As far as I can see the only practical widespread carbon capture process we have is plant growth (and pyrolisis). That might be possible for some fraction of global emissions (maybe 5-10%), but once you get above that you have to be cutting down quite significant amounts of forest.
It all seems like a lot more work than just not extracting the carbon from the ground in the first place.
It could really only be scaled with deep water aquaculture, there's just not enough areable land.
Is hydrogen good enough for long term storage of massive energy?
(Winter summer cycle)?
I heard concerns about density, and also not being able to use conventional gas storage (e.g. German gas network with a capacity sufficient for 3 months energy supply for the whole country) with high hydrogen ratios.
Agora recently had a publication about hydrogen where they also discussed the topic of storage:
https://static.agora-energiewende.de/fileadmin/Projekte/2021...
According to them there's enough potential for geological storage, it's just that ideally one should start now to build it (or repurpose existing natural gas storage).
Hmm, what do you think of my outline of direct air capture in https://news.ycombinator.com/item?id=29327736?
I'm not super motivated to read a long pile of text starting with "If you had unlimited free energy".
My answer is: You don't.
Sunlight.
Also, though, the cost estimates I ended up with are lower at current energy prices than the ones being offered by companies like Climeworks. Thanks to your feedback, I've restructured the comment to be less intimidating.
I've been seen exactly this link thrown at me multiple times when discussing synthetic methane, yet it comes with a fatal flaw: It doesn't consider the process to get the CO2 in the first place.
If this is supposed to produce (close to) climate neutral methane it needs to include Direct Air Capture to gather the CO2. It also needs almost perfect avoidance of methane leaks.
Luckily none of that matters very much: Most people agree that synthetic methane isn't very useful to begin with. We can do storage and many industry applications (like steel) simply with hydrogen and avoid the whole CO2 handling and the methane handling, and the few applications that absolutely need methane can be done with biogas.