>I feel like CO2 sequestration is second only to nuclear in the amount of unfounded concerns
The problem with CO2 capture specifically (specifically from the atmosphere as opposed to at the source) is that CO2 comprises a very small part of air. This means you have to move huge amounts of air through a capture device to capture a very small amount of carbon. How is that ever going to make sense?
It makes sense because brute force engineering solutions are frequently the right ones. If you capture carbon from the air, you can mass produce one kind of capture facility and spam as many copies of this facility as you need (at low cost, thanks to mass production) to give humanity closed-loop control over atmospheric composition.
If you rely on source emissions control only, you need finnicky source-specific installation and control technology everywhere, which greatly increases the cost and complexity of the implementation. And there are places where you can't realistically do carbon capture and sequestration, e.g. jet engines.
On top of all that, we live in a world with multiple governments and jurisdictions, and not all of them agree on the right level of investment in source capture. Do you really expect developing countries to give up on coal generation right away? What are you going to do, bomb them into the stone age? A climate management solution must be robust against the problem of uncooperative actors. We can't rely on everyone getting along and singing carbon kumbaya.
Compared to source mitigations, an atmospheric capture approach is simpler, more robust, and better capable of dealing with uncooperative emitters. Yes, you have to move a lot of air, but that's just energy, and energy is cheap if you're not picky about geography or uptime, and it's especially cheap if you're not squeamish about nuclear.
The paper says 2.0 GJ per tonne CO2. One GJ is 278kWh, and annual emissions about 36 gigatonnes, so that comes to 2.4 terawatts to absorb all our emissions.
Global energy consumption is about 18 TW[1], so 2.4 TW is a lot but not outlandishly so. It makes sense to look at global energy rather than just global electricity, because the input to this process is heat. We'd need clean energy sources, but we have those. Since we need heat and can use a fixed amount of energy constantly, high-temperature nuclear reactors would probably be ideal.
It would be silly to do this instead of decarbonizing electricity production and converting to electric cars, but we also have to deal with steel and concrete production, agricultural emissions, long-haul jets, etc. Let's say we need one TW to cover emissions we can't easily decarbonize.
Nuclear power produced 2657 TWh of electricity in 2019.[2] Divide by hours in a year, that's 0.3 TW. Assuming 50% thermal efficiency, it's 0.6 TW of heat energy. So basically, triple the number of nuclear plants in the world and we can absorb 40% of our emissions.
Some of the high-temperature designs are fast reactors or thorium breeders. If we use either of those, we won't remotely strain our nuclear fuel supply.
There are other methods of absorbing CO2, like reforestation, topsoil restoration, and olivine beaches. But most methods have scaling limits. Direct air capture with basalt sequestration[3] and/or carbon-neutral fuel production could easily play a large role.
That's true, but then it is surely better to cut out the middle-man and just not use fossil fuels for static generation in the first place.
The energy needs which are hard to meet with renewables (aviation, other large-scale transport) are the same places where CCS is non-viable due to the efficiency hit.
The best we can do is decarbonise as quickly as possible, and live with the fallout of our failure to act this far - unless a significant use for captured CO2 is identified, atmospheric capture technology will always struggle with commercial viability.
The best we can do is to do everything we can.
It might also be interesting to start burning biomass and capturing the CO2, which would be net negative.
The problem with CO2 capture specifically (specifically from the atmosphere as opposed to at the source) is that CO2 comprises a very small part of air. This means you have to move huge amounts of air through a capture device to capture a very small amount of carbon. How is that ever going to make sense?