What percentage of CO2 released daily is produced by 6.4 billion people exhaling?

Answer 1

Note that our breath isn't that important. There is a natural "carbon cycle" which recycles natural carbon dioxide. But it's a delicate balance.

We're messing up that balance by digging up carbon the natural cycle buried over a very long time, and burning it really fast. That overwhelms the natural process.

You can see it clearly in this carefully measured data.

http://scrippsco2.ucsd.edu/graphics_gallery/mauna_loa_record/mlo_record.html

The small teeth are the natural cycle in operation. CO2 goes down a little during the summer, when plants are active, and up a little in the winter. The huge push upwards is us burning fossil fuels. Unfortunately we're kicking natures' butt on this one.

Answer 2

It can be calculated by anyone who wants to know if you know how much CO2 an average person exhales. I did this several years ago but don't remember what the estimate was- something like 10% or so of the total human contribution of CO2 is from breathing.