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Comment by jefftk | Hacker News Reader

Bringing in external air (and filtering it, if it's polluted) will be way cheaper than scrubbing CO2 at current levels.

This is true, but mostly because the cost of bring in external air is near $0 in most cases - just open a few windows! But there's a lot of absurdly cool ways to scrub CO2 that are not especially expensive, like the video-game level of serendipity+convenience that's the Sabatier Reaction [1]. Combine hydrogen + CO2 at 300C => methane + water.

It's already being used on the ISS to keep the air fresh. It'll also be a key component on Mars. There you have basically unlimited CO2 and unlimited hydrogen which yields unlimited methane and unlimited water. Carry out electrolysis on some of the water and you get hydrogen + oxygen. The hydrogen can be fed back into the original cycle, and so you end up left with methane + oxygen which is also known as rocket fuel, uncoincidentally the exact sort SpaceX's Starship is using.

Back on Earth you could use this reaction to create practically endless carbon neutral fuel so long as the CO2 was sourced from either the air or a regrown natural capture source like trees or what not. Rockets using this fuel would even have a negative carbon footprint since some of that fuel will get burnt outside the atmosphere. It all seriously feels like a video game where there's just this perfect, but just utterly contrived, rule allowing you to thrive on the next level of difficulty.

[1] - https://en.wikipedia.org/wiki/Sabatier_reaction

The reaction is most interesting, but there are three concerns:

(1) It presumably requires concentrated CO2. It's not trivial to concentrate CO2 from the air without the appropriate technology.

(2) Pure hydrogen can risk an explosion.

(3) What does one do with the methane? Also, it too can risk a fire.

For these reasons, this is not a reaction that one would seek to do at home.

The Sabatier reaction is completely safe. Here [1] is a video of a few kids doing it completely manually with a couple of syringes, a pipe, and a torch. Producing methane is one of the huge benefits. Methane is just a normal fuel - use it to generate electricity, for your oven/stove, heating, whatever. But at home if all you want is CO2 removal then just use some lye, soda lime, or a million other simple capture technologies. Not quite as sexy, but it'll get the job done.

<rant> There's no grand technologies required for any of these things. The only reason it's not done at scale is the same reason we can't have nice things in general. Governments are far more interested in war and cock measuring contests than actually solving problems. We spent literally trillions of dollars on Iraq and Afghanistan, and the latest wars will probably dwarf that. Just imagine all the crazy sci-fi scale of things we could have done with all that money. Alas, humanity seems to be running on loop, except now we have nukes, paired alongside what are likely some of the most idiotic 'leaders' in centuries. Want to know the answer to the Fermi Paradox? </rant>

[1] - https://www.youtube.com/watch?v=VdNPkW9I0fQ

Well said. The root cause as I see it is the nature of money used by the people. If money were gold or bitcoin or a similar limited commodity, with a sufficient layer of anonymization, also with global validity and use, then many of these problems would not happen because the governments just would not have so much money to waste. The governments use their guns to enforce that we use their money instead which is prone to heavy inflation and excessive taxation. Reasonable taxation can still exist even with gold/bitcoin via property taxes. We do not have financial freedom.

ERV/HRV systems exist and their principle of operation is super simple. Labour to install the piping costs more than the system itself.

Definitely. Filtering particulates and tempering the outside air is the way to go in anything but most extreme situations. I suspect even designing a fallout shelter you would want to go that route.

An ERV costs about ~$1000 plus labour (you can install yourself).

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