How much oxygen is consumed by fossil fuels per year?

Oxygen depletion compared to carbon dioxide emissions.

Author’s note: This isn’t one for my usual audience. It’s super heavy on the science. If you want to know the answer to how much oxygen is consumed by fossil fuels and three reasons why oxygen depletion may be the bigger problem, just skip to the bottom. (One reason is that we are burning about 37 times more oxygen than is being replaced.) However, if you are a scientist or environmentalist, you might like to see my proof. Please let me know if you find any errors. This is part of a bigger project that I’m working on.

Introduction

I have the theory that what is causing climate change is NOT carbon dioxide but oxygen depletion. I’m not saying carbon dioxide buildup and global warming aren’t a problem. I do think that the lack of oxygen (could we call this a global cooling gas?) is much more dramatic; and, therefore, much more of a potential problem. In the summary below, you will see three big reasons why I believe oxygen is the bigger problem.

There are lots of articles about how much carbon dioxide is entering the atmosphere every year. But, not many articles explore how much oxygen is left. I started exploring this topic way back in 2005. Since then,  there are a lot more resources to help me refine my math. I’ve done this calculation several different times and different ways and compared my results to the findings in the scientific literature, so I feel reasonably confident in my conclusions.  

This calculation will be a little different. I will assume that oxygen reacts one way or another with fossil fuels. The most obvious way is that we burn gasoline in cars. There is a literal fire inside our cars that propels us forward. I also mean any reaction that consumes oxygen, whether burned, combusted, bonded, decomposed or, in other words, oxidized. This accounts for oxygen used in making chemicals, plastics, pollution, and all the reactions that consume oxygen, like paint drying on the wall. (Paint doesn’t actually dry, it oxidizes.) So, to simplify things, I will do the math as if all fossil fuels produced are burned. This will serve as a proxy measure to guesstimate how much oxygen is being consumed per year by humanity. My goal is just to get this number into the ballpark to see if it merits further exploration. 

First, let’s discuss the method behind my madness and then crunch the numbers. If you want to skip the math, you can see the answers highlighted in yellow below.

How I did my math

Disclaimer: When I say I am making a guesstimate, I don’t mean to belittle myself or this article. Days have gone into researching small pieces of this puzzle; for example, how much oxygen is used in the manufacturing of plastic? (Answer: there are too many different kinds of plastic to get an easy answer.) And, when plastic decomposes, how much oxygen is consumed. (Answer: it’s complicated.) Or, how much oxygen is consumed if methane is leaking into the atmosphere without being burned? (Answer: it’s a series of complicated reactions.) To do each of these calculations would require writing a book. And I would be further hampered by missing data. Many of these areas of science don’t yet have an answer, and the answers we do have are being improved with new theories and new technology. It’s a fast-growing field.  

As for where the numbers come from, I do a lot of research to find the primary sources, preferable articles or research papers by experts. And then I cross-reference and triple-check everything. Luckily, the internet has answers to a lot of these questions. I’ve included footnotes for where my numbers came from, and if I didn’t make a note, it is probably easy to find with a simple online search.

When discussing the composition of the atmosphere, the numbers are incomprehensibly big and small at the same time. Comparing a few molecules to an entire atmosphere is difficult. Two numbers that I needed to learn are gigatonnes and moles. The atmosphere is so big that gases like oxygen are measured in gigatonnes. One gigatonne equals one billion metric tonnes. (It’s hard to imagine air weighing anything unless you are riding a bicycle into a headwind.) 

In the following examples, I’m using exponential notation. So, instead of writing out one gigaton as 1,000,000,000 tonnes, I write it as 1e9 tonnes. That means a 1 followed by 9 zeroes. To complicate things further, I needed to convert tonnes to kilograms, so one gigatonne becomes 1e12 kg, or 1 trillion kilograms. And, as you can see, I abbreviate the measurements and round off the numbers. 

Since we are doing chemistry, I need to know the number of molecules for the chemical formulas. Usually, the number of molecules is expressed as moles. A mole of oxygen is like saying a dozen of eggs. It’s a big number. 1 mole has 6.0221e23 molecules. 

Luckily, some online calculators that made my life a lot easier.

• CalculatorSoup for converting numbers. 
• Aqua-Calc for volumes and weights.

Okay, let’s begin. Below, I will do the math for how much coal, natural gas and petroleum humans burn each year. 

How many moles of oxygen in one kilogram?

This is the base measurement that I will use in all the formulas below. Basically, what I am doing is very simple; I’m just calculating: fossil fuel times oxygen consumed. The hard part is converting all the numbers into something useful. But once I do, I can compare how much oxygen has been burned to how much oxygen is left in the atmosphere, and whether that number is going up or down. Visit this website if you want to visualize how big is a gigatonne.

The weight of 1 mole (molar mass) of molecular oxygen (O₂) = 31.9988 grams/mole. (Note: molecular oxygen is the kind you breathe.)

1000 grams ÷ 31.9988g/mol =
31.2511 moles per kilogram of oxygen (O₂)

Expressing this number as moles is good enough, but if you are wondering how many molecules of oxygen are in a kilogram, here is the math:
31.2511 mol/kg of oxygen (O₂) × 6.0221e23 molecules/mole = 1.8819e25 molecules in 1 kilogram (kg) of breathable oxygen. 

If you want to know how many molecules of oxygen are in the atmosphere, we times that number by the total amount of oxygen in the atmosphere estimated at 1,080,000 Gt or 1.08e18 kg.

Thus, there are 2.0325e43 molecules of oxygen in the earth’s atmosphere. That’s a big number, you would die before you could count them all. 

How much oxygen is consumed by natural gas per year?

We’ll start with the easiest reaction. And I’ll explain my process thoroughly for this first example. Natural gas is mostly methane, which burns very clean. 

The chemical formula of methane is CH₄. And the chemical formula for the combustion of methane is:

CH₄ + 2 O₂ → CO₂ + 2 H₂O 

Note: this is a simplified reaction. It is the end result of a chain of chemical reactions. And, the reactions also produce heat, which is where our energy comes from. The heat creates steam, which spins a turbine, which generates electricity. If you ask me, that sounds very primitive. 

There is an estimated 4084 billion cubic meters (bcm) of methane produced per year. (That equals 4084 cubic kilometers. Imagine that!) Since this measurement is a volume of gas, I need to convert it to kilograms. (I assume the original measure is at standard temperature and pressure.) 

Per my online calculator mentioned above, the weight of 1 cubic meter of methane gas = 0.554 kg. And, converting 4084 bcm to cubic meters, I get 4.084e12 cubic meters. 

So, 4.084e12 cubic meters of methane gas produced per year × 0.554 kg per cubic meter =  2.2625e12 kg of methane produced per year. 

Now I want to know how many molecules of methane there are. Then I can plug it into the chemical equation above and learn how much oxygen we are burning. Again, I am expressing this number in units of moles, like dozens. 

Molar mass of methane = 16.043 gram/mole. (Weight of 1 mole of methane gas.)
1000 g ÷  16.043 g/mol = 62.3324 moles per kilogram.
62.3324 mol/kg × 2.2625e12 kg of methane produced per year = 1.4102e14 moles/methane produced per year. 

Per the chemical formula above, for every 1 molecule of methane, 2 molecules of breathable oxygen are burned. So, 1.4102e14 moles/methane × 2 = 2.8205e14 moles of oxygen burned per year.

To convert this number to gigatonnes, the standard unit of measure when talking about atmospheric oxygen, I divide it by the number we first calculated (moles per kilogram of oxygen) and then convert kilograms to gigatonnes. 
2.8205e14 moles of oxygen burned per year ÷ 31.2511 moles of oxygen per kilogram = 9.0252e12 kilograms of oxygen burned per year. 
9.0252e12 kilograms ÷ 1e12 kg/gigatonne  =
9.025 gigatonnes of oxygen burned by natural gas per year.

Again, when I say burned, I mean any reaction that consumes oxygen: burned, combusted, bonded, decomposed or, in other words, oxidized. This accounts for oxygen used as fuel, making chemicals, plastics, and all the reactions that consume oxygen when these things decompose, like the accidental creation of pollution. 

Natural gas leakage

So far, all my numbers check out with sources online.* But, here is something new that I discovered. The production of methane gas doesn’t include what is lost or leaked into the environment. Even if methane leaks, it indirectly reacts with the oxygen in the atmosphere as if it is being burned.

Multiple sources cite leakage in a brand-new fracking well to be between 3-9%. The Pennsylvania Department of compliance cites 6-8.9% of leakage in new wells. That’s a brand-new well! However, five percent of wells fail immediately and leak even more. How much more is unknown. Within 30 years, half of all wells fail. And eventually, of course, all wells fail. (These statistics are from the documentary Gasland Part II.) Even after the wells are decommissioned, they continue to leak methane and other poisons into the environment.

So, let’s add the leaking methane to our estimate. As I mentioned, it still reacts with oxygen, and, for that matter, it also causes global warming. I’ll use a conservative estimate of 9% leakage (old wells leak much more). So, 9% of the amount of oxygen that we already calculated is being burned by methane is:

9.025 gigatonnes of oxygen burned by mined natural gas per year × 9% extra being leaked =
0.81 gigatonnes of oxygen reacting with leaking natural gas per year.

Update: The journal of Science published a study¹ that methane leaks could 5 times greater than expected. And by the way, the normal method to control these leaks is to burn the methane, which of course consumes oxygen directly.

How much oxygen is consumed by coal per year?

For this example, I’ll show the math, but I won’t do as much explaining. 

I thought coal would be the simplest equation, being just carbon or C, but the actual chemical formula for high-grade anthracite is: 

C₂₄₀H₉₀O₄NS

And, here are a few of the chemical reactions taking place. Note: all the reactions also produce heat energy. 

• C + O2 → CO2 
• S + O2 → SO2 
• 2 H2 + O2 → 2 H2O 
• 2C + O2 → 2CO 

Incomplete combustion of coal can also produce some nasty stuff: 

• Carbon monoxide (CO), which is a poisonous gas,
• Nitric oxides (NOX), also poisonous and highly reactive,
• Sulfur oxides (SOX), acid rain,
• Ash and particulates,
• And more. Now you know why coal is called a “dirty” fuel.

This is getting complicated fast, but it also proves that there is much more oxygen being used than what is accounted for by carbon dioxide and global warming.  

Honestly, my math is not this good. So, I will assume all the coal mined is pure coal, which is pure carbon. Since the other reactions all use one molecule of breathable oxygen, I think it will still put our number in the ballpark of how much oxygen is being consumed.

There is an estimated 7,921 megatonnes (Mt) of coal mined per year. 
= 7921000000000 kilograms of coal mined per year.
= 7.921e12 kgs/coal mined per year.

Molar mass of carbon = 12.011 gram/mole. 
1000 grams ÷ 12.011 g/mol = 83.2570 moles per kilogram.
83.2570 mol/kg × 7.921e12 kgs of carbon (coal) produced per year = 6.5947e14 moles of carbon (coal produced per year).

Above our formula for the combustion of carbon says it is a one-to-one ratio. One carbon for one molecule of breathable oxygen. This means we burn 6.5947e14 moles of oxygen burned per year. 

6.5947e14 moles of oxygen burned per year ÷ 31.2511 moles of oxygen per kilogram = 2.1102e13 kilograms of oxygen burned per year.

Divide this number by 1e12, and we get 21.102 gigatonnes of oxygen burned by coal per year.

Coals spills

For the record, unlike methane, I don’t think that coal reacts with oxygen unless burned. There are coal ash spills, which are detrimental to the environment, but this is coal that has already been burned. So, until I learn more, I won’t estimate any oxygen loss due to coal spills.

How much oxygen is consumed by petroleum per year?

Petroleum is another hard equation. Petroleum composition includes not only crude oil but all liquid, gaseous and solid hydrocarbons. Also, like coal, there are many different impurities.

The basic formula looks like this, where n represents different numbers of molecules depending on the petroleum:
CnH2n. 

Most of the barrel of petroleum is used for liquid fuels (gas, diesel, heating oil, jet fuel, et cetera), about 3% is tar and asphalt, and 18% for all other things, chemicals, paint, fertilizer, medicine. Again, all these things use oxygen both in manufacturing and decomposing, including being burned. Since we just want to know if our numbers are in the ballpark, let’s do our calculation as if the whole barrel is gasoline. 

The chemical formula for gasoline:
2 C₈H₁₈ + 25 O₂ →  18 H₂O + 16 CO₂ + Δ

Wikipedia gives us an easy answer to how much oxygen is used per kilogram of gasoline. (I’m tired of math, aren’t you.) “Molecular weights of the representative octane combustion are C₈H₁₈ 114, O₂ 32, CO₂ 44, H₂O 18; therefore 1 kg of fuel reacts with 3.51 kg of oxygen to produce 3.09 kg of carbon dioxide and 1.42 kg of water.”

There is an estimated 35,442,913,090 barrels of petroleum produced per year. 
One barrel of oil weighs 136 kilograms. So, multiplying by the number of barrels gives 4.8202e12 kilograms of oil produced per year. 

Multiply that number by 3.51 kg of oxygen burned per kilogram of fuel as given by Wikipedia, the greatest encyclopedia ever, and we get = 1.6919e13 kilograms of oxygen burned per year. 

Dividing that number by 1e12 = 16.919 gigatonnes of oxygen burned by oil per year.

Oil spills

Like natural gas, crude oil spilled into the environment would also consume oxygen. This is a difficult number to confirm. The internet seems to agree that even more oil is spilled than natural gas. So, let’s make a conservative guesstimate and assume, like natural gas, that 9% of oil is leaked into the environment. So:

16.919 gigatonnes of oxygen burned by oil per year × 9% =
1.522 gigatonnes of oxygen reacting with spilled oil per year.

Bonus

These two things are indirectly related to fossil fuel consumption.

How much oxygen is consumed by biofuel per year? 

Biofuel is a manmade fuel manufactured from renewable resources like vegetable oil. Interestingly it burns oxygen twice. Once to make it, which probably uses fossil fuels, and once to burn it. Given 143.9 billion liters of biofuel are produced per year and using my previous formula for petroleum = 

0.04 gigatonnes of oxygen burned by biofuels per year.

That’s a negligible amount. 

How much oxygen is consumed by pollution per year? 

Even when fossil fuels are burned in a combustion engine, the reaction doesn’t stop there. The pollution can react with oxygen once again to form smog. No wonder it is hard to breathe in big cities. 

Smog, also known as photochemical oxidation, generates 6 gigatonnes of oxygen per year as of 2012.** This number must be much larger by now.

Go here to see the chemical formation of Smog. Note: this is not the ideal reaction like the above formulas. It involves nitrogen being accidentally burned in your car engine.

Total oxygen burned by fossil fuels per year

Summary 

Natural gas burns 9.025 gigatonnes of oxygen per year.
Natural gas leaks react with 0.81 gigatonnes of oxygen per year, but probably 5x more.¹
Coal burns 21.102 gigatonnes of oxygen per year.
Coal spills. 0.
Oil burns 16.919 gigatonnes of oxygen per year.
Oil spills react with 1.522 gigatonnes of oxygen per year.
Biofuel burns 0.04 gigatonnes of oxygen per year.
Smog reacts with 6 gigatonnes of oxygen per year.

TOTAL = 55.418 gigatonnes of oxygen burned/oxidized by fossil fuels per year.

All these numbers fall into the expected range when compared to the scientific literature. “The global oxygen budget and its future projection” article in Science Bulletin, calculated an average of 21.23 gigatonnes of oxygen being burned per year from 1990-2005. And, eyeballing the chart it is about 46 gigatonnes per 2021. And going up to 100 gigatonnes by the year 2100. But these numbers include more factors than just fossil fuels.

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As we predicted, our number is a little higher to account for all forms of oxidation, the additional oxygen being consumed by the manufacturing of chemicals, plastic, paint, fertilizers, et cetera. Our number is also higher because every year the consumption of fossil fuels goes up. The article predicted the total loss of oxygen, including things like forest fires and animal respiration, will go as high as 100 gigatonnes a year by the end of the century. 

And, even though, this number was just a guesstimate, I think it could be even higher. Atmospheric science is complicated. Many other factors haven’t been taken into account. For example, when fossil fuels are mined there are a lot of spills and leaks, and often gases that can’t be captured are vented and burned. None of these numbers are included in the annual production. And also, I haven’t calculated the oxygen consumed by burning wood (forest fires), but this number is part of the natural decomposition cycle.

Conclusions

Oxygen depletion compared to carbon dioxide emissions 

So, what do these big numbers mean? Well, as I mentioned above, I have the theory that the primary driver of climate change is NOT carbon dioxide but oxygen depletion. So, how much oxygen are we losing versus how much carbon dioxide are we gaining? 

Comparing the numbers:
36.7 gigatonnes of CO2 are added to the atmosphere in 2019. (Source.)
55.4 gigatonnes of breathable oxygen is subtracted from the atmosphere per year. (Photosynthesis adds back a small amount. See below.)

Given our chemical formula methane combustion of carbon, this is close to what we would expect:
CH₄ + 2 O₂ → CO₂ + 2 H₂O.

Keep in mind, carbon dioxide is reabsorbed by plants, whereas the breathable oxygen is essentially lost. It is forever bonded to carbon in one way or another. To make more oxygen, plants break the bond of water via photosynthesis.

Are we running out of air to breathe?

We now know that we are permanently losing about 55.4 gigatonnes of oxygen per year. If you want to put these numbers into perspective, read How much oxygen does a car burn?

In my next articles on global oxygen depletion, I will be comparing how much oxygen is burned to how much oxygen is left in the atmosphere and how much oxygen is produced by photosynthesis. Is it possible that we will run out of air to breathe?

Is climate change twice as bad as we think it is?

At the least, I think The issue of climate change is at least twice as bad as we think it is. I believe oxygen depletion is a problem. And, of course, carbon dioxide emissions causing global warming is a problem. So, think of it this way, the change in our atmosphere is double. We are both subtracting one gas and adding another.