Serum bicarbonate — a standard blood chemistry marker — has risen roughly 7% across the U.S. population since 1999. The increase tracks atmospheric CO2, which rose from 369 to over 420 parts per million in the same period. The mechanism is the body's acid-base buffering system: as inhaled CO2 increases, the kidneys retain more bicarbonate to stabilize blood pH. The compensation works. Nobody is sick from this. But the measured value is drifting toward the upper boundary of the accepted healthy range — 30 milliequivalents per liter — and at current rates, the population average reaches that boundary around 2076.
The finding is not that CO2 is poisoning people. The finding is that the body's successful compensation for an environmental shift consumes the diagnostic margin between “normal” and “abnormal.” The healthy range for bicarbonate was established when atmospheric CO2 was around 320 ppm. The range assumed a stable environment. The environment changed; the range didn't. The body adapted by pushing its chemistry toward the boundary that was drawn under the old conditions.
This is a different kind of risk from acute toxicity. No threshold is crossed. No symptom appears. What happens instead is that the distance between where the population sits and where clinical concern begins gets smaller, steadily, without producing a signal that any individual physician would flag. The margin that absorbs variation — illness, altitude, diet, age — shrinks. The system doesn't fail. It loses the space it needs to fail safely.
The reference frame and the phenomenon are no longer independent. The definition of normal was calibrated against a world that no longer exists, and the body's own homeostatic success is what moves the measured value toward the boundary. The compensation is the problem — not because it fails, but because it works by occupying the space that was supposed to remain empty.