Comment by philipkglass | Hacker News Reader

Comment by philipkglass | Hacker News Reader

I'm going to share my own insane idea for drawing down atmospheric CO2.

Capture CO2 as biomass or with direct air capture. Pyrolyze biomass to charcoal or use the Bosch reaction to recover pure carbon from CO2 chemically [1]. Then combine the carbon with silicon to form silicon carbide via the Acheson process:

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

Silicon carbide is extraordinarily resistant to mechanical erosion, oxidation, or any kind of natural degradation. Put the silicon carbide in a geologically stable desert and it could keep the carbon out of the carbon cycle until the sun grows hot enough to render the Earth uninhabitable. Continually extract and convert CO2 from the atmosphere and oceans until natural CO2 levels drop near zero and the desert is full of silicon carbide mountain ranges.

As a mere mitigation for AGW, this is a stinker. It requires an order of magnitude more energy and complexity than direct air capture of CO2 (which itself is already too energetically demanding and complex). But if you have the Sahara-sized robotic solar farm and industrial complex to put it into practice, it makes a great doomsday weapon!

Most actually-buildable doomsday weapons leave numerous survivors behind. Ordinary global nuclear war would barely deplete uncontacted tribes in the Amazon. Cockroaches would still survive cobalt salted nuclear warfare at the gigaton scale. Even an army of roving Terminators might eliminate multicellular life yet struggle to locate protozoans.

But I think that Total Carbon Sequestration could end all life, not just the visible-to-the-naked-eye species. All life needs carbon. And no species (save humans, via technological means) is capable of extracting carbon from silicon carbide. So with a hundred trillion dollar investment in a fully autonomous complex of solar farms, carbon capture facilities, and silicon carbide factories, I believe that we could solve global warming and end all life on Earth. Just like the Earth will do naturally in about a billion years [2] as CO2 levels fall, but up to 10,000 times faster! I'm still working on a funding model and a rationale for why this should be done at all, but some things are inspiring just because they're possible.

[1] https://en.wikipedia.org/wiki/Bosch_reaction

[2] https://en.wikipedia.org/wiki/Timeline_of_the_far_future

Direct CO2 capture is thermodynamically unviable, and literally every plan and attempt involving it was highly expensive in energy.

Are you familiar with Terraform Industries works?

What does thermodynamically unviable means? There's no thermodynamic laws specifically on carbon.

I haven't crunched the numbers on this, but CO2 air capture is incredibly inefficient, and it consumes energy which itself releases heat. So if the amount of CO2 you capture reduces heat by X degrees but you release Y degrees in energy consumption to achieve that where Y > X, that would be one interpretation of "thermodynamically unviable". It seems implausible to me but not impossible.

The effect of the heat released in the air is negligible compared to the greenhouse effect.

CO2 capture might be economically unviable but nothing physically prevents it from working.

> The effect of the heat released in the air is negligible compared to the greenhouse effect.

And the amount of CO2 gathered by direct air capture is also negligible, so you can't just hand wave a position that one negligible amount is obviously greater than another.

Not all life is connected to earths atmosphere. That that doomsday weapon is missing caves which contain multicellular life across geologic timescales. The ecosystems dependent on chemical synthesis at deep ocean vents would similarly be unaffected.

You might kill off plants though frozen seeds are viable for an extended period, but the incoming ice age is going to preserve aglee until atmospheric CO2 returns to normal even if we’re talking millions of years.

The incoming ice age could be averted by simultaneously adding carbon-free greenhouse gases like nitrous oxide to the atmosphere, but I suppose that kills the "solving global warming" part of the pitch.

Not all life is connected to earths atmosphere. That doomsday weapon is missing caves which contain multicellular life across geologic timescales. The ecosystems dependent on chemical synthesis at deep ocean vents would similarly be unaffected.

That's a good point and I don't see a way around it.

A flawed doomsday weapon but a good mechanism for building a fictional world where the biosphere develops underground.

> But if you have the Sahara-sized robotic solar farm and industrial complex to put it into practice, it makes a great doomsday weapon!

1) Can the other side just nuke most of it?

2) Isn't it cheaper to build a few thousand nukes instead of a Sahara-sized solar farm?

Love it. I'm firmly in the Yes And camp.

Could you also produce for the sizeable and growing SiC market? It'd be cool if your source was competitive (assuming green H2 level subsidies).

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As you know, once we achieve net-zero (2050), we'll have to accellerate into net-negative. From the hip, maintaining current growth of renewables (17% YoY), we'll cover expected demand 2045-2050. Then what?

Methinks each and every carbon sequestion idea and strategy should be attempted. Like starting with obscene funding amounts for yearly DARPA style x-prizes. Winners advance to the next round.

And hopefully some of the strategies are scaling in time to soak up the excess production.

Hmm. Assuming I’m on board with apocalypse, this kinda seems like a hat on a hat. Couldn’t we destroy the magnetosphere and vent the atmosphere with less energy than it would take to get all that carbon out? Or, hell, deorbit the moon one more time? I guess it’s harder to ramp up that tech in secret/with a benign excuse.

Plus a lot of it’s in living beings — you’d either have to find and harvest/burn all of them manually (or wait for the decomposition cycle to get it in the air I suppose?). At that point, you might as well go with a classic Skynet-style small-arms-based doomsday!

Couldn’t we destroy the magnetosphere and vent the atmosphere with less energy than it would take to get all that carbon out? Or, hell, deorbit the moon one more time?

I think that both of these require far more energy than keeping carbon locked out of terrestrial circulation (and hence out of living things). Don't you have to destroy the Earth's iron core to destroy the magnetosphere? You barely have to scratch the Earth's crust in my scheme. Of course my scheme requires much more time to work, so it's not very flashy.

This idea came to me while considering that most science fictional planet-sterilizing weapons use imaginary physics (The Three Body Problem, Revelation Space, the Xeelee Sequence, The Forge of God...) or, at the very least, a stellar-scale expenditure of energy (The Killing Star). What's the most energy-efficient approach that is compatible with known physics?

Total carbon sequestration doesn't work against a prepared adversary with near-peer technology, but it works great as an alien device for quietly exterminating life from selected planets. The thing is like an invasive species made of silicon that no carbon-based life can compete or coexist with.

  > All life needs carbon. And no species (save humans, via technological means) is capable of extracting carbon from silicon carbide.

A "species" doesn't need to do it, simple rock cycling will do the job.

Why not make the silicon Carbide into bricks, and build stuff out of it?

I’d like to have one delivered to my neighbour on Venus please, curious what would happen.

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