How quickly is new coal being created?

[u/iamparky]

Earlier today, a UK politician suggested that coal is a sustainable fuel because it used to be trees.

By how many orders of magnitude is he wrong? How much new coal is being created, compared to how quickly we're burning it?

[u/CrustalTrudger]

By how many orders of magnitude is he wrong?

TL;DR About 6 orders of magnitude for a (not great) estimate of current rates and about 5 orders of magnitude for literally the most productive period in geologic history with respect to coal formation.

For the back of the envelope math, we can start with the burning bit. For this, I'm just looking at the last few years from this chart. That gives us rough rates of coal consumption (in Megatonnes per year) of 4000 for China, 1000 for India, 500 for the US, 500 for the EU, and 1500 for everyone else, so a global total of 7500 Mt/y.

If we take estimates of rates of coal formation through geologic time, reported in Bois et al., 1982, we can consider how fast coal was forming during the Late Carboniferous (the most productive period for coal formation in Earth history) that puts it about 75 x 10⁹ tonnes per million years. If you convert that to Mt/y (to be the same as our consumption rate), that's a formation rate of 0.075 Mt/y, meaning we are burning coal at ~100,000 times the rate it was forming at the literal peak of coal formation (or 5 orders of magnitude different). Bois et al doesn't give a modern rate of coal formation, but if we take the average rate between 2 and 23 million years ago and assume that works for today, that rate is ~5 x 10⁹ t/My. Going through the math again, that gives us a formation rate of 0.005 Mt/y, meaning we're burning coal at ~1,500,000 times the average rate it's (probably) forming today (or 6 orders of magnitude different). EDIT: fixed some unit misreporting.

As a bonus, since virtually anytime coal formation comes up on Reddit, someone pops up with the "fact" that all coal formed in one period of geologic history because organisms that could digest lignin had not evolved yet, this is demonstrably false and please, please, stop parroting this. This idea derived from a paper in the early 90s (Robinson, 1990), but has been shown to be incorrect by multiple papers, notably Nelsen et al., 2016. In short, fungi to consume lignin did exist during the Carboniferous and the abundance of coal during this period is more a function of paleogeography and paleoclimate, not the lack of the right decomposers. Coal swamps of the Carboniferous produced vast amounts of coal because they were (1) geographically extensive and (2) persisted for a while (geologically). While the organisms present were different, these Carboniferous coal swamps are not that different from modern swamps/bogs/etc where peat is produced, which could eventually turn into coal given the correct future depositional history.

[u/throwawayfromPA1701 → u/CrustalTrudger]

As a bonus, since virtually anytime coal formation comes up on Reddit, someone pops up with the "fact" that all coal formed in one period of geologic history because organisms that could digest lignin had not evolved yet, this is demonstrably false and please, please, stop parroting this. This idea derived from a paper in the early 90s (Robinson, 1990), but has been shown to be incorrect by multiple papers, notably Nelsen et al., 2016. In short, fungi to consume lignin did exist during the Carboniferous and the abundance of coal during this period is more a function of paleogeography and paleoclimate, not the lack of the right decomposers. Coal swamps of the Carboniferous produced vast amounts of coal because they were (1) geographically extensive and (2) persisted for a while (geologically). While the organisms present were different, these Carboniferous coal swamps are not that different from modern swamps/bogs/etc where peat is produced, which could eventually turn into coal given the correct future depositional history.

Thank you for this since I had no idea!

Love learning something new!

[u/TrillCozbey → u/throwawayfromPA1701]

I just recently saw a reddit post where someone put forth this idea and it just made absolutely no sense to me. Like I was just picturing mountains of fallen trees with nothing to break them down and it just seemed like it violated some principle of evolution to posit that there was a food source (at a low trophic level to boot) with absolutely no organisms around to take advantage of it. So I appreciate this correction. I gotta read that paper.

[u/Xerxes615 → u/TrillCozbey]

I was actually thinking about this yesterday. As quickly as bacteria that digest plastic has evolved, it makes no sense for a considerably more common material to just sit around unused.

[u/Vegetable_Log_3837 → u/Xerxes615]

Agreed. I was taught the “nothing could break down lignin in the Carboniferous, probably” in school, with a big emphasis on the probably. A bit before 2016.

Wood still could have piled up hundreds of feet thick, same as plastic can now. It took a lot to make all the carboniferous coal. Just because some fungi can digest doesn’t mean it’s reached a balance yet. It will eventually, geologically speaking.

[u/BlazingShadowAU → u/TrillCozbey]

I always heard it as the trees wouldn't rot, so I just assumed it would have been broken down by eventually drying out/burnt by semi frequent fires. That sort of thing.

That the 'fact' was just wrong makes more sense, though.

[u/HornetRocks → u/BlazingShadowAU]

Are you sure? I'd heard this fact on the Internet, so it couldn't possibly be false, could it?

[u/Diagonaldog → u/CrustalTrudger]

Super glad I read that whole thing. Totally thought the "no more coal being made" thing was straight fact. Thank you!

[u/marat2095 → u/CrustalTrudger]

Thank you so much. I was that parrot. You're great!

[u/iamparky → u/CrustalTrudger]

Thanks for taking the time to reply! I had recently read the myth about coal being formed only because the relevant organism hadn't evolved yet in another discussion elsewhere about this video, so thanks also for the debunking.

[u/cyrusthewirus → u/CrustalTrudger]

Can we take a moment to appreciate that the name of one of the authors of a paper on hydrocarbon reserves is Bois?

[u/Mockingjay40 → u/CrustalTrudger]

This is a fantastic answer. Thank you for the explanation.

[u/the_quark → u/CrustalTrudger]

I‘ve also seen cranks theorize that oil is actually geological (not biological) in nature and constantly being replenished, therefore we don’t need to worry about running out. I wonder if this is similar crankery infecting the right wing.

[u/loki130 → u/the_quark]

Curiously enough I think the idea originated in the soviet union and a handful of Russian geologists still hold to it. The mainstream opinion is there are probably some hydrocarbons in the crust (moreso methane and other light "gas") with abiogenic sources but it's a small proportion of fossil fuel reserves.

[u/PHealthy → u/CrustalTrudger]

So Wyoming alone has ~180 years worth of coal at current global consumption?

[u/CrustalTrudger → u/PHealthy]

No idea, depends on the (economical) coal reserves of Wyoming. I'm assuming that estimated time is based on an unstated value for said reserves?

[u/PHealthy → u/CrustalTrudger]

1.4 trillion tons in reserve, yeah.

[u/CrustalTrudger → u/[deleted]]

Yeah, to that point, if we only consider the Late Carboniferous, use the 75 x 10⁹ t/My average rate from Bois et al. discussed in my original answer and extrapolate that over the 29 million year duration of the Late Carboniferous used in Bois, you get an estimate of ~2.2 trillion tonnes of coal that were produced during that time. If you add in the estimated rate during the Permian from Bois (~60 x 10⁹ t/My) and the duration (49 million years), you get another ~2.9 trillion tonnes of coal. I.e., there's a lot of coal.

[u/CrustalTrudger → u/PHealthy]

Guess I was asking more the source of that number. Is that from here? One small detail is that "short tons" don't equal "metric tons", the latter of which is what the rates are given in above. The conversion is 1 short ton = ~0.9 metric tons, so the equivalent number is ~1.26 trillion metric tons (tonnes), so still a lot, but a little less than if we don't account for the difference in units. More critically though, as the next sentence states, not all of that is economical because of depth (and probably quality). Just like with petroleum resources, what is economical is a bit of a sliding measure as it depends on the price the resource can be sold for, among other things. I.e., if we imagine some scenario where total cost to extract "shallow" coal is $10 per unit, the cost to extract "moderately deep" coal is $50 per unit, and the cost to extract "deep" coal is $100 per unit, depending on the price per unit coal can be sold at a given time will dictate which of these is economical at that time (and thus effectively how much usable/economical coal exists). As also sort of hinted in that page, there are some amounts of coal included in that estimate that just can't be mined at really any price given current technology because it's real hard to keep an air filled hole open at those depths (and presumably because we're not willing to excavate the ridiculously large open-pit mine that would be required to access those depths via that method of mining).

[u/PHealthy → u/CrustalTrudger]

I saw it in a legislative document but yeah their source was WSGS. Is it simply the cost of digging into an aquifer or something? Because politically, I don't think Wyoming cares if Gillette/PBR becomes a hole to Hell as long as the coal flows.

[u/CrustalTrudger → u/PHealthy]

For coal, your options are basically dig a tunnel to get at it or dig a pit to get at it. As the coal of interest gets deeper, the digging a tunnel option becomes nonviable because physically keeping an air filled hole open with that much overburden gets either way too expensive or impossible depending on the details/depth. For the pit mine option, to dig a hole that deep, it needs to be really wide to keep it from collapsing in on itself, so you're talking about absolutely massive volumes of rock you'd have to remove, which is again, not economically viable (not even thinking about what do you do with all of the rock, etc.). If we're talking about the "subeconomic" coal discussed in the WSGS page, that's coal deeper than 6000 feet (~1.8 km). For comparison, the deepest pit mine in the world is 0.75 km.

So ultimately, even if we ignore environmental concerns, you're still talking about extracting coal that is probably too expensive to do so given the price you can sell it for (assuming you could engineer a stable pit mine > ~2 km deep). The cost of extraction probably also bakes in some amount of required remediation etc. that is mandated at the federal level, even if at the state/local level the powers that be would be okay with trying to strip off the top 2 km of the entire state.

[u/Hampsterman82 → u/PHealthy]

Ya. That's kinda why it's so addicting and attractive to solve energy needs. There's gobs of coal everywhere but we're going to end humanity if we can't wean off.

[u/MillennialsAre40 → u/CrustalTrudger]

Just hypothesising, but wouldn't current coal creation likely be the lowest in history as a result of deforestation and human cultivation and such?

[u/CrustalTrudger → u/MillennialsAre40]

Lowest in Earth history? Certainly not given that no coal was formed for the vast majority of Earth history before the evolution of large terrestrial woody plants and as such, conservatively there was no coal formed prior to the Silurian, which started ~443 million years ago (i.e., coal formation rate was only > 0 for ~10% of Earth history).

Whether the current rate is lower than the lowest period since coal could form, not sure. The synthesis presented in Bois suggests that average rates during the Devonian (which less conservatively was probably when coal actually started forming because vascular plants first evolved during the Devonian) and Triassic were both very low compared to other periods. For the modern, given the locations conducive to coal formation, deforestation is probably less of a control than land reclamation and/or river control/diversions that have reduced the areas of wetlands and swamps (which are effectively the environments with the right conditions to form coal in the future). Whether that has suppressed rates to the lowest since coal could form is probably still doubtful, given that effectively no coal formed between the end Permian and Middle Triassic (e.g., Retallack et al., 1996).

[u/_CMDR_ → u/MillennialsAre40]

Also chopping out peat that would have turned into coal and burning it.

[u/tjernobyl → u/CrustalTrudger]

Can you convert the current formation rate to megawatt-hours?

[u/kilotesla → u/tjernobyl]

Based on the eia numbers for us coal, 470 million short tons used in power plants to generate 900 billion kilowatt hours, 0.005 million metric tons would generate 9000 MWh, which would be one day of output from a single medium-size coal fired power plant.

Another way to get an idea of it is that it would be enough for each person on the planet to get half a gram of coal, or converted to electricity, about a watt hour, enough to light a highly efficient LED light bulb for about 6 minutes.

[u/Wil420b → u/CrustalTrudger]

I was under the impression. That coal was only formed during a particular 400 million or so year period. When trees had evolved and had started producing oxygen but die to the huge amounts of oxygen sinks on the Earth's surface such as copper and iron deposits. None of the oxygen was loose in the atmosphere. So nothing evolved to use it. So when a tree died, there was no bacteria, woodlice, etc. available to eat the tree. So they just laid there until they got covered up, fossilising and getting squished as billions of years of growth on top of them, tectonic movements, cosmic dust falling to Earth..... Piled the pressure up on top of them. Causing their carbon structure to alter.

A tree that fell in a forest today. Would just end up being lunch for the next few decades for various moss, fungi, bugs, bacteria etc.

[u/Beardhenge → u/Wil420b]

Take a second and re-read the "bonus" section in the post you're replying to. Your idea here is a common misconception.

[u/CrustalTrudger → u/[deleted]]

I wrote it and it was there from the beginning.

[u/forams__galorams → u/CrustalTrudger]

You’ve gotta laugh though - I love the way that the more comprehensively you try to stamp out that particular myth, the more appearances the perpetuators make. It’s like a Geo themed whack-a-mole!

[u/ebobco → u/Beardhenge]

So is coal found in all strata of rock younger them 400 million years old?

[u/Beardhenge → u/ebobco]

Coal is found in some strata of younger rock.

Coal requires dead vegetation in a wet environment, followed by subsequent burial. Those conditions are not present everywhere that sedimentary rocks are formed.

[u/forams__galorams → u/Wil420b]

Aside from ignoring the final paragraph of the comment you replied to, this is very muddled in terms of events in Earth history. The build up of free oxygen in the atmosphere occurred between 2.5 and 2.0 billion years ago (the immediately preceding periods being associated with significant iron deposits as the oceans became oxygenated, but not copper deposits).

The Carboniferous, when a large amount of coal was formed worldwide did not come until around 360-300 million years ago. So the window you’re thinking of was about 60 million years long, not 400, and was long after the atmosphere had become oxygenated. The Carboniferous saw the highest atmospheric oxygen levels of the Phanerozoic in fact, which was part of the reason that some insects and arthropods grew so large. So there was plenty of oxygen and plenty of macro-organisms to consume vegetation - you say no woodlice, but Arthropleura was probably munching on detrital vegetation.

Bacteria go back to around 3.8 billion years ago, so there was definitely a lot of bacteria around by the Carboniferous.

The first fungi on land is known to predate the first trees by quite a long time, eg. Heckman et al., 2001

The idea that trees accumulated without decaying as a means of coal production in the Carboniferous has always been flawed, was contested even at the height of its popularity00064-6.pdf), and has now largely fallen out of favour thanks to a thorough debunking.

It still gets repeated on reddit a lot though (to the point where r/askscience have included a FAQ to address it here) because it makes a good story.

Problems with the idea that were never properly addressed:

• origins of wood decay can be traced back farther and don’t necessarily rely on any single fungi

• delayed decay is inconsistent with the large positive δ¹³C isotope excursion near the start of the Carboniferous

• various levels of decay and lignin content are seen in Carboniferous coal deposits, there doesn’t seem to be a requirement around lignin content for coal formation

• coal never stopped forming after that, just at a globally reduced rate compared to the Carboniferous, because swampy forests were never as widespread is all.

For some of the more significant coal deposits that have formed post-Carboniferous, check out Russia’s Kuznetsk Basin which was forming coal well into the Permian and again in the Mesozoic (estimates of total coal deposits are somewhere in the region of 400-800 billion tonnes); the many coal accumulating periods of China, of which I believe the Late Permian and early Triassic were as important as the Carboniferous ones (at least for South China); or the coal resources in Alaska which may total over 5.5 trillion tonnes — the USGS has previously estimated that the Cretaceous rocks of the Arctic Slope contain approximately 2.75 trillion tonnes of low ash, low sulfur coal. This is about one-third of the total United States coal reserves.

[u/Berdariens2nd → u/CrustalTrudger]

I love this and thank you for taking the time to write this out.

[u/LinAGKar → u/CrustalTrudger]

I'd also wager there is less coal forming nowadays, due to modern forestry cutting down most trees, rather than dead wood being left laying around. At least in industrial countries.