Bold claim first: Rising atmospheric CO2 may be shifting our blood chemistry, not just warming the planet. And this is the part most people miss: the changes are subtle now, but they could accumulate over time if CO2 levels continue to climb.
A new study analyzes 20 years of health data from a U.S. population database and finds blood chemistry shifts that align with higher exposure to carbon dioxide. Researchers say these changes mirror the rising CO2 in the air, suggesting a population-wide physiological response that has not been observed before at this scale.
According to the scientists’ modeling, if current trends persist, average bicarbonate levels in the blood could approach the upper limit of today’s healthy range within the next 50 years. They also project that calcium and phosphorus levels might drift toward the lower ends of their healthy ranges later this century.
Context matters: historically, Earth’s atmosphere held CO2 around 280–300 parts per million (ppm) for roughly the entire span of Homo sapiens. In recent decades, CO2 has surged—from about 369 ppm in 2000 to roughly 420 ppm today—driven largely by human activities.
In the bloodstream, CO2 is converted to bicarbonate. Under normal conditions, bicarbonate helps keep the blood’s pH balanced. The researchers theorize that bicarbonate could serve as a blood marker indicating atmospheric CO2 levels, linking air quality to measurable shifts in blood chemistry.
To test this, they turned to the National Health and Nutrition Examination Survey (NHANES), which collected blood samples from about 7,000 Americans every two years from 1999 to 2020. They tracked population-level changes in bicarbonate, then compared those trends with the rise in atmospheric CO2.
The results show a clear trend: average bicarbonate in blood rose from about 23.8 to 25.3 milliequivalents per liter (an increase of roughly 7 percent, or 0.34 percent per year). This pattern tracks the concurrent rise in CO2. In contrast, calcium and phosphorus moved the other way—calcium declined by around 2 percent and phosphorus by about 7 percent.
Why might this be happening? When CO2 dissolves in the blood, it shifts the body’s acid-base balance. To compensate and keep pH within a tight healthy range, the kidneys conserve bicarbonate. Bones can also release minerals like calcium and phosphorus to buffer acidity. These buffering processes could explain the observed changes in blood chemistry over time.
Right now, the shifts are small and still within what the body can tolerate. Yet the parallel rise is striking, and the researchers caution that population-level physiological changes could emerge if CO2 continues to rise.
As one of the study’s authors, Phil Bierwirth (a retired geoscientist affiliated with the Australian National University), notes, our bodies may not be adapting quickly enough to the higher indoor and outdoor CO2 levels now common in many environments. He emphasizes that the normal balance among air CO2, blood pH, breathing rate, and bicarbonate is delicate, and sustained higher CO2 could push this system beyond its historical range.
The study, published in Air Quality, Atmosphere & Health, highlights a potential bridge between atmospheric science and human physiology. It invites readers to consider not only the climate implications of CO2 but also how rising CO2 might subtly influence our biology over time, reinforcing why reducing atmospheric CO2 remains a critical public health goal.
