Some of it — and the sea makes more
Do Trees Make the Air We Breathe?
Trees release oxygen, but ocean plankton produce roughly half the world's supply.
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Step 1 of 5
Oxygen is a by-product, not a purpose.
Plants split water to get at what they need for building sugar. Oxygen is what is left over, and they simply release it.
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Step 2 of 5
A mature tree makes a lot of it.
A large tree can release enough oxygen in a year for several people. Multiply by the world's forests and it is an enormous flow.
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Step 3 of 5
But the ocean does about half the work.
Microscopic plankton drifting in sunlit surface water photosynthesise constantly. Individually invisible, collectively they rival every forest on Earth.
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Step 4 of 5
Plants use oxygen too.
At night, and in every non-green part, plants respire like animals. A forest's net output is what remains after its own consumption.
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Step 5 of 5
Old forests balance out.
A mature forest that is not growing releases about as much oxygen as its decaying matter consumes. Growing forests are the ones adding to the total.
Trees matter enormously for climate, water and habitat. Oxygen supply is simply not the main reason to keep them.
The short version
Trees release oxygen, but ocean plankton produce about half of it, and mature forests roughly break even.
Try it yourself
Look at a satellite image of ocean chlorophyll. The green swirls are the plankton making half your air.
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