How Rising CO2 Is Quietly Rewriting Human Blood Chemistry

Imagine the air leaving a faint, invisible signature inside your bloodstream. Strange thought. But a new population analysis suggests that the composition of the atmosphere might already be nudging human physiology in measurable ways.

Scientists from The Kids Research Institute Australia, Curtin University and The Australian National University analyzed nearly two decades of U.S. health survey data to look for long-term shifts. Using NHANES results collected about every two years from roughly 7,000 people between 1999 and 2020, they tracked common blood chemistry markers and compared those trends to rising atmospheric CO2 levels.

The patterns are subtle, but consistent. Average serum bicarbonate rose by about seven percent since 1999. At the same time, average calcium and phosphorus concentrations edged downward. Those shifts unfolded as atmospheric CO2 climbed from roughly 369 parts per million around 2000 to more than 420 ppm today.

Bicarbonate is central to how the body buffers acids and bases. When CO2 increases in the air, more CO2 can dissolve into the bloodstream, and the body often compensates by changing bicarbonate levels to keep blood pH stable. That buffering works short term. Maintained over decades, however, it might alter physiology in ways we barely understand.

Associate Professor Alexander Larcombe, one of the paper's authors, says the population-level shift in blood chemistry mirrors the rise in atmospheric CO2. Children and adolescents may be particularly relevant, since they face longer cumulative exposure during development.

At the same time, the team is cautious about claims of direct cause and effect. Retired environmental geoscientist Dr Phil Bierwirth, another author, stresses that correlation is not causation. Still, he argues, the consistent pattern across many people is worrying enough to warrant more study.

If current trends continue, average bicarbonate levels could approach the upper limit of today’s accepted healthy range within fifty years, and calcium and phosphorus could trend toward the lower end of their healthy ranges later this century.

To put that in context, our species evolved when atmospheric CO2 hovered around 280 to 300 ppm. The last decade has averaged an increase of about 2.6 ppm per year, and 2024 alone rose by roughly 3.5 ppm. Those numbers matter because even small shifts in the balance between inhaled CO2, breathing rate, blood pH and bicarbonate can ripple into clinical ranges over long timescales.

The authors suggest a shift in thinking: treat atmospheric CO2 not only as an environmental metric but as a long-term public health variable to be tracked alongside temperatures, sea level and extreme weather. Monitoring human biomarkers and air composition together could reveal slow-moving biological responses that conventional climate indicators miss.

Cutting CO2 emissions remains essential to limit warming. But if the atmosphere is quietly influencing blood chemistry, emission reductions may also be relevant to long-term human health — a dimension worth adding to policy debates and public health surveillance.

If the air is subtly rewriting our blood, shouldn’t we start listening now?