> Build a machine that pulls significant amounts of CO² out of the atmosphere

Or you could plant a tree.

Costs of carbon sequestration range from about $20 to $70 per tonne, as part of exhaust capture (CCS). For direct capture from the atmosphere, values are closer to $150/tonne.

The world is dumping 38 billion tonnes of CO2 into the atmosphere every year. (I'll ignore the additional gigatonnes we've already committed.)

That's $2.6 trillion per year for sequestration, just to stay even. (The value's actually lower than I'd expected.)

For comparison, global GDP is about $70 trillion, so this is 3% of global GDP.

http://www.cbsnews.com/news/carbon-dioxide-emissions-rise-to...

https://en.m.wikipedia.org/wiki/Carbon_sequestration

You also have to keep in mind that it's this expensive because it's not done on a huge scale. If it was, the cost would very likely be much much lower than the quoted $150.

The costs are dominated by the chemical energy requirements, as I understand. They seem unlikely to fall greatly.

And what if this machinery starts taking out CO2 too fast? Who will stop it, taking into a count the beaurocraty level in UN and lobby behind such a money making machine?

Indeed, worth a book.

I think the technology for that is already there, or nearly so; the financial will really isn't. There's no way you can get $1trn for anything other than a war.