How Long Would It Take For Us To Run Out Of Oxygenated Air If All Trees Disappeared

What do you do when you’re bored at work? Probably go for a smoke break or drink chai at the nearest tapri. What do I do when I’m bored? Make up hypothetical situations and see if there’s any mathematical answer to those seemingly random questions.

One such question is ‘How long would it take for us to run out of breathable air if all trees disappeared?’


You know, since we keep hearing people urging us to plant trees to save environment and what not; I was interested in seeing whether we could survive for long if all the trees in the world were to disappear.

Most of the air we breathe actually comes from the ocean. Algae – I am pretty sure.

So without trees, we’d still have sustainable amounts of oxygen. And even if all Oxygen producing plants disappeared at the same time, we would starve to death first.

The problem is that lower Oxygen levels wouldnt kill us so fast, but an increase in Carbon dioxide pretty fast. Without trees we would die because of toxic Carbon dioxide amounts.

It’s even more fun, because higher Carbon dioxide amounts would cause an even more rapid acid-ification(?) of the ocean, which is already killing oxygen-producing algae.

Some people are worried about storms and hunger and war. However I think it is a grand de-oxygenation event which will kill, not just humanity, but most oxygen-dependent life on the planet.

The reason is that one percent less Oxygen (21%->20%) is no problem at all, while one percent more Carbon dioxide (0.04%->1.04%) is toxic. So if trees stop existing, the oxygen level might not drop to toxic levels immediately, but the Carbon dioxide level gets toxic fast.

The atmosphere has a mass of 5×1018 kg. 75% of that is in the troposphere. That leaves about 3.75×1018 kg, about 23% of which is Oxygen and 0.0525% Carbon Dioxide.

That’s 8.625×1017 kg of Oxygen and 2*1015 of Carbon Dioxide. Let’s leave that for a second and look at trees.

They produce an average of 260 pounds of oxygen per tree per year, which sounds fishy to me but I’ll work with it. 3×109 trees on Earth times 118 kg gives 3.54×1011 kg of Oxygen “fixed” from Carbon Dioxide each year. Other things equal, over a year trees would increase the amount of Oxygen on Earth from 8.625×1017 kg to 8.62500354×1017 kg (0.000041% up). In that same year Carbon Dioxide would decrease from 2×1015 to 1.999646×1015 (0.0177% down).

This is how I feel right now.

In a year’s time, the oxygen fixation done by trees alone doesn’t make a very large difference in either breathable Oxygen or harmful Carbon Dioxide. Side effects from the loss of trees like habitat loss and ecosystem collapse would be much more diverse and noticeable effects.

So it’ll take a while for air to become un-breathable if the rate of loss is constant and exactly opposite this hypothetical rate of gain.

That would actually produce reverse effect. Trees ‘disappearing’ would take a ton of carbon dioxide with them, and whatever grew in their place would take some Carbon dioxide, and generate some oxygen.

For a general principle, mature forests do not generate any net oxygen, or absorb any carbon dioxide. And same for all other ecosystems.

In any mature closed ecosystem amount of biomass is stable, so every kg of plant growth is balanced by kg of plant eaten or decomposed or burned in forest fire; and so for all animals etc. Number and size of trees can’t increase indefinitely.

There are some tiny effects because ecosystems are not exactly closed, but it balances long term anyway. For example if people take that wood and build a house, carbon release will be delayed a few decades, but it won’t last forever.

If wood is stored in a way that it can’t decompose, you might eventually get some net oxygen. That’s how we got coal. It requires rare circumstances, takes forever, and is completely tiny portion of total plant growth.


What do you think about this? Are you jobless enough to do the math? Let us know in the comments below.

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