[Retric]

People don’t need to eat 10’s of kilos of plants per day which should suggest your off by an order of magnitude.

Chemistry means converting 1kg of CO2 > O2 would mean removing ~273 grams of carbon. Hydrogen and Wet vs dry weight more than offsets this, but you’re at closer to 2kg than tens of kilos.

This still assumes an air tight system where people never leave home, so plants can make a difference long before they are a 1:1 replacement.

[gpm]

I don't know what portion of a typical plants mass is carbon, and your 273 grams of carbon number is right (the 1kg number is CO2), but I don't think "people don't need to eat 10's of kilos of plants per day" actually justifies your claim about their density or invalidates GPs claim as to how much plant-mass you need to offset what you eat.

We don't just eat random (average) parts of plants, we eat selected ones, primarily things like fruits and bulbs that plants store energy in. If you just tried to eat, say, lettuce... at 2000 calories per day you would need roughly 14kgs [1, 2]. Which is surprisingly close to GPs 10s of kg number all things considered.

Either way, growing 2kg of plant/day or 20kg of plant/day... seems impractical to me. There's also the issue that if you equalize CO2 levels with the outdoors during the day as you open doors and windows, you're going to make night worse as both you and the plants output CO2 during the night.

[1] Lettuce is 14 calories / 100g - https://www.fatsecret.com/calories-nutrition/generic/lettuce...

[2] Math here: https://www.wolframalpha.com/input?i=2000+calories+%2F+%2814...

[Retric]

> We don’t just eat random (average) parts of plants, we eat selected ones

We can’t digest cellulose which throws off the calculations based on what calories are available to us. The question was the minimums not the worst case. Obviously most carbon sequestered by trees isn’t available to us a calories.

In a closed environment simply eating plants wouldn’t result in the correct carbon balance long term. We would need to breakdown our waste via microbes, fungi, or burning.

[hedgehog]

Living on Earth surface all that's necessary is to bring in outdoor air and reduce it to say 300ppm, currently that's only a 120ppm gap.