How much carbon dioxide does a 70 kg human produce in 24 hours with normal breathing?

Question

Then, assuming a world population of 6 billion, what is the carbon load put into the atmosphere daily by this?

Answer 1

to answer the actual question:

A normal minute volume would be 5-8 liters per minute.

During breathing you absorb around 4% of the volume as oxygen and exhale around 80% of that volume as carbon dioxide.

Thus each, during a minute, a human exhales around:

6500cc x 4% x 80% = 208cc (call it 200cc)

Multiply up to a day and that's 288 litres or 0.288m³

CO2 has a weight of 1.98 kg/m³, gas at STP so this amount of gas weighs in at 0.57Kg

But much of that weight is oxygen, and carbon load is measured in carbon tonnes, not carbon dioxide, so this must be multiplied by (approximately) 0.27

That gives us 0.154Kg

Multiply by 6 billion to get 924,000 tonnes

Call it a million tonnes a day.

By comparison, US industrial emissions for just their 250 million people are around 6,000 million tonnes per year, or 16 million tonnes per day. That represents 25% of the world's emissions, so it is safe to say that man-made emissions from our high-energy lifestyles amount to 64 times what we produce by being breathing animals.

It is like each human in the world weighed 4550Kg!

Of course, Americans are, figuratively speaking, more than twice as heavy as Europeans and three times as heavy as Chinese or Indians. They make VERY deep carbon footprints.

Answer 2

Breathing is a carbon-neutral activity. We breathe out carbon dioxide that results from breaking down food molecules. The food molecules trace back to the producers that made the food using carbon dioxide from the air.

The activities that add to the carbon dioxide of the atmosphere are burning fossil fuels (puts ancient carbon dioxide back into the air that hasn't been in the air for millions of years) and deforestation (takes away trees that are usually busy taking carbon dioxide from the air and storing it away in relatively permanent parts like wood).