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:
Total loss since start of industrial revolution
- O2 depletion from fossil-fuel burning through 2004: 35.2 Pmol
- CO2 depletion from fossil-fuel burning through 2004: 26.3 Pmol
Estimated O2 content of preindustrial atmosphere: 37050 Pmol
1 Pmol = 10^15 mol
"So the total estimated industrial O2 depletion on Jan 1, 2005 would have been (35.3)/(37050)x100 = 0.095% of the preindustrial amount."
"For the past 15 years, we have direct measurements of the decrease. But the observations before 1990 aren't good enough to draw inferences. Hence the estimate based on industrial emissions is about the best we can come up with."
Think about that. Since the beginning of the industrial revolution we have removed .095% of the oxygen in our atmosphere. True, that is only a tenth of one percent of the total supply, but oxygen makes up only 20% of the atmosphere. I looked up safety rules regarding oxygen concentrations and according to OSHA rules on atmospheres in closed environments, "if the oxygen level in such an environment falls below 19.5% it is oxygen deficient, putting occupants of the confined space at risk of losing consciousness and death." What happens if the world's atmospheric levels of oxygen fall to 19.5% or lower? Are we all going to have to carry little blue oxygen tanks with us to survive? Not a pleasant possibility.
Plants and certain bacteria take in carbon dioxide, combine it with water to form glucose and produce oxygen as a byproduct in the photosynthesis reaction. The current increase in carbon dioxide levels in our atmosphere indicates that this cycle is no longer in balance. It shows that we have reached the point where the biosphere of the planet can no longer process all of the carbon dioxide that we are producing.
When hydrocarbon fuels such as gasoline are burned in air, gasoline (C8H18) and oxygen (O2) join in an explosive reaction. This reaction releases the energy which we use to propel our vehicles. The two main products of this chemical reaction are carbon dioxide (CO2) and water vapor (H2O). The chemical reaction for the combustion of gasoline (chemical name: isooctane) looks like this:
C8H18 + 12.5 O2 –> 8 CO2 + 9 H2O
This mix of CO2 and H2O vapor are the primary gases which come out of your tailpipe. Interestingly, these two byproducts are also the two things which plants need to take in to produce glucose and release oxygen. As long as the environment is in balance no excess carbon dioxide or water vapor will build up. If the environment cannot absorb the amount of these two gases that we produce on the other hand they would remain in the environment as a measurable surplus. I wondered if this water that was being created by burning hydrocarbons could be contributing to the rise I the planets oceans in a meaningful way.
I asked Dr. Keeling for his opinion on this possibility. He said, "I agree qualitatively with your arguments. Some time ago I also calculated the sea- level rise that would be caused by the water generated as a bi-product of fossil-fuel burning. I got quite a small number. I can make a similar calculation here:
O2 lost into forming water: 35.2 – 26.3 = 8.9 Pmol.
Amount of H2O formed: 8.9×2 = 17.8 Pmol
Volume occupied by water formed:
(17.8×10(15) mol)(18g/mol)/(1000000g/m3) = 3.2×10(11) m3.
Resulting sea-level rise (taking ocean area of 3.6×10(14)m2):
3.2×10(11)/3.6×10(14) = 9×10(-4) m
So the effect is only ~1 millimeter since the industrial revolution. This is small compared to the other factors that have contributed to sea level rise over this period."
In conclusion, it seems that the depletion of atmospheric oxygen will continue until such time as we stop burning hydrocarbons faster than the environment can absorb the byproducts of the reaction and replenish the oxygen. The only solution to this problem is to determine beyond the shadow of a doubt just how much carbon dioxide that our atmosphere and environment in general can absorb and process back into oxygen and then limit our burning of carbon containing fuels so that we stay within that “safe zone” and using non carbon based energy sources to make up for what we can no longer produce via fossil fuels.
The problem with this solution is that, in order to keep our economy cooking along, we need to produce and consume ever increasing amounts of energy and so we can’t stop using fossil fuels, including coal, without a lot of economic pain because there currently are no alternatives in place to pick up the slack. The sequestration of carbon dioxide by pumping it under the ground would only dispose of the carbon dioxide with unknown consequences, but would do nothing to stop the depletion of oxygen from the atmosphere. Dr. Keeling agreed that carbon sequestration would do nothing to stop oxygen depletion but reassured me that "… the O2 loss is too small to be much of a concern."
We currently make estimates of how many years we have left before excess carbon dioxide becomes a bigger problem than it already is but we aren’t really sure of their accuracy. However, to the best of my knowledge, we don’t have estimates of how long it might be, if oxygen continues to be depleted at its current rate, until it might become a problem. After all, while most of us may be willing to wait out the effects of excess carbon dioxide in the atmosphere for a time just to see if we really do get warmer weather and more abundant crops out of the deal; how may of us want to wait and see how little oxygen we can survive on?