# What would happen if we could revert $\mathrm{CO}_2$ production but took it too far?

So recently, scientists managed to produce fuel basically out of thin air (water, air and sunlight).

And in a discussion I had with a friend, the question came up, what would happen if you took that idea too far?

Say you could build an air-to-fuel plant large and efficient enough to take CO2 out of the atmosphere faster than all the things we currently do to increase CO2 levels add it in.

What would happen? First of all, how far could you realistically even take this: Would it be possible with the used process to go all the way down to 0 atmospheric CO2 (or at least approach this arbitrarily closely)? And what effects would this have on the environment?

I immediately had three ideas that could happen but I wonder how realistic those would be:

• Average temperatures would drop (inverse Greenhouse effect) (but how far?)
• Plants would eventually be unable to produce sugar through photosynthesis and die off
• Instead of acidifying, oceans would become increasingly alkaline. Lime might drop out of the oceans rapidly which could, perhaps, have cancer-like effects on coral reefs and anything that heavily depends on lime.

And besides those, are there any other obvious notable effects?

• From a practical perspective, since this system would produce fuel from the CO2 it removed from the atmosphere, we'd just burn that fuel and release the CO2 again... – Semidiurnal Simon May 12 '14 at 9:43
• @SimonW of course. This technology has the potential to be a viable solution with which we might be able to stabilize atmospheric CO2 possibly indefinitely (plus minus the end of all life on Earth). That's not the point of the question though. I specifically asked what would happen if we overshot that goal, if we don't stabilize at, say, pre-industrial levels of CO2 but keep going. – kram1032 May 12 '14 at 9:50
• fair enough ;-) – Semidiurnal Simon May 12 '14 at 14:58
• By extrapolation, reducing atmospheric CO2 levels to pre-industrial levels could have the effects you listed. However, you do realize that at present, the thought of carbon sequestration succeeding to the point of undoing all industrial-era emissions is so hypothetical that it's not even funny? – 200_success May 12 '14 at 22:06
• @200_success but what would happen if you go beyond pre-industrial levels? And I know that this is pretty darn hypothetical. As said, it came up in a discussion about that new technology. And going from a single bottle of air-made fuel to even just stabilizing current oil consumption is quite a long shot, obviously. I'm not oblivious in thinking that this will, in like five years, undo all damage that has been done. Obviously if that can happen at all, it'll take far longer than that. Again, though: That's not the point of the question. – kram1032 May 13 '14 at 18:14