I’m not sure you’re right about that. Of course it’s going to have a footprint of its own, like every manufactured thing, but I can’t find anything that says it’s not basically guaranteed to be net-negative over its expected lifetime. If this were a blue-sky technology and we truly didn’t know if it’d work at all, I’d still be okay with building one of them as an experiment, but I don’t think that’s the case here.
But this is what I was actually trying to push back on in my original post. I’m not calling for a massive all-world effort on building these things—I’m just saying you can always say “but let’s not do anything new because it might be possible to have greater short-term efficiency by incrementally redistributing those resources to the status quo.” That’s sensible enough in a lot of contexts, but I don’t think the carbon crisis is the right place for that kind of analysis paralysis.
There are very possibly arguments based in economics, physics, logistics, or global public-opinion-shaping that would make this technology unsuitable on a big scale. We should all be ready to chuck it overboard if it doesn’t thrive as a useful part of the decarbonizing ecosystem. I’m just saying, the potential upside vastly outweighs the infinitesimal fraction of the world’s concrete output this represents.