Scott Stoll logo world traveler. A bicycle wheel and the globe symbolizes Scott's journey around the world on a bicycle.
A man wearing a gas mask watches television in a smoggy dystopian world.
Will the Earth ever run out of oxygen? Why do humans in all the dystopian movies seem to be oblivious to the world falling apart around them until it is too late? Are we doing the same in real life?

How long before the Earth runs out of oxygen?

This article is part of a series

Is the Earth producing enough oxygen for future generations? 

Have you ever wondered how much breathable air is on Earth and if will we ever run out? Our atmosphere is paper-thin relative to a basketball, and we use its oxygen to power internal combustion engines, like planes, trains and automobiles. Even most electric cars get their power from fossil fuels. The electricity is made from burning coal. Though the world now gets about 26% of its energy from renewables, the consumption of fossil fuels keeps increasing because humanity keeps consuming more and more of everything. We also use fossil fuels and oxygen as an ingredient in chemicals, fertilizers, plastics and tens of thousands of other things. So, given the billions of tonnes of oxygen oxidized (burnt) every year, how long before the Earth runs out of oxygen? Let’s figure it out below. 

Spoiler alert: We don’t need to run completely dry of oxygen; we only need to drop to a level that is detrimental to life. And, yes, the Earth has run out of oxygen in the past, causing mass extinctions. One example is the Huronian glaciation

If you want to skip the explanation and the math, see the answers highlighted below. Rest assured, I triple-check my answers and cross-reference everything multiple times. Though I’ve been as accurate as possible, the numbers do change depending on the source, and the numbers get bigger (worse) every year. However, I’m confident that I have established ballpark numbers that show the Earth is running out of oxygen at a rate fast enough to threaten life on Earth. Recent scientific literature has confirmed this theory.*

To determine if the Earth is running out of oxygen, we need to know how much we have versus how much we consume. I answer these questions in previous articles. I show how I did my math so that you can duplicate my answer. (Science!)

Let’s summarize our answers so far

The world population growth chart of homo infographic sapiens infographic. At the rate we are going the line will be off the chart in a few decades.
The world population growth chart of homo sapiens is exponential, a classic hockey-stick graph. Now imagine every person in the modern world emitting 6 metric tons of greenhouse gases and pollution per year. Now imagine doubling that number. That is roughly how much oxygen humanity is consuming. The red line on this graph is off the charts.

How much oxygen is in the atmosphere?

We calculated the mass of the atmosphere to be about 5,117,073 gigatonnes and the mass of the oxygen in the atmosphere to be 1,184,090 gigatonnes. 

How much oxygen does the Earth produce per year?

As discussed, almost all of the oxygen produced by plants is used in either respiration or decomposition. That being said, photosynthesis is not well understood. So, the estimates of how much excess oxygen is produced per year range from “effectively zero” to 16.01 gigatonnes of oxygen/year. For our purposes, we will use a middling answer of 1.6 gigatonnes of oxygen per year

How much oxygen is consumed by the Earth per year by natural causes?

Below are the major sources of natural oxygen depletion. These numbers are huge, but for the purpose of this calculation, it is offset by the photosynthesis calculation above. If it weren’t, there would be no oxygen build-up in the atmosphere. However, as I demonstrated, the Earth itself is consuming almost all of the oxygen it produces through the following processes:  

  • Respiration
  • Decomposition.
  • Livestock methane emissions. 
  • Forrest fires and deforestation.
  • Land oxidation (rust).
  • Ocean saturation. 
  • Miscellaneous: lost in space, nitrogen fixation, etc. 

How much oxygen is consumed by fossil fuels per year?

There are a lot of ways oxygen is consumed by fossil fuels, including plastic and chemical manufacturing and pollution. If you want to put these numbers into perspective, read How much oxygen does a car burn?

  • Natural gas burns 9.025 gigatonnes of oxygen per year
  • Natural gas leaks react with 0.81 gigatonnes of oxygen per year
  • Coal burns 21.102 gigatonnes of oxygen per year. 
  • Coal spills. O. 
  • Oil burns 16.919 gigatonnes of oxygen per year. 
  • Oil spills react with 1.522 gigatonnes of oxygen per year. 
  • Smog reacts with 6 gigatonnes of oxygen per year. 
  • Biofuel burns 0.04 gigatonnes of oxygen per year.

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

Is the Earth losing oxygen? 

Per our numbers above, the Earth produces 1.6 gigatonnes of oxygen a year due to photosynthesis excess, and mankind consumes 55.418 gigatonnes of oxygen per year. So: 

53.818 gigatonnes of oxygen is lost per year. By lost, I mean consumed, burned, oxidized or in some way bonded into a non-breathable form that is essentially permanent. 

How long before the Earth runs out of air to breathe?

After pages and pages of math, it is a simple matter to get our answer. But first, a little more background information. It’s not possible to burn all the oxygen in our atmosphere. Per Smokey Bear, a fire needs 16% oxygen to burn. And it also depends on elevation. The higher the elevation, the less oxygen. Internal combustion engines also need this much oxygen. And, coincidentally or not so coincidentally, humans need about the same amount of oxygen to survive. It is possible to survive with less, but you must become acclimatized first, and even then, it is a significant strain on the body. (I rode a bicycle to Mt Everest base camp and can testify to this!) Also, plants begin to have difficulty living. Plants also breathe oxygen

Current estimates give the oxygen level in the atmosphere at 20.95%. So:
20.95% – 16% = 4.95%.
4.95% ÷ 20.95% = 23.63%.

That means the Earth only needs a total drop in oxygen of about 24% at sea level before life becomes unlivable, and less the higher in elevation.

If we divide 53.818 gigatonnes of oxygen burned per year by 1,184,090 gigatonnes of oxygen in the atmosphere, we know that humanity is consuming about 0.0045% of the Earth’s atmospheric reserves of breathable oxygen per year. Now we can figure out how long it will take.

4.95% ÷ 0.0045% per year = 1100 years before the Earth runs out of oxygen. 

It doesn’t seem like we will run out anytime soon. 

But wait. It gets much worse. We haven’t accounted for an increase in consumption or a decrease in our biosphere’s ability to produce oxygen. 

But first, let’s double-check my answer. 

Double-checking my answer

Comparing my numbers to the most current research paper on the subject of oxygen depletion published by Science Bulletin: The global oxygen budget and its future projection. (As a side note, I’ve been waiting for an article like this for over a decade.) This research paper concludes that by the end of the 21st century, oxygen concentration will fall from 20.946% to 20.825%, for a difference of -0.121%. So, If we lose this much oxygen every 80 years, that means it will take: 

(4.095% ÷ 0.121%) x 80 years = 
2702 years before most life on Earth suffocates using Science Bulletin’s math.

Wow, their number is not much better. Keep in mind their estimate assumes that carbon dioxide emissions and global warming will increase plant production thus the plants will produce more oxygen. As I have discussed, plants don’t produce that much excess. And, I believe the health of our ecosystems is in decline. More on this below. 

Increase in oxygen consumption

As the population increases, it consumes more and more resources, including oxygen. And as the average lifestyle of citizens increases, so too does their consumption of oxygen — think more people wanting more cars. Since humans have a negative effect on the ecosystem, more humans mean fewer plants, and fewer plants mean less oxygen. 

Per the all-knowing internet: 

  • The world’s population increases by 1.1% per year. 
  • The world’s energy consumption is increasing by 1-2% per year. 
  • The dead zones in the ocean are increasing by 20% per year.
Compounding decline of oxygen. How Long Before The Earth Runs Out Of Oxygen?
Compounding decline of oxygen. (Sorry, since I am working backwards from the future value, this graph appears upside down. Imagine the line starting flat and dropping to zero.)

Let’s assume that the increase in energy consumption accounts for the increase in population. For this calculation, I needed to use a compound interest calculator. For the numbers, I entered:

Present value = 53.818 gigatonnes of oxygen burned per day.
Interest = 2% increase in the world’s consumption of energy. (I think the world will become ever more hungry for energy.)
Compounding continuously, as opposed to daily or yearly. 
Future value = 279,773 gigatonnes of oxygen. As we calculated above, this represents a drop from 20.95% to 16% atmospheric concentration, which becomes life-threatening. 

This gives us what we want to know.
Periods = 427.81 years before we run out of oxygen including an increase in consumption. 

You can see the illustration is another classic hockey-stick graph. Even if there is a small error in my estimates, humanity can’t go long at these rates. 

By the way, I have calculated this number over and over in many different ways, so I’m confident in my result. 

But wait! It gets worse.

Decrease in oxygen production

Phytoplankton produces almost all the excess oxygen. And global warming is linked to phytoplankton populations declining. They prefer colder oceans. This study says that by the year 2100, the production of oxygen by phytoplankton in the ocean could stop. Failing phytoplankton, failing oxygen: Global warming disaster could suffocate life on planet Earth. 

Let’s compromise with the above article and estimate that the Earth’s production of oxygen declines by half due to the destruction of oxygen-producing phytoplankton’s ecosystem. This also accounts for some other things that might happen as a result, like weathering. Fewer plants = more exposed land = increased oxygen absorption by the land. Think rust.

That means, 427.81 ÷ 2 =
213.91 years before the Earth runs out of oxygen, including an increase in consumption and a decrease in oxygen production. 

Measurement errors in oxygen levels

As I wrote about previously, there is probably a lot less oxygen due to multiple errors in measurement. So, where does that put us? Honestly, I have no idea. In my opinion — guessing here — I think that within 50 years, we will be having big problems. That would be about the year 2072. For the record, I’ll be 102 and hope to live that long to see what happens. 

How long before oxygen depletion affects my life?

Most people begin to feel ill at a 1–2% drop in oxygen. Think of doing a hike at a high altitude. Again, I’m just guessing, but some people living at high altitudes or in smoggy cities may already be feeling the limitations of oxygen deprivation. As for the rest of us, I think it will become evident within the lifetime of our children and young adults.

Global oxygen depletion logo. An illustration of the Earth  as a big O2 molecule.

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How long will the oxygen on Earth last?

Through this series of articles, I have shown that at current rates, the Earth will run out of breathable oxygen between 910 – 2702 years. If things continue to get worse, that number drops fast. If the population continues to grow at its current rate and continues to consume more energy, then we may run out of air to breathe in about 420 years. And if we guess that the Earth’s biosphere continues to die back, then the Earth may run out of oxygen in 210 years or less. And if I am correct, and there is less oxygen in the atmosphere than believed due to measurement errors, we could begin to see big problems in 50 years. Most people begin to feel ill at a 1–2% drop in oxygen. Think of doing a hike at a high altitude. 

In the next article, I will discuss a better way to measure how atmospheric oxygen levels are actually going down and by how much. 

Please forward this article to someone who may help do actual field research. 


See links above and previous articles on each topic. 

*Science Bulletin. 

The following article arrives at some similar numbers. The difference is that they calculate for burning all the oxygen in the atmosphere, whereas I calculate needing to burn only 20% of the oxygen before the Earth becomes inhospitable. Modern Records of Atmospheric Oxygen (O2) from Scripps Institution of Oceanography

For an opposing point of view, this article, Earth’s Atmospheric Oxygen Levels Continue Long Slide, makes a convincing case for a small decrease in the Earth’s oxygen of 0.7% as if going from sea level to the 30th floor. However, it gave me a big idea: What if the oxygen levels are remaining constant because of the outgassing from melting glaciers and the ocean itself? Cold water holds more oxygen, and oceans are warming… Makes sense to me. 

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