Random anecdote: A few months ago I had an argument with a PhD student (and blogger and EA forum participant) whose mental model was something like: every second that a plant is alive, it is converting CO2 to O2, and every second that an animal is alive, it is converting O2 to CO2. Therefore, if there are more animals than plants on Earth for a long enough period of time, those two processes will be out of balance, and more and more O2 will get converted on net to more and more CO2, and eventually we won’t have any oxygen to breathe. (Which is absurd, and he probably would have understood that if he had understood that “trees is air”.)
(To his credit, he noticed that nobody else was worried about running out of oxygen and therefore he must be somehow confused, and was trying to figure it out.)
Actually can you explain this more? In the limit where there are no photosynthesizing organisms and animals somehow didn’t die from lack of food first wouldn’t we eventually run out of oxygen?
You can only convert an O2 to a CO2 by adding a carbon atom. The key question is: where did that carbon atom come from? That’s the part where “trees is air” is important.
One possible answer is: the carbon atom could come from the biosphere (trees, and other plant matter, plus animal bodies etc.). But there’s orders of magnitude fewer carbon atoms in Earth’s entire biosphere today than there are O2 molecules in the atmosphere. So you could combust the entire biosphere of Earth, to ash, all at once tomorrow, and that would sure be bad for climate change but it would be a negligible change in atmospheric O2. If instead of combusting the entire biosphere tomorrow, animals instead eat down the whole biosphere over many years, until there’s no plants left, then the animals themselves starve to death, and the scavengers eat the corpses, etc., then that’s the same number of carbon atoms getting attached to O2’s, i.e. all the carbon atoms previously stored in the biosphere, it’s just that they would be getting attached to O2’s more gradually.
I asked some LLM, and it guessed that if we combust the entire biosphere to CO2, that’s enough carbon atoms to reduce atmospheric O2 by <1%. If we also extract and burn all the fossil fuels on Earth, that’s still only enough carbon atoms to reduce atmospheric O2 by <10%. I didn’t check those though.
To your question, “animals somehow didn’t die from lack of food first” is an incoherent hypothetical. In order for animals to get energy and create CO2, they have to be eating carbon-based food. Again, the question is: Where did those carbon atoms come from? See what I mean?
Random anecdote: A few months ago I had an argument with a PhD student (and blogger and EA forum participant) whose mental model was something like: every second that a plant is alive, it is converting CO2 to O2, and every second that an animal is alive, it is converting O2 to CO2. Therefore, if there are more animals than plants on Earth for a long enough period of time, those two processes will be out of balance, and more and more O2 will get converted on net to more and more CO2, and eventually we won’t have any oxygen to breathe. (Which is absurd, and he probably would have understood that if he had understood that “trees is air”.)
(To his credit, he noticed that nobody else was worried about running out of oxygen and therefore he must be somehow confused, and was trying to figure it out.)
Actually can you explain this more? In the limit where there are no photosynthesizing organisms and animals somehow didn’t die from lack of food first wouldn’t we eventually run out of oxygen?
You can only convert an O2 to a CO2 by adding a carbon atom. The key question is: where did that carbon atom come from? That’s the part where “trees is air” is important.
One possible answer is: the carbon atom could come from the biosphere (trees, and other plant matter, plus animal bodies etc.). But there’s orders of magnitude fewer carbon atoms in Earth’s entire biosphere today than there are O2 molecules in the atmosphere. So you could combust the entire biosphere of Earth, to ash, all at once tomorrow, and that would sure be bad for climate change but it would be a negligible change in atmospheric O2. If instead of combusting the entire biosphere tomorrow, animals instead eat down the whole biosphere over many years, until there’s no plants left, then the animals themselves starve to death, and the scavengers eat the corpses, etc., then that’s the same number of carbon atoms getting attached to O2’s, i.e. all the carbon atoms previously stored in the biosphere, it’s just that they would be getting attached to O2’s more gradually.
I asked some LLM, and it guessed that if we combust the entire biosphere to CO2, that’s enough carbon atoms to reduce atmospheric O2 by <1%. If we also extract and burn all the fossil fuels on Earth, that’s still only enough carbon atoms to reduce atmospheric O2 by <10%. I didn’t check those though.
To your question, “animals somehow didn’t die from lack of food first” is an incoherent hypothetical. In order for animals to get energy and create CO2, they have to be eating carbon-based food. Again, the question is: Where did those carbon atoms come from? See what I mean?
Thanks, yes I see what you mean. I hadn’t thought that it would be so negligible. Thanks for explaining further.
I guess over millions of years the oxygen would deplete to practically nothing but this would be due to erosion and tectonics not animal respiration.