> Whatbaoutism is not a valid excuse.

It’s not “whataboutism”. It’s a basic control in a paper that takes population data and asserts a causal link between a complex, personal biological variable and a global phenomenon.

There are probably dozens of factors that matter a lot more to individual blood gas levels than global average co2. At a minimum, I’d expect to see controls for obvious medical factors before taking this argument seriously.

Fair point. I can see how a global rise in antacid use could explain it more easily. If antacids are the culprit, I expect the rise in bicarbonate to eventually asymptote.

Still, we know that very high sustained carbon dioxide does risk respiratory acidosis and a rise in serum bicarbonate. The question then is whether a lower sustained rise also has an observed effect.

Fwiw, as per Figure 2A, thus far we see a linear increase in the data, with no sign of it being asymptotic.