# CO2 + UV → Sugar

What if we (somehow) stupidly destroyed all the stratospheric ozone, and needed to stop the UV artificially? What could we do with the energy? How about "manna" from heaven?

10% of the sunlight at the top of the atmosphere is UV - 136.7 watts per square meter (sun at zenith). 77% is absorbed or reflected by the atmosphere - 105 W/m² . The Earth's disk is πR², R = 6371000 m, so the area facing the sun is 1.27516E14 m², and the total UV intercepted by the atmosphere is 1.34e16 W.

The production of glucose sugar from CO₂ and H₂O is:

6 H₂O + 6 CO₂ + 2805 kJ/mole → C6H12O6 + 6 O₂

So, 2805 kJ eats up 6×44 grams of CO₂, or 10.6 MJ eats up a kilogram of CO₂ (at 100% efficiency, the hallmark of all crackpot calculations including this one).

The atmosphere weighs 5.15e18 kg - 1ppm CO₂ masses 5.15e12 kg. Turning that CO₂ (and some water) into sugar requires 5.47e19 J. If the energy is supplied at the rate of 1.34e16 W, that power would consume 1 ppm CO₂ every 4083 seconds, about 21 ppm per day. We could reduce 400 ppm of atmospheric CO₂ to 280 ppm in less than a week - if we had such magic.

Which we don't, and I have no clue how to make the machinery of such a system. The usual ignorant fearmonger worries aside, if we could make such a system we would certainly make it with a control knob, to dial global CO₂ to any desired value - and given human selfishness, wars would be fought over the optimal value and ownership of the control knob. The system would certainly be mechanical and manufactured rather than biological and self-reproducing - natural biological systems are destroyed by UV. Individual production units (and there would be a LOT of them) would need no more "intelligence" than a radio-controlled toy airplane, which are not known for autonomously reproducing themselves.

Also, true "manna" should be "real food", a lot more complex than sugar. Wars might also fought over which food gets made. That might be a little easier to differentiate - we can rain fish food over the ocean, tofu (minus the phytoestrogen isoflavones) over China, and Twinkies (nutritionally complete, with artificial sweetener) over the US. CO₂ levels can't be localized, but the food rain can be.

The above is nonsense - but of the canonical "what if we built global-scale machinery" genre, which is common among the solar/wind/OTEC "green" energy cult.

CO2plusUVtoSugar (last edited 2015-12-19 21:40:12 by KeithLofstrom)