How much carbon dioxide does a person exhale each day?

About two pounds of carbon dioxide per person per day, approximately — and that CO2 is plant food: plants take it in and release oxygen, completing the loop.

Do trees make most of Earth's oxygen?

No. Forests matter, but NASA's ocean-productivity research shows phytoplankton account for about half of global primary production — roughly matching all land plants combined.

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Where Does the Oxygen You Breathe Actually Come From?

Q: Where does the oxygen we breathe come from?

About half comes from the ocean: microscopic drifting organisms called phytoplankton produce roughly half of Earth's oxygen through photosynthesis. Land plants, forests included, produce the other half.

About half of it comes from the ocean. Tiny drifting organisms called phytoplankton produce roughly half of Earth's oxygen through photosynthesis — and the carbon dioxide you breathe out, about two pounds a day, goes right back to feed the plants making more.

Quick facts

Your output: about two pounds of carbon dioxide exhaled per person, per day (approximate)
The loop: you take in oxygen and release CO2; plants take in CO2 and release oxygen
The twist: phytoplankton — microscopic ocean drifters — make about half of Earth's oxygen
The other half: land plants, forests included
Estimates vary somewhat by study; "about half" is the careful phrasing

The loop you're part of

Every breath runs the same trade. Your body burns food using oxygen and exhales the leftover as carbon dioxide. Plants run the trade in reverse: they pull in carbon dioxide, use sunlight to build their food from it, and release oxygen as their leftover. Neither side's waste is garbage — it's the other side's supply. You are, quite literally, breathing out plant food with every breath, about two pounds of it a day.

The twist: it's mostly the ocean

Ask most people where oxygen comes from and they'll point at a forest. Forests matter — but the bigger producer has no trunk. Phytoplankton are microscopic plant-like organisms drifting in the sunlit surface of the ocean, and there are so many of them that together they account for roughly half of all photosynthesis on Earth — and about half the oxygen in the air you just inhaled. NASA's ocean-productivity research puts their role at about half of global primary production, alongside an outsized role in the planet's carbon cycle.

So the honest picture of "the lungs of the Earth" is split: one lung is green and standing in the Amazon, and the other is invisible, floating, and covering most of the planet.

Where does your CO2 actually go?

Not straight into a tree, and not straight into the sky forever. The CO2 you exhale mixes into the air, and from there it's drawn down by plants on land and phytoplankton at sea, dissolved into ocean water, and cycled through soil and rock over longer spans. Some of the carbon in your last breath will end up in a leaf; some in a seashell. The loop has no single path — it has a whole planet running it.

Watch it

See the short version in the LOE PRESSURE "Things You Didn't Know" series — "You're Breathing the Ocean's Leftovers."

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Keep learning

→ Are sharks really older than trees?

→ Why does rain smell like that?

Fascinating facts you didn't know. Come learn with me — no pressure.

Sources: NASA Earth Observatory, "Ocean Productivity" (phytoplankton account for about half of Earth's oxygen production and roughly half of global primary production) — http://earthobservatory.nasa.gov/Features/OceanProductivity/page2.php. Checked 2026-10-14; figures kept approximate ("about half," "about two pounds") per the packet's accuracy notes.