8 ms·

Genuinely curious - while Methane is a far more potent greenhouse gas, isn’t its half life in the atmosphere only 9 years? Wouldn’t this make it far less concer

by gpt5 5y ago

Genuinely curious - while Methane is a far more potent greenhouse gas, isn’t its half life in the atmosphere only 9 years? Wouldn’t this make it far less concerning than CO2 with its half life of 120 years? Looking for serious answers.

twayt 5y ago
Methane has ~25 times the global warming effect as an equivalent amount of carbon dioxide. Source: https://www.epa.gov/ghgemissions/understanding-global-warming-potentials https://www.epa.gov/ghgemissions/understanding-global-warmin...
- tangjurine 5y ago
  So methane should be 25 / (120 / 9) = 1.875 times as harmful as CO2 in the long run? How much does the long run matter in this case?
  - twayt 5y ago
    The GWP is computed for a period of 100 years to account for the various half-lives. The 25x figure is normalized over a 100 year period. Over a 20 year period, it is about 85x more harmful
    - drallison 5y ago
      So methane control is a significant handle to control global warming. It is not a solution but it will buy time if we globally "burn" methane to COP2. See BlueDotChange.org.
  - antod 5y ago
    Doesn't methane eventually break down into carbon dioxide? If it does then it's much worse than just being co2 in the first place.
scroot 5y ago
The concern is faster warming and an out of control positive feedback loop.
istorical 5y ago
Carbon emissions are correlated to human activity. We can dial them up or down theoretically through human action. Methane emission through permafrost (both land and submarine) could end up as a cascading natural emission that forms a feedback loop. I think that's a big part of why people are panicking.
- mjevans 5y ago
  The cheap option of going out of our way to do less (so we emit less) is very probably off the table at this point. As a species we need another plan. I like a mixed approach of sequestering atmospheric gasses via processes that synthesize useful compounds from the components we don't want in the air as well as hard scifi concepts like giant reflective surfaces in space. Throttling the quantity of sunlight by reflecting a portion away from the earth sounds super expensive... but that might be the only viable option left.
  - rTX5CMRXIfFG 5y ago
    Or we could go with the cheap option. If there’s anything that the global pandemic taught us, it is that nothing about human behavior is ever set in stone and there will always be a way to make even draconian policies like lockdowns and mandatory face masks politically viable. The billions we’d spend building the crazy ideas you suggested which also have no guarantee of success, could be channeled into whatever it takes to get people to care more about the planet.
    - quickthrower2 5y ago
      Lockdowns were heavily resisted even with millions dying right now. It will be hard to lock people down in what they can do, politically, because of something that will kill people in the future. People that might not be “me” from the point of view of each individual.
    - nicbou 5y ago
      The pandemic also told us that people won't even do something as mildly inconvenient as wearing a mask. Forget about major life changes.
wizardforhire 5y ago
Clathrate Gun https://en.wikipedia.org/wiki/Clathrate_gun_hypothesis https://en.wikipedia.org/wiki/Clathrate_gun_hypothesis
- asdfasgasdgasdg 5y ago
  Note the "current outlook" section, where the TL;DR: is that this is not happening and there is pretty good reason to believe it won't over predictable time-frames.
  - evil-olive 5y ago
    > the "current outlook" section from the article: > according to data released in January by the US National Oceanic and Atmospheric Administration (NOAA) an encyclopedia like Wikipedia is, by its very nature, going to lag behind the cutting edge of published research on this topic. this article might eventually become a source cited in an edit to the Wikipedia page for that "current outlook" section.
    - asdfasgasdgasdg 5y ago
      The NOAA data is about methane in general, not clathrates.
- trsohmers 5y ago
  If we haven’t fired the clathrate gun already, I’m personally convinced it is inevitable in the next ~decade. Practically no one I talk to, who are generally concerned about climate change, have the same fear I do about the clathrate gun and most just point to the Wikipedia article downplaying it as “proof” it isn’t a big deal. While it is super depressing to think we have already lost the climate change battle, intelligent people keeping their heads in the sand and not seriously looking at what the next steps are assuming the clathrate gun has already fired are doing a huge disservice to humanity. Absolutely none of the 2030/2050/2100 climate change measures are taking this into account and it is mind boggling to me.
deleted 5y ago
[deleted]
breakyerself 5y ago
A couple things. First is that we are on track to overshoot the goal of limiting warming to 1.5C. It's now more a question of how much we are going to blow past 1.5C. Every bit counts now and a pulse of very potent greenhouse gasses at this time is very unhelpful. 2. There could be tipping points that aren't predictable. Methane may temporarily add a small increase to the global average temps, but could end up being the difference for whether permafrost melt begins releasing large amounts of co2 and even more methane that take us up to some even higher temperatire equilibrium. Global warming is a massive unplanned, uncontrolled experiment with the thermal and chemical properties of the only biosphere we know of. The sooner we stop that experiment the safer humanity will be overall.
- julienb_sea 5y ago
  Alternatively, attempting to curtail human emissions to some arbitrary level will, unquestionably, have drastic impact on human quality of life worldwide and the impact will be particularly acute on the developing world and those in poverty in the developed world. Large, influential emitters like China and India will not play ball. As such, the climate experiment will inevitably continue unabated, despite any of the self-damaging choices made by the developed world. Additionally, our ability to actually combat the acute impacts of climate change (i.e. construction of flood barriers, land reclamation, movement of people out of flood-prone areas) could easily be actively hampered by overzealous limits on human development associated with attempt to reduce emissions. In other words, this is a nuanced issue and we have little choice but to press onwards.
  - KerrAvon 5y ago
    “Better things aren’t possible.”
  - tonyedgecombe 5y ago
    Given enough time climate change will have a drastic impact on human quality of life and it's the poorer parts of the world that will feel it most. We seem to be going through stages of climate denialism: Climate change doesn't exist -> it does exist but it isn't man made -> it is man made but it's too expensive and disruptive to fix -> ???
__MatrixMan__ 5y ago
I hadn't thought of carbon emissions in terms of half lives before. I thought that carbon emissions (presumably from fossil fuels) were more of a permanent change. The carbon used to be deep underground, and now it's in the atmosphere. Where does half of it go? I know that it ends up as part of a photosynthetic organism, but then later that plant decays and its back in the atmosphere again, right? And given a changing climate, can we rely on the atmosphere->plant rate remaining constant for enough for our ideas about the half lives of various greenhouse gasses to remain relevant?
- sa1 5y ago
  Methane breaks down into CO2 and water in a few years, which is why half life of methane is relevant. My understanding is that for CO2, thinking in terms of half-life is less relevant, the CO2 goes to plants and to the ocean, and if those two sinks are at saturation, then CO2 levels in the atmosphere will keep increasing. But there's a good article I found now which might shed more light : https://euanmearns.com/the-half-life-of-co2-in-earths-atmosphere-part-1/ https://euanmearns.com/the-half-life-of-co2-in-earths-atmosp...
- XorNot 5y ago
  Some amount of carbon is sequestered by plants getting buried when they die, though not as much as in the past because we have well- slated decay organisms in the biosphere. Some makes its way into the sea and gets stuck there. And a decent chunk is bound up as carbonate minerals from the weathering of the Earth (one of the future biosphere death states is when this process outstrips CO2 production due to the increase in the sun's luminosity about 700 million years from now).
- abc_lisper 5y ago
  When it rains, Co2 in atmosphere leaches the calcium in rocks forming calcium carbonate that runs off to the sea eventually. Hundreds of millions of years from now, our actions leave their mark on some ancient seabed, as a thick white stone(like Dover, England) . The higher the Co2 in the atmosphere, the more it rains, because more water evaporates due to higher temperature, causing faster reduction of Co2 in the atmosphere. Thus there is a natural balance in the cycle. Unfortunately for us, it is way slower than the speed with which we pumped the Co2 out. It takes tens of millions of years to get back to preindustrial levels (of < 200 ppm) Co2
deleted 5y ago
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masklinn 5y ago
Methane is CH4. It decays to CO2 + 2 H2O. So as long as it’s methane it’s hundreds of times worse than CO2, then it becomes the same as co2[0]. Never better. Which is why despite a short half life it has a global warming potential of ~25 over 100 years (Co2 is 1). Then you also have the issue that even if it’s short (relatively, it takes multiples of the half-life to really taper off) for that duration your GW effect really shoots up, which tends not to be a good thing, 120 years is already quite short for biological systems to adapt, 10 is basically infeasible. [0] actually a bit worse still as 1t ch4 yields 2.7t co2 and gwp is mass-relative
- actually_a_dog 5y ago
  Let’s not forget that water vapor is also a greenhouse gas. That makes methane worse than CO2 100% of the time.
  - raverbashing 5y ago
    I suspect that's not so much worrying as there are plenty of vapour sources on Earth (like the vast oceans) More water -> less evaporation (but the partial pressure will remain the same more or less)
  - kergonath 5y ago
    Water vapour is a greenhouse gas, but it comes back down as rain quite quickly. It's also more or less in (dynamical) equilibrium, because there is always a huge source of atmospheric water in the form of evaporation from the oceans' surface. The way to meaningfully increase atmospheric water content is to increase atmospheric temperature, which methane contributes to, but that's a second order effect.
teslabox 5y ago
> Wouldn’t this make it far less concerning than CO2 with its half life of 120 years? In the pre-industrial era the oceans outgassed CO2 to the atmosphere to prevent land plants from suffocating themselves by sequestering all the carbon dioxide. In the post-industrial era the oceans capture a significant percentage of the CO2 that humans generate (because CO2 is heavier than air, and easily dissolves in water). The most important considerations for the earth's atmospheric heat balance are the heat inputs from the sun (solar cycle) and underwater volcanoes, and the shielding provided by volcanic eruptions. The oceans store heat during the summer, and release heat during the winter. My previous comments: https://news.ycombinator.com/item?id=20002823 https://news.ycombinator.com/item?id=20002823 / https://news.ycombinator.com/item?id=20013166 https://news.ycombinator.com/item?id=20013166
deleted 5y ago
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badgley 5y ago
I think you're spot on in your observation. Reducing methane would help and definitely has its place, but CO₂ is a totally different beast. CO₂ is best thought of as a "stock pollutant" meaning that the more you have of it, the worse the effects. This follows directly from that fact that CO₂ sticks around in the atmosphere for millennia, increasing atmospheric radiative forcing. Methane, on the other hand, is better framed as a "flow pollutant" - it's harm is ~proportional to the rate of emission. This is a direct consequence of its much shorter atmospheric lifetime. Here's a useful twitter thread from a real expert: https://twitter.com/hausfath/status/1425572803508465664 https://twitter.com/hausfath/status/1425572803508465664 And if you're up for a pretty technical (but still fairly approachable) read, check out R.T. Pierrehumbert ''Short-Lived Climate Pollution.'' Annual Review of Earth and Planetary Sciences 2014 42:1, 341-379 [https://doi.org/10.1146/annurev-earth-060313-054843 https://doi.org/10.1146/annurev-earth-060313-054843]. Near the end of the paper, he delivers this gem: "Methane mitigation is like trying to stockpile bananas to eat during retirement. Given the short lifetime of bananas, it makes little sense to begin saving them until your retirement date is quite near."
- mtsr 5y ago
  Except that as masklinn writes above, methane gets converted into CO2 and so over its full lifecycle is worse by about a factor of 25.
deleted 5y ago
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evil-olive 5y ago
the answer, or part of it, lies with methane clathrate [0] > a large amount of methane is trapped within a crystal structure of water, forming a solid similar to ice. Originally thought to occur only in the outer regions of the Solar System, where temperatures are low and water ice is common, significant deposits of methane clathrate have been found under sediments on the ocean floors of the Earth. deposits of solid methane ice can exist trapped on the seafloor [1]. this is possible only at the extreme pressures of the seafloor [2]. so, on its own, a little methane in the atmosphere is not a big deal, because of the short half-life. except, you have methane ice deposits in the ocean that can melt if the oceans get a little bit warmer. this can enter into a fun little runaway feedback loop pretty quickly. little bit of methane melts, causing a little bit more ocean warming, causing more methane to melt, etc. if this feedback loop were to occur, the evidence you would expect to see would be spontaneous release of methane emissions from the ocean, and you would expect it to be happening in places where the warming ocean put methane clathrates right at their melting point for that depth & pressure of seawater. which...is exactly what's happening [3] > The study, to appear in the journal Geochemistry, Geophysics, Geosystems, a journal of the American Geophysical Union, shows that of 168 bubble plumes observed within the past decade, a disproportionate number were seen at a critical depth for the stability of methane hydrates. > "We see an unusually high number of bubble plumes at the depth where methane hydrate would decompose if seawater has warmed," said lead author H. Paul Johnson, a UW professor of oceanography. "So it is not likely to be just emitted from the sediments; this appears to be coming from the decomposition of methane that has been frozen for thousands of years." a similar feedback loop is possible in the Arctic tundra [4], where permafrost can melt and release trapped bubbles of gases that include methane, which in turn will warm the planet a bit and cause more permafrost to melt. and of course the two feedback loops are able to reinforce each other, because a bit of methane released from the arctic also helps heat the oceans, and a bit of methane released by the oceans also helps melt the permafrost. 0: https://en.wikipedia.org/wiki/Methane_clathrate https://en.wikipedia.org/wiki/Methane_clathrate 1: https://en.wikipedia.org/wiki/Methane_clathrate#/media/File:Gashydrat_mit_Struktur.jpg https://en.wikipedia.org/wiki/Methane_clathrate#/media/File:... 2: https://en.wikipedia.org/wiki/File:Methane_Hydrate_phase_diagram.jpg https://en.wikipedia.org/wiki/File:Methane_Hydrate_phase_dia... 3: https://www.ocean.washington.edu/story/Bubble_plumes_suggest_release_of_frozen_methane https://www.ocean.washington.edu/story/Bubble_plumes_suggest... 4: https://en.wikipedia.org/wiki/Arctic_methane_emissions https://en.wikipedia.org/wiki/Arctic_methane_emissions
it_does_follow 5y ago
While Methane has a shorter half-life it is also a much more effective GHG. The common way to look at this is Global Warming Potential, which is measure in CO2 equivalents. You can find this on the wikipedia: https://en.wikipedia.org/wiki/Global_warming_potential https://en.wikipedia.org/wiki/Global_warming_potential Notice that you can look at the GWP potential over time spans. For methane, over the next 100 years (which is the period that will impact most HNers the most) it is at least 20x as impactful as CO2. The reason this matters is because the biggest unknown with climate change is positive feed backs. A classic example of this is that as the arctic has less ice it also reduces the albedo of the oceans allowing them to absorb even more heat faster. Another, methane related, theoretical, positive feed back is methane clathrates which are essentially frozen stores of methane deep in the arctic ocean. If the ocean were to warm up enough this might rapidly release methane leading to a catastrophic runaway warming scenario, leading to what is suspected to have caused rapid climate change in the Quanternary period [1]. It is currently believed by many researchers that, in the specific case of the 'clathrate gun' firing, it is unlikely to happen. The trouble is we don't know for sure. That is just one unknown, potentially devastating positive feed back. If you read Peter Ward's work (and some others as well) it looks like at various times in the history of the planet there was very rapid, very destructive climate change that was caused by a cascading series of positive feed backs. We don't know exactly where these are, but the more methane we release (and CO2) and the faster the planet warms the more likely we are to find these. It is important to note also, that these positive feedbacks are not factored into the IPCC report (just like the potential collapse of Thwaites Glacier is not) because the is no way to effectively model this and make predictions about them. It means that if you think the IPCC report sounds bad (or even if you don't) there is a lot of potential risk not mentioned in the various pathways there. 1. https://en.wikipedia.org/wiki/Clathrate_gun_hypothesis https://en.wikipedia.org/wiki/Clathrate_gun_hypothesis
omgitsabird 5y ago
https://en.wikipedia.org/wiki/Global_warming_potential https://en.wikipedia.org/wiki/Global_warming_potential
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jillesvangurp 5y ago
Depends on how much methane ends up in the atmosphere. A lot of methane released in a short time, could end up having very dramatic effects. For example, Siberian permafrost melting and releasing a lot of methane would probably have some measurable and dramatic, but short term effects. However, the addition of a couple of giga tons of methane released per year is not going to help slow that melting process down. If that's a process that lasts a few decades/centuries, it would raise methane levels more or less permanently throughout that period. It would recover once methane release stops/slows down. We'd be looking at a very different planet by then with higher see levels, higher temperatures, and a lot less ice on Greenland, Antartica, and most mountains. You can haggle about just how bad things would get in terms of temperature rises, and sea level rises. But lets just say it wouldn't be very good. It would recover eventually. But the problem is that that recovery process is going to take thousands of years.

by gpt5 5y ago

twayt 5y ago

Methane has ~25 times the global warming effect as an equivalent amount of carbon dioxide. Source: https://www.epa.gov/ghgemissions/understanding-global-warming-potentials https://www.epa.gov/ghgemissions/understanding-global-warmin...

tangjurine 5y ago
So methane should be 25 / (120 / 9) = 1.875 times as harmful as CO2 in the long run? How much does the long run matter in this case?
- twayt 5y ago
  The GWP is computed for a period of 100 years to account for the various half-lives. The 25x figure is normalized over a 100 year period. Over a 20 year period, it is about 85x more harmful
  - drallison 5y ago
    So methane control is a significant handle to control global warming. It is not a solution but it will buy time if we globally "burn" methane to COP2. See BlueDotChange.org.
- antod 5y ago
  Doesn't methane eventually break down into carbon dioxide? If it does then it's much worse than just being co2 in the first place.

scroot 5y ago

The concern is faster warming and an out of control positive feedback loop.

istorical 5y ago

Carbon emissions are correlated to human activity. We can dial them up or down theoretically through human action. Methane emission through permafrost (both land and submarine) could end up as a cascading natural emission that forms a feedback loop. I think that's a big part of why people are panicking.

mjevans 5y ago
The cheap option of going out of our way to do less (so we emit less) is very probably off the table at this point. As a species we need another plan. I like a mixed approach of sequestering atmospheric gasses via processes that synthesize useful compounds from the components we don't want in the air as well as hard scifi concepts like giant reflective surfaces in space. Throttling the quantity of sunlight by reflecting a portion away from the earth sounds super expensive... but that might be the only viable option left.
- rTX5CMRXIfFG 5y ago
  Or we could go with the cheap option. If there’s anything that the global pandemic taught us, it is that nothing about human behavior is ever set in stone and there will always be a way to make even draconian policies like lockdowns and mandatory face masks politically viable. The billions we’d spend building the crazy ideas you suggested which also have no guarantee of success, could be channeled into whatever it takes to get people to care more about the planet.
  - quickthrower2 5y ago
    Lockdowns were heavily resisted even with millions dying right now. It will be hard to lock people down in what they can do, politically, because of something that will kill people in the future. People that might not be “me” from the point of view of each individual.
  - nicbou 5y ago
    The pandemic also told us that people won't even do something as mildly inconvenient as wearing a mask. Forget about major life changes.

wizardforhire 5y ago

Clathrate Gun https://en.wikipedia.org/wiki/Clathrate_gun_hypothesis https://en.wikipedia.org/wiki/Clathrate_gun_hypothesis

asdfasgasdgasdg 5y ago
Note the "current outlook" section, where the TL;DR: is that this is not happening and there is pretty good reason to believe it won't over predictable time-frames.
- evil-olive 5y ago
  > the "current outlook" section from the article: > according to data released in January by the US National Oceanic and Atmospheric Administration (NOAA) an encyclopedia like Wikipedia is, by its very nature, going to lag behind the cutting edge of published research on this topic. this article might eventually become a source cited in an edit to the Wikipedia page for that "current outlook" section.
  - asdfasgasdgasdg 5y ago
    The NOAA data is about methane in general, not clathrates.
trsohmers 5y ago
If we haven’t fired the clathrate gun already, I’m personally convinced it is inevitable in the next ~decade. Practically no one I talk to, who are generally concerned about climate change, have the same fear I do about the clathrate gun and most just point to the Wikipedia article downplaying it as “proof” it isn’t a big deal. While it is super depressing to think we have already lost the climate change battle, intelligent people keeping their heads in the sand and not seriously looking at what the next steps are assuming the clathrate gun has already fired are doing a huge disservice to humanity. Absolutely none of the 2030/2050/2100 climate change measures are taking this into account and it is mind boggling to me.

deleted 5y ago

[deleted]

breakyerself 5y ago

A couple things. First is that we are on track to overshoot the goal of limiting warming to 1.5C. It's now more a question of how much we are going to blow past 1.5C. Every bit counts now and a pulse of very potent greenhouse gasses at this time is very unhelpful. 2. There could be tipping points that aren't predictable. Methane may temporarily add a small increase to the global average temps, but could end up being the difference for whether permafrost melt begins releasing large amounts of co2 and even more methane that take us up to some even higher temperatire equilibrium. Global warming is a massive unplanned, uncontrolled experiment with the thermal and chemical properties of the only biosphere we know of. The sooner we stop that experiment the safer humanity will be overall.

julienb_sea 5y ago
Alternatively, attempting to curtail human emissions to some arbitrary level will, unquestionably, have drastic impact on human quality of life worldwide and the impact will be particularly acute on the developing world and those in poverty in the developed world. Large, influential emitters like China and India will not play ball. As such, the climate experiment will inevitably continue unabated, despite any of the self-damaging choices made by the developed world. Additionally, our ability to actually combat the acute impacts of climate change (i.e. construction of flood barriers, land reclamation, movement of people out of flood-prone areas) could easily be actively hampered by overzealous limits on human development associated with attempt to reduce emissions. In other words, this is a nuanced issue and we have little choice but to press onwards.
- KerrAvon 5y ago
  “Better things aren’t possible.”
- tonyedgecombe 5y ago
  Given enough time climate change will have a drastic impact on human quality of life and it's the poorer parts of the world that will feel it most. We seem to be going through stages of climate denialism: Climate change doesn't exist -> it does exist but it isn't man made -> it is man made but it's too expensive and disruptive to fix -> ???

__MatrixMan__ 5y ago

I hadn't thought of carbon emissions in terms of half lives before. I thought that carbon emissions (presumably from fossil fuels) were more of a permanent change. The carbon used to be deep underground, and now it's in the atmosphere. Where does half of it go? I know that it ends up as part of a photosynthetic organism, but then later that plant decays and its back in the atmosphere again, right? And given a changing climate, can we rely on the atmosphere->plant rate remaining constant for enough for our ideas about the half lives of various greenhouse gasses to remain relevant?

sa1 5y ago
Methane breaks down into CO2 and water in a few years, which is why half life of methane is relevant. My understanding is that for CO2, thinking in terms of half-life is less relevant, the CO2 goes to plants and to the ocean, and if those two sinks are at saturation, then CO2 levels in the atmosphere will keep increasing. But there's a good article I found now which might shed more light : https://euanmearns.com/the-half-life-of-co2-in-earths-atmosphere-part-1/ https://euanmearns.com/the-half-life-of-co2-in-earths-atmosp...
XorNot 5y ago
Some amount of carbon is sequestered by plants getting buried when they die, though not as much as in the past because we have well- slated decay organisms in the biosphere. Some makes its way into the sea and gets stuck there. And a decent chunk is bound up as carbonate minerals from the weathering of the Earth (one of the future biosphere death states is when this process outstrips CO2 production due to the increase in the sun's luminosity about 700 million years from now).
abc_lisper 5y ago
When it rains, Co2 in atmosphere leaches the calcium in rocks forming calcium carbonate that runs off to the sea eventually. Hundreds of millions of years from now, our actions leave their mark on some ancient seabed, as a thick white stone(like Dover, England) . The higher the Co2 in the atmosphere, the more it rains, because more water evaporates due to higher temperature, causing faster reduction of Co2 in the atmosphere. Thus there is a natural balance in the cycle. Unfortunately for us, it is way slower than the speed with which we pumped the Co2 out. It takes tens of millions of years to get back to preindustrial levels (of < 200 ppm) Co2

deleted 5y ago

[deleted]

masklinn 5y ago

Methane is CH4. It decays to CO2 + 2 H2O. So as long as it’s methane it’s hundreds of times worse than CO2, then it becomes the same as co2[0]. Never better. Which is why despite a short half life it has a global warming potential of ~25 over 100 years (Co2 is 1). Then you also have the issue that even if it’s short (relatively, it takes multiples of the half-life to really taper off) for that duration your GW effect really shoots up, which tends not to be a good thing, 120 years is already quite short for biological systems to adapt, 10 is basically infeasible. [0] actually a bit worse still as 1t ch4 yields 2.7t co2 and gwp is mass-relative

actually_a_dog 5y ago
Let’s not forget that water vapor is also a greenhouse gas. That makes methane worse than CO2 100% of the time.
- raverbashing 5y ago
  I suspect that's not so much worrying as there are plenty of vapour sources on Earth (like the vast oceans) More water -> less evaporation (but the partial pressure will remain the same more or less)
- kergonath 5y ago
  Water vapour is a greenhouse gas, but it comes back down as rain quite quickly. It's also more or less in (dynamical) equilibrium, because there is always a huge source of atmospheric water in the form of evaporation from the oceans' surface. The way to meaningfully increase atmospheric water content is to increase atmospheric temperature, which methane contributes to, but that's a second order effect.

teslabox 5y ago

> Wouldn’t this make it far less concerning than CO2 with its half life of 120 years? In the pre-industrial era the oceans outgassed CO2 to the atmosphere to prevent land plants from suffocating themselves by sequestering all the carbon dioxide. In the post-industrial era the oceans capture a significant percentage of the CO2 that humans generate (because CO2 is heavier than air, and easily dissolves in water). The most important considerations for the earth's atmospheric heat balance are the heat inputs from the sun (solar cycle) and underwater volcanoes, and the shielding provided by volcanic eruptions. The oceans store heat during the summer, and release heat during the winter. My previous comments: https://news.ycombinator.com/item?id=20002823 https://news.ycombinator.com/item?id=20002823 / https://news.ycombinator.com/item?id=20013166 https://news.ycombinator.com/item?id=20013166

deleted 5y ago

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badgley 5y ago

I think you're spot on in your observation. Reducing methane would help and definitely has its place, but CO₂ is a totally different beast. CO₂ is best thought of as a "stock pollutant" meaning that the more you have of it, the worse the effects. This follows directly from that fact that CO₂ sticks around in the atmosphere for millennia, increasing atmospheric radiative forcing. Methane, on the other hand, is better framed as a "flow pollutant" - it's harm is ~proportional to the rate of emission. This is a direct consequence of its much shorter atmospheric lifetime. Here's a useful twitter thread from a real expert: https://twitter.com/hausfath/status/1425572803508465664 https://twitter.com/hausfath/status/1425572803508465664 And if you're up for a pretty technical (but still fairly approachable) read, check out R.T. Pierrehumbert ''Short-Lived Climate Pollution.'' Annual Review of Earth and Planetary Sciences 2014 42:1, 341-379 [https://doi.org/10.1146/annurev-earth-060313-054843 https://doi.org/10.1146/annurev-earth-060313-054843]. Near the end of the paper, he delivers this gem: "Methane mitigation is like trying to stockpile bananas to eat during retirement. Given the short lifetime of bananas, it makes little sense to begin saving them until your retirement date is quite near."

mtsr 5y ago
Except that as masklinn writes above, methane gets converted into CO2 and so over its full lifecycle is worse by about a factor of 25.

deleted 5y ago

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evil-olive 5y ago

the answer, or part of it, lies with methane clathrate [0] > a large amount of methane is trapped within a crystal structure of water, forming a solid similar to ice. Originally thought to occur only in the outer regions of the Solar System, where temperatures are low and water ice is common, significant deposits of methane clathrate have been found under sediments on the ocean floors of the Earth. deposits of solid methane ice can exist trapped on the seafloor [1]. this is possible only at the extreme pressures of the seafloor [2]. so, on its own, a little methane in the atmosphere is not a big deal, because of the short half-life. except, you have methane ice deposits in the ocean that can melt if the oceans get a little bit warmer. this can enter into a fun little runaway feedback loop pretty quickly. little bit of methane melts, causing a little bit more ocean warming, causing more methane to melt, etc. if this feedback loop were to occur, the evidence you would expect to see would be spontaneous release of methane emissions from the ocean, and you would expect it to be happening in places where the warming ocean put methane clathrates right at their melting point for that depth & pressure of seawater. which...is exactly what's happening [3] > The study, to appear in the journal Geochemistry, Geophysics, Geosystems, a journal of the American Geophysical Union, shows that of 168 bubble plumes observed within the past decade, a disproportionate number were seen at a critical depth for the stability of methane hydrates. > "We see an unusually high number of bubble plumes at the depth where methane hydrate would decompose if seawater has warmed," said lead author H. Paul Johnson, a UW professor of oceanography. "So it is not likely to be just emitted from the sediments; this appears to be coming from the decomposition of methane that has been frozen for thousands of years." a similar feedback loop is possible in the Arctic tundra [4], where permafrost can melt and release trapped bubbles of gases that include methane, which in turn will warm the planet a bit and cause more permafrost to melt. and of course the two feedback loops are able to reinforce each other, because a bit of methane released from the arctic also helps heat the oceans, and a bit of methane released by the oceans also helps melt the permafrost. 0: https://en.wikipedia.org/wiki/Methane_clathrate https://en.wikipedia.org/wiki/Methane_clathrate 1: https://en.wikipedia.org/wiki/Methane_clathrate#/media/File:Gashydrat_mit_Struktur.jpg https://en.wikipedia.org/wiki/Methane_clathrate#/media/File:... 2: https://en.wikipedia.org/wiki/File:Methane_Hydrate_phase_diagram.jpg https://en.wikipedia.org/wiki/File:Methane_Hydrate_phase_dia... 3: https://www.ocean.washington.edu/story/Bubble_plumes_suggest_release_of_frozen_methane https://www.ocean.washington.edu/story/Bubble_plumes_suggest... 4: https://en.wikipedia.org/wiki/Arctic_methane_emissions https://en.wikipedia.org/wiki/Arctic_methane_emissions

it_does_follow 5y ago

While Methane has a shorter half-life it is also a much more effective GHG. The common way to look at this is Global Warming Potential, which is measure in CO2 equivalents. You can find this on the wikipedia: https://en.wikipedia.org/wiki/Global_warming_potential https://en.wikipedia.org/wiki/Global_warming_potential Notice that you can look at the GWP potential over time spans. For methane, over the next 100 years (which is the period that will impact most HNers the most) it is at least 20x as impactful as CO2. The reason this matters is because the biggest unknown with climate change is positive feed backs. A classic example of this is that as the arctic has less ice it also reduces the albedo of the oceans allowing them to absorb even more heat faster. Another, methane related, theoretical, positive feed back is methane clathrates which are essentially frozen stores of methane deep in the arctic ocean. If the ocean were to warm up enough this might rapidly release methane leading to a catastrophic runaway warming scenario, leading to what is suspected to have caused rapid climate change in the Quanternary period [1]. It is currently believed by many researchers that, in the specific case of the 'clathrate gun' firing, it is unlikely to happen. The trouble is we don't know for sure. That is just one unknown, potentially devastating positive feed back. If you read Peter Ward's work (and some others as well) it looks like at various times in the history of the planet there was very rapid, very destructive climate change that was caused by a cascading series of positive feed backs. We don't know exactly where these are, but the more methane we release (and CO2) and the faster the planet warms the more likely we are to find these. It is important to note also, that these positive feedbacks are not factored into the IPCC report (just like the potential collapse of Thwaites Glacier is not) because the is no way to effectively model this and make predictions about them. It means that if you think the IPCC report sounds bad (or even if you don't) there is a lot of potential risk not mentioned in the various pathways there. 1. https://en.wikipedia.org/wiki/Clathrate_gun_hypothesis https://en.wikipedia.org/wiki/Clathrate_gun_hypothesis

omgitsabird 5y ago

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

deleted 5y ago

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jillesvangurp 5y ago

Depends on how much methane ends up in the atmosphere. A lot of methane released in a short time, could end up having very dramatic effects. For example, Siberian permafrost melting and releasing a lot of methane would probably have some measurable and dramatic, but short term effects. However, the addition of a couple of giga tons of methane released per year is not going to help slow that melting process down. If that's a process that lasts a few decades/centuries, it would raise methane levels more or less permanently throughout that period. It would recover once methane release stops/slows down. We'd be looking at a very different planet by then with higher see levels, higher temperatures, and a lot less ice on Greenland, Antartica, and most mountains. You can haggle about just how bad things would get in terms of temperature rises, and sea level rises. But lets just say it wouldn't be very good. It would recover eventually. But the problem is that that recovery process is going to take thousands of years.