Should We Stop Breathing?

If CO2 CAUSES climate change, and we EXHALE CO2, what happens if a billion people (like CHINA) stop exhaling for a minute? A measurable effect?

Lung capacity is about 3 L according to Lung Volumes and Capacities

Exhaled air contains about 100 times the concentration of carbon dioxide that inhaled air does, or about 4% CO2 by volume via Carbon dioxide comparison between inhaled and exhaled air

So the amount of CO2 sequestered in the lungs of a billion people is 4 % of 3 billion liters or 120 million liters at roughly 1 atmosphere pressure. At 2 g / L (What is the density of carbon dioxide (CO2) at STP if 1 mole occupies 22.4 L?) we get the lungs of China holding 0.002 * 1.2e8 = 240,000 kg.

The entire atmosphere has 5 x 10^18 kg total, of which 0.04% is CO2 so that amounts to 2 trillion kg.

So the fraction of the earth's CO2 in a billion lungs holding their breath is
240,0002,000,000,000,0o0 = about a tenth of a part per million. If they held it forever, they would be uncomfortable, but the effect on CO2 would be so tiny as to be hard to measure.

As a global warming question this is sort of misguided, because CO2 breathed out balances carbohydrates eaten - there is no new net carbon injected into the system. That is, it seems to confuse fluxes and reservoirs, or as economists call it, stocks and flows. In fact, breathing contributes nothing to global warming at all, if food is produced in a carbon neutral way. It makes more sense to look at the carbon footprint of food production than of breathing, though in practice that is quite substantial, perhaps 10% of the total. This link says 9%: Agriculture Sector Emissions

I am sure you are responding to somebody who snarkily suggested we stop breathing. In fact, this boils down roughly speaking to whether we stop eating. If somehow we could live our lives otherwise the same without eating, we'd reduce our emissions by around 10%, and the accumulation in the atmosphere would be somewhat slowed. It's probably not a promising approach, though. But that's all about agricultural practices, not about agriculture itself. It's probably still possible to feed the earth's population entirely in a carbon neutral way.