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Comment by nine_k | Hacker News Reader

Sequestering CO2 where it's highly concentrated, e.g. at power plants or cement factories exhausts, would be one way to emit less.

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This is called Carbon Capture and Storage and so far it has never been worth it energetically. And the only companies doing it are oil companies in a process known as enhanced recovery which pushes more co2 out than is pushed in. The OP was right. Better to leave it in the ground

You can have 100% renewable energy. You can't realistically produce cement or steel without using and exhausting large amounts of CO2. This has to be addressed, even if it costs energy (which, as we agreed, can be 100% carbon-neutral).

there is no world in which it is cheaper to produce steel releasing CO2 and recapturing than fobbing off recapture until later. the thermodynamics just don't work.

Sorry, I don't understand. You're comparing 2 things. For the 2nd thing, are you including the cost of later recapture or not?

If you're not including the cost of later recapture, then it's not a fair comparison.

If you are including the cost of later recapture, why is it cheaper to recapture later than to do so immediately?

I've wondered if capturing carbon emissions from industrial-scale compost facilities would be a net positive. It would have the added benefit of the carbon initially being captured by natural organic processes (i.e. growing food), so it avoids the problem of the energy requirements from trying to just pull carbon from the ambient atmosphere. I don't know if this is feasible but I haven't seen any research on it.

What we need to offset the last 3 centuries of coal use is to reverse the process. Plant large amounts of trees, cut them, burn the hydrogen part of them, producing char and reclaiming some energy, then bury the resulting coal back in the abandoned coal mines.

Yeah, that too. There's not going to be one single solution, the problem is just too big for that. The idea with compost is that growing plants for food and dealing with the waste and excess (which is substantial) is something we're already doing, so can we tack carbon sequestration on top of that

> burn the hydrogen part of them

Could you elaborate

I guess Coke.

https://en.wikipedia.org/wiki/Coke_(fuel)

How are we getting that out of a tree

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

Did you ever do a barbecue? You first burn the light, hydrogen-rich substances of the firewood, with a large beautiful flame; that flame would burn down the meat, but it burns off quickly. What remains is charcoal, the source of most heat in the firewood; it does no produce a visible flame, but emits a lot of heat. It is mostly carbon.

Make char coal and store it underground.

I think OPs point is this tech is good only if you sink it after.

I. e. Collection is half the problem.

Collecting it in a way it's cheap to get it back again is potentially just less than minus half the problem.

Did a bit of searching: fizzy drinks companies sometimes go and get stored CO2 to put in drinks or make it.

Any atmospheric extraction has a net positive compared to that.

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