According to a study conducted by scientists from the Scripps Institute there is less oxygen in the atmosphere today than there used to be. The ongoing study, which accumulated and interpreted data from NOAA monitoring stations all over the world, has been running from 1989 to the present. It monitored both the rise of carbon dioxide in the atmosphere and the decline in oxygen. The conclusion of that 20 year study is that, as carbon dioxide (produced primarily by burning fossil fuels) accumulates in the atmosphere, available oxygen is decreasing.
Carbon dioxide seems to be almost the total focus of attention in the climate change model as it exists today. After reviewing the results of this study and talking with Dr. Ralph Keeling (one of the lead scientists on the study), it seemed to me that the consequences of atmospheric oxygen depletion should be included in any discussion of atmospheric change.
In order to make sure that I was interpreting the data correctly I asked Dr. Keeling to clarify a few points. I asked him if the rise in carbon dioxide levels and the decrease in oxygen levels were proportional to each other in the sense that this would indicate that the decrease in atmospheric oxygen was a direct result of the buildup of carbon dioxide. His response:
It is roughly true that the oxygen depletion is equivalent to a displacement by carbon dioxide. But it is not exactly true. First, some of the carbon dioxide produced has been absorbed by the oceans. This process involves inorganic chemical reactions which have no effect on O2. Second, the O2:C combustion ratio of a fossil-fuel depends on the hydrogen content. The ratio varies from about 1.2 for coal, 1.45 for liquid fuels, and 2.0 for natural gas. Taking these factors together, we are losing nearly three O2 molecules for each CO2 molecule that accumulates in the air.
We are losing three oxygen molecules in our atmosphere for each carbon dioxide molecule that is produced when we burn fossil fuels. Studies of ice cores and recent data from direct atmospheric sampling have shown that there has been a 30% increase in carbon dioxide since the beginning of the industrial age. With that in mind I asked Dr. Keeling how much oxygen has been depleted from the atmosphere in that same time frame. He responded that, "A reasonable estimate for how much O2 has been lost since the beginning of the industrial revolution can be based on the estimated loss due to fossil-fuel emissions, which can be calculated from records of the amount of each fuel type burnt and its combustion ratio. Such records are not readily available online, but I have figures handy: