# 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... May 12, 2014 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. May 12, 2014 at 9:50
• fair enough ;-) May 12, 2014 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? May 12, 2014 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. May 13, 2014 at 18:14

The average global warming due to greenhouse gases corresponds to a 33 Kelvin temperature increase. If you remove all greenhouse gases the average global temperature would then decrease 33 Kelvin (from 288K to 255K).

You might want to check out: http://www.nasa.gov/topics/earth/features/co2-temperature.html which estimates the CO2 portion of global warming to be about 80%.

"... it is the 25 percent non-condensing greenhouse gas component, which includes carbon dioxide, that is the key factor in sustaining Earth’s greenhouse effect. By this accounting, carbon dioxide is responsible for 80 percent of the radiative forcing that sustains the Earth’s greenhouse effect."

Simple math might suggest then that the average global temperature of Earth would be ~262K if CO2 were completely removed. There are always sources of CO2 though, so you could never remove it all as it is constantly being replenished when animals breathe and things burn.

• This answer mixes numbers from anthropogenic and total green house effect, thus the conclusion (262 K) seems to be wrong.
– BHF
Jun 4, 2014 at 19:56
• I don't mention anything about anthropogenic portions... this is just total greenhouse effect.
– f.thorpe
Jun 4, 2014 at 23:05
• The question mentions only CO₂. There are other greenhouse gases such as water and CH₄. 80% is the proportion of the anthropogenic increased greenhouse effect due to CO₂. Overall, water vapour is the most important greenhouse gas, so we could never cool it down to 262K simply by removing CO₂. To answer this question properly requires a climate model, because feedbacks are complicated.
– gerrit
Jun 5, 2014 at 17:12
• Perhaps you didn't read the link completely? It is not just the anthropogenic portion. It says: "... it is the 25 percent non-condensing greenhouse gas component, which includes carbon dioxide, that is the key factor in sustaining Earth’s greenhouse effect. By this accounting, carbon dioxide is responsible for 80 percent of the radiative forcing that sustains the Earth’s greenhouse effect." Yes water vapor is the most powerful GHG as a molecule... but it is not long lived and does not contribute to the greenhouse effect nearly as much as CO2. IPCC radiative forcing charts confirm this.
– f.thorpe
Jun 5, 2014 at 17:19