Christian Bohr

Here is the mechanism, and it goes back further than you would guess.

In 1904, a Danish physiologist named Christian Bohr, whose son Niels went on to become the physicist you have heard of, published the finding that hemoglobin's affinity for oxygen is not fixed, it changes.

And what changes it is carbon dioxide.

When carbon dioxide is high in a tissue, hemoglobin loosens its grip and releases the oxygen it is carrying.

When carbon dioxide is low, hemoglobin holds on.

That is the Bohr effect, and it is not fringe science.

It is on page one of every respiratory physiology textbook printed since.

A decade later, Christensen, Douglas, and Haldane described the reciprocal, which is that hemoglobin loaded with oxygen carries less carbon dioxide, which is what lets you dump carbon dioxide at the lungs.