If they make it that far

 

Rising atmospheric CO2 concentrations also means decreasing ocean pH.  Climate (and Earth system) change deniers say that calling that "ocean acidification" is misleading, because the ocean pH is alkaline, and so decreasing pH doesn't mean the oceans are acidifying, it just means they're become less alkaline.

Seriously.

Decreasing ocean pH changes the balance of carbonate and bicarbonate ions in seawater, with the equilibrium shifting toward bicarbonate (HCO3 -) from carbonate (CO3 2-).  If you're a chemist you know that the 3 should be subscripted and the minus or 2- should be superscripted.  More bicarbonate and less carbonate changes the saturation state of seawater with respect to calcium carbonate, CaCO3, making CaCO3 more soluble.  In other words, more of it can dissolve.

The subject now is sharks. Sharks may have cartilaginous skeletons, but they have teeth similar to ours -- made of fluoroapatite (calcium phosphate with fluorine). Sharks and other fish have teeth made of enameloid, similar to human enamel.  These substances are subject to dissolution, and the lower the pH, the more subject they are to dissolving.

That's what the study was about. Making use of a naturally occurring raw material (lost shark teeth at the bottom of an aquarium tank), the researchers compared dissolution at pH of 8.1 to dissolution at pH of 7.3, which the oceans are predicted to reach in 2300.  (By the way, that would be incredibly bad.)  The shark's teeth in 7.3 pH seawater were "significantly more damaged".  No surprise there.

Now, as I note, if Earth still has sharks in 2300, I will be both surprised and spectacularly happy, even though I will have been deceased for much more than a century. Even if their teeth are in bad shape.

Sharks May Be Losing Their Teeth to Ocean Acidity
A leading cause of a rising pH value in the world’s oceans is human CO2 emission.

"Blacktip reef sharks must swim with their mouths permanently open to be able to breathe, so teeth are constantly exposed to water. If the water is too acidic, the teeth automatically take damage, especially if acidification intensifies, the researchers said. “Even moderate drops in pH could affect more sensitive species with slow tooth replication circles or have cumulative impacts over time,” Baum pointed out. “Maintaining ocean pH near the current average of 8.1 could be critical for the physical integrity of predators’ tools.”

Reference: Maximilian Baum M, Haussecker T, Walenciak O, et al. Simulated ocean acidification affects shark tooth morphology. Frontiers in Marine Science, 2025. doi: 10.3389/fmars.2025.1597592