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?
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
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.
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.
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]. 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."
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.
Honestly, at this point, we need to be doing BOTH and to such a degree that it feels painful. We need to cut our global energy use massively to slow the runaway acceleration, and we need carbon capture solutions, ridiculous sci-fi mirror solutions, pretty much all of it, to get it back under control. And even then, we're going to have quite a few years of fucked-up weather worse than this.
The problem is, I despair of us doing EITHER, and "quite a few years of fucked-up weather" is going to sound like a fantasy story.
Creating “useful” compounds from atmospheric green house gasses isn’t some “have your cake and eat it, too” type thing. It is going to be extremely inefficient and expensive. Emitting less is still cheaper.
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.
I believe it also showed us the limit of individual action on climate change. It's doubtful I could have gotten 100% work from home out of my employers sans pandemic. My partner stopped going to work because her industry was on government provided life support.
Despite that CO2 emissions in 2020 dropped by 6%. A change which would be wiped out in a few years by the natural growth.
Getting individuals to do anything meaningful about climate change is like those people telling millennials to stop buying Starbucks and cancel Netflix in order to buy a home.
There is that terrible idea that you know what should be best for others. Just forget it, it is not how society works. Totalitarian states trying that idea use over and over and fail with terrible costs.
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.
I’ve burnt 12 cars after lockdowns to ensure that you don’t get the idea that climate lockdowns would be a nice solution after Covid lockdowns. My CO2 emissions now far outweigh (perhaps 10x) the base level, not to talk about the poor grandmas who can’t afford a new car.
Lockdowns are absolutely horrible. I don’t get why you don’t kill us directly, and pretend to do it for our health. Suicide, harm, family violence, just having a life with no leisure, no secret why solitary confinement is used as a means of torture in US prisons.
You just don’t have the stats yet, but the harm you have caused by choosing lockdowns is incommensurable. PLEASE build stats on well-being and how many hours-in-good-health were actually saved by lockdowns, and wait a few years for those studies to surface before concluding that lockdowns are a fine way to deal with a problem. Taking harm upon others may satisfy your feeling of dealing a problem, but the base problem, Covid, has not even been squashed, it spread in waves and became widespread and endemic anyway like doctors always said it would. Not - solved, but saddistic measures were taken against the weaker of us.
With global warming, I have no doubt you’ll crush our lives again without solving anything about global warming itself.
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.
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.
That is a lame excuse, mostly used by people from developed countries that are responsible for the issue, so you dodge responsibility and also try to put blame on the developing country why you are continuing screwing the environment. It is like you have a history of you and your ancestors abusing your children and you don't want to stop because the new neighbor is also abusing his children too (I am thinking especially at coal plants and cars that have effects locally too, so cleaning yup your house means you will have healthier population and less CO2)
> It is like you have a history of you and your ancestors abusing your children and you don't want to stop because the new neighbor is also abusing his children too
This is a poor metaphor. It's more akin to having a family history of child abuse, trying to stop the cycle, explaining to your neighbor why it's bad, and then your neighbor saying "well, your grandpa beat the shit out of your dad, so we get to beat our kids too!"
And of course, the largest producer of CO2 isn't the US as you imply, it's China.
The US is the largest historical emitter of co2. Meaning that the US is still responsible for the largest share of excess co2 in the atmosphere. If co2 emissions are a race then the US has slowed and China is now running faster, but the US lapped china 3 times before China started gaining on them.
Additionally the idea that deploying new technologies equates to economic self harm is absurd. The price per kilowatt hour of renewable energy has been dropping continuously for decades in a pattern similar to moores law. Soon renewable energy will be so much cheaper than fossil fuels that it will be similar to what the discovery of crude oil deposits did to the whale oil industry. Betting on fossil fuels from an economic perspective is stupid as hell in 2022 and risking the survival of worldwide ecosystems and society on that bet is literally the stupidest thing I can think of people advocating for.
China is a problem. We absolutely need China to reduce their emissions much more aggressively than they are. Instead of using them as an excuse to sleepwalk humanity towards potential catastrophe we should be reducing our own emissions so as to have a legitimate position from which to argue about what China should be doing while using our significant economic leverage to incentivize China to reduce their emissions.
I thought it was pretty well understood by now that given that manufacturing of goods destined for the US is happening in China or SE Asia, that there's effectively a miscount.
It's not like china is sitting there burning coal for no reason. And all those ships are going to ports in the US and the like.
Of course this is all a shared responsibility, but let's not act like all of those "CO2 emissions by country" calculations are not extremely fudged by how consumption, manufacturing, and recycling happen in various parts of the world.
This is a poor metaphor. A lot of the CO2 is for producing stuff for the western world. So your neighbor is saying: If I don't beat my kids, they won't come over to you and do slave work, and you'll have to beat your own kids again.
Or we can just agree that this metaphor doesn't work.
>And of course, the largest producer of CO2 isn't the US as you imply, it's China
Only if you ignore per capita and history.
A better analogy, Someone was selling meat, 50% horse and 5-% rabbit , he was using q horse at 1 rabbit ratio, this are your stats , bullshit.
>It's more akin to having a family history of child abuse, trying to stop the cycle
Except you are trying not to stop the cyucle and finding s shitty excuse, I will continue poisoning this city with coal related toxic waste because China has even worse pollution. I should continue throwing plastic garbage in the river and kill our river life because the neighboring country/cities does the same.
My phrasing likely could have been more clear. China and India cannot curtail emissions without reducing energy availability and increasing costs to their population. This has direct and immediate impact on quality of life and human development within their borders. It is actually rather hypocritical for the developed world, which has benefitted from years of development on the back of low cost energy, to push for emissions reductions from countries that have decades of development to undergo.
To be clear, there are intermediate actions they could and should take, such as phase out of coal in favor of natural gas.
Watching climate change deniers periodically change up their bullshit because the old bullshit got too obviously wrong has been equal parts hilarious and frustrating.
I guess now we're at the "okay okay fine, it's a problem, and humans are causing it. But we should still do nothing to fix it, because... China?"
Screaming right past the acceptance stage and in for another loop of denial.
It is interesting that you term me as a climate denier, when in no part did my comment imply I deny the effects and future impact of climate change. I made a point about how global policymaking can and will realistically react to the situation.
Because accepting the potential demise of modern complex society and the collapse of ecosystems and biodiversity world wide and a mass exctinction event because "Fuck it China and India are bad so lets just party until the end." Is fucking stupid.
The proper framing is we need to reduce emissions and so does China and India so how do we facilitate that. The answer is to
1.) Reduce our own emissions to have the moral basis to push other countries to reduce their emissions.
2.) Tax imported goods based on the emissions created in their production. Incentivizing foreign countries to reduce their emissions to be competitive in US markets.
3.) Lobby other countries to do the same using the diplomatic means we have at our disposal.
That's complete bullshit. Global warming isnt a binary of either we're fucked or we're not fucked. It's a gradient of more fucked the look get we wait to phase out emissions. It's never too late because it can always be
Made worse by continuing to emit more.
It's funny how reactionaries have gone from "it's not really happening", "it's not man made" to "it's too late anyways" in no time. The same goal remains; to keep doing nothing.
Moving to higher ground only considers the first-order effects of climate change - floods and severe weather. Potential further effects include reduced agricultural output/efficiency, massive migrations of climate refugees, and the destabilization or collapse of national governments. If we do nothing, natural disasters will be the least of our concerns.
It depends how it goes to zero. US is a significant importer from China. If they go to zero through enforcement of produce-or-import-at-zero laws, it would also push China to improve or lose lots of business.
> US emissions are actually lower than in the past.
> But the US could go to zero and if China and India don't lower emission it won't matter.
Because if the US cut its emissions by half, the standard of living of US citizens (and its associated carbon cost) will become about the same as in China, and will still be a whopping 3.5 times better than India.
Looking at total emissions is actually meaningless, as reducing emissions (significantly) necessarily involves lowering the standard of living - less meat, less transportation, more expensive electricity, less stuff, less construction, less heating etc. The US and EU have a lot of place for reducing our CO2 by reducing our standards of living than India (which produces less CO2 per person than Sweden or any other country in the EU).
Sure, there is some amount of CO2 reduction that can be achieved by green power, but nowhere near enough at the scale and speed needed to avoid catastrophic climate change.
We don't need to reduce our standard of living. We need to change our energy sources to renewables and nuclear. Incentivizing density over sprawl would be good too. As well as efficiency. The only people arguing we need to drastically reduce energy usage are people arguing against doing anything. It's a strawman.
We will have to. I know it can seem like an argument against doing anything, but that is not where I'm coming from. I'm also not arguing in favor of self flagellation or individual action in the face of huge social forces.
But, given how grave and urgent the situation is getting, there is no way to convert all curent energy generation to green energy AND increase energy generation capacity to keep up with normal economic growth AND increase it many times over to electrify all transportation AND electrify all heating. And even if we were to succeed in all that, that only covers about half of US emissions at best - the other half is coming from agriculture, industry and residential emissions. Not to mention the massive emissions that are happening in China but ultimately serving the US market.
It's simply not possible to achieve the necessary time frames (net 0 in 20 years) without significantly reducing economic activity and standards of living in the short term - then growing back to current activity and standards of living in the longer term.
China and India are nothing compared to the US, if you look at the relevant metrics - emissions per capita. The US is emitting the same as China or near enough not to matter, but doing so at less than a third of the population. The comparison with India is even more one-sided.
Not to mention, much of China's emissions are actually coming from its factories supplying the US and Europe with goods. If we just give up on buying some of the goods, emissions will go down.
Finally, to call any measures on combatting climate change that were enacted anywhere in the world "overzealous" is laughable. The only measure stat can actually put a dent in the ever increasing temperatures are those that will come with economic contraction - not just stopping the growth, but actually downsize our economies for a decade or two - but this is completely unthinkable to liberals.
The best measures that are being taken today would have helped if they had been taken in the 1960s when the problem was first understood. Instead, we sacrificed the future for economic growth in the present, and are now doing minor improvements (wind and solar, electric cars) that will barely even reduce the rhythm at which emissions are increasing.
Emissions per capita is only relevant if you want to assign moral blame rather than solve the problem. Canada and Australia are higher per capita than the US [0], and you can demonize and crucify them all you want, but it doesn't stop more than 3% of the total problem.
Similarly, you can send every person in the US back to the stone age, and you're still going to have about 80% of the problem unless you can get other countries to join along.
Edit: If every country on Earth had India's emissions per capita, we would be cutting global emissions to less than 25% of what they are today.
Emissions per capita are relevant if you want to discuss a realistic expectation of how low a country's emissions can go. They are also directly relevant: every citizen of a country must be fed, must be given electricity, must use transportation, and must consume goods - each of these cost CO2 in quite direct proportion to the number of citizens.
For example, China has a lot of room for improvement, but India does not, as it's already at lower emissions per capita than half the world (much lower than any EU country, for example).
Global warming is not exclusively the problem of the global south. Poor people in China or India have the same rights to affordable electricity as people in Norway or Germany, which have higher emissions than China per person, despite the fact that they have outsourced plenty of emissions to China.
Overall, if say we needed to reduce emissions by 50%, countries with higher emissions per capita will likely have to reduce MORE than that, as China and particularly India would incur much more harm to their hundreds of millions of citizens than Germany or the USA if they were to significantly reduce emissions.
> Emissions per capita are relevant if [...] each of these cost CO2 in quite direct proportion to the number of citizens.
Forgive the aggressive editing of your quote, but multiplying emissions per capita times the number of citizens is exactly emissions per country.
> want to discuss a realistic expectation of how low a country's emissions can go
Theoretically, most countries emissions could go to zero with nuclear, wind, solar, hydro, and/or geothermal. You can dive into the touchy feely stuff about people's quality of life, but it's easy to imagine a high quality of life in a country that went pure nuclear (zero added CO2). No new technology (battery storage) needed. However, if we're being realistic, you shouldn't expect any country to change much at all, and you'll find out how many people fear nuclear more than they fear fossil fuels.
In the link I posted above there are 15 sovereign nations which produce a higher CO2 per capita than the US. (As an aside, several of those countries have a strong interest in selling oil, so you aren't likely to sway them.) If you treat per capita as the important metric, and you successfully convince those 15 countries to go pure solar/nuclear/whatever, you've solved less than 5% of the problem. Lock your heels and stick to your guns, refuse to admit you're wrong, but this is an inefficient approach.
Contrast that with converting just China, the US, and India, to wind/geothermal/whatever and you've solved 50%.
> Theoretically, most countries emissions could go to zero with nuclear, wind, solar, hydro, and/or geothermal.
I think this is the bad assumption that is causing you to think emissions per capita are not important. Power generation is only a fraction of the problem. Most clearly, GHG emissions from cows and pigs will not go down even if all electricity energy is produced with 0 emissions. Incidentally, India's widespread vegetarianism may be a big component of how its emissions are so low.
Then, transportation will not magically become electric even if the whole grid is green. Perhaps cars are a solved problem, but electric trucks, electric air planes, and electric cargo boats are definitely not solved problem, not for anywhere near today's costs.
There are of course numerous other industrial processes which emit massive amounts of CO2 that can't be electrified at all - cement production, smelting, plastic recycling, many chemical processes etc.
Also, new nuclear, hydro, solar, and wind are not competitive with already built coal or natural gas power plants - so moving to a new entirely green grid would massively increase the costs of electricity, which in turn will increase the costs of basically all consumer goods.
And while many in the USA and Europe could afford to pay twice the price of electricity and all basic necessities (though nowhere close to all), few would in India or China.
Now, would it be important and good to pressure and fund China, US and India to replace what they can of their electrical grids with nuclear and other green energies? Absolutely! But it only addresses a small part of the problem, and does so at tremendous cost.
Edit: electricity generation accounts for ~50% of China's GHG emissions, ~35% of India's and ~25% of the US's. So even entirely greenifying their grids will not reduce world GHG emissions by anywhere near 50%.
Take your argument to its logical conclusion and maybe you'll see the contradiction: Qatar has the worst CO2 emissions per capita, so clearly that's where you should focus your efforts.
> Also, new nuclear, hydro, solar, and wind are not competitive with already built coal or natural gas power plants [...] costs
While this is completely true, if you stick to financial justification for changes, you aren't going to succeed anywhere. If any of the other methods were more cost effective in the short term, they'd already have switched.
I doubt it's fruitful to talk about any of this. You seem pretty certain you're right, and I doubt I could change your mind on anything.
> Qatar has the worst CO2 emissions per capita, so clearly that's where you should focus your efforts.
That's not what I'm arguing. I'm arguing that no one country, or even small group of countries, can stop climate change alone, at least not without causing massive harm to their citizens. The entire world needs to participate, and countries that are producing the most GHG for the least amount of people need to do so most of all (though of course once you get to really really small countries, say Luxembourg, other factors become dominant).
My point is that India, particularly, can't realistically reduce emissions (without harming their citizens tremendously in the short term) by more than a few percents. Meanwhile, Europe, the Middle Eastern oil states, Russia, and the USA have much more room to reduce their emissions more drastically, and, combined, they will have a bigger effect, with much less harm to their own people. China absolutely needs to do more as well, and for them in particular green energy generation is lower hanging fruit (since so much of their emissions are coming from this).
The goal of this whole thing is to move as fast as possible to ensure the planet remains livable 100 years from now, without sacrificing poor peasants' already meager lifestyles in China and India (and anywhere else) today.
And now sure, an argument could be made that rather than building nucelar reactors in France, French money could be better invested in building nuclear reactors in China - that is, that the world's limited capacity for building green energy should be best invested in the places that need power the most while currently having the worst way of getting it. I would be amenable to such an argument, though I think it's more utopic than my previous ones.
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 -> ???
> Large, influential emitters like China and India will not play ball.
This is not true. We are all in the same frying pan and I don't know why people keep insisting that the others don't understand it. Of course they do. They have political pressures from industrialists and deniers just as we do here that might prevent immediate action, but they are not fundamentally different. Quite the opposite.
Either way, why do we have to wait for others to move first. We know there's a problem, we know there are solutions, get to it.
Even if the choice was between quality of life now and addressing climate change you haven't made a convincing argument for why maintaining peoples quality of life as it is now is worth risking a mass extinction event in the future.
That being said I see no reason why doing any of the things mainstream scientists and economists are calling for would in any way diminish anyone's quality of life. If anything it will improve quality of life at the very least by reducing air pollution and it will prevent drastic reductions in quality of life in the coming decades from the effects of unchecked global warming.
I really don't know where this crap even comes from. Like we get x amount of energy from fossil fuels. Therefore we must reduce energy usage by that much? Do you think that's what we're advocating for?
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.
> 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.
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.
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.
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?
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.
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).
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
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
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.
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.
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.
Looking for serious answers.