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A balanced carbon cycle produces as much CO2 as O2, and yet, there are 209,460 ppm of oxygen in the atmosphere and only 440 ppm of CO2 (up from the recent baseline of 275).

My first thought was that the CO2 is temporarily stored in vegetation, but the vegetative carbon sink doesn't store anywhere near enough CO2 to affect the O2 levels in the atmosphere. If we burned ALL THE VEGEATATION ON EARTH the oxygen concentration of the planet would drop by less than 1%.

The CO2 storage of live vegetation is massively important for global warming, but it has no effect on our ability to breathe.

SO WHY CAN WE BREATHE!? I got curious, so I made this video.

Thanks to this article for starting me on the path to making this video: https://www.pbs.org/newshour/science/no-the-amazon-fires-wont-deplete-the-earths-oxygen-supply-heres-why

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Good morning, John!

Last week, I joined an extremely unexclusive club of people who said that the Amazon rainforest produces 20% of the world's oxygen. I've since deleted it from the video because it's a fake fact. No one even knows where it came from?

All of the land plants on the Earth combined produce around 25% of the world's oxygen. The rest comes from the oceans, mostly phytoplankton, which are like teeny tiny plants.

Except it turns out that we are imagining all of this incorrectly. The frame we're in here indicates that if the phytoplankton and the plants stopped producing oxygen, within a year, we would run out.

We would not.

We would all die immediately if there was no O2 being produced that means there would be no photosynthesis and photosynthesis is where all food originates. So we would stop, everything would die. But there would still be plenty of oxygen in the atmosphere.

[Hank snaps with finger guns as Charlie Sheen's famous "winning" interview pops up]

So let's do this, an introduction to the Carbon Cycle, I guess 'cause I of all people should know this. Plants use energy to turn carbon dioxide into carbohydrates and oxygen in a process called photosynthesis. And then those carbohydrates get turned back into CO2 and energy, and that consumes a molecule of O2. If this happens inside an organism, that's called respiration. If it happens outside an organism, it's called combustion. 

I'm gonna lump those two together and call them both burning, because I'm frustrated there is no collective word that includes both of these things except for I guess oxidation which is just too broad. This is just one of my science communicator beefs. We're sticking with "burning". Fire.

Carbohydrates are, as Olive Garden has effectively capitalized on, delicious. They are unstable reservoirs of energy so on a geological time scale all carbs get burned. And when a carb gets burned, that molecule of O2 that the plant produced gets sucked back up. Every. Single. Time. It's a one to one cycle.

So now you're like, "Okay Hank, yes, but I can breathe so you're wrong." And you're right. I was lying to you. Not every carb gets burned. Here on land, almost always there's oxygen around to do the burning. In the oceans, there's a fairly common exception. Sometimes phytoplankton can bloom so successfully that the organisms that consume them after they die eat up all of the oxygen in an area and no oxygen is left for more burning. The carbohydrate just falls to the bottom of the ocean where it can never get burned. This process upsets the balance between CO2 and oxygen. It's the reason I'm breathing right now. 

The photosynthesis produces that oxygen, but that oxygen doesn't get evenly distributed throughout the Earth, so there are some areas where the burning can't happen. Overtime that results in a giant reservoir of O2 in the atmosphere. So if the Amazon rainforest disappeared, there would be less oxygen produced, but over time there would also be less oxygen consumed because oxygen consumption - and there's an asterisk here but like, basically oxygen consumption - only happens when plant material is burned. Either in a fire or in an organism.

Since oxygen is abundant in the atmosphere, carbon dioxide is the limiting agent in this carbon cycle. Which is why there's such a tiny amount of CO2 in the atmosphere. That carbon dioxide gets trapped and brought to the bottom of the ocean when these blooms. There, over geologic time, they're compressed from carbohydrates into hydrocarbons - fossil fuels. And when we burn those fossil fuels yes, that consumes oxygen and we can see the oxygen concentration of the Earth going down, but it's not a big percentage of the total amount of oxygen in the atmosphere because there's a lot. 

But the carbon dioxide concentration is extremely low, and we are well on our way to doubling it. And that's one of the very real reasons why it's a bad idea to burn rainforests. The Amazon rainforest is a sink for something like 90 billion tons of carbon dioxide, and that is a huge service that we need.

So we're not going to suffocate. Very happy about that. Sounds miserable.

But I kinda wish we could see the threats to the other services that the Earth provides to us as similarly significant. Because they are. 

John, I'll see you on Tuesday.

We're gonna be okay, alright? We're gonna make it through this.