Carbon dioxide is stealing our oxygen

Our air is getting news coverage today, as the benchmark atmospheric carbon dioxide measurement at a spot in Hawaii has passed 400 parts per million, probably for the first (non-volcanic) time in at least hundreds of thousands of years.

400 ppm is an arbitrary benchmark, relevant to primates with ten fingers.  It’s still important; it’s the atmosphere we must breathe.

From plots like this, it’s clear that the carbon dioxide content of our atmosphere is rising. It is probable that the rising temperature of the globe, the loss of Arctic ice, and the melting of our precious glaciers is related to human activity. I’m a cautious scientist; I’d like to see this experiment played out with many Earths and many rises of civilization to be sure. If forced, I’d have to bet on the prevailing scientific view that human emissions are driving global warming.

That’s not what this post is about. The rise of ~100 ppm over the span of the plot above has an alternate interpretation. 100 ppm is 0.01% of the atmosphere. That’s not a lot. But, our atmosphere is only one fifth (20.946%) oxygen, so it’s an effect that’s at least five times larger. Our oxygen is being burned into stuff we cannot breathe.

The combustion of hydrocarbons (composed of hydrogen and carbon) means that atmospheric oxygen is burned to produce energy. Oil, gas, and coal are mined from the ground and oxidized by atmospheric oxygen.  The major products of combustion are water (H₂O) and carbon dioxide ( CO₂). Both are quite stable in our environment. Any rise in CO₂ level is related to a drop in O₂ level. Mike Johnson, citing Dr. Keeling, claims that the drop in oxygen fraction is actually 2-3 times the rise in CO₂ fraction.

This is easy to check, in part. For octane, a major component of gasoline (2 C₈H₁₈ + 25 O₂ → 16 CO₂ + 18 H₂O), it’s 1.56  O₂/CO₂.  For natural gas, (CH₄ + 2 O₂ → 1 CO₂ + 2 H₂O) it’s 2  O₂/CO₂ . Keeling further claims that, as there are CO₂ sinks, some CO₂ is stored again, making the atmospheric content under-represent the oxygen consumed. That, I cannot check.

The IPCC projections for atmospheric carbon dioxide in 2100 span 550-1000 ppm, or an 0.1-0.3% drop in breathable oxygen since the 1950s.  If Keeling’s calculus is correct, then the high end of that scale corresponds to a 1% loss in breathable oxygen.

1% is not a lot, it’s an extra breath every six minutes, but it’s a reminder that our planet is finite. With the ~0.08% O₂ depletion implied by the plot above alone, which has already happened (and doesn’t include human history), it’s perhaps an extra breath every hour and a half.