Is there any known approach to CO2 sequestration that could reach a scale that would even remotely make a difference for climate change? They either require an enormous amount of energy and/or machinery and/or space.
crystal_revenge · 7h ago
The absolute best way to decrease the amount of atmospheric CO2 over time is to keep fossil fuels in the ground. If we don’t do this, no other solution really matters.
To date we have been unsuccessful at deciding to do this and in fact there are currently multiple wars going on the extract more at a faster rate.
ju-st · 4h ago
We have already perfectly sequestered CO2 in the ground and still dig it up and burn it. Insane.
adrianN · 7h ago
What do you mean exactly? We could plant lots of trees and make charcoal from them and bury it. That scales with the amount of money spent. The problem is that nobody wants to invest a big chunk of gdp into burying coal.
gg82 · 5h ago
It would be better to create bio-char and use it to improve the soil for farmers to grow food. This would also help them with the changing climate, because bio-char assists with moisture retention.
yread · 6h ago
It's about 10 times cheaper to not burn fossil fuels than to sequester
boxed · 7h ago
I don't understand the objection. We are un-terraforming Earth now. Terraforming it back is worth is basically no matter the cost, since the alternative is to not have a livable Earth.
black_puppydog · 4h ago
hahaha, that would require us stopping to terraform it first, by stopping to burn fossil fuels.
exoverito · 3h ago
CO2 levels were triple current levels at 1500 ppm about 50 million years ago. This was during the Cenozoic era when mammals first rose to dominance. Clearly the Earth was livable then.
Consider the possibility that you are mistaken, and the victim of propaganda.
tda · 2h ago
Did you check the sea levels back then? It is estimated to be 100m higher than now. And you know around half of the earths population live on land that would be sea in that case? So yes the earth can survive higher CO2 levels and higher sea levels, especially if the changes are gradual (over millions of years).
But the chances you will personally be adverse affected by anthropogenic climate change in your lifetime is pretty damn high. Humanity will survive, but many humans will die in horrible conditions
chownie · 3h ago
Of course it goes without saying, the ecological niches and evolutionary adaptations different species earned through 50m years of CO2 lowering, they can obviously just do it again if we were to drastically change the CO2 numbers over like a hundred years instead.
We can tell that this is right and logical because the number of insects, a population more sensitive to environmental trends, hasn't visibly and obviously changed at all.
kragen · 7h ago
Yes, if large amounts of energy are available. I haven't done the calculations in a long time, but I thought I came up with a ballpark of 10% of current global marketed energy consumption for a few decades for atmospheric carbon capture. We can place a very firm upper bound of about four times current world marketed energy consumption.
To avoid any concerns about scalability, as well as about energy supply intermittency, I made my estimate using only the oldest process in the chemical industry, lime burning, which predates plastics, oil drilling, steel, iron, bronze, writing, cities, ceramic, and possibly even agriculture. The only difference from the Neolithic method is that you have to retort the lime in a sealed chamber so you can collect the carbon dioxide it absorbed from the atmosphere after the last time you calcined it. This doesn't require an enormous amount of machinery, just very large machinery. Basically, a giant tin can similar to a water tower, maintained at a mildly negative gauge pressure as it's heated up.
My estimate, IIRC, was that, without soda for process intensification, you would need an amount of limestone a few times larger than the amount mined by the cement industry every year. That's fine, though; limestone is about 20% of all sedimentary rock, and sedimentary rock is 73% of Earth's land surface and 8% of the entire crust.
Very roughly, Earth is 6e24 kg, her crust is 6e22 kg, and its limestone is 1e21 kg. By contrast, the 427 ppm of carbon dioxide we need to capture half of is only 3.34 teratonnes, 3e15 kg. Limestone is 44% carbon dioxide by mass, so it absorbs 44% of its mass in carbon dioxide each time through the cycle. This absorption takes about 5 years if it's sitting in a paper bag dry, about a month when you whitewash a wall with it, or a second or so when you catalyze the absorption with a few percent of lye, like in a scuba diving rebreather.
The USGS publishes a lot of information about the world lime market at https://www.usgs.gov/centers/national-minerals-information-c.... From it, we can see that current US lime prices are 20¢/kg, 3.2 billion dollars for a total yearly production of 16 million tonnes. (They say that prices at the plant were as low as US$131/tonne in 02020, so probably the production cost is closer to 13¢/kg, including the cost of mining.) That's probably tonnes of CaO, which is the other 56% of limestone that isn't carbon dioxide. If burning lime in a giant tin can to capture the gas were about as expensive as how it's done today, that's about 24¢ per kg of carbon dioxide, not counting the cost of warehousing the resulting lime until it's absorbed the gas so you can calcine it again. (Remember, you can reuse the same lime every few hours if you dope it with a soda catalyst.)
World lime production is closer to 420 million tonnes per year, mostly of course in China, 26 times US production.
1.8 trillion tonnes of lime is 4300 years of total world production (or 120,000 years of current US production), so we're talking about a significant scale up. It's not just a few times global cement energy production. But it's still only two millionths of the limestone in the crust of the earth, and maybe you'd want to reuse the same lime many times so you don't have to mine it again.
But probably some process involving more sophisticated sorbents like triethanolamine, combined with point source capture, will end up being cheaper in the end. And see my notes in https://news.ycombinator.com/item?id=44461843 about accelerated olivine weathering. The lime approach serves only as an easily computable upper bound on difficulty.
The USGS mineral commodities summaries also have an entry for "stone (crushed)", which is 70% limestone. This is 1.5 billion tonnes per year in the US, which I guess is a billion tonnes of limestone, so 1.8 trillion tonnes of quicklime (3.4 billion tonnes of limestone) is only about 3400 years of US mine production. It only costs about 1–2¢/kg, which is in accordance with what I've seen. No world production figures are given, but we can probably guess that that's another thing China produces 20 or 30 times more of.
So, the cost of quicklime is almost all (>80%) calcination, and I believe that almost all of that number is energy. We can put an upper bound on its energy consumption based on that 13-cent cost in 02020: coal is often the cheapest source of the heat needed for calcination, and in 02020, it reached a low around US$60/tonne ( https://fred.stlouisfed.org/series/PCOALAUUSDA). So we know that producing a kg of quicklime can't require more than about 2 kg of coal, which provides 33MJ/kg or less (0.7¢/kWh or US$1.80/GJ), so 70MJ per kg of quicklime or of carbon dioxide. That's probably not a very tight upper bound, but I doubt it's high by more than a factor of 3.
Removing 1.4 teratonnes of carbon dioxide over 40 years is 1.1 million kg per second. At 70MJ/kg this multiplies out to 78 terawatts, roughly four times world marketed energy consumption.
Today, devoting a couple of terawatts to the problem would be unreasonably expensive, and tens of terawatts would require expanding world energy production considerably. At 24¢ per kg of carbon dioxide, removing 1.6 trillion tonnes of it would cost 400 trillion dollars, four years of world GDP (say, 10% of world GDP over 40 years). But that's just because the rollout of photovoltaic energy has just begun; the majority of the 18 terawatts or so of world marketed energy consumption is still supplied by fossil fuels, although they are clearly no longer cost-competitive with PV. PV manufacturing is still scaling up, though, and presumably PV energy production will exceed current world marketed energy consumption in a few years, and then continue to increase as new uses are found for the newly much cheaper energy.
78 terawatts is 0.04% of the 174 petawatts of terrestrial insolation.
throwpoaster · 33m ago
Thank you for this detailed response.
deadbabe · 8h ago
No. Not even a little bit.
And if there was, any sequestration would just be used as an excuse to find ways to conduct more CO2 producing activities.
gsf_emergency_2 · 7h ago
It should be made a crime to mention CO2 sequestration when sane avenues (short of geoengineering) like large scale (night activated) radiatively-cooled floating solar panels, or roads are more likely to help (& even be profitable)
However.. climate change is a chiefly a political problem, not a tech problem.
graeme · 7h ago
It is exceedingly likely that any sequestration will take substantially more energy than burning fossils fuels produced. I couldn't explain it properly in physics terms but when you burn fuel you are releasing stored energy and when you sequester carbon you are storing the energy.
If we could store energy cheaper than we could use it we'd have a perpetual motion machine, I think? Fairly sure this would be physically impossible. Where this might be wrong is if we found a process to use another energy source (the sun, something that uses the sun, etc) to do it for us, but we haven't go anything that works in that vein either. Trees are actually one of the better options, but to reverse climate change you'd need to reforest the earth AND sequester all the oil we burned.
Burning carbon is effectively debt. If we stopped burning carbon right this second, billions would die, as our whole system depends upon it. But if we don't stop burning it, we increase our future problems.
This is unpleasant to reckon with so most don't. I don't think it makes the problem intractable, but it gets harder the more we delay.
We do need sequestration because simply eliminating all carbon sources wouldn't be enough, we also have to reduce current levels. Also there are some cases where fossil fuel might be the best solution (rocketry?) so we'd need to be able to deal with the waste.
kragen · 7h ago
This is not correct.
Your reasoning would be correct if carbon sequestration involved reducing carbon dioxide back to elemental carbon, or hydrocarbons, or whatever form you burned it in. In fact, though, almost all proposed methods for carbon sequestration sequester the carbon dioxide, not just the carbon. Consequently, point-source carbon capture uses only a fraction of the energy released by burning the fuel.
It's a significant fraction, though, and atmospheric carbon capture uses more energy because it has to extract the carbon dioxide from air, which is 99.96% things that are not carbon dioxide. As I understand it, the energy dissipation thermodynamically required by that separation is quite small, but getting anywhere close to that thermodynamic limit is going to be a large engineering effort.
graeme · 7h ago
Ah, thanks, you're right. Though I was thinking mainly of direct air capture. Point source is great, but not actually net sequestration.
Need to look into this a bit more, but what would you say the theoretical efficiency is, could we reach a point where you can actually burn fossil fuel to net extract CO2 via direct air capture or another sequestration method that can be scaled?
kragen · 5h ago
Point source capture is net sequestration if the fuel is made by direct air capture. That sounds stupid but biomass fuel actually achieves this. It probably can't scale high enough, though.
I don't know enough about thermodynamics to calculate the fundamental limits. I suspect that low-temperature sorbents like triethanolamine can currently do direct air capture for less than the energy produced by the fuel, but the process is complicated, involving things like embodied energy in fan motors and hard-to-predict maintenance costs. In a cousin comment (https://news.ycombinator.com/item?id=44461370) I did an upper-bound calculation with a very-well-understood atmospheric carbon capture process that people have been doing inadvertently in a no-net-sequestration fashion for thousands of years. It came up with burning no more than 2 kg of coal per kg of carbon dioxide removed, which is theoretically significant net sequestration (if you do point-source capture on the coal burning) but far too expensive to make a dent.
Sequestration processes like serpentinization are actually exothermic. The idea there is that you react carbon dioxide with olivine and get serpentine and heat. There's vastly more olivine available than any crustal rock such as limestone. You can do this in lots of ways; for example, you can pump concentrated carbon dioxide down a well into fracked olivine, where it reacts, or you can crush olivine from an olivine quarry into olivine sand and just dump it on beaches, or build artificial islands out of it in Dubai or disputed areas of the South China Sea. Crushing the olivine costs energy, though, and it's energy that's mostly not stored for the process; it just provides more surface area for the same reaction.
I don't actually favor this approach (what do you do if you decide the beaches are removing too much carbon dioxide? Beaches don't have emergency stop buttons) but it does show that in principle the effective energy consumption of direct air capture doesn't even have to be positive.
briandw · 11h ago
Nuclear Explosions for Large Scale Carbon Sequestration:
https://arxiv.org/abs/2501.06623
seems more promising, I love that there is more research and interest in accelerated weathering
joegibbs · 9h ago
Could there be any possible negative effects from an 81 gigaton nuke exploding though? A 100 megaton Tsar Bomba would wipe out all of New York, a thousands times more than that might have some adverse impact.
colechristensen · 9h ago
This is a very shallow analysis, feels like an undergrad wrote that.
You just wouldn't build a bomb that big, if it were a uranium bomb you'd need on the order of 100 tons of highly enriched uranium and one of the problems would be "how do I get that much uranium close enough together to even build a bomb". The damn thing would be the size of a small to medium ship. And the guy is talking about burying it under kilometers of seabed.
When it went of it would be (not cause, be) a 8+ scale earthquake.... one could go on but you get the point.
It's a silly napkin math idea that someone decided to put on arxiv.
If you wanted to blow up the seabed with nukes to sequester carbon practically, you could do it, but it would take a lot of them and there would be a lot of effects to the local ocean.
verisimi · 7h ago
I don't get it. A solution for co2 is to carry extra stone on a ship for 10 years? It sounds like a bad joke.
ricardobeat · 4h ago
They propose the equivalent of twelve containers carrying stone, out of ten thousand on the ship - 0,1% extra weight.
MrBuddyCasino · 4h ago
I don't understand how people can propose these ridiculous schemes with a straight face. I suspect it is because "climate change" is a good source of grant money right now, so you have to get creative to come up with a new approach.
black_puppydog · 4h ago
On the other hand, if you're in climate science, what are you supposed to do? The science is pretty clear right now, what we lack is political action.
Yet when climate scientists stop using the carefully-weighed language of academia to demand actual, effective and efficient action now, they get scolded as activists, emotional, non-objective, etc...
This is just to say I can understand that people just want to contribute within their realm of possibilities.
tocs3 · 12h ago
I thought for a moment ht this could be an argument for global trade. as it only reduces the CO2 output it is good but not carbon negative.
Joel_Mckay · 10h ago
In general, green-washing never truly confesses the scale of the problem. The data driven conclusion is exhausting every mine on every landmass would only buy another 5 to 7 years at most. Geoengineering is currently mostly BS idealism.
The planet will be fine again in 30 thousand years or so, after the current population of psychotic primates go extinct. It is ultimately a self-correcting problem regardless of what humans collectively choose to do. =3
energy123 · 7h ago
Geoengineering should probably happen even if we achieved net zero tomorrow. We have already had about 1.4C of warming, which is too much for humans near the equator given how hot it already was. It's either that or migration away from the equator, pick one.
Joel_Mckay · 6h ago
In general, renewable carbon free energy sources are the only practical options, and have even proven economically beneficial in many places.
There is a cascade failure point that likely will arrive in a few decades based on our current trajectory. Geoengineering, planting trees, and or carbon credit systems does nearly nothing about long-term carbon cycles driving the issue.
In general, migration won't happen much as resource constraints can't relocate nor feed 12 Billion people. Maybe something like "The Silo" fiction will become popular, or Elon and his 1600 passenger (based on current designs) company will make it off planet. lol =3
01HNNWZ0MV43FF · 7h ago
I've seen better villain speeches written on bathroom stalls
Joel_Mckay · 7h ago
Good and evil don't really apply to inescapable facts. The earth was fine without humans before we arrived, and will likely continue on after our species is gone.
Have a great day =3
trhway · 11h ago
>(iii) ships moving at ~15 knots are water pumps themselves, overcoming the limitation of high energy demand in AWL
i think there is a flaw in that logic.
Btw, if doing it on ships is that great, why not build(repurpose) large [old] ships/barges by making them solar and/or wind powered and set them just to follow tradewinds and/or to just loiter in the tropical belt, mostly [semi]autonomously.
moralestapia · 10h ago
That's a lot of power, you'd need a lot of solar/wind.
"Then just use batt..."
Yeah and then you have grid loss, more carbon emissions and a bunch of other issues.
zmgsabst · 10h ago
I was curious, so I found random numbers on Google:
- a Panmax ship is 8000 sq m (250m long x 32m wide)
- using 150w per sq m this is 1.2Mw
- a Panmax ship has a 40,000hp engine, which is 30Mw
So you’re off by a factor of around 20x using solar power for a Panmax ship.
trhway · 10h ago
Yes, a solar powered ship would at best do ~3 knots. Which is slow, yet it is practically free. Sail/wind powered would do somewhat better while being more complex/expensive. An autonomous ship/barge though doesn't need speed.
Terr_ · 7h ago
> An autonomous ship/barge though doesn't need speed
The underlying problem for all this is the time value of money/capital.
I recall someone arguing that we could drop sea-cargo CO2 emissions by a third if the boats went a quarter slower... But the opportunity cost of that extra time is significant.
ZeroGravitas · 5h ago
There's an initiative to do this without opportunity cost, as currently ships follow a "hurry up and wait" schedule because if they happen to miss a connection they bear all the costs. Simply agreeing to share the costs for ocatisional missed deadlines means everyone can go slower, save fuel as well as carbon and share the benefits.
sandworm101 · 8h ago
No. 3knots would be moving backwards much of the time. And cargo stuck at sea for an extended period costs money. Air frieght exists for a reason.
trhway · 8h ago
I actually meant those ships specifically for AWL discussed in the article and for other similar loitering endeavors, not for cargo.
moralestapia · 10h ago
I guess the "you" in there is generic because I didn't give any numbers.
But yeah, following up on your numbers, you'd need 200,000 sq m of solar panels (about the size of the pentago, lmao); assume no clouds or night.
Per engine. That's infeasible.
moralestapia · 10h ago
Good idea and I do not diminish their creativity, findings and methods.
The reason why this and many other CO2 sequestration techniques don't work to solve the carbon pollution problem is that they always measure "gains" on a very narrow context, irl the inputs to the system incur some carbon emissions as well.
If you account for (just off the top my head):
* Grinding the limestone down to dust
* Limestone transport from whenever is sourced to the ships
* Extra weight of limestone on the ship (they say 12 TEU for a 10k container ship, small but not insignificant)
* Any difference in propulsion efficiency due to this change in the fluid dynamics that has to be compensated by ... burning more fuel (but this one could actually be negligible)
You might be emitting much more carbon than the one your system was designed to absorb.
You cannot beat the 2nd law of thermodynamics.
Smaht[1] people have been trained to quickly and loudly dismiss perpetual motion machines, but also buy the whole "revert carbon emissions" scam which is proven impossible by the exact same principles.
Btw, this is an accurate litmus test to see if someone actually understands what's going on or if its just another smaht guy parroting back what xi's been told to.
1: smaht. smart in appearance but actually dumb
philipkglass · 7h ago
Atmospheric CO2 cannot be converted back into hydrocarbons without expending more energy than the fuel originally released in combustion. Atmospheric CO2 can be converted into stable minerals that no longer drive global warming, at an energy cost less than the fuel released when it first burned.
See this chapter from the IPCC Special Report on Carbon Dioxide Capture and Storage:
In particular, section 7.2.2, "Chemistry of mineral carbonation." The carbonation of magnesium and calcium silicates is thermodynamically spontaneous but kinetically hindered. The kinetic hindrance is why an additional energy input is needed to draw down atmospheric CO2 in less than geological time: the mineral's accessible surface area must increase dramatically for fast silicate weathering. The thermodynamic spontaneity is why the additional energy input can be small compared to the original energy embodied in the fuels that generated the CO2.
raphman · 8h ago
Dirk Pässler (carbon-drawdown.de) did some back-of-the-napkin calculations for their experiments (enhanced weathering of basalt dust on cropland):
> In the end we calculated the actual emissions to be 44,6 tons CO₂, due to the fact that we drove more truck kilometers than we had planned. This is less than 10% of 1217 t basalt’s CDR potential of 509 t CO₂. In summary: The mining and transport emissions are one order of magnitude smaller than the CDR effect, even with 300-500 km transport distances. This will only get better in the future with more green energy, electric trucks and optimized logistics.
>If rock powder was produced exclusively for ERW applications, a proportional share of the scope 1-3 emissions of the mining facility will be attributed by the methodology.
They purposely ignore what could be the most carbon intensive step in their process. But it's good they considered all other steps and gave an estimate of them.
gusgus01 · 10h ago
This feels like the difference between science and engineering. Although to be fair to you, this paper really feels like somewhere on that spectrum and not fully on the side of science. It's similar to how every battery advancement doesn't always make it to manufacturing.
To address the things that you thought of off the top of your head:
* Anything done on land will be less carbon intensive as we transition to renewables.
* Trains are incredibly efficient at transport, and depending on the quarry might already be established.
* Boats are so good at shipping heavy weights because of those hydrodynamics, so as long as some reduced returns are okay (reduced cargo space), there's plenty of space on those cargo ships. The real limiter is stability of steering in canals and depth of ports/canals.
moralestapia · 10h ago
>This feels like the difference between science and engineering.
I really like that analogy and will adopt it going fwd. Thanks.
Indeed, very interesting science, cool paper and much more of this research is definitely needed.
This begs a follow up study, perhaps by a different team, where they measure the feasibility of it; including, yes, the points you address.
rotis · 4h ago
All that and who will pay for it? Politicians? They use taxpayers money. Companies? They will pass on the bill to the customers. So in the end same group will experience higher prices. I can't wait for all the poor becoming poorer.
comrade1234 · 12h ago
Would have been better if they put a few barrels of aquavit on deck.
https://attheu.utah.edu/science-technology/geoscientists-map...
Modern temperatures are actually near an all time low for the past 485 million years.
https://www.climate.gov/media/16817
Consider the possibility that you are mistaken, and the victim of propaganda.
But the chances you will personally be adverse affected by anthropogenic climate change in your lifetime is pretty damn high. Humanity will survive, but many humans will die in horrible conditions
We can tell that this is right and logical because the number of insects, a population more sensitive to environmental trends, hasn't visibly and obviously changed at all.
To avoid any concerns about scalability, as well as about energy supply intermittency, I made my estimate using only the oldest process in the chemical industry, lime burning, which predates plastics, oil drilling, steel, iron, bronze, writing, cities, ceramic, and possibly even agriculture. The only difference from the Neolithic method is that you have to retort the lime in a sealed chamber so you can collect the carbon dioxide it absorbed from the atmosphere after the last time you calcined it. This doesn't require an enormous amount of machinery, just very large machinery. Basically, a giant tin can similar to a water tower, maintained at a mildly negative gauge pressure as it's heated up.
My estimate, IIRC, was that, without soda for process intensification, you would need an amount of limestone a few times larger than the amount mined by the cement industry every year. That's fine, though; limestone is about 20% of all sedimentary rock, and sedimentary rock is 73% of Earth's land surface and 8% of the entire crust.
Very roughly, Earth is 6e24 kg, her crust is 6e22 kg, and its limestone is 1e21 kg. By contrast, the 427 ppm of carbon dioxide we need to capture half of is only 3.34 teratonnes, 3e15 kg. Limestone is 44% carbon dioxide by mass, so it absorbs 44% of its mass in carbon dioxide each time through the cycle. This absorption takes about 5 years if it's sitting in a paper bag dry, about a month when you whitewash a wall with it, or a second or so when you catalyze the absorption with a few percent of lye, like in a scuba diving rebreather.
The USGS publishes a lot of information about the world lime market at https://www.usgs.gov/centers/national-minerals-information-c.... From it, we can see that current US lime prices are 20¢/kg, 3.2 billion dollars for a total yearly production of 16 million tonnes. (They say that prices at the plant were as low as US$131/tonne in 02020, so probably the production cost is closer to 13¢/kg, including the cost of mining.) That's probably tonnes of CaO, which is the other 56% of limestone that isn't carbon dioxide. If burning lime in a giant tin can to capture the gas were about as expensive as how it's done today, that's about 24¢ per kg of carbon dioxide, not counting the cost of warehousing the resulting lime until it's absorbed the gas so you can calcine it again. (Remember, you can reuse the same lime every few hours if you dope it with a soda catalyst.)
World lime production is closer to 420 million tonnes per year, mostly of course in China, 26 times US production.
1.8 trillion tonnes of lime is 4300 years of total world production (or 120,000 years of current US production), so we're talking about a significant scale up. It's not just a few times global cement energy production. But it's still only two millionths of the limestone in the crust of the earth, and maybe you'd want to reuse the same lime many times so you don't have to mine it again.
But probably some process involving more sophisticated sorbents like triethanolamine, combined with point source capture, will end up being cheaper in the end. And see my notes in https://news.ycombinator.com/item?id=44461843 about accelerated olivine weathering. The lime approach serves only as an easily computable upper bound on difficulty.
The USGS mineral commodities summaries also have an entry for "stone (crushed)", which is 70% limestone. This is 1.5 billion tonnes per year in the US, which I guess is a billion tonnes of limestone, so 1.8 trillion tonnes of quicklime (3.4 billion tonnes of limestone) is only about 3400 years of US mine production. It only costs about 1–2¢/kg, which is in accordance with what I've seen. No world production figures are given, but we can probably guess that that's another thing China produces 20 or 30 times more of.
So, the cost of quicklime is almost all (>80%) calcination, and I believe that almost all of that number is energy. We can put an upper bound on its energy consumption based on that 13-cent cost in 02020: coal is often the cheapest source of the heat needed for calcination, and in 02020, it reached a low around US$60/tonne ( https://fred.stlouisfed.org/series/PCOALAUUSDA). So we know that producing a kg of quicklime can't require more than about 2 kg of coal, which provides 33MJ/kg or less (0.7¢/kWh or US$1.80/GJ), so 70MJ per kg of quicklime or of carbon dioxide. That's probably not a very tight upper bound, but I doubt it's high by more than a factor of 3.
Removing 1.4 teratonnes of carbon dioxide over 40 years is 1.1 million kg per second. At 70MJ/kg this multiplies out to 78 terawatts, roughly four times world marketed energy consumption.
Today, devoting a couple of terawatts to the problem would be unreasonably expensive, and tens of terawatts would require expanding world energy production considerably. At 24¢ per kg of carbon dioxide, removing 1.6 trillion tonnes of it would cost 400 trillion dollars, four years of world GDP (say, 10% of world GDP over 40 years). But that's just because the rollout of photovoltaic energy has just begun; the majority of the 18 terawatts or so of world marketed energy consumption is still supplied by fossil fuels, although they are clearly no longer cost-competitive with PV. PV manufacturing is still scaling up, though, and presumably PV energy production will exceed current world marketed energy consumption in a few years, and then continue to increase as new uses are found for the newly much cheaper energy.
78 terawatts is 0.04% of the 174 petawatts of terrestrial insolation.
And if there was, any sequestration would just be used as an excuse to find ways to conduct more CO2 producing activities.
However.. climate change is a chiefly a political problem, not a tech problem.
If we could store energy cheaper than we could use it we'd have a perpetual motion machine, I think? Fairly sure this would be physically impossible. Where this might be wrong is if we found a process to use another energy source (the sun, something that uses the sun, etc) to do it for us, but we haven't go anything that works in that vein either. Trees are actually one of the better options, but to reverse climate change you'd need to reforest the earth AND sequester all the oil we burned.
Burning carbon is effectively debt. If we stopped burning carbon right this second, billions would die, as our whole system depends upon it. But if we don't stop burning it, we increase our future problems.
This is unpleasant to reckon with so most don't. I don't think it makes the problem intractable, but it gets harder the more we delay.
We do need sequestration because simply eliminating all carbon sources wouldn't be enough, we also have to reduce current levels. Also there are some cases where fossil fuel might be the best solution (rocketry?) so we'd need to be able to deal with the waste.
Your reasoning would be correct if carbon sequestration involved reducing carbon dioxide back to elemental carbon, or hydrocarbons, or whatever form you burned it in. In fact, though, almost all proposed methods for carbon sequestration sequester the carbon dioxide, not just the carbon. Consequently, point-source carbon capture uses only a fraction of the energy released by burning the fuel.
It's a significant fraction, though, and atmospheric carbon capture uses more energy because it has to extract the carbon dioxide from air, which is 99.96% things that are not carbon dioxide. As I understand it, the energy dissipation thermodynamically required by that separation is quite small, but getting anywhere close to that thermodynamic limit is going to be a large engineering effort.
Need to look into this a bit more, but what would you say the theoretical efficiency is, could we reach a point where you can actually burn fossil fuel to net extract CO2 via direct air capture or another sequestration method that can be scaled?
I don't know enough about thermodynamics to calculate the fundamental limits. I suspect that low-temperature sorbents like triethanolamine can currently do direct air capture for less than the energy produced by the fuel, but the process is complicated, involving things like embodied energy in fan motors and hard-to-predict maintenance costs. In a cousin comment (https://news.ycombinator.com/item?id=44461370) I did an upper-bound calculation with a very-well-understood atmospheric carbon capture process that people have been doing inadvertently in a no-net-sequestration fashion for thousands of years. It came up with burning no more than 2 kg of coal per kg of carbon dioxide removed, which is theoretically significant net sequestration (if you do point-source capture on the coal burning) but far too expensive to make a dent.
Sequestration processes like serpentinization are actually exothermic. The idea there is that you react carbon dioxide with olivine and get serpentine and heat. There's vastly more olivine available than any crustal rock such as limestone. You can do this in lots of ways; for example, you can pump concentrated carbon dioxide down a well into fracked olivine, where it reacts, or you can crush olivine from an olivine quarry into olivine sand and just dump it on beaches, or build artificial islands out of it in Dubai or disputed areas of the South China Sea. Crushing the olivine costs energy, though, and it's energy that's mostly not stored for the process; it just provides more surface area for the same reaction.
I don't actually favor this approach (what do you do if you decide the beaches are removing too much carbon dioxide? Beaches don't have emergency stop buttons) but it does show that in principle the effective energy consumption of direct air capture doesn't even have to be positive.
You just wouldn't build a bomb that big, if it were a uranium bomb you'd need on the order of 100 tons of highly enriched uranium and one of the problems would be "how do I get that much uranium close enough together to even build a bomb". The damn thing would be the size of a small to medium ship. And the guy is talking about burying it under kilometers of seabed.
When it went of it would be (not cause, be) a 8+ scale earthquake.... one could go on but you get the point.
It's a silly napkin math idea that someone decided to put on arxiv.
If you wanted to blow up the seabed with nukes to sequester carbon practically, you could do it, but it would take a lot of them and there would be a lot of effects to the local ocean.
Yet when climate scientists stop using the carefully-weighed language of academia to demand actual, effective and efficient action now, they get scolded as activists, emotional, non-objective, etc...
This is just to say I can understand that people just want to contribute within their realm of possibilities.
The planet will be fine again in 30 thousand years or so, after the current population of psychotic primates go extinct. It is ultimately a self-correcting problem regardless of what humans collectively choose to do. =3
There is a cascade failure point that likely will arrive in a few decades based on our current trajectory. Geoengineering, planting trees, and or carbon credit systems does nearly nothing about long-term carbon cycles driving the issue.
In general, migration won't happen much as resource constraints can't relocate nor feed 12 Billion people. Maybe something like "The Silo" fiction will become popular, or Elon and his 1600 passenger (based on current designs) company will make it off planet. lol =3
Have a great day =3
i think there is a flaw in that logic.
Btw, if doing it on ships is that great, why not build(repurpose) large [old] ships/barges by making them solar and/or wind powered and set them just to follow tradewinds and/or to just loiter in the tropical belt, mostly [semi]autonomously.
"Then just use batt..."
Yeah and then you have grid loss, more carbon emissions and a bunch of other issues.
- a Panmax ship is 8000 sq m (250m long x 32m wide)
- using 150w per sq m this is 1.2Mw
- a Panmax ship has a 40,000hp engine, which is 30Mw
So you’re off by a factor of around 20x using solar power for a Panmax ship.
The underlying problem for all this is the time value of money/capital.
I recall someone arguing that we could drop sea-cargo CO2 emissions by a third if the boats went a quarter slower... But the opportunity cost of that extra time is significant.
But yeah, following up on your numbers, you'd need 200,000 sq m of solar panels (about the size of the pentago, lmao); assume no clouds or night.
Per engine. That's infeasible.
The reason why this and many other CO2 sequestration techniques don't work to solve the carbon pollution problem is that they always measure "gains" on a very narrow context, irl the inputs to the system incur some carbon emissions as well.
If you account for (just off the top my head):
* Grinding the limestone down to dust
* Limestone transport from whenever is sourced to the ships
* Extra weight of limestone on the ship (they say 12 TEU for a 10k container ship, small but not insignificant)
* Any difference in propulsion efficiency due to this change in the fluid dynamics that has to be compensated by ... burning more fuel (but this one could actually be negligible)
You might be emitting much more carbon than the one your system was designed to absorb.
You cannot beat the 2nd law of thermodynamics.
Smaht[1] people have been trained to quickly and loudly dismiss perpetual motion machines, but also buy the whole "revert carbon emissions" scam which is proven impossible by the exact same principles.
Btw, this is an accurate litmus test to see if someone actually understands what's going on or if its just another smaht guy parroting back what xi's been told to.
1: smaht. smart in appearance but actually dumb
See this chapter from the IPCC Special Report on Carbon Dioxide Capture and Storage:
https://www.ipcc.ch/site/assets/uploads/2018/03/srccs_chapte...
In particular, section 7.2.2, "Chemistry of mineral carbonation." The carbonation of magnesium and calcium silicates is thermodynamically spontaneous but kinetically hindered. The kinetic hindrance is why an additional energy input is needed to draw down atmospheric CO2 in less than geological time: the mineral's accessible surface area must increase dramatically for fast silicate weathering. The thermodynamic spontaneity is why the additional energy input can be small compared to the original energy embodied in the fuels that generated the CO2.
> In the end we calculated the actual emissions to be 44,6 tons CO₂, due to the fact that we drove more truck kilometers than we had planned. This is less than 10% of 1217 t basalt’s CDR potential of 509 t CO₂. In summary: The mining and transport emissions are one order of magnitude smaller than the CDR effect, even with 300-500 km transport distances. This will only get better in the future with more green energy, electric trucks and optimized logistics.
https://www.carbon-drawdown.de/blog/2022-12-14-how-cdr-with-...
They purposely ignore what could be the most carbon intensive step in their process. But it's good they considered all other steps and gave an estimate of them.
To address the things that you thought of off the top of your head: * Anything done on land will be less carbon intensive as we transition to renewables. * Trains are incredibly efficient at transport, and depending on the quarry might already be established. * Boats are so good at shipping heavy weights because of those hydrodynamics, so as long as some reduced returns are okay (reduced cargo space), there's plenty of space on those cargo ships. The real limiter is stability of steering in canals and depth of ports/canals.
I really like that analogy and will adopt it going fwd. Thanks.
Indeed, very interesting science, cool paper and much more of this research is definitely needed.
This begs a follow up study, perhaps by a different team, where they measure the feasibility of it; including, yes, the points you address.