this post was submitted on 10 Dec 2023
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Thermodynamics tells us it takes exactly as much to put the carbon back in as you got out of it by taking it out. So best case scenario we double the price of energy (which also means increasing the price of everything by a lot due to production costs increasing with higher energy costs) and capture as much carbon as we release.
However this is the real world and in the real world processes aren't 100% efficient. Even a hyper efficient combustion engine is only like 40% efficient in converting the stored energy into a usable form. Our carbon capture techniques suck hard at the moment, but say we improve the tech. That means in the real world we would need to increase energy costs by 4-6 times. Which probably means increasing the pricing of everything by a factor of 10.
That shows just how unsustainable our current consume heavy economy actually is. And that is assuming we have a way of capturing carbon out of the atmosphere in a way that's both efficient and long term. And do this in time before the processes we've set into motion spiral out of control.
And like you say, it puts into perspective how big of a win not releasing the carbon is.
Thermo says it takes at least as much energy to put the carbon back in. If the process is done in a reversible way (reversible in the thermo sense), it would take exactly as much energy. And since real-world spontaneous processes are never reversible, it will always have energy lost.
I know you said down below that energy is lost, but I'm just saying that from a physics POV, there is not a possible way that reactions can ever be done in a reversible way, so it's not like there's even a possible theoretical world where you could approach 100% efficiency.
By definition, you will always pay the heat tax to the second law of thermodynamics.
To be extremely pedantic, operations on physical systems can be performed and perfectly reversed without loss of energy, but you couldn't ever extract anything anywhere along the way - not even direct evidence that it happened. Our models predict that this happens literally all the time in quantum mechanics.
Edit: fun fact: this prediction is actually central to what makes quantum computers work.
That's a good point. I hadn't considered that, as I'm a chemist approaching thermo from the stat mech/free energy POV. I was mostly just thinking that a process where ΔG<0 is spontaneous but if ΔG=0, the system is at equilibrium, so nothing happens.
Now that I type it out, even I know that's not exactly accurate as equilibrium is a dynamic state with lots of things happening at the molecular/electronic scale, so I guess I should have added a qualifier of "at the macroscopic scale" to my original post.
There's nothing thermodynamically wrong with burning methane, releasing the water, and putting the CO2 back underground. Sequestration does not require un-oxidizing the carbon.
Though if we're going to bury harmful waste underground, nuclear power reduces the quantity of waste by a factor of a million.
Maaaaybe if the CO2 is captured at the point source of the methane burner. But if you've already let it disperse into the atmosphere, forget about it ever making sense to try to compensate for that huge increase in entropy by collecting and re-concentrating it.
Tick…tick…tick…
I'm not sure what you're trying to convey here. Carbon sequestration is unarguably a way to mitigate climate change, and sequestration of CO~2~ is probably the most reasonable way to do so. It doesn't need to be as a gas, as taking CO~2~ and exposing it to various oxides creates carbonates, which are generally very stable compounds like limestone.
The other commenter simply said carbon could be captured as CO~2~ and sequestered without being reduced, which is absolutely true and frankly makes much more sense from a physics/thermodynamics POV.
You guessed right - without reductions or conversion it simply becomes a ticking time bomb. Anything secure enough to capture and contain a gas reliably for millennia without maintenance will be too expensive to be practical.
Methane is a greenhouse gas more potent than CO2 that was stored underground for millennia. You would need actual data to conclude that storing CO2 is too expensive.
There are no manmade Methane stores from before the Christian era and there never have been. If you're going to argue that methane that was produced underground millions of years ago is a valid human goal, you may as well propose the simpler method of just increasing the Earth's orbit by a few tenths of a percent to offset the heating due to CO2. Done and done.
Caveat: it's been a few weeks since I read up on this so I'm fuzzy.
It's also worth noting we will need carbon capture to actually keep catastrophic global warming from occurring. Even if we cut emissions to 0 by 2035 we're blowing past 1.5C and maybe even 2 as I recall.
Doesn't mean that we can fix the climate with CC, but we can't fix it without.
This wouldn't be wrong, because historicaly the price for polluting the environment and cleaning up the mess afterwards has never been priced in.