaiming of a very similar mistake:

> Despite the common public perception of the patch existing as giant islands of floating garbage, its low density (4 particles per cubic metre (3.1/cu yd)) prevents detection by satellite imagery, or even by casual boaters or divers in the area.

https://en.wikipedia.org/wiki/Great_Pacific_garbage_patch

Is there a connection between ozone and hydroxyl?

http://en.wikipedia.org/wiki/Ozone

"Ozone reacts directly with some hydrocarbons such as aldehydes and thus begins their removal from the air, but the products are themselves key components of smog. Ozone photolysis by UV light leads to production of the hydroxyl radical HO• and this plays a part in the removal of hydrocarbons from the air, but is also the first step in the creation of components of smog such as peroxyacyl nitrates, which can be powerful eye irritants. The atmospheric lifetime of tropospheric ozone is about 22 days; its main removal mechanisms are being deposited to the ground, the above-mentioned reaction giving HO•, and by reactions with OH and the peroxy radical HO2•."

Making more ozone is quite easy: take a UV-C disinfection lamp as used for an aquarium, and pump air through it.

At some concentration, the ozone itself could be hazardous, and it would be messy to clean up the soot from the smog as it falls.

I do wonder whether a little more surface ozone might help to make more hydroxyl to speed up the cleanup effort, especially if paired with a HEPA filter.

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.

AP Chemistry: the year I took it was the first (only?) year a free response question didn’t feature reaction rates. I learned my lesson on the risks of studying to the historic exam contents!

As someone whose academic background was in nuclear stuff (but ~10 years ago alas), I had fun read of this article for the considerations like "ohh, a 'half life' with multiple decay modes of varying weights depending on the environment, etc. Gives an itch to dive back into numbers wrangling/plotting!

I agree that an accurate description of the (atmospheric in this case) systems over time definitely needs reaction rates, but similar considerations are also needed with nuclear radiation in a lot of situations too: e.g. the overall uhh radioactivity (for lack of recollection of precise terms) is a function of the chain of decay products, which are also often radioactive. That is to say, you might start with half-lives in calculations for dose estimation as a function of time, but you quickly get into more complex things. Also in the nuclear realm, add sources, like a running reactor, or a fresh set of fuel rods, and you get some very interesting effects over time!

I think this article was a fair example walkthrough of how things quickly get more complex than the numbers (mis)quoted to the public. I was hoping it would go further, even.

Additional source describing the difference between CH4 and CO2 in the atmosphere:

> "Methane makes up just 0.00018 percent of the atmosphere, compared to 0.039 percent for carbon dioxide. (CO2 is roughly 200 times more abundant.) Yet scientists attribute about one-sixth of recent global warming to methane emissions; what methane lacks in volume it makes up for in potency. Over a 20-year period, one ton of methane has a global warming potential that is 84 to 87 times greater than carbon dioxide. Over a century, that warming potential is 28 to 36 times greater. The difference occurs because methane is mostly scrubbed out of the air by chemical reactions within about ten years, while carbon dioxide persists in the atmosphere for much longer than a century."

https://earthobservatory.nasa.gov/features/MethaneMatters

A big uncertainty is the future of permafrost and shallow marine sediments, which store carbon in various forms. Some scenarios are, well, not good:

https://climatemodeling.science.energy.gov/presentations/imp...

> "Our simulations include a plausible release from clathrates in the Arctic that increases global methane emissions by 22%, as well as a scenario with 10 times those clathrate emissions. The CESM model includes a fully interactive physical ocean... The results indicate that such Arctic clathrate emissions (1) increase global methane concentrations by an average of 38%, non-uniformly; (2) increase surface ozone concentrations by around 10% globally, and even more in polluted regions; (3) increase methane lifetime by 13% ..."

It's kind of like defrosting a freezer full of 25,000 year old fish guts...

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.

I believe the answer is yes, but I imagine it would be far too diffuse to actually achieve ignition. Same issue applies to various schemes for putting a pilot light at cow's butts to eliminate the "cow fart emissions" issues.

(Quite apart from the fact that it's belches not farts that are the issue anyway, so the pilot light would be at the wrong end...)

Wait, are you telling me that we need fire breathing cows for the good of the environment?

Yep. It's also the same idea why we have gas flares on oil wells. It might look like it's oil companies setting stuff on fire for no reason, but it's better than just letting it leak.

Throwing that natural gas through a generator and an exhaust system is even better (more "net negative"). Compared to flaring, you can achieve a ~98% methane reduction and a ~60% CO2e reduction (source: https://www.crusoeenergy.com/digital-flare-mitigation).

Disclosure: I work for Crusoe Energy, who's goal is to eliminate routine flaring and align the future of computing with the future of the climate. We colocate data centers serving crypto miners and a high performance GPU cloud (crusoecloud.com). Our GPUs are indeed "carbon reducing", offsetting the emissions of a car over the course of a year.

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.

Yes, by the same mechanism burning waste also has a lower impact then letting it sit on a landfill (even excluding using the heat for something usefull like electricity production, or a heat network).

It's this level of understanding that can't be pushed out to the general population. It is far too complicated for people to grasp. Add on to these complexities is that if we are trying to price carbon - the impacts change with the concentrations in the atmosphere.

The market needs to be dumbed down to simplistic values (which thankfully they have) so that we have a sense on where to target and incentivize change for policy makers otherwise it is far to easy for mud-rakers to try and undo meaningful work/change in our policy/business arenas. Abstract away the complications.

Great piece.

I think it is the dumbing down that makes it easier for mud-rakers. People know it's complicated anyway, and the average person can grasp complicated things as well as you.

As an environmental engineer that deals with the interface between the public and policy makers, I think I'm inclined to agree with you. The public IS dumb, but every time they try to dumb down the principles they regulate on, it always comes at the detriment of the environment and the 'little guy'. It's almost always better to delegate policy to smart qualified people with correctly aligned interests. Getting that latter part right is hard, but that is the job of a competent public official.

It's a difficult place to be - damned if you do and damned if you don't.

I disagree. There is an inherent risk that dumbing down or abstracting away the complexities of the science to have an appropriate discourse on appropriate policy action creates blowback but trying to create a system that accounts for the complexities of the science would just cause infinite headaches.

The business mechanism to try and solve this needs to be simple and relatively clear and should align with the science. The general population doesn't have the time or capabilities to understand the complexities. I am not saying hide the complexity - I am just saying don't have it in the forefront of the policy decisions - and don't constantly change the regulatory mechanism unless it is grossly misaligned with the science.

I am glad you think the average person has the same capability to understand the problems and has taken environmental science engineering programs - I feel much better about that.

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.

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.

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.

Albedo is included in every single atmospheric model.

Cloud albedo? Its effects depending on surface temps? Cloud cover changes wrt local climate change?

Do you have any sources for that?

>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.

> 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...

>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.

> 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’.

Ok, so as I'm thinking about this, and forgetting about the edges of the absorption bands -- in steady state, all the heat of the sun must be radiated out into space, otherwise the earth would be hot enough to have killed off all life millions of years ago.

When you think about it, an IR photon that returns to earth is not really done, it doesn't get "stuck" to the earth. The surface of the earth either reflects it back up, or absorbs it and its energy, and then re-emits it some time later. Even with 0.9997 probability of returning to earth, if you try enough times, you'll eventually escape, and photons get a lot of tries, really fast. That 0.0003 probability matters, and if you change it to 0.0002, it seems to me like it's a really, really big deal.

To take it the other way -- if any given IR photon had, say, a 50% chance of escaping the earth, my intuition says that it would let the earths temperature drop extremely drastically at night, like the moon or mercury. The sheer speed at which photons get "tries" to escape means that the greenhouse gas blanket has to absorb and send back almost all photons in order for the earth not to become icy every night.

So that question was addressed in the 1950s I believe by one Gilbert Plass who was initially involved in getting data for infrared guidance systems for air-to-air rockets (homing in on jet engines). The simple answer is that those frequencies are not saturated at altitude, i.e. 12 km up or so. Hence this is where CO2 exerts most of its effect. For a full discussion:

> "Plass pursued a thorough set of one-dimensional computations, taking into account the structure of the absorption bands at all layers of the atmosphere. In 1956 he explained clearly, for the first time, that the water vapor absorption lines did not block the quite different CO2 absorption spectrum, adding that there was scarcely any water in the upper atmosphere anyway. He further explained that although some of the CO2 band itself was truly saturated, there were many lines to the side where adding more of the gas would increase the absorption of radiation. His arguments and calculations showed convincingly that adding or subtracting CO2 could seriously affect the radiation balance, layer by layer through the atmosphere, altering the temperature by a degree or more down to ground level."

https://history.aip.org/climate/Radmath.htm

Here's an additional bit of data that explains this rather oft-repeated old trope about CO2 saturation:

> "The early experiments that sent radiation through gases in a tube, measuring bands of the spectrum at sea-level pressure and temperature, had been misleading. The bands seen at sea level were actually made up of overlapping spectral lines, which in the primitive early instruments had been smeared out into broad bands. Improved physics theory and precise laboratory measurements in the 1940s and after encouraged a new way of looking at the absorption. Scientists were especially struck to find that at low pressure and temperature, each band resolved into a cluster of sharply defined lines, like a picket fence, with gaps between the lines where radiation would get through."

You can't push it out in a single news blurb. But if it were covered as some math/physics/chemistry sections building on each other in secondary education it should be manageable. Especially if you already covered exponential decays. Add the secondary effect of the exponential decay parameter varying based on concentration.

Beyond methane and climate change, this is a lovely step through of simply grappling with a new concept to understand it, one site/paper at a time. I wish I could teach my parents how to do this, they never get beyond the first page

>> 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.

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

Very interesting, and a great description of methane self-feedback.

The perturbation lifetime analysis - the idea that the time constant of the atmospheric response to methane is longer than the time constant of the reaction that removes methane - comes from a beautiful paper by Michael Prather that may be of interest to anyone with some linear algebra. See https://unfccc.int/files/meetings/workshops/other_meetings/a....

> never trust a number

One pet peeve of me is the water consumption of everything. Take milk production for example, it disregards so many things, local climate, soil conditions, ecology of having cow on land, biodiversity and so on. Somehow milk production boils down to a single number and is compared with e.g. almond milk. Almond milk uses less water hence good.

At least we are way over the age of line of code..

Yup.

In Iowa we put porous pipes in the ground to drain rain into the rivers faster because otherwise about half the state would have standing water on the surface.

Water consumption of Iowa cows does not matter at all, water consumption of a lot of cows doesn't matter at all. There is very little irrigation in Iowa.

There are places where water is a limiting factor, and places where it isn't.

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 reaches of the atmosphere. Does it keep going? What stops it from getting to the thermosphere and (ultimately) exosphere?

> 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 GWP of ~80 over 20 years, ~30 over 100 years, but is still around 7 over 500 years, despite a lifetime of only 12 years.

What about the H2O?

[OP here] thank you! I see those ratios for 20 vs. 100 years everywhere, but I've never been able to put together a mental model that explains them. You've supplied the missing piece.

This is very enlightening!

Key fact is how much methane is already there when your gout entered matters a great deal, because its rate of clearance is limited by how much hydroxyl radicals it can muster.

As a self professed what? Ive read pop-sci books with more graphs and equations over breakfast.

Why is there this celebration of mediocrity in dealing with equations and instead citing percentages.

tl;dr

> I finally have some confidence that I understand how methane lifetimes work, and that for my purposes it can be summarized as:

Methane emissions decay gradually, with an average lifetime of about 12 years (“perturbation lifetime”, which is what matters for climate purposes).

This will increase by roughly 35% if methane concentrations double, or decrease roughly 25% if concentrations return to pre-industrial levels.

> This will increase by roughly 35% ...

I was a bit confused by this sentence (which is a direct excerpt from the piece). Reading the whole article, the `this` refers to the methane lifetime. Oddly (to me), the lifetime methane in the atmosphere increases with the amount of methane in the atmosphere. That's what the author has been working to understand. Very interesting!

It makes sense, if you take into account that, apparently, absorbing methane from the atmosphere depletes the atmosphere's capacity for absorbing methane. Hence the more methane that exists, the more methane is getting absorbed, the less capable the atmosphere is at absorbing methane.

If I'm thinking clearly, using "absorbing" here implies that atmospheric concentrations of methane have an effect on the amount of methane that can be released. A lower absorption would then be "good" because it would slow the rate of accumulation of methane in the atmosphere.

The opposite is true, that the higher the methane concentration, the lower the rate of effect would be to degrade all atmospheric methane. The rates of methane accumulation and its degradation are inversely proportional beyond the limit of the atmosphere to degrade it.

Yeah, and to simplify further, the atmosphere's got a fixed amount of methane-removing capability, and as we exceed this capability it can't absorb methane any faster, so the ratio of methane that gets absorbed starts dropping even though the amount being absorbed doesn't drop.

The reality is more complicated because the cut off is very blurry - absorbsion does still increase as methane increases, just not fast enough to keep up, and it falls further behind the more methane we put out.

Which to me raises the question: Are there any possibilities to increase the absorption of methane somehow?

And it seems like there are methods for capturing methane: https://news.mit.edu/2022/dirt-cheap-solution-common-clay-ma...

(Physicist/Engineer of sorts here. Zero atmosphere knowledge)

That half life depends on concentration is not surprising to me; ethanol's half life in the blood also depends on it's concentration and the reason is rather straight forward: the liver has limited amounts of enzymes needed to process booze.

What is surprising to me, though, is that there is a mechanism that has such a massive effect at the extremely low concentrations of methane that are present in the atmosphere. Sure, OH is rare, but I'd guess is generated in large amounts in the upper atmosphere (UV + H2O -> OH- + O+ + momentum to keep them away from each other).

Does anyone here have any hard math on this?

FWIW, and this is a rather minor and pedantic point, these are hydroxyl radicals, not hydroxide ions, so it's:

H2O + γ -> OH• + H•

Rather than:

H2O + γ -> OH- + H+

Oh, and whichever way, H2O splits into OH and H, not OH and O, but i assume that was a typo!

> OH•

https://en.wikipedia.org/wiki/Hydroxyl_radical “Notation: The unpaired electron of the hydroxyl radical is officially represented by a middle dot, •, beside the O.”

Note that article uses a superscripted dot <sup>•</sup>OH, and the dot is usually prefixed in the article (presumably so as to put the dot next to the O that doesn’t have a full shell?).

However the article sometimes suffixes the dot, to put it beside the R organic radical. Weird.

Don't forget about those deep ocean Methane Clathrates !

The next step would be understanding Rust lifetimes ;)

I finally understand methane lifeforms...

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