The volume of air inhaled and exhaled during normal respiration, the so-called “tidal volume,” is about 500ml.

Adults respire at a rate of about 12 breaths per minute under normal circumstances. Undertaking strenuous exercise increases the respiration rate to 45 breaths per minute.
After the gaseous exchange has taken place in the lungs, the exhalation comprises 5% of the exhaled volume as CO2.

Carbon dioxide comprises roughly 0.038% by volume of the air – for the purposes of these calculations we can consider that to be zero. Further, in the same light, we can consider the respiratory rate to be the same regardless of age or physical fitness.

Thus we can say that the average person under normal circumstances exhales 0.05 X 500 ml = 25 ml of CO2 per exhalation.  At a rate of 12 breaths per minute, that’s 300 ml per minute or 157,788 litres of CO2 per year. At 22.4 litres per mole, that volume represents 7000 moles per year. The atomic weight of carbon is 12 and that of oxygen is 16 so a mole of CO2 is 44 grams. Thus, a year’s exhalations produce 310 kg of CO2.

Now the world population is roughly 6.8 billion. Thus do Homo sapiens exhale 2,100,000,000 tonnes of CO2 annually. Over 2 billion anthropogenic tonnes!

Does Al Gore know this?

When you consider that strenuous exercise produces a four-fold increase in carbon dioxide emissions, it is clearly time for us to initiate a license fee - a carbon tax for joggers, hill-hikers and anyone named “Dudley.”