Reply #5: The answer is yes, but these measurements are extremely difficult to make... [View All]

[jpak]

...as the reduction in atmospheric oxygen due to fossil fuel combustion is vanishingly small compared to the (huge) mass of oxygen in the atmosphere.

Researchers get around this by determining precise changes in the ratio of oxygen to nitrogen in the atmosphere...

What Atmospheric Oxygen Measurements Can Tell Us About the Global Carbon Cycle (1993) Keeling, R. F. et al., Global Biogeochemical Cycles, Vol. 7, pp. 37-67

The ratio of O:N is declining...and it's due to combustion of fossil fuels.

We will not suffocate, however, as the amount of fossil fuel carbon in the Earth's crust could not significantly reduce atmospheric oxygen levels - even if we burned it all.

edit: some "light reading" on the subject...

http://www.nature.com/nature/journal/v426/n6964/full/nature02131.html

http://www.nature.com/nature/journal/v381/n6579/abs/381218a0.html