It's just carbon neutral, not "technically" carbon neutral.
The reason we even care about CO2 emissions is that industrial emissions reconnect carbon reservoirs that were disconnected from the atmosphere for millions of years, i.e. underground oil, gas and coal deposits, back to the atmosphere. Not that CO2 in itself is harmful in any way.
The fact that we have ~8 billion people now vs ~1 billion in 1800 does make a difference to the equation, in terms of our own respiration and not just our deliberate use of fossil fuels. Admittedly it's minor, and I don't know what's happened to other biomass in that time. But still. The point is: having people eat more so that they could pedal a stationary bike hooked up to an electric generator, would not give "clean" power at the margin.
No, you are not getting what people are trying to tell you: growing the food for the extra 7 billion completely cancels out the co2 emitted from the 7 billion pairs of lungs. We know that because the C in that emitted CO2 all comes from food eaten by the person at some point in the person's life.
I think you might be missing the point too. Yes, the carbon in the food we eat is where the carbon in our breath comes from. But the carbon that we used to get the ingredients in that food didn't certainly come from the atmosphere (e.g. half of the nitrogen used in agriculture comes from fossil fuels). You can't be a perfectly optimal salad eating machine. One of your fellow humans will ruin the equation the moment they buy produce from the modern supply chain.
No, all the carbon in food plants comes from CO2 from the atmosphere. (Ditto nitrogen by the way: the natural gas used in making nitrogen fertilizers is a source of hydrogen and possibly reaction energy, but not a significant source of N.)
> No, all the carbon in food plants comes from CO2 from the atmosphere.
Yes, this is what I said.
> the natural gas used in making fertilizer is a source of hydrogen and energy, but not a significant source of N.
There is no nitrogen at all in natural gas.
Plants cannot use atmospheric nitrogen on their own. They depend on either bacteria or humans to create some usable form of nitrogen. Any carbon captured in a plant that depended on a fossil fuel source of nitrogen cannot be considered carbon neutral, unless you draw a useless system boundary.
> Any carbon captured in a plant that depended on a fossil fuel source of nitrogen cannot be considered carbon neutral, unless you draw a useless system boundary.
What? That sounds really confused.
"Carbon neutral" in this context means a process that shuttles an atom of carbon around in a closed loop between the atmosphere and living organic matter.
To paraphrase what you're saying, human agriculture is not carbon neutral, so human breathing contributes to climate change, because humans require agriculture.
It's the kind of statement that is maybe technically correct if you look at it from the right perspective, but totally unhelpful to understanding ecological flows of atoms.
We are carbon neutral against the earth as a whole. The problem is that sequestered carbon is now in the atmosphere. It doesn't matter how many people are breathing out carbon. It matters where that carbon came from, and where it ends up. Of course we now have so many humans that the majority of them are dependent on fossil fuels to survive, and as others have pointed out, not just for energy.
