Carbon is fungible.
https://x.com/ncdave4life/status/1671700516525551616โฆ
The natural sinks which remove CO2 from the air do not remove some "fraction of the CO2 produced by humans." They remove mixed CO2 from the atmosphere, with negligible discrimination between anthropogenic CO2 and CO2 which was already there.
There's no practical limit to the amount of carbon that the oceans and terrestrial biosphere / soil can take up. The oceans contain about 50ร as much CO2 as the atmosphere. So the movement of CO2 from air to water affects the air far more than it affects the water.
The usual concern expressed about CO2 dissolved into the oceans is "ocean acidification." But that's both a red herring, and a misnomer. The oceans are alkaline (caustic), everywhere. They are not acidic, anywhere, and ocean chemistry ensures that the oceans can never become acidic.
Freshwater lakes and rivers are often slightly acidic, and so is rain, but never oceans.
"Ocean acidification" is a red herring because the effect is both minuscule & benign. It's a misnomer because it doesn't even acidify the oceans according to any dictionary's definition of the word:
โโโโโโ โโ โโโโโโ โโ โโโโโโ โโ acidify. v. To make or become acid.
It's estimated that, as a consequence of 70 years of CO2 emissions, average ocean surface water pH has declined a measly and harmless 0.1 pH point.
That estimate is from modeling, not measurements, because the trend is too slight and slow to measure with confidence, and because the tiny change is dwarfed by natural seasonal & diurnal pH variation, pH variation with depth, and even pH differences between ocean basins:
https://sealevel.info/ocean_pH_vs_depth.pngโฆ
What's more, so-called ocean acidification is confined almost entirely to the part of the ocean which is most caustic (alkaline): the surface layer. That means so-called "ocean acidification" really just reduces the extreme high end of ocean pH variation, slightly.
What's more, through >98% of the Earth's history, atmospheric CO2 levels were far higher than they are now, and, in fact, far higher than we could ever raise them, by burning recoverable fossil fuels. During the lush Cretaceous, when complex life flourished, including aquatic life, atmospheric CO2 concentrations are believed to have averaged nearly four times the current level. During the equally lush Jurassic, CO2 levels were even higher.
Yet, even with those much higher atmospheric CO2 levels, the oceans were still alkaline, rather than acidic, and there's no evidence that the high atmospheric CO2 levels were harmful to aquatic life.